New covalent hybrids of graphene oxide with core modified and -expanded porphyrins: Synthesis, characterisation and their non linear optical properties

Novel covalent adducts of core modified (mono-thiaporphyrin and dithiaporphyrin), core modified expanded (trithiasapphyrin) porphyrin with graphene oxide are synthesized to improve the dispersability in organic solvents. The nonlinear, photo physical, thermal properties and morphology of graphene oxide -porphyrin hybrid materials are investigated. The covalent bonding of mono-thiaporphyrin, di-thiaporphyrin and tri-thiasapphyrin with graphene oxide is confirmed by various spectroscopic techniques. The strong fluorescence quenching in composites suggests strong interactions between the modified porphyrin molecules and graphene oxide molecules. The nonlinear optical (NLO) properties are investigated by open aperture Z-scan technique at 532 nm in nanosecond regime. At same transmission intensity, the graphene oxide-modified porphyrin hybrids showed enhanced NLO properties in comparison to the neat graphene oxide and modified porphyrins. Nonlinearity present in GO-modified porphyrin, ascribed due to the photo-induced electron or energy transfer from the porphyrin moiety to the graphene or due to combination of two-photon absorption with reverse saturable absorption and/or nonlinear scattering.

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