UNUSUAL DYNAMIC RELAXATION OF TRIPLET-EXCITED MESO-PHENYL-SUBSTITUTEDPORPHYRINS AND THEIR CHEMICAL DIMERS AT ROOM TEMPERATURES

It has been found that for mono- and di-meso-phenyl-substituted octaet hylporphyrin (OEPs), etioporphyrins, corresponding Zn complexes and OE P chemical dimers (with a meso-phenyl spacer) a drastic shortening of triplet lifetimes from a ms to mu s timescale in deaerated toluene sol utions at 295 K takes place without any changes of the spectral-kineti c parameters of the S-0 and S-1 states. The observed effects are conne cted with torsion librations of the phenyl ring around a single C-C bo nd in sterically encumbered porphyrins leading to non-planar dynamic d istorted conformations in excited T-1 states accompanied by an enhance ment of the T-1-state nonradiative deactivation pathways. (C) 1998 Els evier Science B.V. All rights reserved.