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 -styrylnaphthalene ( 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, BrDMA) and acceptors ( p -dicyanobenzene, DCNB) were studied in polar and nonpolar solvent at room temperature by absorption picosecond laser flash photolysis. The transient absorption formed within the laser pulse, already attributed to S 1 → S n and S 2 → S n transitions, were replaced, in the presence of amine quenchers, by the absorption of the exciplex (nonpolar solvent) or of contact radical ion pairs (CRIP, polar solvent). The time evolution of these transients showed the formation of the solvent-separated radical ion pair (SSRIP) and then of the longer-lived absorption of triplet state and/or radical anions. In the presence of DCNB in polar solvent the evolution of the first excited singlet showed the formation of CRIP, SSRIP, and radical cations. The criteria of the transient attribution and the spectral and kinetic characteristics of the transients are reported.