DYNAMICS OF THE SINGLET EXCITED-STATES OF DIARYLETHENES IN THE PRESENCE OF CHARGE-TRANSFER INTERACTIONS - A PICOSECOND LASER FLASH-PHOTOLYSIS STUDY

Charge-transfer interactions of singlet excited trans isomers of n-sty rylnaphthalene (n-StN, with n = 1 and 2), 9-styrylanthracene (9-StAn), and n-styrylphenanthrene (n-StPh, with n = 1, 2, and 9) with electron donors (N,N-diethylaniline, DEA, and 4-bromo-N,N-dimethylaniline, BrD MA) and accepters (p-dicyanobenzene, DCNB) were studied in polar and n onpolar solvent at room temperature by absorption picosecond laser fla sh photolysis. The transient absorption formed within the laser pulse, already attributed to S-1 --> S-n and S-2 --> S-n transitions, were r eplaced, in the presence of amine quenchers, by the absorption of the exciplex (nonpolar solvent) or of contact radical ion pairs (CRIP, pol ar solvent). The time evolution of these transients showed the formati on of the solvent-separated radical ion pair (SSRIP) and then of the l onger-lived absorption of tripler state and/or radical anions. In the presence of DCNB in polar solvent the evolution of the first excited s inglet showed the formation of GRIP, SSRIP, and radical cations. The c riteria of the transient attribution and the spectral and kinetic char acteristics of the transients are reported.