High-resolution optical spectroscopy of polyenes related to the visual chromophore

Abstract

High-resolution optical spectroscopy has been used to elucidate several features of polyene excited states. Spectra at 4.2 K of 2,lO-dimethylundecapentaene in n-nonane and 2,12-dimethylundecapentaene in n-undecane are presented. Vibrational analyses of these spectra support the lA, assignment for the lowest excited singlet states in these and other linear polyenes. The energy gap between the lA, and the higher lying lB, state increases from 3000 cm-1 in the pentaene to almost 4000 cm-l in the hexaene. The tridecahexaene can be produced in several distinct n-undecane crystal sites. Differences in the spectra of these sites provide indications of the extreme sensitivity of polyene electronic structure to the details of local environments. The extension of these findings toward an understanding of the spectra of polyenes related to the visual chromophore is discussed.