Grafting P3HT brushes on GO sheets: distinctive properties of the GO/P3HT composites due to different grafting approachesElectronic supplementary information (ESI) available: Synthesis of GO, synthesis of amino- and ethynyl-terminated P3HT, characterization methods, NMR data for the covalent bonding of P3HT and GO sheets, differential TGA curves of GO, amino-terminated P3HT, ethynyl-terminated P3HT, GO(C)/P3HT and GO(E)/P3HT composites, survey XPS of GO/APTMS composite, C 1s XPS of GO, GO(C)/P3H

In this study, we have grafted poly(3-hexylthiophene) (P3HT) brushes on GO sheets via a silylation reaction of the surfaces of GO sheets and a succeeding "click" reaction (GO(C)/P3HT composite). Compared with pure P3HT and the blend of P3HT and GO, the GO(C)/P3HT composite shows a red-shifted optical absorption maximum because of increased conjugation length of the grafted P3HT, which might be due to the crowding of the P3HT chains grafted on GO sheets. For comparison, P3HT chains were also grafted on GO sheets via the amidation reaction of the carboxylic acid groups (GO(A)/P3HT composite). However, the GO(A)/P3HT composite doesn't show a red shift in the UV-visible spectrum. The overall fluorescence quenching in the GO(C)/P3HT composite includes both dynamic quenching and forming a non-fluorescent ground-state complex. Additionally, thermogravimetric analysis and X-ray photoelectron spectroscopy results demonstrate that the efficiency of grafting P3HT on GO sheets via the "click" reaction approach is higher than via the amidation reaction approach. Atomic force microscopy and transmission electron microscopy observations show that the GO(C)/P3HT composite sheets are much thicker than the GO(A)/P3HT composite sheets, due to the higher grafting efficiency of the "click" reaction approach. Therefore, this work opens a novel avenue to tuning the optical properties of conjugated polymers via surface grafting chemistry. Densely grafting P3HT brushes on GO sheets leads to a red shift in the optical absorption maximum for the grafted P3HT.