Flash photolysis of tricarbocyanine dyes

Abstract

1. Flash photolysis of solutions of tricarbocyanine dyes leads to the formation of short-lived photoisomers which absorb in the 770–900 nm region of the spectrum. Rate constants for the relaxation of these products into the basic isomer, and activation energies and preexponential factors for the relaxation process, have been determined. 2. Triplet-state dye molecules, and ion-radicals resulting from reactions of the latter with ground state molecules, are also formed in oxygen-free solutions. A study has been made of the formation and destruction of these short-lived particles, and their absorption spectra and extinction coefficients were determined. T-T annilation makes a minor contribution to dye ion-radicals formation. 3. The introduction of electron donors and acceptors into the system promotes the formation of dye anion- and cation-radicals through reaction of the triplet state and additive molecules. Under T-T energy transfer with anthracene, the triplet-state anthracene molecule reacts with a ground-state tricarbocyanine dye molecule, extracting an electron from the latter.