Lowest energy excited singlet states of isomers of alkyl substituted hexatrienes

Vibrationally resolved S0→S1 excitation spectra for the alkyl substituted linear polyenes heptatriene, octatriene, and decatriene seeded into a supersonic He expansion have been measured by resonance enhanced multiphoton ionization spectroscopy. As is the case for the parent compound hexatriene, the lowest energy excited singlet state in all of these molecules is the 2 1Ag state. The measurement of S0→S1 excitation spectra of three of the four double bond isomers of heptatriene gives a detailed picture of the dependence of the electronic structure of the 2 1Ag state on molecular conformation. The three isomers for which spectra are presented have the cis configuration at either the central or the alkyl substituted double bond, or both. For the case of the mono cis species with the cis configuration at the alkyl substituted double bond the spectra show the presence of two single bond conformers. Because of the increased number of distinguishable isomers and conformers for octatriene and decatriene we were ...

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