Graphene nanoribbons with controlled modifications

Abstract

The present invention relates to a graphene nanoribbon, comprising a repeating unit which comprises at least one modification, wherein the modification is selected from a heteroatomic substitution, a vacancy, a sp.sup.3 hybridization, a Stone-Wales defect, an inverse Stone-Wales defect, a hexagonal sp.sup.2 hybridized carbon network ring size modification, and any combination thereof.

Claims

1. A graphene nanoribbon, comprising: a repeating unit RU1 which comprises at least one modification, wherein the modification is selected from the group consisting of a heteroatomic substitution, a vacancy, a sp.sup.a hybridization, a Stone-Wales defect, an inverse Stone-Wales defect, a hexagonal sp.sup.2 hybridized carbon network ring size modification, and any combination thereof.

2. The graphene nanoribbon according to claim 1, wherein the at least one heteroatomic substitution modification of the repeating unit RU1 comprises a heteroatom or a heteroatomic group selected from nitrogen, boron, phosphor and oxides thereof, silicon, oxygen, sulphur and oxides thereof, hydrogen, and any combination thereof.

3. The graphene nanoribbon according to claim 1, wherein the repeating unit RU1 is derived from at least one aromatic monomer compound which is selected from the group consisting of at least one substituted or unsubstituted polycyclic aromatic monomer compound, at least one substituted or unsubstituted oligo phenylene aromatic monomer compound, and any combination thereof.

4. The graphene nanoribbon according to claim 3, wherein the aromatic monomer compound comprises at least one aromatic or non-aromatic heterocyclic ring.

5. The graphene nanoribbon according to claim 3, wherein the polycyclic aromatic monomer compound comprises two or more annelated aromatic rings and at least one of the annelated aromatic rings comprises one or more heteroatoms.

6. The graphene nanoribbon according to claim 3, wherein the polycyclic aromatic monomer compound comprises two or more annelated aromatic rings and at least one non-annelated heterocyclic residue is attached to at least one of the annelated aromatic rings; and/or the oligo phenylene aromatic monomer compound comprises at least one heterocyclic residue being attached to the phenylene group.

7. The graphene nanoribbon according to claim 3, wherein the aromatic monomer compound has one of the following formulas 2 to 4: ##STR00006## wherein: X is each independently a leaving group; Y is alkyl, aryl, or hydrogen; and R is each independently selected from the group consisting of hydrogen; linear or branched or cyclic C.sub.1-C.sub.12 alkyl which is unsubstituted or substituted by one or more OH, C.sub.1-C.sub.4 alkoxy, phenyl, or CN; C.sub.2-C.sub.12 alkyl which is interrupted by one or more non-consecutive O; halogen; OH; OR.sub.3; SR.sub.3; CN; NO.sub.2; NR.sub.1R.sub.2; (CO)R.sub.3; (CO)OR.sub.3; O(CO)OR.sub.3; O(CO)NR.sub.1R.sub.2; O(CO)R.sub.3; C.sub.1-C.sub.12 alkoxy; C.sub.1-C.sub.12 alkylthio; (C.sub.1-C.sub.6alkyl)-NR.sub.7R.sub.8; O(C.sub.1-C.sub.6alkyl)NR.sub.1R.sub.2; aryl or heteroaryl which is unsubstituted or substituted by one or more C.sub.1-C.sub.4-alkyl, CN, OR.sub.3, SR.sub.3, CH.sub.2OR.sub.3, (CO)OR.sub.3, (CO)NR.sub.1R.sub.2 or halogen); or two R's together with the carbon atoms they are attached to form a 5-8-membered cycle or heterocycle; wherein: R.sub.1 and R.sub.2 independently of each other are hydrogen, linear or branched C.sub.1-C.sub.6 alkyl or phenyl, or R.sub.1 and R.sub.2 together with the nitrogen atom to which they are bonded form a group selected from the group consisting of ##STR00007## R.sub.3 is selected from the group consisting of H, C.sub.1-C.sub.12 alkyl, phenyl which is unsubstituted or is substituted by one or more C.sub.1-C.sub.4 alkyl, phenyl, halogen, C.sub.1-C.sub.4 alkoxy and C.sub.1-C.sub.4alkylthio.

8. The graphene nanoribbon according to claim 3, wherein the aromatic monomer compound has the following formula 1: ##STR00008## wherein X is each independently a leaving group.

9. The graphene nanoribbon according to claim 7, wherein the graphene nanoribbon comprises one of the following structures: ##STR00009## wherein: X, Y, and R are as defined in claim 7, and n2500.

10. A process for preparing the graphene nanoribbon according to claim 1, which comprises: (a) providing at least one aromatic monomer compound which is selected from the group consisting of at least one substituted or unsubstituted polycyclic aromatic monomer compound, at least one substituted or unsubstituted oligo phenylene aromatic monomer compound, and combinations thereof, on a solid substrate, (b) polymerizing the aromatic monomer compound and forming at least one polymer on the surface of the solid substrate, and (c) at least partially cyclodehydrogenating the at least one polymer of (b).

11. The process according to claim 10, wherein the polymerizing in (b) is induced by thermal activation.

12. The process according to claim 10, wherein the aromatic monomer compound is a polycyclic aromatic monomer compound and/or an oligo phenylene aromatic monomer compound.

Description

EXAMPLES

1. Experimental Details

(1) 5,10-Dibromo-1,3-diphenyl-2Hcyclopenta[l]phenanthrene-2-on is prepared according to WO2008/012250, Example 1a.

(2) The monomer 5,5-(6,11-Dibromo-1,4-diphenyltriphenylen-2,3-diyl)dipyrimidine (1) is prepared as follows:

(3) ##STR00005##

(4) A dry and inert 25 ml Schlenk tube which is equipped with a magnetic stirrer and contained 5,10-dibromo-1,3-diphenyl-2H-cyclopenta[l]phenanthrene-2-on (0.711 g, 1.316 mmol) and dipyrimidyl tolan (0.200 g, 1.097 mmol) was repeatedly evacuated and purged with argon. Then, diphenyl ether (6 ml) was added. A freezing-thawing cycle was carried out and repeated twice so as to remove water and residual oxygen. Subsequently, the medium was stirred at 220 C. for 14 hours under a moderate argon flow. The light green solution turned into a brown suspension. After cooling the reaction medium to room temperature, a precipitation step was carried out in hexane: dichloromethane (hexane: dichloromethane, 200:2, v:v). The glaucous residue was separated via flash column chromatography (silica, ethyl acetate:hexane, 3:1 v:v) and compound 1 was obtained as an orange powder in an amount of 73 mg (0.105 mmol, 8%).

(5) .sup.1H-NMR: (300 MHz, CD.sub.2Cl.sub.2)=8.81 (s, 2H); 8.31 (s, 1H); 8.28 (s, 1H), 8.10 (s, 4H); 7.74 (d, 2H); 7.59 (d, 1H); 7.57 (d, 1H); 7.3-7.2 (m, 6H); 7.1-7.0 (m, 4H) ppm.

(6) Melting point: 349.1 C. (ethyl acetate/hexane), discolouration

(7) Preparation of GNRs.

(8) Au(111) single crystals (Surface Preparation Laboratory, Netherlands) as well as 200 nm Au(111) thin films epitaxially grown on mica (Phasis, Switzerland) were used as substrates for GNR growth. Substrate surfaces were cleaned by repeated cycles of argon ion bombardment and annealing to 470 C. Precursor monomers were deposited onto the clean substrate surfaces by sublimation from a 6-fold evaporator (Knudsen-cell-type) at rates of 2 /min. For the fabrication of the nitrogen substituted N=6/N=9 chevron-type armchair GNRs, the substrate was maintained at 200 C. during monomer deposition to induce dehalogenation and radical addition. After deposition, the sample was post-annealed at 400 C. for 10 min to cyclodehydrogenate the polymers and form GNRs. All these steps were performed under ultra-high vacuum conditions.

(9) STM Characterization of GNRs.

(10) A variable-temperature STM (VT-STM) from Omicron Nanotechnology GmbH, Germany, was used to characterize the morphology of the GNR samples. Images were taken in the constant current mode under ultra-high vacuum conditions at sample temperatures of 298 K (room temperature) or 35 K (LHe cooling).

(11) XPS Characterization of GNRs.

(12) An ESCA system from Oimcron Nanotechnology GmbH, Germany, working under ultra-high vacuum conditions was used to determine the chemical composition of the GNRs. X-ray photoelectron spectroscopy (XPS, hv=1486.7 eV) of the C1s and N1s core levels is used for a quantitative intensity analysis, as described by P. Ruffieux et al. (Rev. Sci. Instr. 2000, 71, 3634-3639). GNR samples are grown in the STM chamber as described above and transferred through ambient conditions to the ESCA system. Transfer related volatile contaminations are removed by annealing the sample directly in the ESCA system to 200 C. under ultra-high vacuum conditions. Overview spectra assure that no contributions other than from GNR and the clean Au substrate are present.

(13) FIG. 14 shows the bottom-up fabrication of nitrogen substituted chevron-type GNRs, i.e. a graphene nanoribbon having a repeating unit which comprises heteroatomic substitution modifications. The repeating unit comprising heteroatomic substitution modifications is derived from the aromatic monomer compound 1.

(14) Precursor 1 is for bottom-up fabrication of nitrogen substituted chevron-type GNRs with two steps: formation of linear polymers by covalent interlinking of the dehalogenated intermediates after annealing at 470K; formation of fully aromatic GNRs by cyclodehydrogenation at 670K.

(15) FIGS. 15a to 15d show measurements of the nitrogen substituted chevron-type GRN prepared according to the process described above. FIG. 15a shows an overview STM image of chevron-type GNR in the polymer state after surface-assisted CC coupling of monomer 1 (T=35 K, U=1.0 V, 1=0.05 nA). The inset displays a line profile along the indicated (line in bottom left corner) path and reveals an apparent polymer height of 0.31 nm. FIG. 15 b shows a small-scale STM image of the polymer chains (T=35 K, U=1.0 V, 1=0.07 nA) with partly overlaid chemical model. FIG. 15 c shows an overview STM image after cyclodehydrogenation at 670K (T=35 K, U=1.0 V, I=0.1 nA). The inset displays the profile along the indicated line path in the bottom left corner in c and reveals a cyclodehydrogenation-related reduction of the apparent height to 0.20 nm. FIG. 15d shows a small-scale STM image with partly overlaid structural model of the ribbon (T=35 K, U=1.3 V, I=0.3 nA).

(16) FIGS. 16a to 16c show STM and XPS measurements of nitrogen substituted chevron-type GNR prepared according to the process described above. FIGS. 16d to 16f show reference measurements for chevron-type ribbons based on monomer 5. FIG. 16a shows an STM overview image of a monolayer sample of nitrogen substituted chevron GNRs on Au(111) based on monomer 1 (T=35 K, U=1.5 V, I=0.03 nA). FIGS. 16b and 16c show C1s and N1s core-level spectra, respectively, for a monolayer sample of nitrogen-substituted chevron GRNs on Au(111) sample. The intensity ratio of I.sub.N1s/I.sub.C1s is 0.140.05, in agreement with the expected ratio of 0.20. FIG. 16d shows an STM image of a monolayer sample of unmodified chevron GNRs on Au(111) (T=300K, U=2.0 V, I=0.02 nA) based on precursor monomer 5 (inset). FIGS. 16e and 16f show C1s and N1s core-level spetra, respectively, of chevron-type GNRs based on 5 using exactly the same analysis parameters as for FIGS. 16b and 16c, respectively.