Dimerization kinetics of thiacarbocyanine dyes by photochemically induced concentration jump

A novel photochemically induced concentration jump method was used to study the fast kinetics of dimerization of thiacarbocyanine dyes in aqueous solution. Perturbation of the monomer–dimer equilibrium is due to fast production of monomers which takes place as a result of an electron transfer reaction photosensitized by a cationic ethyl meso-thiacarbocyanine (1) and similar anionic dyes (2–6) in the triplet state. The subsequent restoration of the equilibrium was monitored by changes of monomer absorbance and characterized by a single relaxation time. The kinetics of dimerization were analyzed and the rate constants of dimerization and deaggregation determined.