Spectroscopic properties of polyenes. I. The lowest energy allowed singlethyphen;singlet transition forcishyphen; andtranshyphen; 1,3,5hyphen;hexatriene

摘要

The absorption spectra ofcishyphen; andtranshyphen; 1,3,5hyphen;hexatriene are reported for the region of the first allowed singlethyphen;singlet electronic transition, 2600 to 2100 A. A leasthyphen;squares procedure in which a Lorentzian line shape is assumed for each band was used to fit the spectra. Progressions are found of 408, 1262, and 1626 cmminus;1for thecisisomer and of 350, 1232, and 1628 cmminus;1for thetransisomer. The 0ndash;0 transition for theciscompound, 39668 cmminus;1, lies about 130 cmminus;1lower than that for the trans, 39800 cmminus;1. The fact that the 0ndash;0 transition energy forcisis less than that fortransis interpreted as evidence that thecisisomer has a nonhyphen;planar geometry in the electronic ground state. The extinction coefficient for the 0ndash;0 band of thetransisomer is about 1.5 times that for thecis.