Synthesis and Electronic Spectroscopy of Bromo Carbazoles. Direct Bromination of N- and C-Substituted Carbazoles by N-Bromosuccinimide and N-Bromosuccinimide ? Silica Gel System

B. PONCE, MARIA; M. CABRERIZO, FRANCO; M. BONESI, SERGIO; ERRA BALSELLS, ROSA

HELVETICA CHIMICA ACTA

ELSEVIER

Lugar: AMSTERDAM; Año: 2006 vol. 98 p. 1123 - 1139

0018-019X

Abstract. The preparation, isolation and characterization (elemental analysis, M.p., 1H-NMR, 13C-NMR and MS) of the bromo derivatives of N-substituted carbazoles (N-methylcarbazole (1), N-phenylcarbazole (2), N-benzylcarbazole (3), 2-methoxy-N-methylcarbazole (4)) and C-substituted carbazoles (2-acetyloxycarbazole (5) and 3-nitrocarbazole (6)) are reported. As brominating reagents, N-bromosuccinimide and N-bromosuccinimide ? silica gel in dichloromethane and in acetic acid and KBrO3/KBr mixtures in (i) ethanol doped with catalytic amount of sulphuric acid and in (ii) acetic acid have been used and their uses have been compared. The brominating reaction of carbazoles 3, 4, 5 and 6 and the characterization of the corresponding bromo derivatives are described for the first time. Semi empirical PM3 calculations have been performed in order to predict reactivity of N-substituted and C-substituted carbazoles and their bromo derivatives. Theoretical and experimental results are discussed briefly. Electronic spectra (UV-absorption, fluorescence and phosphorescence emission spectra) of bromocarbazole derivatives in acetonitrile solution at 298 K and in solid matrix at 77 K have been recorded and compared with those of the corresponding carbazoles 1 ? 6. The dynamic properties of the lowest excited singlet and triplet states (tf, tp, ff and fp) have been measured in the same experimental conditions. The bromine and nitro intramolecular spin ? orbital coupling effect on the spectroscopic data, photo physical parameters and on the photo reactivity are also analyzed briefly.