Nonlinear optical absorption and refraction properties of fluorinated trans-dicationic pyridinium porphyrin and its metal complexes

Here, we present the experimental investigation on the third order nonlinear optical properties of a series of fluorinated trans-dicationic pyridinium porphyrins namely, 5,15-di(pentafluorophenyl)-10,20-bis(4-N-methylpyridyl) porphyrin and its Cu(II) and Zn(II) derivatives, using single beam Z-scan method with nanosecond pulses at 532 nm. The major contribution to the absorptive nonlinearity exhibited by these porphyrins comes from excited state absorption assisted reverse saturable absorption. The value of nonlinear absorption coefficient is found to be maximum for the Zn(II) complex and is attributed to the extended delocalization due to heavy atom effect. Optical limiting efficiency is also found to be enhanced for Zn(II) porphyrin, with a limiting threshold value of 1.89 J/cm(2), which indicates its potentiality as an optical limiter for the smart filtering of optical energy in direct viewing systems. Considering the dispersive contribution to the optical nonlinearity, self defocusing effect is observed in all porphyrins and the magnitude of nonlinear refraction coefficient is obtained as higher in free base porphyrin than that in the metalated compounds. The weakest negative nonlinear effect in Zn(II) porphyrin is attributed to the interplay between the coordination interaction and the thermal effects.