Transient absorption, time-resolved fluorescence and resonance Raman spectroscopic studies of bis(meso-tetraphenylporphyrin)zirconium and bis(meso-tetraphenylporphyrin)zirconium hexachloroantimonate

Transient absorption, time-resolved fluorescence, and resonance Raman measurements are reported for Zr(TPP)2 and for the complex Zr(TPP)2(SbCl6) in which an electron is removed from the porphyrin pi-system. The singlet excited-state lifetime of Zr(TPP)2 in dichloromethane was measured to be 1.9 +/- 0.1 ns through the transient absorption technique and 1.95 +/-0.05 ns using the time-correlated single photon counting method, respectively. By contrast, the excited-state lifetime of Zr(TPP)2(SbCl6) was found to be 40 +/- 10 ps, which is much shorter than that of the neutral species. The fast nonradiative deactivation of the cationic complex is likely caused by the rapid quenching of the initially excited doublet (pi,pi*) state via one or more of the states seen in the near-IR ground-state absorption spectrum. These low energy states correspond to transitions between the molecular orbitals derived from the a2u and a1u monomer orbitals through the pi,pi interaction of the two porphyrin subunits. In addition, resonance Raman spectroscopic C data confirm that in Zr(TPP)2(SbCl6) one electron is removed from a dimer orbital derived from the monomer a2u orbital with a hole delocalized over the two porphyrin rings.