Multiple Fluorescences. 6. The Case of 1,8-Naphthosultam

Article abstract of DOI:10.1021/j100216a015

The emission from 1,8-naphthosultam (2H-naphth<1,8-dc>isothiazole 1,1-dioxide) (1a) is composed of two bands, one for the acid (λ_max=480 nm) and one for the corresponding anion (2, λ_max=600 nm).The fluorescence of both 1a and 2, as well as that of the N-methyl- and N-ethyl-1,8-naphthosultams (1b and 1c), has a modest sensitivity to solvent polarity.The ground-state pK_a for 1a is 6.2, with pK_a* of -3.0.The proton transfer rate for 1a to water is >5xE10 s^-1, from the rise time of anion fluorescence by picosecond pulse techniques.The fluorescence lifetimes for 1a and 2 are 16 (Φ_f = 0.37, dioxane) and 1.4 (Φ_f = 0.005, H2O pH 10) ns, respectively.