Electron Donating 2,7-Carbazole Derivatives: Synthesis and Characterization

Carbazoles (Cbz)s are well known electron-donating materials because of the conjugated π-electrons present in their structures, they are one of the most suitable candidates for construction of electronic devices. In the present work, we synthesized a 2,7-dibromo-N-dodecyl carbazole (dodecylcbz) via a two step procedure. In the first step, 2,7-dibromocarbazole (cbz) was synthesized (via another two step procedure–nitration of dibromobiphenyl and consequent cadogan ring closing steps). In the second step, the targeted dodecylcbz was synthesized via nucleophilic substitution. The synthesized compounds were characterized by mp, FTIR, UV-vis, NMR, and emission techniques. The FTIR spectra confirm the structures. The solubility is very high for both the cbz and dodecylcbz in all common organic solvents. The absorption spectra of both cbz and dodecylcbz show high energy forbidden S0→S2 transition absorptions with high intensity at around 240 nm comparing to π→π* electronic transition absorptions at around 303 nm, respectively in all of the common organic solvents studied. Most importantly, π→π* electronic transition absorptions of both carbazole and dodecylcarbazole were unchanged with respect to the polarity and type of the solvent. Whereas, S0→S2 transition absorptions have undergone solvent-dependent shifts. Both the cbz and dodecylcarbazole exhibited intense excimer emissions in all of the solvents. These interesting optical properties are very useful for present-day organic-based optoelectronic applications. Keywords: Carbazole, 2,7-Dibromocarbazole, Excimer Emission, Forbidden Transitions