The nature of electronic transitions in linear conjugated systems

The current state of investigations of the relationship between electronic transitions and molecular topology of linear conjugated systems, viz. polymethine dyes and α,ω-disubstituted polyenes, is considered. The effect of parity of methine groups in a polymethine chain, of filling of the electronic shell, molecular symmetry, and the topology of terminal groups on the electronic structure of polymethines and polyenes are described. Spectral effects arising upon changes in the structures of chromophores, and the nature of the first and higher transitions in linear conjugated compounds containing several chromophores are discussed. The localisation of transitions in molecular fragments and the conditions for the inversion of the polymethine and local electronic transitions in polyenes and polymethines are considered. The bibliography includes 242 references.