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 study the complexation of Ba2+ with a benzothiazolium styryl azacrown ether dye and two derivatives, one without an azacrown and one with an alkylsulfonate pendant to the benzothiazolium group. Studies of the thermal cis-trans isomerization on the kilosecond time scale, and of the excited state leading to trans-cis photoisomerization on the picosecond time scale, are reported which enable a quantitative analysis of the kinetics and complexation equilibria to be obtained. The photophysics are interpreted by a scheme which includes rotation around both the olefinic C=C bond and adjacent C-C bonds in the excited state. A comparison of the data for this dye with those for other derivatives studied here and reported elsewhere indicates that the extent of intramolecular charge transfer in the excited state is a key factor in controlling the properties. An overall mechanism is proposed for the thermal and photochemical reactions of this dye which indicates that it is a good candidate for applications which require the photocontrolled complexation/release of barium cations in solution.