Nonlinear optical properties tuning in meso-tetraphenylporphyrin derivatives substituted with donor/acceptor groups in picosecond and nanosecond regimes

meso-Tetraphenylporphyrin (TPP) and its two substituted derivatives (meso-tetrakis(4-cyanophenyl)porphyrin [TPP(CN)₄] and meso-tetrakis(4-methoxyphenyl)porphyrin [TPP(OMe)₄]) were synthesized. Their nonlinear absorption and refraction properties were studied using the Z-scan technique in the picosecond (ps) and nanosecond (ns) regimes. The open aperture Z-scan results reveal that TPP and TPP(CN)₄ display an identical reverse saturable absorption (RSA) character in the ps and ns regimes. While TPP(OMe)₄ exhibits a transition from saturable absorption (SA) to RSA in the ps regime and a typical RSA character in the ns regime. The closed aperture Z-scan results show that TPP(CN)₄ and TPP(OMe)₄ have regular enhancement of the magnitude of nonlinear refraction as compared to their parent TPP in both the ps and ns regimes. In addition, the second-order molecular hyperpolarizabilities (γ) of these three porphyrins are calculated, and the γ values of TPP(CN)₄ and TPP(OMe)₄ are remarkable larger than that of TPP. The introduction of the electron-withdrawing group CN and the electron-donating group OMe into TPP has enhanced its nonlinear refraction and γ value, and tuned its nonlinear absorption (TPP(OMe)₄), which could be useful for porphyrin-related applications based on the desired NLO properties.