Functionalization of reduced graphene oxide with axially-coordinated metal-porphyrins: Facile syntheses and temporally-dependent nonlinear optical properties

Reduced graphene oxide-tin porphyrin (RGO-SnTPP) nanohybrids with good dispersibility have been prepared by two covalent functionalization approaches. The microscopic structure and morphology of the RGO-SnTPP nanohybrids were characterized by various spectroscopic techniques including Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy. Ground-state absorption and steady-state fluorescence studies indicate considerable π-π interactions and effective photo-induced electron and/or energy transfer from the porphyrin moieties to the RGO. Their nonlinear optical properties were investigated using the Z-scan technique at 532 nm with both picosecond and nanosecond laser pulses. The RGO-SnTPP hybrids were found to exhibit large nonlinear optical responses due to a combination of mechanisms, while significant differences in their nonlinear optical responses were observed, highlighting the influence on photophysical properties of the degree of functionalization and the synthetic approach employed.