PHOTOCONTROL OF CATION COMPLEXATION WITH A BENZOTHIAZOLIUM STYRYL AZACROWN ETHER DYE - SPECTROSCOPIC STUDIES ON PICOSECOND AND KILOSECOND TIME SCALES

UV-visible absorption and emission spectroscopy have been used to stud y the complexation of Ba2+ with a benzothiazolium styryl azacrown ethe r dye and two derivatives, one without an azacrown and one with an alk ylsulfonate pendant to the benzothiazolium group. Studies of the therm al cis-trans isomerization on the kilosecond time scale, and of the ex cited state leading to trans-cis photoisomerization on the picosecond time scale, are reported which enable a quantitative analysis of the k inetics and complexation equilibria to be obtained. The photophysics a re interpreted by a scheme which includes rotation around both the ole finic C=C bond and adjacent C-C bonds in the excited state. A comparis on of the data for this dye with those for other derivatives studied h ere and reported elsewhere indicates that the extent of intramolecular charge transfer in the excited state is a key factor in controlling t he properties. An overall mechanism is proposed for the thermal and ph otochemical reactions of this dye which indicates that it is a good ca ndidate for applications which require the photocontrolled complexatio n/release of barium cations in solution.