Graphene nanoribbons (GNRs) have attracted attention as one of the next generation semiconductor materials. Their electrical properties are controlled by the structure of the width and edge. There are now two methods for processing GNR, "top to bottom" and "bottom to top". The liquid-phase processing method of "bottom to top" can produce graphene nanoribbons with designed structures on a large scale. However, because chemically synthesized GNRs have no side groups and functional groups, only short alkyl chains, which severely limits the processability of solutions, more basic research is needed.
Recently, Professor Feng Xinliang of the School of Chemistry and Chemical Engineering of Shanghai Jiao Tong University and Mai Yiyong (co-corresponding author), a special researcher at Shanghai Jiao Tong University, reported on JACS that they developed a polyethylene oxide functionalized graphene nanoribbon, which greatly improved the solubility of graphene nanoribbon in common organic solvents, providing the possibility to study the performance of GNRs: GNRs are easily aggregated in conventional solvents, thus affecting the fluorescence and luminescence of GNRs; scanning probe microscopy found the self-assembly behavior of PEO-GNR; the carrier mobility of thin film field effect transistors based on GNR can reach 0.3 cm ²/(Vs), etc.
Figure 1: Synthesis roadmap for polyethylene oxide functionalized graphene nanoribbons
Figure 2: Structure and properties characterization of polyethylene oxide-functionalized graphene nanoribbons
The grafting rate of PEO in polyethylene oxide-functionalized graphene nanoribbons is 46%, so the obtained GNRs exhibit strong dispersion in organic solvents. It can be seen from Raman spectroscopy that the structure of GNRs is not affected by functional functional groups, and still exhibits a precise small-size structure.
Figure b shows that the effect of different functionalized groups on the dispersibility of GNRs is different. The solubility can reach 1mg/mL in THF (mainly GNR), and the dispersion is stable for at least 1 day. GNR-COOCH 3 and GNR-COOH cannot be uniformly dispersed in tetrahydrofuran, and precipitation will be seen a few minutes after ultrasound. The highest solubility of GNR-COOCH 3 and GNR-COOH in THF is 0.02 mg/mL and 0.05 mg/mL, respectively. From this, the authors conclude that PEO-GRN has good dispersibility in conventional solvents.
Figure c shows the ultraviolet spectrum. In tetrahydrofuran, the spectra of GNR-COOCHS, GNR-COOH, and GNR-PEO are not much different, while in water, GNR-PEO has a significant shift, indicating that its structure has changed.
Figure d shows that the fluorescence effect is completely lost due to the strong aggregation of PEO-GNR in water.
Good dispersibility not only provides the possibility for a deeper understanding of the physicochemical properties of GNRs, but also has a good development prospect. Therefore, polymer functionalization provides opportunities for the development of GNRs-related research.
Literature link: Poly (ethylene oxide) Functionalized Graphene Nanoribbons with Excellent Solution Processability (JACS, 2016, DOI: 10.1021/acs.jacs.6b07061)
