ELECTRONIC STATES AND (PI,PI-STAR) ABSORPTION AND EMISSION CHARACTERISTICS OF STRONGLY COUPLED PORPHYRIN DIMERS - SANDWICH COMPLEXES OF HF(IV) AND SR(IV)

Time-resolved and steady state optical measurements are reported for the sandwich complexes consisting of two tetraphenylporphyrin macrocycles held within 3 angstrom by either a Zr(IV) or Hf(IV) ion. Compared to monoporphyrins and weakly coupled bisporphyrins, the transition-metal sandwich complexes show new features in both the ground and excited state absorption spectra as well as a broad fluorescence red-shifted to almost-equal-to 1-mu-m. A model is presented that describes the electronic states responsible for these optical features. The states arise from strong interactions between the porphyrin macrocycles and contain significant charge resonance character.