Theory Of Molecular Excitons | A. S. Davydov

The exciton concept was introduced into solid-state physics by Frenkel in 1931, in connection with the transformation of excitation energy into heat in rare-gas solids. Not until Davydov’s now-famous 1948 paper on the splitting of electronic terms in the naphthalene crystal was the concept applied to geometry-determined molecular problems. Since then the treatment of an impressive variety of problems has been pub­ lished by Davydov and his colleagues and by numerous other researchers. The exciton model has now been used in treating general formulations of energy transfer, in the crystal splitting of electronic states which are nondegenerate in the isolated molecule, in the splitting of infrared bands and Raman lines in molecular crystals corresponding to nondegenerate vibrational modes in the isolated molecule, in the calculation of excited states of molecules consisting of two or more isolated or not-strongly- conjugated chromophoric units, in optical rotatory power of helical polymers containing nonconjugated chromophoric units, etc. Alto­ gether, the range of problems covered suggests that the role of the exciton model may be as great in the fields of molecular physics and quantum chemistry as that of the molecular orbital model, the valence-bond model, or the charge-transfer model. Davydov’s book summarizes many of the problems, and its perceptive treatment suggests many starting points for further extensions.

TRANSLATED FROM THE FIRST RUSSIAN EDITION BY

Michael Kasha and Max Oppenheimer, Jr.