Surface-enhanced Raman spectroscopy of hexabenzobenzene,C24H12, an analogue of a graphene nanostructure

While large scale fabrication of graphene nanoribbons remains a challenge, there exist materials which can be fabricated in quantities such as hexabenzobenzene,HBZB, (C₂₄H₁₂) and which have a two-dimensional (2D) carbon structure similar to graphene nanostructures. Using a 632 nm laser, no Raman spectra could be obtained from the solid material because of a strong luminescence produced by the laser. However, surface-enhanced Raman spectroscopy enabled the measurement of some of the Raman active modes. The G and D modes, which are characteristic fingerprints of a 2D graphene structure, were observed at 1331 and 1600 cm^?1, respectively. Density functional theory at the B3LYP/6-31G^* level was used to calculate the minimum energy structure and the Raman active vibrational frequencies of HBZB. The calculated minimum energy structure was 2D having D_6h symmetry in agreement with the experimental structure in the liquid phase. The calculated frequencies were in good agreement with the measured values.