Photochemical Processes in Molecular Polymethine Dye Probes in the Presence of Bile Salts

Primary photochemical processes in polymethine dye probes 3,3′-di(γ-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine betaine (DEC) and 3,3′,9-trimethylthiacarbocyanine iodide (Cyan 2) in micellar systems of bile-acid salts (BASs) sodium cholate, deoxycholate, and taurocholate and sodium dodecyl sulfate (SDS) as a reference are studied by flash photolysis. Signals due to photoisomerization of dye trans-isomers and dark reverse isomerization of the resulting cis-photoisomers are observed during pulse photolysis of air-saturated aqueous dye solutions in the presence of BAS and SDS micelles. The lifetimes of the photoisomers are 60–190 μs. Pulse photolysis of Cyan 2 and DEC solutions without oxygen and with BAS and SDS micelles induced photoisomerization and transition of the dyes into an excited triplet state followed by the reverse transition (intersystem crossing) into the initial singlet state. Triplet–triplet absorption spectra of these dyes isomers in polar (EtOH, i-PrOH) and nonpolar (dioxane) solvents were obtained for comparison using triplet–triplet energy transfer from anthracene. The conclusion was drawn that the photochemical behavior of the dyes in BAS and SDS micellar systems were similar.