Excited State Behavior of Diarylethenes in the Subnanosecond Timescale: The Role of an Upper Singlet

Abstract

Picosecond absorption measurements of the trans isomers of 9-styrylanthracene (9-StAn), n-styrylnaphthalene (n-StN, with n = 1 and 2), and n-styrylphenanthrene (n-StPh, with n = 1, 2, and 9) were carried out in a number of solvents at room temperature. In all cases, a short-lived transient (with τS = 0.1 ÷ 0.8 ns) was produced monophotonically within the laser pulse. This transient, which absorbs in a wide wavelength range (400−750 nm), was assigned to the S2 state. At longer delay time, the S1 → Sn absorption (with lifetime τL) replaced that of S2, its assignment being strongly supported by the comparison between τL and the fluorescence lifetime of these diarylethenes. The S1 → Sn absorption of two distinct rotamers was detected for 2-StN in solvents of different polarity, while for the other compounds only one longer-lived transient was detected. Complementary fluorimetric measurements by phase-modulation technique confirmed the presence of a second decay component in the picosecond region with a lifeti...