Electronic Energy Levels in a Homologous Series of Unsubstituted Linear Polyenes

Article abstract of DOI:10.1021/ja00526a003

Absorption, emission, and exitation spectra of 1,3,5,7-octatetraene, 1,3,5,7,9-decapentaene, and 1,3,5,7,9,11-dodecahexaene have been obtained in room temperature solutions and 77 K glasses.All spectra exibit the chracteristic gap between the origin of the strongly allowed absorption (¹A_g --> ¹B_u) and the origin of fluorescence (¹A_g^* --> ¹A_g).Comparison with results previously obtained for methyl-substituted polyenes shows that the ¹B_u-¹A_g^* energy gap is a sensitive function of the degree of substitution.Solvent-effects studies have been used to extrapolate transition energies of the unsubstituted polyenes to gas-phase conditions.For the tetraene, pentaene, and hexaene the ¹B_u-¹A_g^* energy differences are 6380, 7050, and 7420 cm^-1, respectively.These results are discussed in terms of current theoretical descriptions of polyene electronic states.