Infrared and Raman activity of polyenes in pristine and doped state

Abstract

The activity of a normal mode in vibrational spectra of polyenes (short, long or infinite) can be essentially represented by the quantity δΦ/δяL яi. Φ is the molecular dipole moment μ in IR and the molecular polarizability ((α)) in Raman respectively. я is the “effective conjugation coordinate” and L яi is the content of in the i-th mode. δ μ/δя vanishes in pristine compounds and is large in doped and photoexcited ones; δ((α))/δя is large for udoped chains and practically vanishing for doped ones. This statement originates from the interpretation of vibrational spectra [1] but is also supported by results of ab-initio calculations made by Villars, Dupuis and Clementi [2].