DUAL LASER EXCITATION OF A PHOTOCHROMIC SYSTEM - APPLICATION TO DODCI

A technique based on a combination of pump-and-probe fluorescence and absorption detection was developed in order to obtain the emission parameters of the photoisomeric (P) species of dyes with noncompletely overlapped absorption spectra of P and the starting species (N). Near total population transfer to the ground state of P was achieved using a continuous wave high-fluence pump laser. A pulsed laser probed this population in its absorption region in such a way that the pulsed emission corresponded to fluorescence from P. Absorption measurements allowed us to follow the P population and to establish its relationship with pump fluence and wavelength. The direct monitoring of the P concentration increased the accuracy of the previously reported values for several photophysical parameters. Temperature-dependent fluorescence quantum yield and lifetime, emission spectrum, and Arrhenius parameters of the nonradiative decay processes of P from 3,3'-diethyloxadicarbocyanine iodide (DODCI) are given. The mechanism for the direct transformation between N and P through the singlet excited states of DODCI is re-evaluated.