Use of dithiocarbamate esters and bis-dithiocarbamate esters in the preparation of organic-inorganic nanocomposites

Abstract

The invention relates to tuned multifunctional linker molecules for charge transport through organic-inorganic composite structures. The problem underlying the present invention is to provide multifunctional linker molecules for tuning the conductivity in nanoparticle-linker assemblies which can be used in the formation of electronic networks and circuits and thin films of nanoparticles. The problem is solved according to the invention by providing a multifunctional linker molecule of the general structure
CON.sub.1-FUNC.sub.1-X-FUNC.sub.2-CON.sub.2
in which X is the central body of the molecule, FUNC.sub.1 and FUNC.sub.2 independently of each other are molecular groups introducing a dipole moment and/or capable of forming intermolecular and/or intramolecular hydrogen bonding networks, and CON .sub.1 and CON .sub.2 independently of each other are molecular groups binding to nanostructured units comprising metal and semiconductor materials.

Claims

1. A nanoparticle-linker assembly comprising: at least two nanoparticle units; and a multifunctional linker molecule; wherein the at least two nanoparticle units are at least two units selected from the group consisting of a nanowire, a nanotube, and a nanobelt, the multifunctional linker molecule is bound to each of the at least two nanoparticle units, and the multifunctional linker molecule is of the structure
CON.sub.1-FUNC.sub.1-X-FUNC.sub.2-CON.sub.2 wherein X is a central body of the molecule which comprises one selected from the group consisting of an alkane, an alkene of 3 to 12 carbon atoms, an alkyne, and an aromatic -system, FUNC.sub.1 and FUNC.sub.2 independently of each other are molecular groups which are not hydrocarbon groups and which provide to the multifunctional linker molecule a capability of forming intermolecular and/or intramolecular hydrogen bonding networks, and CON .sub.1 and CON .sub.2 independently of each other are molecular groups which bind to the at least two nanoparticle units.

2. The nanoparticle-linker assembly according to claim 1, wherein CON.sub.1 and CON.sub.2 are identical or different and FUNC.sub.1 and FUNC.sub.2 are identical or different.

3. The nanoparticle-linker assembly according to claim 1, wherein a length of the multifunctional linker molecule is between about 8 and about 30 .

4. The nanoparticle-linker assembly according to claim 1, wherein a structure of X comprises a hydrocarbon skeleton with two identical or different substituents that connect to or form the molecular groups FUNC.sub.1 and FUNC.sub.2.

5. The nanoparticle-linker assembly according to claim 4, wherein X comprises two substituents selected from the group consisting of an amine, a carboxylic acid, a sulfonic acid and a phosphonic acid.

6. The nanoparticle-linker assembly according to claim 4, wherein the substituents of X are directed at an angle relative to one another such that 90<<270.

7. The nanoparticle-linker assembly according to claim 4, wherein X comprises at least one structural component selected from the group consisting of: a conjugated system, an aromatic -system; a heteroatom selected from the group consisting of N, O and S; an electron donating substituent selected from the group consisting of CH.sub.3, O.sup., COO.sup., N(CH.sub.3).sub.2 and NH.sub.2; and an electron accepting substituent selected from the group consisting of CN, COCH.sub.3, CONH.sub.2, CO.sub.2CH.sub.3, N(CH.sub.3).sub.3.sup.+, NO.sub.2, F, Cl, Br, I, OCF.sub.3, and SO.sub.2NH.sub.2.

8. The nanoparticle-linker assembly according to claim 4, wherein X is a structure selected from the group consisting of: a structure having a formula selected from the group of formulae consisting of: ##STR00017## and a derivative thereof further comprising N, S, and/or O, or electron donating or accepting substituents; wherein R is methyl, phenyl or alkoxyl and wherein FUNC.sub.1 and FUNC.sub.2 are attached via the N-atoms of the two amine substituents indicated by N; a structure having a formula selected from the group of formulae consisting of: ##STR00018## and derivatives thereof containing electron donating or accepting substituents wherein FUNC.sub.1 and FUNC.sub.2 are attached via the N-atoms of the amine substituents indicated by N; a structure having a formula selected from the group of formulae consisting of: ##STR00019## and derivatives thereof comprising N, S, and/or O, or electron donating or accepting substituents; and wherein FUNC.sub.1 and FUNC.sub.2 are attached via the carbon atoms of the two carboxylic acid substituents indicated by C; a structure having a formula selected from the group of formulae consisting of: ##STR00020## wherein FUNC.sub.1 and FUNC.sub.2 are attached via the carbon atoms of the two carboxylic acid substituents indicated by C; a structure having a formula selected from the group of formulae consisting of: ##STR00021## and derivatives thereof containing electron donating or accepting substituents wherein FUNC.sub.1 and FUNC.sub.2 are attached via the N- or S-atoms of the two amine or sulfonic acid substituents indicated by N and S; a structure having a formula selected from e group of formulae consisting of: ##STR00022## wherein Z represents amine (ZN) or a carboxymethyl (ZCH(R)C) residue, wherein R is an amino acid side chain and FUNC.sub.1 and FUNC.sub.2 are attached via Z; and c) an electron donor selected from hydroquinones substituted with at least two groups selected from the groups consisting of an amine, a carboxylic acid, a sulfonic acid and a phosphonic acid; and d) an electron acceptor selected from quinones and diimides substituted with at least two groups selected from the groups consisting of an amine, a carboxylic acid, a sulfonic acid and a phosphonic acid.

9. The nanoparticle-linker assembly according to claim 8, wherein FUNC.sub.1 and FUNC.sub.2 independently of each other are connected to X via N, C, S, or P, and are selected from the group consisting of: NH, NHCO, NHCONH, NHCSNH, NHCONHNH, NHCSNHNH, NHCONHNHCO, and NHCONHNHCO in case of a connection via N; CONH, CONHNH, and CONHNHCO in case of a connection via C; SO.sub.2NH, SO.sub.2NHNH, and SO.sub.2NHNHCO in case of a connection via S; and PO.sub.2NH, PO.sub.2NHNH, and PO.sub.2NHNHCO in case of a connection via P.

10. The nanoparticle-linker assembly according to claim 9, wherein CON .sub.1 and CON .sub.2 connected to FUNC.sub.1 and FUNC.sub.2 via NH or CO, independently of each other are selected from the groups consisting of: (CHR).sub.nCOOH; (CHR).sub.nNC; (CHR).sub.nNH.sub.2; (CHR).sub.nNHCS.sub.2H; (CHR).sub.nOPO.sub.3H.sub.2; (CHR).sub.nOSO.sub.3H; (CHR).sub.nPO.sub.3H.sub.2; (CHR).sub.nSH; (CHR).sub.nSO.sub.3H; CSOH; and CS.sub.2H in case of a connection via NH; and (CHR).sub.nCOOH; (CHR).sub.nNC; (CHR).sub.nNH.sub.2; (CHR).sub.nNHCS.sub.2H; (CHR).sub.nOPO.sub.3H.sub.2; (CHR).sub.nOSO.sub.3H; (CHR).sub.nPO.sub.3H.sub.2; (CHR).sub.nSH; and (CHR).sub.nSO.sub.3H in case of a connection via CO; and ionic forms thereof, wherein R is H, CH.sub.2OH, or CH.sub.3 and n is 1 or 2.

11. The nanoparticle-linker assembly according to claim 10, wherein CON .sub.1 and CON .sub.2 independently of each other comprise branched molecular structures.

12. The nanoparticle-linker assembly according to claim 10, wherein CON .sub.1 and CON .sub.2 independently of each other comprise dithiocarbarnateesters or bis-dithiocarbamateesters.

13. The nanoparticle-linker assembly according to claim 1, wherein the multifunctional linker molecule is one selected from the group consisting of 1,4-dimercaptoacetamidobenzene of the formulae: ##STR00023## wherein R.sub.1,2 is independently selected from CH.sub.3 and/or Cl; 1,4-dimercaptoacetamidocyclohexane, 1,4-dimercaptoacetamido-9,10-anthraquinone, 1,5-dimercaptoacetamido-9,10-anthraquinone, 1,8-dimercaptoacetamidooctane, 1,4-dithiocarbamatobenzene, 1,4-dithiocarbamatocyclohexane, dimethyl-N,N-1,4-cyclohexylaminebis(dithiocarbamate), and dimethyl-N,N-1,4-phenyleneaminebis(dithiocarbamate).

14. A 1-, 2-, or 3-dimensional assembly of nanostructured units comprising the nanoparticle-linker assembly according to claim 1, wherein the conductivity of the assembly is determined by the structure of the multifunctional linker.

15. The 1-, 2-, or 3-dimensional assembly of nanostructured units according to claim 14, wherein the nanoparticle units comprise gold.

16. A film comprising the 1-, or 3-dimensional assembly of nanostructured units according to claim 14.

17. An electronic circuit element, electrode or metal coating comprising the 1-, 2-, or 3-dimensional assembly of nanostructured units according to claim 14 wherein the circuit element, electrode or metal coating is self-assembled.

18. A film comprising the 1-, 2-, or 3-dimensional assembly of nanostructured units according to claim 15.

19. An electronic circuit element, electrode or metal coating comprising the 1-, 2- or 3-dimensional assembly of nanostructured units according to claim 15, wherein the circuit element, electrode or metal coating is self-assembled.

20. The 1-, 2- or 3-dimensional assembly of nanostructured units according to claim 15, wherein a size of a gold nanoparticles in the nanoparucle unit is from about 5 nm to about 20 nm, a resistivity of the assembly is of the order of 10.sup.2 cm for a film thickness of about 30 nm, and the resistivity decreases with decreasing temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: Schematic representations of possible bonding of dithiocarbamate compounds to gold surfaces. (a) Dithiocarbamate salt, purely electrostatic. (b) Dithiocarbamate salt, purely covalent. (c) Dithiocarbamate ester (deprotonated), purely electrostatic. (d) Dithiocarbamate ester, purely covalent.

(2) FIG. 2: Schematic drawing of the synthetic routes for substituting amino functionalized molecules with mercaptoacetamido groups (a) or with dithiocarbamates (b).

(3) FIG. 3: Schematic drawing of the linker molecules synthesized according to the routes described in FIG. 2 (a and b). 1,4-dimercaptoacetamidobenzene (1), 1,4-dimercaptoacetamido-2,5-dimethylbenzene (2), 1,4-dimercaptoacetamido-2,5-dichlorobenzene (3), 1,4-dimercaptoacetamidocyclohexane (4), 1,4-dimercaptoacetamido-9,10-anthraquinone (5), 1,8-dimercaptoacetamido-9,10-anthraquinone (6), 1,4-dithiocarbamatobenzene disodium salt (7), 1,4-dithiocarbamatocyclohexane disodium salt (8) 1,8-dimercaptoacetamidoctane (9), and the commercially available 1,9-nonanedithiol (10).

(4) FIG. 4: I-V characteristics of Au-nanoparticles interconnected by the linker molecules 1 (-) 2 ( - - - ), 3( . . . ), 4 ( . - . - . ) and 10 ( - - - ) and self-assembled onto interdigitated Au-electrode structures by the layer-by-layer assembly technique to a film thickness of approx. 30 nm.

(5) FIG. 5: Temperature dependence of the conductivity of Au-nanoparticles interconnected by the linker molecules 1 (-) and 7 ( - - - ) and self-assembled onto interdigitated Au-electrode structures by the layer-by-layer assembly technique to a film thickness of approx. 30 nm.

(6) FIG. 6: I-V characteristics of Au-nanoparticles interconnected by the linker molecules 5 (-), 6 ( - - - ), 7 ( . . . ), 8 ( . - . - . ), and 9 ( - - - ) and self-assembled onto interdigitated Au electrode structures by the layer-by-layer assembly technique to a film thickness of approx. 30 nm.

(7) FIG. 7: UV-visible absorption spectra of Au-nanoparticles interconnected by linker molecules 1 (-), 6 ( - - - ), and 7 ( . . . ) assembled onto a silanized glass substrate by the layer-by-layer assembly technique to a film thickness of approx. 30 nm. The absorption spectra are due to two identical films, one on each side of the substrate.

(8) FIG. 8: UV-visible absorption spectra of films of Au-nanoparticles interconnected by the linker molecule dimethyl-N,N-1,4-diaminocyclohexane-bis(dithiocarbamate) (11) assembled onto a silanized glass substrate by the layer-by-layer assembly technique. The thickness of the film after cycle 23 is approx. 20 nm. The absorption spectra are due to two identical films, one on each side of the substrate.

(9) FIG. 9: UV-visible absorption spectra of films of Au-nanoparticles interconnected by the linker molecule dim ethyl-N,N-1,4-diaminobenzene-bis(dithiocarbamate) (12) assembled onto a silanized glass substrate by the layer-by-layer assembly technique. The thickness of the film after cycle 14 is approx. 15 nm. The absorption spectra are due to two identical films, one on each side of the substrate.

(10) FIG. 10: Temperature dependence of the resistivity of Au-nanoparticles interconnected by the linker molecule dimethyl-N,N-1,4-diaminocyclohexane-bis(dithiocarbamate) (11) and self-assembled onto interdigitated Au-electrode structures by the layer-by-layer assembly technique to a film thickness of approx. 20 nm.

(11) FIG. 11: Temperature dependence of the resistivity of Au-nanoparticles interconnected by the linker molecule dimethyl-N,N-1,4-diaminobenzene-bis(dithiocarbamate) (12) and self-assembled onto interdigitated Au-electrode structures by the layer-by-layer assembly technique to a film thickness of approx. 15 nm.

(12) All experimental examples provided in the following section were achieved by assembling dodecylamine stabilized Au-nanoparticles into films interconnected by various linker molecules using the layer-by-layer assembly technique and substrates with interdigitated electrode structures. The nanoparticles were synthesized according to a method described by Brust et al. (Brust, M., Bethell, D., Kiely, C. J., Schiffrin, D. J. (1998) Langmuir 14, 5425-5429 Self-assembled gold nanoparticle thin films with nonmetallic optical and electronic properties), using dodecylamine as a capping molecule. Prior to the assembly process, the electrodes were functionalized with a (3-aminopropyl)dimethylethoxysilane. For the assembly process, a 1 mM solution of the linker molecule was used and the concentration of the Au-nanoparticle solution was approx. 0.5 mM. The assembly process was monitored using UV-visible absorption spectroscopy. The film thickness for all assemblies was adjusted to an optical density (OD) of approximately 0.32-0.35 at the maximum of the plasmon band, which amounts to a film thickness of roughly 30 nm as determined by AFM. The thickness of the films varies slightly from assembly to assembly. It has been verified, that these observed alterations in the film thickness introduce only a small uncertainty of 5% in the I-V characteristics. With all assemblies, temperature dependent measurements of the conductivity were performed between 100 K and 300 K. The resistivity of the assemblies were calculated according to =RAL.sup.1, with A being the cross sectional area (A=30 nm200 mm) and L=60 m.

(13) It has to be pointed out that the results obtained from these assemblies are for the following reasons average values for the multifunctional linker molecules:

(14) The sizes of the Au-nanoparticles vary between approx. 3 and 30 nm.

(15) The assembly of the nanoparticles was performed by the layer-by-layer assembly technique and as a result of the flexibility of the linker molecules the particle-particle distance can vary and the assembled films might contain some inhomogenieties.

(16) Phenylene-1,4-diamine derivatives with different substituents in the 2- and 5-positions of the conjugated -system have been used to synthesize dithiol linker molecules (dimercaptoacetamido-benzene, RH (1), RCH.sub.3 (2), and RCl (3)), depicted in FIG. 3. The change in the electron density on the ring structure itself can be described using the so-called Hammett parameter (.sub.p.sup.+). The Hammett equation for the calculation of substituent effects on reaction rates and chemical equilibria was introduced by Hammett using the ionization of meta- and para-substituted benzoic acids. From this equation the substituent constant .sub.p.sup.+ can be obtained which are negative for electron donating substituents and positive for electron accepting groups. These linker molecules were synthesized according to the route described in FIG. 2a. The I-V characteristics of the thin film assemblies using the three different dimercaptoacetamido-benzene derivatives provide evidence, that the substituents in positions 2 and 5 provides a means for fine tuning the conductivity through such assemblies (FIG. 4). The resistances obtained for these assemblies are summarized in Table 1. Temperature dependent measurements of the conductivity provide evidence for a thermal activated transport process (FIG. 5). The activation energy was obtained from fitting the plots (T.sup.1) to

(17) $={}_0.Math.\exp \left(\frac{E_A}{k_B.Math.T}\right)$

(18) The activation energies obtained for these molecules are also summarized in Table 1.

(19) TABLE-US-00001 TABLE 1 Summary of the resistivity and the activation energy E.sub.A for the linker molecules 110 (see FIG. 3). Linker molecule ( cm) E.sub.A (meV) 1 18 .Math. 10.sup.1 74 2 10 .Math. 10.sup.1 110 3 .sup.3 .Math. 10.sup.2 96 4 6.9 .Math. 10.sup.2 88 5 6.41 31 6 6.0 112 7 9.1 .Math. 10.sup.1 8 10.2 .Math. 10.sup.1 25 9 4.2 .Math. 10.sup.1 15 10 8.7 .Math. 10.sup.2 42

(20) Using the same synthetic route that was used for substituting the benzene derivatives (FIG. 3), diaminocyclohexane was used to synthesize a dimercaptoacetamido-cyelohexane (4) linker molecule. This system thus provides us with the possibility to directly obtain information to which degree the conductivity in these assemblies is reduced, when a conjugated system is exchanged with a non-conjugated system. The I-V characteristic of this linker molecule is also depicted in FIG. 4. The resistivity of the assembly obtained for this linker molecule is =6910.sup.2 cm. This provides evidence that changing the degree of conjugation of the linker molecule influences the conductivity through these assemblies.

(21) The effect of introducing an electron acceptor as a linker molecule is demonstrated using 1,4-dimercaptoacetamido-anthraquinone (5) and 1,8-dimercaptoacetamido-anthraquinone (6). Both linker molecules were synthesized according to the route described in FIG. 2a. The room temperature resistivity of these assemblies was found to be 2 orders of magnitude smaller than the resistances obtained from assemblies interlinked with substituted diaminobenzene compounds. For both compounds 5 and 6, the resistance was of the same order of magnitude, =6.41 cm (5) and =6.00 cm (6), respectively. The I-V room temperature are shown in FIG. 6. These measurements show that introducing electron-accepting properties of linker molecules has a pronounced effect on the conductivity through the assembly. A pronounced difference between the assemblies of An nanoparticles interconnected with the anthraquinone derivative and the benzene derivatives is also evident in the absorption spectra of these molecules. In case of the linker molecules (1-4) the maximum of the plasmon absorption band peaked at 550 nm, while in case of the anthraquinone linker molecules the maximum was red shifted to 620 nm (FIG. 7). Since the dielectric vicinity of the particles is similar for all of the above-described assemblies this red shift could be an indication for a strong interaction between the nanoparticles induced by the linker molecule. These results show, that cross conjugation as described by Hush et al. (Hush, N. S., Reimers, J. R., Hall, L. E., Johnston, L. A., Crossley, M. J. (1998) Ann. New York Acad. Sci. 852, 1-21 Optimization and chemical control of porphyrin-based molecular wires and switches) may not necessarily cause an attenuation of the coupling between the particles (vide supra). Hence considering the effect of cross-conjugation for tuning the conductivity in assemblies, the electron accepting properties have to be taken into consideration.

(22) The molecular groups establishing the connection between the different nanostructured units, e.g. nanowires, nanoparticles, and possibly electrodes has a central function in the charge transport since the molecular design of this group is defining the type of bond that is formed between interconnected units. Included is also that the electrode or wire metal can be altered to alter the bonding group from the electrode/wire that participates in establishing the contact to the linker molecule depending on what type of tunnel barrier should be established for a specific interconnect.

(23) Two dithiocarbamate derivatives, 1,4-dithiocarbamatobenzene disodium salt (7) and 1,4-dithiocarbamatocyclohexane disodium salt (8), respectively, were synthesized according to the route described in FIG. 2b. Both bis-dithiocarbamate salts have the same central body X as the dithiols (1) and (4) in FIG. 3. The absorption characteristics of Au-nanoparticles interconnected with the 1,4-bis-dithiocarbamatobenzene (7) shows the typical characteristics of bulk gold (Kreibig, U., Genzel, L. (1985) Surf. Sci. 156, 678-700 Optical absorption of small metallic particles). Such absorption characteristics have been also observed using 2-mercaptoethanol for assembling Au-particles into films exhibiting a thickness of 150 nm (Aguila, A., Murray, R. W. (2000) Langmuir 16, 5949-5954 Monolayer-protected clusters with fluorescent dansyl ligands). In contrast, the assembly using the 1,4-dithiocarbamato-cyclohexane (8) exhibits absorption characteristics similar to the ones observed for the anthraquinone-substituted linker molecules. The plasmon band peaks at 620 nm and there is an increase in absorption in the near infrared. Temperature dependent studies of the dithiocarbamate assembly show typical metal behavior, i.e. with decreasing temperature an increase in the conductivity could be observed (FIG. 5). The I-V characteristics at room temperatures are shown in FIG. 6. The resistivities obtained for substances 7 and 8 are 9.110.sup.1 cm and 10.210.sup.1 cm, respectively. The corresponding value for bulk gold at 20 C. is =2.410.sup.4 cm (Weast, R. G. (Edt.) (1988) CRC Handbook of Chemistry and Physics, 69.sup.th Ed.). Similar resistivities have also been achieved by using a very short linker molecule, 2-mercaptoethanol, and by increasing the film thickness (Aguila, A. Murray, R. W. (2000), Langmuir, 16, 5949-5954 Monolayer-protected clusters with fluorescent dansyl ligands). These measurements provide evidence that the binding of linker molecules to the particle has a significant effect on the room temperature resistance of these assemblies, as it has been suggested by the theoretical calculations of Emberly and Kirczenow (Emberly, E. G., Kirczenow, G. (1998) Ann. New York Acad. Sci. 852, 1-21 Theory of electrical conductance through a molecule).

(24) 1,8-Dimercaptoacetamidooctane (9) (FIG. 3) was also used for interconnecting Au-nanoparticles into thin films. This molecule was synthesized for comparison of the I-V characteristics obtained from the commercially available 1,9-nonanedithiol (10), which has been studied in detailed in the literature. In the case of (10), the resistivity of the assembly is =8.710.sup.2 cm, whereas in the case of the amide substituted linker molecule (9) =4.210.sup.1 cm. Thus, although both linker molecules are of comparable length, the resistivities vary by three orders of magnitude. This result indicates that hydrogen-bond network between the amide groups can influence the charge transport, leading to a considerable enhancement of conductivity, although the linker molecules are quite flexible and it is also possible that the distances between the particles may be different in the two kinds of assemblies.

(25) This invention extends the class of molecules to be used in the referred assembly process to polyfunctional dithiocarbamate esters, in particular bis-dithiocarbamate esters, which can be used for the assembly of molecule interlinked metal-nanoparticle composites. To the knowledge of the inventors, there is no report on the use of polyfunctional dithiocarbamate esters for the preparation of the said assemblies. Dithiocarbamate esters may be used instead of the dithiocarbamates as interlinking molecules without any restriction. It has been observed that the said assembly process can be performed in the same manner as it is performed with any other dithiol or dithiocarbamate salt.

(26) The UV-visible spectra measured during the assembly of gold nanoparticle films interlinked with dithiocarbamate esters, dimethyl-N,N-1,4-cyclohexylamine-bis(dithiocarbamate) (11) and dimethyl-N,N-1,4-diaminobenzene-bis(dithiocarbamate) (12), are shown in FIG. 8 and FIG. 9, respectively. The spectra in both cases resemble gold films, indicating metallic characteristics of the films. Plots of the temperature dependence of the resistivity further demonstrate the metallic electrical characteristics of the films, since the resistivity decreases with decreasing temperature in films of gold nanoparticles interlinked with both 11 (FIG. 10) and 12 (FIG. 11).

(27) A detailed explanation of the optical and electrical characteristics of the corresponding assemblies prepared with dithiocarbamate salts is given by Wessels et al. (Wessels, J. M., Nothofer, H.-G., Ford, W. E., von Wrochem, F., Scholz, F., Vossmeyer, T., Schroedter, A., Weller, H., Yasuda, A. (2004) J. Am. Chem. Sec. 126, 3349-3356, Optical and electrical properties of three-dimensional interlinked gold nanoparticle assemblies). In brief, these finding indicate that by using dithiocarbamate esters having either aliphatic or conjugated core X it is possible to tune the conductivity through such organic-inorganic composites from insulating to metallic behavior.