As. Tatikolov et al., INFLUENCE OF INERT COUNTERIONS ON THE PHOTOCHEMISTRY OF SOME CATIONICPOLYMETHINE DYES, Journal of physical chemistry, 99(17), 1995, pp. 6525-6529
The effects of ''inert'' counterions on some photochemical processes i
nvolving cationic polymethine dyes have been studied in ion pairs form
ed in low-polar media. In particular, the counterion effects on the ba
ck isomerization kinetics of photoisomers of benzimidacyanine and indo
tricarbocyanine dyes and on the triplet state decay of the benzimidacy
anine dyes have been investigated by flash photolysis. The increase in
the rate constant and decrease in the activation energy of back isome
rization of benzimidacyanines are observed when dye-counterion ion pai
rs are formed in low-polar media, whereas the increase in the activati
on energy is observed for indocyanines under the same conditions. For
benzimidacarbocyanine with the I- counterion, ion pair formation gives
rise to an increase in the decay rate constant of its triplet state d
ue to interaction of the dye cation with the I- heavy atom; meanwhile,
there is no appreciable rise in S-1 --> T intersystem crossing. The e
nhancement of the S-1 --> S-0 internal conversion in ion pairs has bee
n revealed for all benzimidacyanines with the I- counterion.