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 Iand ClO 4 anions in highly and slightly polar solvents were studied as functions of dye concentration (C d ). The yield of singletoxygen formation (γ Δ ) by HITC (I -) increased in slightly polar solvents as its concentration increased. It was shown that HITC with C d < 10 -7 M in CHCl 3 and <5•10 -6 M 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 singletoxygen formation for HITC with ClO 4 counterion was stable in various solvents as C d was varied over a wide range.