Synthesis and photophysical properties of fluorescent 8,9‐diarylbenzo[def]carbazoles

Abstract

Background Benzocarbazole has attracted much attention from scientists in the past few decades for a variety of applications in materials science. Objective Herein we report the synthesis and photophysical properties of N‐acyl and N‐free 8,9‐diarylbenzo[def]carbazoles. Methods These benzo[def]carbazoles were prepared by Pd(II)‐catalyzed C‐H bond activation and deacetylation as the key steps, and their photophysical properties were studied by measurement of absorption and emission spectra in chloroform at room temperature. Results The 8,9‐diarylbenzo[def]carbazoles show lower LUMO energy levels and smaller HOMO/LUMO gap compared to the parent benzo[def]carbazole, and the N‐unprotected 8,9‐diarylbenzo[def]carbazoles show more red‐shifted fluorescent emission compared to the N‐acyl ones. The absorption and emissionmaxima of these 8,9‐diaryl‐substituted benzo[def]carbazoles in CHCl3 were in the ranges of 278–350 and 365–426 nm, respectively, and with quantum yields (ΦF) up to 0.62. Conclusions We have demonstrated the photophysical properties of 8,9‐diaryl substituted benzo[def]carbazoles with or without N‐acetyl group. These 8,9‐diaryl substituted benzo[def]carbazoles could be good candidates for the future development of functional organic molecules.

Preparation of Carbazoles Involving 6π‐Electrocyclization, Photoredox‐, Electrochemical‐, and Thermal Cyclization Reactions: Mechanistic Insights

“…An interesting Pd II -catalyzed CÀ H bond activation procedure has been applied to convert diphenylphenanthrene derivatives into substituted N-acetyl benzo[def]carbazoles in good to excellent yields utilizing a modified Buchwald method in the presence of sodium acetate which promotes the activation of the CÀ H bond. [67] The cyclization reaction proceeded successfully with Pd(OAc) 2 (10 mol %) and Cu(OAc) 2 (2.0 equiv.) in toluene under oxygen at 120 °C for 24 h providing the desired N-acetyl carbazole derivatives in good to excellent yields (up to quantitative yield; Scheme 34) showing good tolerance with electron-donor and electron-withdrawing groups.…”