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Theory of the J-band: from the Frenkel exciton to charge transferPhotochemistry Center, Russian Academy of Sciences, Novatorov str. 7a, Moscow, 117421, Russian Federation This review concerns the current status of the theory of formation of the so-called J-band (Jelley, Scheibe, 1936), an abnormally narrow, high-intensity, 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 one based on Frenkel’s statistical exciton model, the specific structure of the dye is considered irrelevant, and the J-band is explained by assuming that the quickly moving Frenkel exciton acts to average out the quasistatic disorder in electronic transition energies of molecules in the linear J-aggregate (Knapp, 1984). In the second approach, on the contrary, the specific structure of the dye (the existence of a quasilinear polymethine chain ) is supposed to be very important. This new approach is based on a new theory of charge transfer. The explanation of the J-band here is that an elementary charge transfer along the J-aggregate’s chromophore is dynamically pumped by the chaotic reorganization of nuclei in the nearby environment at a resonance between electronic and nuclear movements — when the motion of nuclei being reorganized is only weakly chaotic (Egorov, 2001).
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