| Abstract
| - The photophysics of 3,3‘-diethylthiacarbocyanine iodide (DTCI) in liquid mixtures of dimethyl sulfoxide(DMSO) with toluene was studied by means of steady-state and time-resolved optical spectroscopy. By variationof the diminution of the volume fraction of DMSO, the solvation shell around a DTCI species significantlydecreases the quantum efficiency of its photoisomerization. The character of the fluorescence decay, observedupon excitation at 570 nm, also changes. For DMSO volume fractions larger than 14 vol %, a single-exponentialfunction with a lifetime of about 300 ps is found; in the range from 14−8 vol % of DMSO, biexponentialfunctions with time components of 200 and 500 ps are observed, and when the DMSO volume fractiondecreases from 8 to 1.6 vol %, the fluorescence decay is again single exponential (lifetimes 500−700 ps).These findings will be explained in terms of the Rullière model by assuming a fast equilibrium betweenelectronically excited trans and cis isomers of DTCI.
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