Near-Infrared Excitation of the Q Band in Free Base and Zinc Tetratolyl-porphyrins

The photophysics of 5,10,15,20-tetra-p-tolyl-21H,23H-porphyrin (TTP-H2) and 5,10,15,20-tetra-p-tolyl-porphyrinato zinc II (ZnTTP) have been investigated by means of pump-probe and transient anisotropy experiments. After excitation to the Q band, the molecules were probed by NIR pulses in the range between 950 and 1350 nm in order to study states of gerade symmetry in the vicinity of the Soret band. Examination of transient spectra and anisotropy delivered the first direct observation and the excitation energies of the two lowest so-called dark states. The experimental results were compared with predictions from theoretical calculations.