Excited State Dynamics of mesotetrasulphonatophenyl porphyrin (TPPS4)

In this work we present the study on the excited state characteristics of meso tetrasulphonatophenyl porphyrin (TPPS4) complexes with Zn(II), Fe(III) and Mn(III). Z-scan technique using 532 nm (70 ps and 120 fs) single laser pulses, as well as pulse trains (200 ns), was employed along with steady-state absorption spectroscopy. The five-energy-level diagram was used to describe the excited state dynamics. The singlet and triplet excited state cross sections and lifetimes were calculated. Zn(II)TPPS4 complex was shown to possess RSA on a picosecond timescale and cumulative effect on a nanosecond one. Fe(III)TPPS4 and Mn(III)TPPS4 demonstrated nonlinear absorption on a femtosecond timescale and cumulative effect on a picosecond one only for highly intensive laser excitation. This might result from ultrafast deactivation of excited states of these complexes due to metal-porphyrin charge transfer and the increase of spin-electron coupling in porphyrin π conjugated electronic system. The RSA effect was observed for Mn(III)TPPS4 and Fe(III)TPPS4 at pH 9.0 and the SA effect was observed for Fe(III)TPPS4 at pH 4.0