Knowledge Bank

Absorption, fluorescence, magnetic circular dichroism (MCD), magnetic circularly polarized luminscence (MCPL) and longitudinal Zeeman spectra were measured for the $Q(1Ag1(\pi ))\to 1Eu(\pi \ast e)$ transition of zinc tetra benzoporphyrin isolated in an argon matrix (ZnTBP/Ar). Moment analysis of the MCD and absorption yield an excited-state orbital g value of $g1=7.7\pm 0.4$. The large value of this parameter is consistent with a four-orbital interpretation of the Q transition for metallophthalocyanines. The magnetic field dependence of the zero-phonon Zeeman shifts and moment analysis of the emission spectra independently yield information concerning Jahn-Teller (JT) effects in the excited state. These data have been interpreted in the context of a single effective JT-active coordinate and local crystal-field distortions of both $b1g$ and $b2g$ symmetry. [FIGURE].