PHOTOPHYSICAL AND PHOTOCHEMICAL DEACTIVATION BEHAVIOR OF STREPTOPOLYMETHINES

The photophysical and photochemical deactivation behaviour of the homo logous series of streptopolymethines 1,3-bis(dimethylamino)tri-, -pent a-, -hepta- and -nonamethine has been investigated and is discussed on the basis of an energy scheme. The deactivation of the S-1-states occ urs by fluorescence and thermally activated photochemistry (E-Z isomer ization). With the exception of the trimethine the fluorescence domina tes at low temperature. The ab initio calculated potential curves of t he S-1 states indicate an increase in the rotation barrier with increa sing length of the molecule. In the case of the nonamethine a multiple E-Z isomerization is discussed.