Structure-Dependent All-Optical Switching in Graphene-Nanoribbon-Like Molecules: Fully Conjugated Tri(perylene bisimides)

We present the structure-dependent nonlinear optical (NLO) properties of fully conjugated tri(perylene bisimides) (triPBIs) toward the understanding of the role of conformational flexibility and pi-electron conjugation in molecular NLO properties of model graphene-nanoribbon (GNR)-like molecules. In the present paper, we report the NLO absorption properties of the triPBIs in toluene excited at 532 nm with nanosecond laser pulses, where the observed transient excited state is determined to be a triplet and presented in the nonlinear process similar to the NLO properties that occur in C-60. As a result, the all-optical switching in both visible and near-infrared regions upon excitation at 532 nm was demonstrated, suggesting that the chemically synthesized model GNRs act well as smart all-optical switching devices without the need of external control. Furthermore, Raman spectral measurement was further used to characterize the conjugated structure properties of model compounds of functionalized graphene nanoribbons (F-GNRs), while the dispersion and splitting of the G-band and D-band in both frequency and intensity can help to distinguish the pi-conjugation and conformational flexibility of the two different triPBI isomers, showing the opportunity to tailor their optoelectronic properties by precisely controlling the edge orientation, edge width, and chemical termination of the edges in the synthesized F-GNRs.