Fluorescence spectroscopy of C.W. and pulsed laser induced transient photoisomers

A stationary concentration of 'transient' photoisomer of DODCI-3,3'-diethyl oxadicarbocyanine - is obtained when a low concentrated (C approximately 10-7M) ethanolic solution of this dye is excited with a C.W. Ar+ laser operating at 514,5 nm. The fluorescence spectrum obtained under these conditions is compared to a reference spectrum, characteristic of a single isomer, and the differences are studied as a function of the output power of the laser. The results thus obtained provide new information on the absorption and emission spectra of the thermally unstable isomer and the photoisomerisation process. The overall results obtained from the polarized-light fluorimetry and picosecond fluorescence relaxation technique -using linear primary alcohols up to decanol as solvents- are discussed in terms of the interaction of the solute molecules with their immediate environment