Abstract:
This review concerns the current status of the theory of formation of the so-called J-band (Jelley, Scheibe, 1936), àn abnormally narrow, high-iïteïsity, red-shifted optical absorption band arising from the aggregation of polymethine dyes. Two opposite approaches to explaining the physical nature of the J-band are given special attention. In the first of these, the old înå based on Frenkel's statistical exciton model, the specific structure of the dye is considered irrelevant, and the J-band is explained Üó assuming that the quickly moving Frenkel exciton acts to average out the quasistatic disorder in electronic transition energies îf molecules in the linear J-aggregate (Ênàðð, 1984). In the second approach, on the contrary, the specific structure îf the dye (the existence îf à quasilinear polymethine chain) is supposed to bå very important. This new approach is based în à new theory îf charge transfer. Òhå explanation îf the J-band here is that àn elementary charge transfer along the J-aggregate's chromophore is dynamically pumped bó the chaotic reorganization îf nuclei in the nearby environment at à resonance between electronic and nuclear movements — when the motion îf nuclei being reorganized is only weakly chaotic (Egorov, 2001).
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