The binding of 3;3′-diethylthiacarbocyanine iodide (DTCC) with molecules of DNA was investigated
by different photochemical methods. Absorption spectra were investigated under various concentration
of DNA. Isosbestic points observed in these spectra are attributable to existence of two different
complexes DTCC with DNA. Equilibrium constants of the formation of complexes I and II were determined
(K1≈106M−1, K2≈5×104M−1 accordingly). Differential absorption spectra of two photoisomers of DTCC
were obtained by flash photolysis method; it was found that the quantum yield of the short-lived photoisomer
decreases and the quantum yield of the second long-lived photoisomer builds up with the increase in
the DNA concentration. Kinetics of interaction between the triplet state of the dye and oxygen were investigated
under various concentration of DNA. The growth of the quantum yield of fluorescence and intersystem
crossing was observed with the increase in the DNA concentration.
