Triplet Dynamics of Conformationally Distorted Porphyrins: Time-Resolved Electron Paramagnetic Resonance

摘要: The photoexcited triplet states of the nonplanar porphyrins, free base and zinc 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyri ns (OETPPs), were examined by laser excitation-time resolved EPR spectroscopy. Measurements carried out at low temperatures in glassy matrices, over a wide temperature range uniaxial liquid crystal (LC). [sup 3]H[sub 2]OETPP exhibits mainly X,Y in-plane population sublevels, whereas 3]ZnOETPP, preferred is through out-of-plane Z axis. Both chromophores are characterized relatively small zero-field splitting values, D, sizable E values (D [approximately] 3E), parameters more akin to those analogous TPP rather than OEP derivatives. LC spectra depend on specific chromophore, temperature, phase matrix. Line-shape analysis suggests fast exchange processes between different conformers attributable fluxional conformational excursions from X-ray structures OETPPs their ground states. 42 refs., 8 figs., 3 tabs.