Cationic porphyrin-functionalized graphene oxide: A novel platform for ultrafast femtosecond nonlinear optical...

The fabrication and spectroscopic characterization of a self-assembled composite comprising the electron-donating 5,10,15,20-tetrakis(4-triethylammoniophenyl)porphyrin tetra(p-toluenesulfonate) (TTMAPP) and the electron-accepting graphene oxide (GO) nanosheet has been examined in an aqueous medium using different spectroscopic techniques. The fluorescence lifetime measurements demonstrated a notable reduction in the singlet excited state lifetimes of TTMAPP when combined with GO. Based on these measurements, the rate constant and efficiency of the electron transfer from TTMAPP to GO in an aqueous medium were quantified to be 3.3 × 10⁹ s^-1 and 96.9 %, respectively, indicating a rapid and highly efficient electron transfer process. The nonlinear optical properties of TTMAPP and GO@TTMAPP were explored using femtosecond laser pulses with varying excitation wavelengths and incident power levels, as analyzed through the Z-scan technique. The TTMAPP dye demonstrated a self-defocusing phenomenon in its nonlinear refractive index and exhibited reverse saturable absorption behavior in its nonlinear absorption coefficient. The real and imaginary parts of the third-order nonlinear optical susceptibility of the TTMAPP dye were determined to be approximately (4.75 × 10^-13 esu). The results demonstrate that TTMAPP solutions exhibit a substantially high two-photon absorption cross-section across a range of excitation wavelengths. Furthermore, the incorporation of additional amounts of GO into the TTMAPP formulation led to a significant enhancement in the real and imaginary components of the third-order nonlinear optical susceptibility within the composite material (11.15 × 10^-13 esu). These findings suggest that the GO@TTMAPP composite holds promise as a candidate for various nonlinear optical applications, particularly in the realm of optical limiting.