Abstract
A comparative study of the photophysical properties of a linear ketocyanine dye and its structurally rigid analogue containing a cyclohexanone fragment in the polymethine chain is carried out in this paper. It was found that the introduction of a fixing fragment limits the conformational mobility of the molecule and has a decisive influence on the redistribution of the pathways for deactivation of electronic excitation energy. Restricting the flexibility of the polymethine chain leads to a decrease of the fluorescence quantum yield, that is consistent with a more efficient population of the triplet state. It is shown that the delayed fluorescence lifetimes of both dyes in evacuated solution are practically identical, that indicates comparable kinetic characteristics of the decay of long-lived excited states. The quantum yield Φ∆ of singlet oxygen O2(1∆g ) generation is 0.30 ± 0.02 for the linear dye and 0.38 ± 0.03 for the structurallyrigid dye. Thus, modifying the chromophore chain by introduction of a cyclohexanone fragment allows for the redirection of excitation energy from the fluorescent channel to the triplet channel. It makes the structurally rigid dye a more effective and promising photosensitizer for use in photodynamic therapy and photocatalysis