Triplet-state photophysics of anthracene sulphonates

Abstract

Four anthracene sulphonates (1-AS, 2-AS, 1,5-AS and 1,8-AS), containing SO^–₃ group(s) at the positions indicated, have been examined for triplet-state photophysical properties by nanosecond laser flash photolysis. Except for bathochromic shifts in wavelength maxima and partial loss of resolution of vibrational structures, the triplet–triplet absorption spectra of the sulphonates in water are reminiscent of anthracene. The triplet yields in water are high (0.6–0.9) and their temperature dependence suggests an activated nature of intersystem crossing (except for 1,8-AS). Results are presented for singlet and triplet quenching by I^–, Cs⁺, O₂ and di-t-butylnitroxy radical (DTBN) and the fraction (δ_T) of singlet quenching events that lead to triplet formation. δ_T are found to be high (0.7–1.0) for O₂, I^– and Cs⁺, but relatively low (0.30–0.5) for DTBN. The oxygen quenching of both singlets and triplets of 1-AS and 1,5-AS in methanol results in singlet-oxygen photosensitization with high quantum efficiencies (0.6–0.8).