Theoretical investigations on one- and two-photon absorptions for a series of covalently functionalized hybrid materials based on graphene

Recently, the covalently linked porphyrin-graphene composite materials with excellent nonlinear optical (NLO) properties and solubility have been experimentally studied, but their two-photon absorption (TPA) properties have not been reported yet. In this work, a series of novel graphene-like molecules and their corresponding hybrids with porphyrin have been designed to study their one-photon absorption (OPA) and TPA properties, as well as the structure-property relationships by employing quantum-chemical calculations. The maximum TPA cross sections (δ_max) calculated by the ZINDO method, combined with the FTRNLO-JLU program compiled by our group, are as large as ∼913.0-3904.3 GM. Moreover, both molecular size and porphyrin result in a significant increase of the δ_max values. Furthermore, the hybrid molecules possess a higher TPA response resulting from intramolecular charge transfer, compared with their counterparts without a porphyrin. The calculated results support the experimentally observed trends, as well as indicate that the designed compounds with large TPA cross-sections have potential for applications involving optical limiting and two-photon fluorescence microscopy (TPFM). We expect that this study will provide a theoretical perspective for designing novel TPA materials based on graphene for further applications in the future.