The near ultraviolet spectra of 2,1,3-benzothiadiazole and its deuterated and substituted derivatives

Abstract

Polarized mixed crystal spectra of 2,1,3-benzothiadiazole (BTD) confirm a previous assignment, based on band contour analysis, of the 3280 and 3060 Å systems to 1B 2 ← 1A 1 and 1A 1 ← 1A 1 transitions, respectively. The pure crystal spectrum was also studied. A comparison of the vapor absorption spectra of BTD- d 0, BTD- d 4, and 4-amino-BTD leads to a more complete understanding of the vibrational structure in the weak 3280 Å system, including a case of Fermi resonance between Herzberg-Teller-active b 2 vibrations; and to an assignment of the sharp bands beyond 32 400 cm −1 to the stronger 3060 Å system. Differences between the spectra of BTD and of related heteroaromatic molecules such as benzothiazole are discussed.