Synthesis and structural, spectroscopic and nonlinear optical measurements of graphene oxide and its composites with metal and metal free porphyrins†

In this paper we present the structure and spectroscopic, photophysical and nonlinear optical studies of covalently functionalized novel graphene oxide–[Cu, Zn, Sn, H2 (metal free), VO] porphyrin composites. The composites were characterized by Field Enhanced Scanning Electron Microscopy (FE-SEM), micro-Raman, optical absorption, Fourier transform infrared (FT-IR), steady state and time resolved fluorescence spectroscopic techniques. The composites exhibit strong fluorescence quenching, suggesting strong electronic interactions between the porphyrin and graphene oxide molecules. Nonlinear optical absorption (NLA) studies of graphene oxide–porphyrin composites were investigated using the Z-scan technique at 532 and 800 nm with nanosecond (ns) and femtosecond (fs) laser pulses. Composites show strong two-photon absorption (TPA) as well as excited state absorption (ESA) leading to reverse saturable absorption (RSA) behaviour in the ns regime and saturable absorption (SA) behaviour was observed in fs regime. The metal free porphyrin–graphene oxide (GO) composite shows significant nonlinear absorption behaviour as well as highest fluorescence quenching behaviour compared to other GO–porphyrin composites. We further observed the enhanced figure of merit (FOM) values for composites in comparison with individual molecules.