Luminescence of N-arylbenzamides in low-temperature glasses

The low-temperature luminescence of benzamide and six additional N-arylbenz amides has been investigated in a methyltetrahydrofuran glass. The luminesc ence of microcrystalline benzamide has also been studied. Assignments of th e fluorescence and phosphorescence have been made on the basis of compariso ns with the spectra of benzamide and the six aminoarenes and with the resul ts of semiempirical ZINDO calculations for the amines and amides. This info rmation was used to construct state-energy diagrams for the six amides. The 430 nm fluorescence of benzanilide and the amides derived from 4-aminobiph enyl and 4-aminodiphenyl-acetylene is assigned to a n,pi* state having a re laxed geometry and localized on the benzoyl group. The structured fluoresce nce of the amides derived from 4-aminostilbene and 2-aminoanthracene is att ributed to a delocalized pi,pi* singlet slate, The amide derived from 2-ami nophenanthrene displays dual fluorescence. The amides derived from 4-aminos tilbene and 2-aminoanthracene are nonphosphorescent. The structured phospho rescence of the amides derived from the other aminoarenes is assigned to a pi,pi* triplet state similar to that for the aminoarene. These results serv e to further elucidate the unusual luminescence properties of the benzamide s in solution as well as in low-temperature glasses.