Photophysical and photochemical deactivation behaviour of streptopolymethines

Abstract The photophysical and photochemical deactivation behavior of the homologous series of streptopolymethines 1,3-bis(dimethylamino)-tri-, -penta-, -penta-, -hepta- and -nonamethine has been investigated and is discussed on the basis of an energy scheme. The deactivation of the S 1 -states occurs by fluorescence and thermally activated photochemistry (E-Z isomerization). With the exception of the trimethine the fluorescence dominates at low temperature. The ab initio calculated potential curves of the S 1 states indicate an increase in the rotation barrier with increasing length of the molecule. In the case of the nonamethine a multiple E-Z isomerization is discussed.