Fluorescent whitening agents. VII. Photodimerization of a naphthotriazolylstilbene derivative

Abstract

Photolysis of the trans (E) isomer of N-butyl-4-(2H-naphtho[1,2-d Itriazol-2-y1)stilbene-2-sulphonamide(1) in dioxan results in isomerization and dimerization. A fluorescent photodimer of trans(1) has been isolated and characterized. Fluorescence and photochemical quantum yields and ultravioletspectra of trans (1) and its photoproducts are given.Although trans (1) photodimerizes rapidly in polymer films, this causes no change in the fluorescenceemission spectrum. The absence of the characteristic fluorescence of the dimer is attributed tolong-range resonance transfer of energy from the excited dimer to a neighbouring molecule of trans(1) in the polymer.