Concentration increase of the singlet-oxygen generation quantum yield by an indotricarbocyanine dye

Abstract

Regularities in the generation of singlet oxygen sensitized by the indotricarbocyanine dye HITC with I– and ClO4– anions in highly and slightly polar solvents were studied as functions of dye concentration (Cd). The yield of singlet-oxygen formation (γΔ) by HITC (I–) increased in slightly polar solvents as its concentration increased. It was shown that HITC with Cd < 10–7 M in CHCl3 and <5·10–6M in o-dichlorobenzene with any anion was found primarily in the form of free ions. It was established that the concentration increase of singlet-oxygen generation by HITC (I–) was due to the heavy-atom effect of the anion as a result of their existence as contact ion pairs and an increase of the fraction of such pairs in a solution with an increased photosensitizer concentration. The quantum yield of singlet-oxygen formation for HITC with ClO4– counterion was stable in various solvents as Cd was varied over a wide range