Infrared spectroscopy of graphene nanoribbons and aromatic compounds with sp3C–H (methyl or methylene groups)

Graphene nanoribbon (GNR) has attracted attention because of the adjustable band gap, depending on the width and functional groups. The introduction of sp3C–H on edges is one of the choices to reduce the agglomeration between GNRs and to change their various properties. Infrared spectroscopy is among the powerful tools to analyze the edge structures of carbon materials, but the number of detailed reports is almost nonexistent for sp3C–H in carbon materials. In this work, the influence of the presence of sp3C–H on the peak position of sp2C–H on zigzag and armchair edges of GNR was revealed by comparing experimental and computational infrared spectra of aromatic compounds. The introduction of methylene and methyl groups next to sp2C–H affected peak positions of in-plane stretching and out-of-plane bending vibration of sp2C–H. The peak position of sp2C–H was further shifted by introducing methylene and methyl groups on both sides of sp2C–H. The presence of either methylene or methyl groups can be clearly distinguished from the difference in coupled vibration of out-of-plane vibration of sp2C–H and quadrant stretching vibration of C=C because the presence of methylene groups affects the conjugated system significantly, whereas methyl groups did not affect the conjugated system.