Chromophores with New Acceptors that Increase Refractive Index

Abstract

The present disclosure is directed, in general, to (1) nonlinear optical (NLO) chromophores, including (2) compositions/materials/resistive layers comprising NLO chromophores, and the methods of making the compositions/materials/resistive layers comprising NLO chromophores (e.g., methods of poling and/or drying, and the like), (3) uses of NLO chromophores in electro-optic devices (e.g., electro-optic modulators (EOMs)). NLO chromophores disclosed herein not only have large EO effect, but also have fast modulation speed. In addition, NLO chromophores disclosed herein have superior refractive index, photostability and thermal stability compared to other EO Materials. As a consequence, NLO chromophores herein are particularly suited for use as EO materials in connection with low power and small footprint devices, including devices used in data acquisition systems, analog I/O modules, field transmitters, lab and field instrumentation, servo drive control modules, direct current (DC) power supply, alternating current (AC), and/or electronic load.

Claims

1. A nonlinear optical chromophore of a general formula (I): ##STR00030## wherein D represents an organic electron-donating group; A represents an organic electron-accepting group having an electron affinity greater than the electron affinity of D; and represents a -bridge between the organic electron-accepting group and the organic electron-donating group; wherein A comprises electron acceptors having a following formula (A.sup.1): ##STR00031## wherein R.sub.1 and R.sub.2 each independently represent a moiety selected from the group consisting of a substituted or unsubstituted aryl, a substituted or unsubstituted alkyl, or a hydrogen; and wherein X is S, Se, or Te.

2. The nonlinear optical chromophore according to claim 1, wherein at least one of R.sub.1 and R.sub.2 is a C.sub.6-C.sub.20 aryl.

3. The nonlinear optical chromophore according to claim 1, wherein at least one of R.sub.1 and R.sub.2 is a linear, branched, cyclic bicyclic, or tricyclic C.sub.1-C.sub.20.

4. The nonlinear optical chromophore according to claim 1, wherein at least one of R.sub.1 and R.sub.2 is a halogen-substituted alkyl or a halogen-substituted aryl.

5. The nonlinear optical chromophore according to claim 4, wherein at least one of R.sub.1 and R.sub.2 is a trifluoromethyl group.

6. The nonlinear optical chromophore according to claim 1, wherein at least one of R.sub.1 and R.sub.2 is a methyl, an ethyl, or an isopropyl.

7. The nonlinear optical chromophore according to claim 1, wherein at least one of R.sub.1 and R.sub.2 is a phenyl or an anisole.

8. The nonlinear optical chromophore according to claim 1, wherein at least one of R.sub.1 and R.sub.2 is a phenyl or a substituted phenyl.

9. The nonlinear optical chromophore according to claim 1, wherein the nonlinear optical chromophore has a refractive index greater than or equal to about 2.

10. A resistive film comprising the nonlinear optical chromophore according to claim 1 dispersed and poled within a matrix material.

11. An electro-optic device comprising one or more resistive film, wherein the one or more resistive film each comprising a nonlinear optical chromophore dispersed and poled within a host polymer matrix, wherein the nonlinear optical chromophore of a general formula (I): ##STR00032## wherein D represents an organic electron-donating group; A represents an organic electron-accepting group having an electron affinity greater than the electron affinity of D; and represents a -bridge between the organic electron-accepting group and the organic electron-donating group; wherein A comprises electron acceptors having the following formula (A.sup.1): ##STR00033## wherein R.sub.1 and R.sub.2 each independently represent a moiety selected from the group consisting of a substituted or unsubstituted aryl, a substituted or unsubstituted alkyl, or a hydrogen; and wherein X is S, Se, or Te.

12. The electro-optic device according to claim 11, wherein at least one of R.sub.1 and R.sub.2 is a C.sub.6-C.sub.20 aryl.

13. The electro-optic device according to claim 11, wherein at least one of R.sub.1 and R.sub.2 is a linear, branched, cyclic bicyclic, or tricyclic C.sub.1-C.sub.20.

14. The electro-optic device according to claim 11, wherein at least one of R.sub.1 and R.sub.2 is a halogen-substituted alkyl or a halogen-substituted aryl.

15. The electro-optic device according to claim 14, wherein at least one of R.sub.1 and R.sub.2 is a trifluoromethyl group.

16. The electro-optic device according to claim 11, wherein at least one of R.sub.1 and R.sub.2 is a methyl, an ethyl, or an isopropyl.

17. The electro-optic device according to claim 11, wherein at least one of R.sub.1 and R.sub.2 is a phenyl or an anisole.

18. The electro-optic device according to claim 11, wherein at least one of R.sub.1 and R.sub.2 is a phenyl or a substituted phenyl.

19. The electro-optic device according to claim 11, wherein the nonlinear optical chromophore has a refractive index greater than or equal to about 2.

20. The electro-optic device according to claim 11, wherein the electro-optic device is an electro-optic modulator (EOM).

Description

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

[0022] The foregoing summary, as well as the following detailed description of preferred embodiments of the disclosure, will be better understood when read in conjunction with the appended drawings. The embodiments of the drawings are shown for illustration. It should be understood, however, that the disclosure is not limited to the precise arrangements and instrumentalities shown.

[0023] In the drawings:

[0024] FIG. 1 is an end view of a slot modulator with highly doped silicon slab and rail.

[0025] FIG. 2 illustrates an example poling process of a nonlinear electro-optic material.

[0026] FIG. 3A is a partial side sectional diagram of an integrated electro-optic circuit.

[0027] FIG. 3B is a partial cross-sectional diagram of the integrated electro-optic circuit of FIG. 3A.

[0028] FIG. 4 is a perspective diagram of an optical waveguide according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0029] In some aspects, the disclosure concerns nonlinear optical chromophores of the general formula (I):

##STR00005##

wherein D represents an organic electron-donating group; A represents an organic electron-accepting group having an electron affinity greater than the electron affinity of D; and represents a -bridge between the organic electron-accepting group and the organic electron-donating group; wherein A is of the formula (A.sup.1):

##STR00006##

R.sub.1 and R.sub.2 each independently represent a moiety selected from the group consisting of an aryl, an alkyl, or a hydrogen. X is S, Se, or Te, as well as compositions having such nonlinear optical chromophores described herein exhibit a high refractive index. Thus, the nonlinear optical chromophores described herein may be applied in various electro-optic devices (e.g., nonlinear optical waveguide) in a variety of environments with improved performance. In certain embodiments, the acceptors with X being S, Se, or Te show advantageously increased refractive index versus an analogous compound where X is O.

Terms and Concepts

[0030] As used herein, the following terms have the following meanings unless expressly stated to the contrary.

[0031] As used herein, the term about, in the context of concentrations of components of the formulations or in property values, typically means +/5% of the stated value, more typically +/4% of the stated value, more typically +/3% of the stated value, more typically, +/2% of the stated value, even more typically +/1% of the stated value, and even more typically +/0.5% of the stated value.

[0032] When values are expressed as approximations, by use of the antecedent about, it will be understood that the particular value forms another example.

[0033] All ranges are inclusive and combinable. In addition, when a range is recited, it is contemplated that all values within the range, including end points, are combinable in all possible combinations.

[0034] As used herein, the singular forms a, an, and the and similar referents in the context of describing the elements (especially in the context of the following claims) include plural references unless the context clearly dictates otherwise. For example, reference to a substituent encompasses a single substituent as well as two or more substituents, and the like. It is understood that any term in the singular may include its plural counterpart and vice versa, unless otherwise indicated herein or clearly contradicted by context.

[0035] Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section.

[0036] As used herein, the terms for example, for instance, such as, or including are meant to introduce examples that further clarify more general subject matter.

[0037] As used herein, the term nonlinear optical chromophore (NLO chromophore) refers to molecules or portions of a molecule that create a nonlinear electro-optic effect when irradiated with light.

[0038] As used herein, the term electron-donating group refers to an atom and/or a functional group that donates some of its electron density into a conjugated system via resonance and/or inductive effects.

[0039] As used herein, the term electron-accepting group refers to an atom and/or a functional group that accepts some of the electron-donating group's electron density in a conjugated system via resonance and/or inductive effects.

[0040] As used herein, the term bridging group refers to a functional group that bridges between the electron-donating group and the electron-accepting group in a conjugated system.

[0041] As used herein, the term substituted compound refers to an organic compound with one or more atoms or groups each replaced by a substituent. In various embodiments, the organic compound includes a C.sub.1-C.sub.10 alkyl, a C.sub.2-C.sub.10 alkenyl, a C.sub.2-C.sub.10 alkynyl, an aryl, an alkylaryl, a carbocyclic, and/or a heterocyclic. In some embodiments, the substituent includes a halogen, a cyano group, a sulfonyl group, and/or a trifluoromethyl group.

[0042] As used herein

##STR00007##

represents a point of bonding to another portion of a larger molecular structure.

[0043] As used herein, the term four-wave mixing (FWM) refers to an interaction of four spatially or spectrally distinct fields.

[0044] As used herein, the term r.sub.33 refers to an electro-optic coefficient, a function of a first-order hyperpolarizability, that represents the relationship between the change in applied electric potential versus the change in the refractive index of the material. The r.sub.33 is expressed in units of pm/V. The r.sub.33 is the principal element of the Pockels EO effect tensor and is a function of first-order hyperpolarizability () which denotes the magnitude of refractive index shift () obtained for an applied low-frequency electric field that represents the relationship between the change in applied electric potential versus the change in the refractive index of the material.

[0045] As used herein, the term c refers to a dielectric constant, which is also known as permittivity. The dielectric constant is a measure of the extent to which a substance is polarized under an applied (external) electric field. Polarization amounts to net separation of charge across the substance.

[0046] As used herein, the term susceptibility refers to the degree to which a material can be polarized by an external electric field. There are different orders of susceptibility such as linear susceptibility (.sup.(1)), second-order susceptibility (.sup.(2)), third-order susceptibility (.sup.(3)) and other higher-order susceptibilities. Second-order susceptibility describes the material's response to two electric fields of different frequencies. The electro-optic effect occurs when an electric field is applied to a material with a non-zero second-order susceptibility. When an electric field is applied to such a material, the polarization of the material changes, resulting in a change in the refractive index. The change in the index of refraction and the magnitude of the externally applied electric field is proportional. Third-order susceptibility (.sup.(3)) describes the material's response to three electrical fields of different frequencies. The third-order susceptibility coefficient associated with each electrical field will be different due to the ever-present dispersion (i.e. frequency dependence) of the susceptibilities.

[0047] As used herein, the terms optic nonlinearity, nonlinearity, and nonlinear refer to the behavior of light in nonlinear media, that is, media in which the polarization density P responds non-linearly to the electric field (E) of the light. The nonlinearity is typically observed only at very high light intensities (when the electric field of the light is >108 V/m and thus comparable to the atomic electric field of 1011 V/m) such as those provided by lasers.

[0048] As used herein, the term nonlinear electro-optic material refers to materials that include both the nonlinear optical chromophore and one or more matrix material, also referred to as host polymer, in which the one or more nonlinear optical chromophore may be incorporated. EO materials can exhibit a nonlinear EO effect. Suitable matrix materials can include polymers, such as, for example: poly(methylmethacrylate)s (PMMA); polyimides; polyamic acid; polystyrenes; poly(urethane)s (PU); and amorphous polycarbonates (APC). NLO materials are anisotropic in the presence of electromagnetic radiation. When the intensity of the electric field is very high, it creates a very large displacement of the electrons in the material from their equilibrium position. As a result of this, anharmonic behavior comes into the picture of electronic oscillation. So, the general linear relationship becomes nonlinear. The polarization (P) of the medium is a nonlinear function of the electric field (E) and it could be expressed as follows:

[00002]$P=E$

Herein, is the electrical susceptibility. .sup.(n) is the tensor quantity and n is the order of the process. (.sup.(1)=linear polarizability, .sup.(2), .sup.(3) . . . =the first, second . . . hyperpolarizability coefficient, etc.). The nonlinearity is observed only at very high light intensities such as those provided by lasers.

[0049] As used herein, the term compositions refers to one or more mixed composition(s) that may include both a nonlinear electro-optic material and solvents.

[0050] As used herein, the term resistive layer refers to one or more layer(s) that may be formed from the compositions defined above through one or more procedures.

[0051] As used herein, the term electro-optic devices refers to devices with electro-optical function that contain one or more resistive layer(s) described above. For example, the electro-optic devices may include electro-optic modulators (EOMs), which are optical devices in which a signal-controlled element exhibiting an electro-optic effect is used to modulate a beam of light.

[0052] As used herein, the term refractive index of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index may determine how much the path of light is bent, or refracted, when entering a material, as described by Snell's law of refraction, n.sub.1 sin .sub.1=n.sub.2 sin .sub.2, where .sub.1 and .sub.2 are the angle of incidence and angle of refraction, respectively, of a ray crossing the interface between two media with refractive indices n.sub.1 and n.sub.2. The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as the critical angle for total internal reflection, their intensity (Fresnel's equations) and Brewster's angle. The refractive index may also reflect the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is v=c/n, and similarly the wavelength in that medium is =.sub.0/n, where .sub.0 is the wavelength of that light in vacuum. This implies that vacuum has a refractive index of 1 and assumes that the frequency (f=v/) of the wave is not affected by the refractive index.

[0053] As used herein, the term electro-optic (EO) effect is the modification of the optical phase delay (i.e., refractive index) of a medium, caused by an electric field. The strength of an EO effect is correlated with the strength of the material's Pockels effect. The Pockels effect (or linear EO effect) is a directionally dependent linear variation in the refractive index of an optical medium that occurs in response to the application of an electric field. Macroscopically, the Pockels coefficient r relates the change in the index of refraction to an applied electric field as: where n.sub.0 is the index of

[00003]$n\left(E\right)=n_0-\frac{1}{2}{\mathrm{rn}}_0^{3}E$

refraction under no field and n is the index of refraction under a given electrical field with the voltage equals to E. The applied electrical field shifts the electron cloud to the excited-state molecular orbitals, which alters the refractive index of the EO materials. In optical media, the Pockels effect causes changes in birefringence that vary in proportion to the strength of the applied electric field.

Nonlinear Optical Chromophore

[0054] An electro-optic (EO) effect is a change in the optical properties of a material in responses to an electric field that varies slowly compared with the frequency of light. For example, the electro-optic effect may indicate that a refractive index changes under an electric field. The refractive index change under the electric field may be explained through Pockels effect. Under Pockels effect, the electric field may shift the electron cloud to excited-state molecular orbitals and alter the refractive index of the material, which in turn may cause a phase change to any transiting optical signal.

[0055] Materials having the electro-optic effect may include liquid crystals, lithium niobate and/or other inorganic crystals, and/or organic nonlinear optical chromophores. Liquid crystals may have large EO effect but may be slow in modulation speed. Lithium niobate and/or other inorganic crystals may be fast in modulation speed but may have small EO effect. By comparing organic nonlinear optical chromophores with liquid crystals and lithium niobate and/or other inorganic crystals, organic nonlinear optical chromophores may have both large EO effect and fast modulation speed.

[0056] As used herein, the term nonlinear optical chromophore (NLO Chromophore) refers to molecules or portions of a molecule that create a nonlinear electro-optic effect when irradiated with light. The chromophores are any molecular unit whose interaction with light gives rise to the nonlinear optical effect. The desired effect may occur at resonant or nonresonant wavelengths. The activity of a specific chromophore in a nonlinear electro-optic material is stated as its electro-optic coefficient (r.sub.33), which is related to the molecular dipole moment and hyperpolarizability. The various embodiments of NLO chromophores of the present disclosure are useful structures for the production of NLO effects.

[0057] Nonlinear optical chromophores in accordance with the various embodiments of the disclosure have the general formula (I):

##STR00008##

wherein D represents an organic electron-donating group; A represents an organic electron-accepting group having an electron affinity greater than the electron affinity of D; and represents a -bridge between A and D. The terms electron-donating group (donor or D), -bridge (bridging group or ), and electron-accepting group (acceptor or A), and general synthetic methods for forming D--A chromophores are well known in the art.

[0058] A donor is an atom or group of atoms that has a low oxidation potential, wherein the atom or group of atoms can donate electrons to an acceptor through a -bridge. The donor (D) has a lower electron affinity than the acceptor (A), so that, at least in the absence of an external electric field, the chromophore is generally polarized, with relatively less electron density on the donor (D). Typically, a donor group contains at least one heteroatom that has a lone pair of electrons capable of being in conjugation with the p-orbitals of an atom directly attached to the heteroatom such that a resonance structure can be drawn that moves the lone pair of electrons into a bond with the p-orbital of the atom directly attached to the heteroatom to formally increase the multiplicity of the bond between the heteroatom and the atom directly attached to the heteroatom (i.e., a single bond is formally converted to double bond, or a double bond is formally converted to a triple bond) so that the heteroatom gains formal positive charge. The p-orbitals of the atom directly attached to the heteroatom may be vacant or part of a multiple bond to another atom other than the heteroatom. The heteroatom may be a substituent of an atom that has bonds or may be in a heterocyclic ring. Exemplary donor groups include but are not limited to R.sub.2N and R.sub.nX.sup.1, where R is alkyl, aryl or heteroaryl, X.sup.1 is O, S, P, Se, or Te, and n is 1 or 2. The donor group may be substituted further with alkyl, aryl, or heteroaryl.

[0059] In some embodiments of the present disclosure, D can represent any organic electron donating group, so long as D is bound to the core at two atomic positions on the core other than the two atomic positions at which A is bound to the core such that at least a portion of D forms a ring fused to the core.

[0060] Examples of organic electron donating groups suitable for incorporation into the chromophores of Formula (I) include, but are not limited to, the following structures, wherein the dashed lines represent the two atomic positions at which D forms a ring fused to the core:

##STR00009##

wherein each R independently represents a pendant spacer group.

[0061] Preferably, examples of suitable electron-donating groups according to the various embodiments of the present disclosure may include the following structures:

##STR00010##

[0062] An acceptor is an atom or group of atoms that has a low reductive potential, wherein the atom or group of accept electrons from a donor through a -bridge. The acceptor (A) has a higher electron affinity than the donor (D), so that, at least in the absence of an external electric field, the chromophore is generally polarized in the ground state, with relatively more electron density on the acceptor (D). Typically, an acceptor group contains at least one electronegative heteroatom that is part of a bond (a double or triple bond) such that a resonance structure can be drawn that moves the electron pair of the bond to the heteroatom and concomitantly decreases the multiplicity of the bond (i.e., a double bond is formally converted to single bond or a triple bond is formally converted to a double bond) so that the heteroatom gains formal negative charge. The heteroatom may be part of a heterocyclic ring. Exemplary acceptor groups include but are not limited to NO.sub.2, CN, CHO, COR, CO.sub.2R, PO(OR).sub.3, SOR, SO.sub.2R, and SO.sub.3R where R is alkyl, aryl, or heteroaryl. In some embodiments, the acceptor group may be substituted further with alkyl, aryl, and/or heteroaryl.

[0063] In various nonlinear optical chromophores in accordance with various embodiments of the present disclosure, suitable electron-accepting groups include those according to general formula (A.sup.1):

##STR00011##

X is S, Se, or Te. R.sub.1 and R.sub.2 each independently represent a moiety selected from the group consisting of a substituted or unsubstituted aryl, a substituted or unsubstituted alkyl, a substituted or unsubstituted ring-locked aryl, or a hydrogen. In certain embodiments, preferably at least one of R.sub.1 and R.sub.2 is a C.sub.6-C.sub.20 aryl. In certain embodiments, preferably at least one of R.sub.1 and R.sub.2 is a phenyl or a substituted phenyl. In certain embodiments, preferably at least one of R.sub.1 and R.sub.2 is a linear, branched, cyclic bicyclic, or tricyclic C.sub.1-C.sub.20. In certain embodiments, preferably at least one of R.sub.1 and R.sub.2 is a halogen-substituted alkyl or a halogen-substituted aryl, more preferably a trifluoromethyl group. In certain embodiments, preferably at least one of R.sub.1 and R.sub.2 is a methyl, an ethyl, or an isopropyl. In certain embodiments, preferably at least one of R.sub.1 and R.sub.2 is a phenyl or an anisole

[0064] Preferably, examples of suitable electron-accepting groups may include the following structures:

##STR00012##

[0065] A -bridge includes an atom or group of atoms through which electrons may be delocalized from an electron donor (defined above) to an electron acceptor (defined above) through the orbitals of atoms in the bridge. Such groups are very well known in the art. Typically, the orbitals will be p-orbitals on double (sp.sup.2) or triple (sp) bonded carbon atoms such as those found in alkenes, alkynes, neutral or charged aromatic rings, and neutral or charged heteroaromatic ring systems. Additionally, the orbitals may be p-orbitals on atoms such as boron or nitrogen. Additionally, the orbitals may be p, d or f organometallic orbitals or hybrid organometallic orbitals. The atoms of the bridge that contain the orbitals through which the electrons are delocalized are referred to here as the critical atoms. The number of critical atoms in a bridge may be a number from 1 to about 30. The critical atoms may be substituted with an organic or inorganic group. The substituent may be selected with a view to improving the solubility of the chromophore in a polymer matrix, to enhance the stability of the chromophore, or for other purposes.

[0066] -bridge may represent a fused, offset, polycyclic, optionally heteroatom-containing, pi-conjugated core. Core structures in accordance with the various embodiments of the present disclosure are pi-conjugated meaning that the core structure contains at least two double bonds separated by a single bond, and preferably more than two double bonds each separated by a single bond. Core structures in accordance with the various embodiments of the present disclosure are polycyclic and fused, meaning that the core structure contains at least two rings which share two atoms between the two rings.

[0067] Suitable -bridges for nonlinear optical chromophores according to the various embodiments of the present invention are organic moieties containing charge transporting groups and having at least one end capable of bonding to an electron-donating group and at least one end capable of bonding to an electron-accepting group, and include those described in the previously incorporated references. Suitable charge-transporting groups include, for example, arylamines, in particular triarylamines; and heteroaromatics, including fused and oligomeric heteroaromatics such as oligothiophene or fused thiophenes, as well as phthalocyanine-based compounds, porphyrin-based compounds, azobenzene-based compounds, benzidine-based compounds, arylalkane-based compounds, aryl-substituted ethylene-based compounds, stilbene-based compounds, anthracene-based compounds, hydrazone-based compounds, quinone-based compounds, and fluorenone-based compounds.

[0068] In various preferred embodiments, bridging groups () for nonlinear optical chromophores according to general formula (I) of the present invention include those of the general formula (.sup.c):

##STR00013##

wherein each Y independently represents: a diamondoid-containing group covalently bound to the bridging group through any of the various linkages described herein below including but not limited to ether and thioether linkages; or each Y may represent a hydrogen, an alkyl group, aryl group, sulfur or oxygen linked alkyl or aryl group, or a branched or unbranched, optionally heteroatom-containing C.sub.1-C.sub.4 substituent; wherein each a and b independently represents an integer of 0 to 3; z represents an integer of 1 to 3; and wherein each arc A independently represents a substituted or unsubstituted C.sub.2-C.sub.4 alkyl group, which together with the carbon bearing the Y substituent and its two adjacent carbon atoms forms a cyclic group. Substituted or unsubstituted C.sub.2-C.sub.4 alkyl groups which constitute arc A may include 1 to 4 hydrogen substituents each comprising a moiety selected from the group consisting of substituted or unsubstituted C.sub.1-C.sub.10 alkyl, substituted or unsubstituted C.sub.2-C.sub.10 alkenyl, substituted or unsubstituted C.sub.2-C.sub.10 alkynyl, substituted or unsubstituted aryl, substituted or unsubstituted alkylaryl, substituted or unsubstituted carbocyclic, substituted or unsubstituted heterocyclic, substituted or unsubstituted cyclohexyl, and (CH.sub.2).sub.nO(CH.sub.2).sub.n where n is 1-10. In various preferred embodiments, z represents 1. In various embodiments according to the present invention, the electron-donating group or electron-accepting group can include one or more covalently bound diamondoid groups, and Y in general formula .sup.c may represent any of the above substituents. In certain preferred embodiments, a chromophore may include an electron-donating group including one or more covalently linked diamondoid groups, preferably adamantyl, and the bridging group may include an isophorone group in accordance with general formula .sup.c wherein Y represent an aryl thioether substituent.

[0069] In various preferred embodiments, bridging groups () for nonlinear optical chromophores according to general formula (I) of the present invention include those of the general formula (.sup.d):

##STR00014##

wherein each Y independently represents: a diamondoid-containing group covalently bound to the bridging group through any of the various linkages described herein below including but not limited to ether and thioether linkages; or each Y may represent a hydrogen, an alkyl group, aryl group, sulfur or oxygen linked alkyl or aryl group, an aryl group (optionally bearing a diamondoid group) linked directly by a carbon-carbon bond (e.g., adamantly anisole), a halogen, a halogenated alkyl group, a halogenated aryl group, or a branched or unbranched, optionally heteroatom-containing C.sub.1-C.sub.4 substituent; wherein each a and b independently represents an integer of 0 to 3; and z represents an integer of 1 to 3. In various embodiments, each of the geminal methyl groups on the isophorone bridge of the general formula .sup.d can instead independently represent a moiety selected from the group consisting of substituted or unsubstituted C.sub.1-C.sub.10 alkyl, substituted or unsubstituted C.sub.2-C.sub.10 alkenyl, substituted or unsubstituted C.sub.2-C.sub.10 alkynyl, substituted or unsubstituted aryl, substituted or unsubstituted alkylaryl, substituted or unsubstituted carbocyclic, substituted or unsubstituted heterocyclic, substituted or unsubstituted cyclohexyl, halogens, halogenated alkyl groups (e.g., CF.sub.3), halogenated aryls and heteroaryl groups (e.g., pentafluorothiophenol), and (CH.sub.2).sub.nO(CH.sub.2).sub.n where n is 1-10.

[0070] Preferably, example of suitable -bridge according to the various embodiments of the present disclosure may include the following structure:

##STR00015##

[0071] Examples of chromophores with a furanyl accepting group according to the various embodiments of the present disclosure may include the following chromophores:

##STR00016##

[0072] The first-order hyperpolarizability () is one of the most common and useful NLO properties. An electro-optic coefficient (r.sub.33) is a function of , and a sufficient value of r.sub.33 may indict a good electro-optical property in a given NLO. For example, the sufficient value of r.sub.33 may be equal to or more than 100 pm/V.

[0073] The second-order hyperpolarizability (y) or third-order susceptibility (.sup.(f)), are the normal measures of third-order NLO activity. While there are several methods used to measure these properties, degenerate four-wave mixing (DFWM) is very common. The term four-wave mixing (FWM) is usually reserved for the interaction of four spatially or spectrally distinct fields. In most common FWM processes, some of the frequencies, wave vectors, and polarizations are degenerated. For example, FWM may reduce to most common FWM processes when two or more off the frequencies are degenerate. The most common FWM processes may include, but not limited to, coherent anti-stokes Raman spectroscopy (CARS), coherent stokes Raman spectroscopy (CSRS), stimulated Raman gain spectroscopy (SRS), the inverse Raman effect spectroscopy (TIRES), and/or Raman induced Kerr effect spectroscopy (RIKES). FWM may be used to probe either one-photon resonances or two-photon resonances in a material by measuring the resonant enhancement as one or more of the frequencies are tuned. A method of evaluating third-order NLO properties of thin films, known in the art as degenerate four-wave mixing (DFWM), may be illustrated in FIG. 1. In FIG. 1, Beams 102 and 104 are picosecond, coherent pulses, absorbed by the NLO film 110 deposited on a glass substrate 112. Beam 106 is a weaker, slightly delayed beam at the same wavelength as Beams 102 and 104. Beam 108 is the resulting product of the wave mixing, diffracted off of the transient holographic grating, produced by interferences of beams 102 and 104 in the NLO material of the film 110. Beam 106 can be a control beam at a telecom wavelength which produces a signal beam at a frequency not absorbed by the NLO material.

[0074] The EO property of the poled nonlinear electro-optic material that incorporates nonlinear optical chromophore may be tested as follows. Polarized light, often from a laser, is passed through the poled material that incorporates the poled nonlinear optical chromophore, then through a polarizing filter, and to a light intensity detector. If the intensity of light received at the detector changes as the electric potential applied to the electrodes is varied, the material incorporates a nonlinear optic chromophore and has an electro-optically variable refractive index.

[0075] The relationship between the change in applied electric potential versus the change in the refractive index of the material may be represented as its EO coefficient r.sub.33. This effect is commonly referred to as an electro-optic, or EO, effect. Devices that include materials that change their refractive index in response to changes in an applied electric potential are called electro-optical (EO) devices. For compositions having nonlinear optical chromophore described herein, the EO coefficient r.sub.33 of 150 pm/V, or even larger, and the refractive index of 2.0 or even larger, may be achieved.

Nonlinear Electro-Optic Material

[0076] As used herein, the term nonlinear electro-optic material refers to materials that include both the nonlinear optical chromophore and one or more matrix material, also referred to as host polymer, in which the one or more nonlinear optical chromophore may be incorporated. Suitable matrix materials can include polymers, such as, for example: poly(methylmethacrylate)s (PMMA); polyimides; polyamic acid; polystyrenes; poly(urethane)s (PU); and amorphous polycarbonates (APC).

[0077] Glass transition temperature (T.sub.g) is a temperature at which an amorphous polymer changes from a hard/glassy state to a soft/rubbery state, or vice versa. In various embodiments the matrix material can comprise a poly(methylmethacrylate), for example having a molecular weight of about 120,000 and a glass transition temperature T.sub.g of about 100-165 C., or an APC having a T.sub.g of about 150-220 C.

[0078] The nonlinear optical chromophore can generally be incorporated within the matrix material in virtually any amount or can be used with no matrix material (i.e., neat or 100% chromophore). For example, suitable electro-optic material can comprise a nonlinear optical chromophore in an amount of from about 1% to 90% by weight, based on the entire weight of combined nonlinear optical chromophores and matrix materials. In various embodiments, suitable electro-optic compositions can comprise a nonlinear optical chromophore in an amount of from about 2% to 80% by weight, based on the entire weight of combined nonlinear optical chromophores and matrix materials. In various embodiments, suitable electro-optic compositions can comprise a nonlinear optical chromophore in an amount of from about 3% to 75% by weight, based on the entire weight of combined nonlinear optical chromophores and matrix materials. For example, one or more chromophores can be combined with an amorphous polycarbonate or mixtures of matrix materials at 70 wt % chromophore(s)/30 wt % matrix material(s). In various embodiments, chromophores can be crosslinked with matrix materials or other polymers.

Compositions

[0079] As used herein, the term compositions refers to one or more mixed composition(s) that may include both a nonlinear electro-optic material and solvents. Solvents which are suitable for use may include regular boiling point solvents and high boiling point solvents. As used herein, high boiling point solvents refers to solvents having a boiling point greater than or equal to 100 C. (at 1 atm). In various embodiments, suitable solvents have a boiling point greater than or equal to 110 C., greater than or equal to 120 C., greater than or equal to 130 C., greater than or equal to 140 C., greater than or equal to 150 C., greater than or equal to 160 C., greater than or equal to 170 C., greater than or equal to 180 C., greater than or equal to 190 C., greater than or equal to 200 C., greater than or equal to 210 C., greater than or equal to 220 C., greater than or equal to 230 C., greater than or equal to 240 C., and greater than or equal to 250 C.

[0080] Nonlinear optical chromophores described herein, as well as compositions having nonlinear optical chromophores described herein, may exhibit high thermal stability. The thermal stability of a nonlinear optical chromophore may be evaluated based on a decomposition temperature (T.sub.d) of the chromophore, and/or a thermal decay of the chromophore. The decomposition temperature (T.sub.d) is the temperature at which the chromophore chemically decomposes. For example, the nonlinear optical chromophores described herein may have a decomposition temperature greater than or equal to 225 C. The thermal decay is the percentage of chemically decomposed chromophore under a given temperature for a given period of time.

Methods of Forming Resistive Layers

[0081] As used herein, the term resistive layer refers to one or more layer(s) that may be formed from the compositions defined above through one or more procedures. The one or more procedures may include, but not limited to, spin-coating and/or an atomic layer deposition (ALD) process. Spin-coating may be a procedure to deposit nonlinear electro-optic material onto flat substrates to form resistive layers. For example, a small amount of nonlinear electro-optic material may be applied on the center of the substrate. The substrate may be rotated at speeds up to 10,000 rpm to spread the nonlinear electro-optic material to form resistive layers by centrifugal force. ALD may be an ultrathin film deposition technique controlled by gas phase and sequential self-limiting chemical reactions of the precursors at the material surface.

[0082] In addition, the composition may go through drying and/or poling before the one or more procedures to achieve the desired EO effect. An electro-optic material can be dispersed in a suitable solvent in virtually any amount that provides a homogenous solution and suitable properties for resistive layer formation. For example, the solids content of an electro-optic material in a solvent according to various embodiments described herein can be adjusted depending upon desired resistive layer thickness and spin speed of a spin coating apparatus. As is known in the art, a less viscous solution generally results in a thinner spin coated resistive layer. In various embodiments, the solids content of an electro-optic material in a solvent can be from about 1% to about 25%. In various embodiments, the solids content of an electro-optic material in a solvent can be from about 2% to about 20%. In various embodiments, the solids content of an electro-optic material in a solvent can be from about 5% to about 15%. In the poling process, the electro-optic material may obtain a high EO coefficient r.sub.33 if the chromophores are well aligned under the electrical field. Mathematically, the EO coefficient r.sub.33 can be positively correlated with a strength (e.g., voltage) of the poling electrical field below a maximum voltage. For example, the EO coefficient r.sub.33 and the voltage of the poling electrical field may have a positive relationship (i.e., the higher the voltage, the higher the poling electrical field and so too the r.sub.33) before reaching the maximum voltage. However, the r.sub.33 may decrease after the maximum voltage is reached, probably due to other mechanisms such as dielectric breakdown.

[0083] Example methods in accordance with various embodiments of the present disclosure include providing a composition as described herein, forming a resistive layer comprising the composition, drying the resistive layer (i.e., removing solvent), and poling the resistive layer.

[0084] A suitable resistive layer can be formed on a substrate using, for example, a spin-coating process or ink jet printing. Suitable substrates can include indium-tin-oxide (ITO) coated surfaces, conductive materials, silicon, semi-conductors and the like. Resistive layers can be formed at various thicknesses from submicron to several microns.

[0085] FIG. 2 illustrates an example poling process of a nonlinear electro-optic material. Since the electron density is not evenly distributed inside the nonlinear optical chromophore, the electron density of the electron-accepting group is higher than the electron density of the electron-donating group. Therefore, each nonlinear optical chromophore molecule may comprise a dipole 202, which exhibits positive charge on the electron-donating group side and negative charge on the electron-accepting group side. When no voltage 204 is applied, there is no charge on electrodes 206. The dipoles are randomly directed with no alignment. However, when voltage 204 is applied, electrodes 206 may have charges (e.g., positive charges or negative charges) on them and form an electrical field in between. The dipoles 202 are poled and aligned under the electrical field to make non-centrosymmetric, nonlinear electro-optic materials.

[0086] Resistive layers prepared in accordance with various method embodiments disclosed herein can be poled by applying a suitable voltage across the material at a suitable temperature. Electrodes can be formed or positioned on opposing sides of a resistive layer, or above and below a resistive layer in various devices and structures and a suitable voltage applied across the resistive layer in such a manner. Electrodes can be formed from, for example, gold. Suitable voltages can be from about 50 V/m to about 150 V/m. Suitable temperatures for poling the resistive layer are generally higher than the nonlinear optical chromophore's glass transition temperature (T.sub.g), which is high enough to allow arrangement of the nonlinear optical chromophore within the material. Suitable poling field voltages vary with the thickness of the sample. In some embodiments, poling of the instant nonlinear optical chromophores may be larger or equal to 120 V/m. In addition, the solvent is completely removed from the composition prior to poling.

[0087] After poling the resistive layer, while still maintaining the field of applied voltage, a resistive layer in accordance with various embodiments described herein can be dried or densified by removing the remaining solvent. Solvent is generally removed until the glass transition temperature of the resistive layer approaches the T.sub.g of the chromophore. Drying or removal of the solvent can be undertaken, for example, by slowly and slightly increasing temperature while the poling field is maintained until solvent is removed, then cooling. Drying or removal of the solvent can be undertaken, for example, by cooling while maintaining the applied poling field to a lower temperature such that de-poling does not occur at a substantial rate and then applying vacuum to remove solvent.

[0088] Resistive layers in accordance with the various embodiments herein can be incorporated in various devices including electro-optic devices having open-top or coplanar designs, and devices having permeable layers, opening or the like such that solvent can be driven off after poling. Examples of various devices may include, but not limited to, hybrid electro-optic polymer and TiO.sub.2 double-slot waveguide modulators, ultrabroadband electro-optic modulator based on hybrid silicon polymer dual vertical slot waveguide, plate slot polymer waveguide modulator, electro-optic polymer/TiO.sub.2 multilayer slot waveguide modulators, and/or coplanar electrode polymer modulator.

[0089] As discussed above, the first-order hyperpolarizability () is one of the most common and useful NLO properties. Higher-order hyperpolarizabilities are useful in other applications such as all-optical (light-switching-light) applications. To determine if a nonlinear electro-optic material, such as a compound or polymer, includes a nonlinear optic chromophore with hyperpolarizability and a sufficient electro-optic coefficient (r.sub.33), which is a function of , the material in the form of a resistive layer is placed in an electric field to align the dipoles. This may be performed by sandwiching a resistive layer of the nonlinear electro-optic material between electrodes, such as indium tin oxide (ITO) substrates, gold films, or silver films, for example. To generate a poling electric field, an electric potential is then applied to the electrodes while the nonlinear electro-optic material is heated to its glass transition (T.sub.g) temperature. After a suitable period of time, the temperature is gradually lowered while maintaining the poling electric field. Alternatively, the nonlinear electro-optic material can be poled by corona poling method, where an electrically charged needle at a suitable distance from the resistive layer provides the poling electric field. In either instance, the dipoles in the nonlinear electro-optic material tend to align with the field. Various embodiments according to the present disclosure may include electro-optic materials having a material glass transition temperature greater than or equal to 175 C.

Electro-Optic Devices

[0090] As used herein, the term electro-optic devices refers to devices with electro-optical function that contain one or more resistive layer(s) described above. For example, the electro-optic devices may include electro-optic modulators (EOMs), which are optical devices in which a signal-controlled element exhibiting an electro-optic effect is used to modulate a beam of light. The modulation may be imposed on the phase/frequency, amplitude, and/or polarization of the beam. One EOM may conduct one or more (e.g., one or all) modulations among the phase/frequency, amplitude, or polarization modulations.

[0091] Phase modulation (PM) is a modulation pattern that encodes information as variations in the instantaneous phase of a carrier wave. The phase of a carrier signal is modulated to follow the changing voltage level (amplitude) of the modulation signal. The peak amplitude and frequency of the carrier signal remain constant, but as the amplitude of the information signal changes, the phase of the carrier changes correspondingly.

[0092] Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. Mach-Zehnder (MZ) interferometer as an example. The MZ interferometer may often be used in integrated optics where the requirements of phase stability are more easily achieved. The beam splitter may divide the laser light into two paths, one of which has a phase modulator. The beams may then be recombined. Changing the electric field on the phase modulating path may then determine whether the two beams interfere constructively or destructively at the output, and thereby control the amplitude or intensity of the exiting light. In one example of the MZ interferometer, the modulator may have two arms of electro-optic material. One arm may have electrodes, where a changing voltage can be applied. The other arm may have no voltage applied.

[0093] Polarization modulation in EO materials may be used as a technique for time-resolved measurement of unknown electric fields. Depending on the type and orientation of the EO material, and on the direction of the applied electric field, the phase delay may depend on the polarization direction. For example, EOM used in antenna may conduct the polarization modulation.

[0094] In EOMs, the nonlinear electro-optic materials are spun onto silicon wafers and standard microfabrication techniques are used to deposit and pattern metal electrodes and optical waveguides. For example, one well-known EOM device is the above-mentioned Mach-Zehnder interferometer. The light output is changed by changing the relative phase between the two arms. One common trick to double the effect for the same available drive voltage is to drive the two arms in opposite directions (push-pull mode). Nonlinear electro-optic materials have an interesting advantage over most other electro-optic materials which are crystalline. The direction of nonlinear electro-optic materials' electro-optic activity is entirely determined by the direction of the applied poling field. By poling the two arms of the MZ in opposite directions, the resulting device automatically has push-pull operation with a single applied signal.

[0095] Each EOM may include one or more integrated polymer electro-optic semiconductor circuits. FIGS. 3A and 3B are respective side sectional and cross-sectional views of an integrated polymer electro-optic semiconductor circuit 301, according to an embodiment. A semiconductor substrate 302 includes at least one doping layer 304 patterned across the semiconductor substrate to form portions of semiconductor devices. At least one resistive layer 306 is patterned over the semiconductor substrate. A planarization layer 308 is disposed at least partly coplanar with the at least one conductor layer 306. A polymer optical stack 310 is disposed over the planarization layer 308.

[0096] At least one via 312 may at least partially extend through the polymer optical stack 310. The at least one via may be operatively coupled to a corresponding location on the at least one patterned conductor layer 306. A top conductor layer 314 is disposed over the polymer optical stack and in electrical continuity with the at least one via 312.

[0097] As an alternative to a via 312, other conductors may be substituted to electrically couple the top conductor layer to at least one location on the at least one patterned conductor layer 306. For example, the at least one conductor may be formed entirely or in combination from a via, a wire bond, a conductive bump, and/or an anisotropic conductive region.

[0098] The top conductor layer 314 may be formed to include a metal layer or a conductive polymer, for example. The top conductor may be plated to increase its thickness. The top conductor layer may include at least one high speed electrode 316 formed as a pattern in the top conductor layer 314, the high speed electrode 316 being operatively coupled to receive a signal from the at least one via 312 or other conductive structure from the corresponding location on the at least one patterned conductor layer 306. Thus, the at least one via 312 or other conductive structure is configured to transmit an electrical signal from semiconductor electrical circuitry formed on the semiconductor substrate 302 to the at least one high speed electrode 316 through or around the polymer optical stack 310.

[0099] According to embodiments, the at least one patterned conductor layer 306 is configured to form a ground electrode 318 parallel to the at least one high speed electrode 316. An active region 320 of the polymer optical stack 310 is positioned to receive a modulation signal from the high speed electrode 316 and the ground electrode 318. The active region 320 includes a poled region that contains at least one hyperpolarizable organic chromophore.

[0100] The polymer optical stack 310 is configured to support the active region 320 as well as receive and guide light 322 to and from the active region. The polymer optical stack 310 may include at least one bottom cladding layer 324 and at least one top cladding layer 326 disposed respectively below and above an electro-optic layer 328. The bottom 324 and top 326 cladding layers, optionally in cooperation with the planarization layer 308, are configured to guide inserted light 322 along the plane of the electro-optic layer 328. Light guiding structures 330 are formed in the polymer optical stack 310 to guide the light 322 along one or more light propagation paths through the electro-optic layer 328 and/or non-active core structures (not shown). In the embodiment of FIGS. 3A and 3B, the guidance structures 330 are formed as trench waveguides that include etched paths in the at least one bottom cladding layer 324.

[0101] The integrated polymer electro-optic semiconductor circuit 301 includes a semiconductor electrical circuit formed from a complex of the doping layer pattern 304 and the at least one patterned conductor layer 306. According to an embodiment, the semiconductor electrical circuit is configured, when in operation, to drive the electrodes 316, 318 with a series of modulated electrical pulses. A resultant modulated electrical field is thus imposed across the active region 320 and results in modulated hyperpolarization of the poled organic chromophores embedded therein. A complex of electrodes 316, 318, active region 320 and light guidance structures 330. The modulated hyperpolarization may thus modulate the velocity light passed through the poled active region 320 of the polymer optical stack 310. Repeatedly modulating the velocity of the transmitted light creates a phase-modulated light signal emerging from the active region. Such an active region 320 may be combined with light splitters, combiners (not shown), and other active regions to create light amplitude modulators. Light amplitude modulators herein include MZ optical modulators. Other light amplitude modulators may include ring resonator modulator, which includes one or more ring resonators which is a set of waveguides in which at least one is a closed loop coupled to some light input and output. Other light amplitude modulators may include in-phase and quadrature (I/Q) modulator, which modulates based on the summation of two I/Q signals that are in quadrature.

[0102] A combination of at least one electro-optic active region 320, at least two electrodes 316, 318, and corresponding light guiding structures 324, 326, 330 may be considered an electro-optic device 332, 334. A two-channel electro-optic device 334 may be formed from one ground electrode 318 and corresponding pairs of active regions 320 and high speed electrodes 316a, 316b. The two channels of a two channel electro-optic device 334 may operate in cooperation, such as in a push-pull manner to form an MZ optical modulator.

[0103] Additional devices may be formed using electrodes or resistors 336 that are not configured for high-speed operation. The operation of one such illustrated device is described below in conjunction with the description of an optical phase bias device.

[0104] FIG. 4 illustrates an end view of a slot modulator with highly doped silicon slab and rail. Referring specifically to FIG. 4, an end view of a slot modulator 400 is illustrated which in this example is a Mach-Zehnder modulator including two slot waveguides 412 and 414 in parallel and driven in push-pull with a single coplanar transmission line 416. It should be understood that a single slot waveguide can be used to form a slot modulator in accordance with the present invention. In this example, a typical SiO.sub.2 box 418 is formed on a silicon substrate 419. Transmission line 416 is formed of spaced apart aluminum conductors positioned on SiO.sub.2 box 418 with G conductors 420 and 421 on each edge and an S conductor 422 extending midway therebetween. Slot waveguide 412 includes a slab 424 extending inwardly from G conductor 420 and a slab 426 extending inwardly from S conductor 422. A vertically extending rail 428 is attached to the inner end of slab 424 and a vertically extending rail 430, spaced from rail 428, is attached to the inner end of slab 426. Rails 428 and 430 primarily form slot waveguide 412. The area between G conductor 420 and S conductor 422, including the slot formed between rails 428 and 430, is filled with EO polymer cladding material 432. Slot waveguide 414 is a mirror image of slot waveguide 412 with slabs and rails positioned and connected as described in conjunction with slot waveguide 412. In the following disclosure, only slot waveguide 412 is discussed in detail with the understanding that all of the details apply similarly to slot waveguide 414.

[0105] To aid in understanding the size of the structure being discussed, the thickness of transmission line 416 is 1 m, slabs 424 and 426 are each 70 nm tall and 0.5 to 1 m wide. Rails 428 and 430 are each 220 nm tall (lower surface to upper end) and 240 nm wide with a 200 nm spacing between the centers. The total length of slot waveguide 412 from G conductor 420 to S conductor 422 is 10 m long.

[0106] In the prior art, slab 424 and rail 428 are integrally formed and also integrally formed with G conductor 420. Similarly, slab 426 and rail 430 are integrally formed and also integrally formed with S conductor 422. In a similar fashion, the slabs and rails of slot waveguide 414 are integrally formed with G conductor 421 and S conductor 422. In slot modulator 400 slabs 424 and 426 and rails 428 and 430 are formed of silicon that is highly doped (N.sup.+++) to reduce resistivity and to achieve a high bandwidth.

[0107] EOMs comprising various embodiments of nonlinear optical chromophores according to the present disclosure may include modulators applied in, for example, slot modulators (e.g., slot modulators for wafer-level poling), photonic integrated circuits (e.g., polymer photonic integrated circuits), datacenter switching, high voltage sensing equipment relevant to electric power industry, electrical-to-optical signal transduction equipment which transmits multiple television signals relevant to cable television (CATV) or satellite television, broad bandwidth acoustic spectrum analyzers, optical gyroscopes, phased array radar (e.g., integrated antenna/electro-optic modulator or w-band optical modulator), photonically detected radar, time stretching and ultrafast analog-to-digital conversion equipment, components for fiber optical and satellite telecommunications, generation equipment and detection equipment of ultrafast electrical fields, electric field sensor (e.g., electro-optic E-field sensor), land mine detection equipment, device related to wavelength division multiplexing, optical switching, devices related to spatial light modulation (e.g., devices related to beam steering), and/or augmented reality (AR)/virtual reality (VR) equipment (e.g., full-spectrum visible electro-optic modulator).

[0108] For example, the photonic integrated circuit (PIC) is a chip that performs optical signal processing. The chip may contain two or more photonic components (e.g., resistive layer with nonlinear electro-optic materials) which form a functioning circuit to utilize photons to detect, generate, transport, and process light. The PICs have demonstrated huge potentials in delivering the performance (e.g., speed, size and efficiency) required for upcoming applications, such as 6G, automotive light detection and ranging (LiDAR), consumer healthcare, artificial intelligence (AI), optical computing, virtual reality (VR), and/or augmented reality (AR).

[0109] EO polymer materials herein may also be used with plasmonic-based devices, including semiconductor modulators and plasmonic slot modulators. A semiconductor slot modulator for use consistent with the present disclosure is a type of photonic slot modulator where the high-refractive-index materials on either side of the slot are semiconductors (e.g., silicon). Modulation is typically achieved by changing the refractive index of the semiconductor via the plasma dispersion effect, where an applied voltage alters the concentration of free charge carriers.

[0110] A plasmonic slot modulator for use consistent with the present disclosure is another type of photonic slot modulator that utilizes a slot waveguide. However, in this case, the slot is generally formed between two metallic structures, often filled with a dielectric material. The light is guided as a surface plasmon polariton (SPP), a hybrid electromagnetic wave coupled to the oscillation of free electrons at the metal-dielectric interface. This allows for extremely strong light confinement and is often used to create ultra-compact, high-speed modulators.

SYNTHESIS EXAMPLE

Synthesis Example 1: Preparation of 2-(3-cyano-4-((1E,3E)-3-(3-((E)-4-(diphenylamino)styryl)-5,5-dimethyl-2-(phenylthio)cyclohex-2-en-1-ylidene)prop-1-en-1-yl)-5-phenyl-5-(trifluoromethyl)thiophen-2(5H)-ylidene)malononitrile

Example 1a: Synthesis of 4-(diphenylamino)benzaldehyde

##STR00017##

[0111] A solution of triphenylamine in DCM was treated with DMF (10 eq). POCl3 (1.5 eq) was added dropwise, and the mixture was stirred at room temperature until analysis indicated full conversion. The DCM was evaporated, then the remaining solution was poured into icy 10% aqueous sodium carbonate. The slushy mixture was stirred until the ice had melted, then the resultant solids were isolated and dried by vacuum filtration to afford the title compound.

Example 1b: Synthesis of (E)-3-(4-(diphenylamino)styryl)-5,5-dimethyl-2-(phenylthiol)cyclohex-2-en-1-one

##STR00018##

[0112] A suspension of 4-(diphenylamino)benzaldehyde and 3,5,5-trimethyl-2-(phenylthio)cyclohex-2-en-1-one (1.2 eq) in EtOH were treated with LiOEt (2 eq) and piperidine (2 eq). The mixture was heated to 70 C. and stirred until analysis indicated full conversion. The reaction mixture was quenched with MeOH, then the resultant solids were isolated by vacuum filtration to afford the title compound.

Example 1c: Synthesis of (E)-2-(3-((E)-4-(diphenylamino)styryl)-5,5-dimethyl-2-(phenylthio)cyclohex-2-en-1-ylidene)acetonitrile

##STR00019##

[0113] A suspension of NaH (2 eq) in THF was stirred at room temperature. Then diethyl (cyanomethyl)phosphonate (2.2 eq) was added, and the mixture stirred. To this was added (E)-3-(4-(diphenylamino)styryl)-5,5-dimethyl-2-(phenylthiol)cyclohex-2-en-1-one, and the solution was stirred at 70 C. until analysis indicated full conversion. The reaction mixture was concentrated then quenched with MeOH. The resultant solids were isolated by vacuum filtration to afford the title compound.

Example 1d: Synthesis of (E)-2-(3-((E)-4-(diphenylamino)styryl)-5,5-dimethyl-2-(phenylthio)cyclohex-2-en-1-ylidene)acetaldehyde

##STR00020##

[0114] A solution of (E)-2-(3-((E)-4-(diphenylamino)styryl)-5,5-dimethyl-2-(phenylthio)cyclohex-2-en-1-ylidene)acetonitrile in DCM was treated with dropwise addition of DIBAL-H (1.5 eq). The mixture was stirred at room temperature until analysis indicated full conversion. The mixture was quenched by addition of sodium sulfate decahydrate, then the slurry was adsorbed onto silica gel for chromatography. The product fractions were concentrated to afford the title compound.

Example 1e: Synthesis of 4,4,4-trifluoro-3-hydroxy-3-phenylbutan-2-one

##STR00021##

[0115] A solution of Tributyl(1-ethoxyvinyl)tin in THF was treated with n-butyllithium at 0 C. under a blanket of N.sub.2. Then 2,2,2-trifluoro-1-phenylethan-1-one was added. The reaction was stirred at the same temperature until analysis indicated full conversion. The reaction mixture was quenched with 6N HCl, then the resultant solids were isolated to afford the title compound.

Example 1f: Synthesis of S-(1,1,1-trifluoro-3-oxo-2-phenylbutan-2-yl) ethanethioate

##STR00022##

[0116] A solution of 4,4,4-trifluoro-3-hydroxy-3-phenylbutan-2-one in toluene was treated sequentially with NaHDMS then triflic anhydride at 0 C. After full conversion to the intermediate, the reaction mixture was treated with thioacetic acid and stirred at 100 C. until full conversion. The mixture was worked up and purified by crystallization to afford the title compound.

Example 1g: Synthesis of 4,4,4-trifluoro-3-mercapto-3-phenylbutan-2-one

##STR00023##

[0117] A solution of S-(1,1,1-trifluoro-3-oxo-2-phenylbutan-2-yl) ethanethioate in EtOH was treated with 6N HCl. The reaction was stirred at 40 C. until analysis indicated full conversion. The mixture was worked up and purified by crystallization to afford the title compound.

Example 1h: Synthesis of 2-(3-cyano-4-methyl-5-phenyl-5-(trifluoromethyl)thiophen-2(5H)-ylidene)malononitrile

##STR00024##

[0118] A solution of 4,4,4-trifluoro-3-mercapto-3-phenylbutan-2-one and malononitrile in ethylene glycol was treated with lithium carbonate at stirred at 100 C. until analysis indicated full conversion. The reaction mixture was diluted with DCM and washed with brine. The organics were isolated, dried, and concentrated to afford the title compound.

Example 1i: Synthesis of 2-(3-cyano-4-((1E,3E)-3-(3-((E)-4-(diphenylamino)styryl)-5,5-dimethyl-2-(phenylthio)cyclohex-2-en-1-ylidene)prop-1-en-1-yl)-5-phenyl-5-(trifluoromethyl)thiophen-2(5H)-ylidene)malononitrile

##STR00025##

[0119] A suspension of (E)-2-(3-((E)-4-(diphenylamino)styryl)-5,5-dimethyl-2-(phenylthio)cyclohex-2-en-1-ylidene)acetaldehyde and 2-(3-cyano-4-methyl-5-phenyl-5-(trifluoromethyl)thiophen-2(5H)-ylidene)malononitrile (1.1 eq) in EtOH was stirred at 60 C. until analysis indicated full conversion. The reaction mixture was cooled and filtered. The solids were recrystallized from MeOH to afford the title compound.

ENUMERATED EMBODIMENTS

[0120] The following list of enumerated embodiments presents claims with multiply dependent claims depending from multiply dependent claims for presentation in those jurisdictions where such dependencies are allowed as well as additional claims, which may be presented during the examination of the application or any divisional or continuation thereof. [0121] EE 1. A nonlinear optical chromophore of a general formula (I):

##STR00026## [0122] wherein D represents an organic electron-donating group; A represents an organic electron-accepting group having an electron affinity greater than the electron affinity of D; and represents a -bridge between the organic electron-accepting group and the organic electron-donating group; wherein A comprises electron acceptors having a following formula (A.sup.1):

##STR00027## [0123] wherein R.sub.1 and R.sub.2 each independently represent a moiety selected from the group consisting of a substituted or unsubstituted aryl, a substituted or unsubstituted alkyl, or a hydrogen; and wherein X is S, Se, or Te. [0124] EE 2. The nonlinear optical chromophore according to EE 1, wherein at least one of R.sub.1 and R.sub.2 is a C.sub.6-C.sub.20 aryl. [0125] EE 3. The nonlinear optical chromophore according to EE 1 or EE 2, wherein at least one of R.sub.1 and R.sub.2 is a linear, branched, cyclic bicyclic, or tricyclic C.sub.1-C.sub.20. [0126] EE 4. The nonlinear optical chromophore according to any one of EEs 1-3, wherein at least one of R.sub.1 and R.sub.2 is a halogen-substituted alkyl or a halogen-substituted aryl. [0127] EE 5. The nonlinear optical chromophore according to any one of EEs 1-4, wherein at least one of R.sub.1 and R.sub.2 is a trifluoromethyl group. [0128] EE 6. The nonlinear optical chromophore according to any one of EEs 1-5, wherein at least one of R.sub.1 and R.sub.2 is a methyl, an ethyl, or an isopropyl. [0129] EE 7. The nonlinear optical chromophore according to any one of EEs 1-6, wherein at least one of R.sub.1 and R.sub.2 is a phenyl or an anisole. [0130] EE 8. The nonlinear optical chromophore according to any one of EEs 1-7, wherein at least one of R.sub.1 and R.sub.2 is a phenyl or a substituted phenyl. [0131] EE 9. The nonlinear optical chromophore according to any one of EEs 1-8, wherein the nonlinear optical chromophore has a refractive index greater than or equal to about 2. [0132] EE 10. A resistive film comprising the nonlinear optical chromophore according to any one of EEs 1-9 dispersed and poled within a matrix material. [0133] EE 11. An electro-optic device comprising one or more resistive film, wherein the one or more resistive film each comprising a nonlinear optical chromophore dispersed and poled within a host polymer matrix, wherein the nonlinear optical chromophore of a general formula (I):

##STR00028## [0134] wherein D represents an organic electron-donating group; A represents an organic electron-accepting group having an electron affinity greater than the electron affinity of D; and represents a -bridge between the organic electron-accepting group and the organic electron-donating group; wherein A comprises electron acceptors having the following formula (A.sup.1):

##STR00029## [0135] wherein R.sub.1 and R.sub.2 each independently represent a moiety selected from the group consisting of a substituted or unsubstituted aryl, a substituted or unsubstituted alkyl, or a hydrogen; and wherein X is S, Se, or Te. [0136] EE 12. The electro-optic device according to EE 11, wherein at least one of R.sub.1 and R.sub.2 is a C.sub.6-C.sub.20 aryl. [0137] EE 13. The electro-optic device according to EE 11 or EE 12, wherein at least one of R.sub.1 and R.sub.2 is a linear, branched, cyclic bicyclic, or tricyclic C.sub.1-C.sub.20. [0138] EE 14. The electro-optic device according to any one of EEs 11-13, wherein at least one of R.sub.1 and R.sub.2 is a halogen-substituted alkyl or a halogen-substituted aryl. [0139] EE 15. The electro-optic device according to any one of EEs 11-14, wherein at least one of R.sub.1 and R.sub.2 is a trifluoromethyl group. [0140] EE 16. The electro-optic device according to any one of EEs 11-15, wherein at least one of R.sub.1 and R.sub.2 is a methyl, an ethyl, or an isopropyl. [0141] EE 17. The electro-optic device according to any one of EEs 11-16, wherein at least one of R.sub.1 and R.sub.2 is a phenyl or an anisole. [0142] EE 18. The electro-optic device according to any one of EEs 11-17, wherein at least one of R.sub.1 and R.sub.2 is a phenyl or a substituted phenyl. [0143] EE 19. The electro-optic device according to any one of EEs 11-18, wherein the nonlinear optical chromophore has a refractive index greater than or equal to about 2. [0144] EE 20. The electro-optic device according to any one of EEs 11-19, wherein the electro-optic device is an electro-optic modulator (EOM).