New conjugated carbazole derivatives: synthesis and photophysical properties catalysed by Pd–Cu@rGO

Abstract

Carbazole derivatives are widely used to make highly efficient optoelectronic materials. In this context, we developed a method for synthesizing conjugated carbazole derivatives using bimetallic Pd–Cu nanoparticles (NPs) immobilized on reduced graphene oxide (rGO) sheets. Pd–Cu NPs were synthesised in a one-pot wet chemical process with ascorbic acid as the reducing agent. The Pd–Cu NPs have an average diameter of 3.8 ± 1.2 nm. X-ray diffraction, SEM, TEM, EDS, and cyclic voltammetry were used to characterise the structure and morphology of the Pd–Cu@rGO NPs. N-Protected-3-aryl/heteroaryl carbazoles were efficiently synthesized using the Pd–Cu@rGO catalyst, which enabled the Suzuki–Miyaura (SM) cross-coupling reaction between N-protected-3-bromo-carbazoles and a range of aryl/heteroaryl boronic acids. The prepared compounds were characterized by NMR (¹H & ¹³C) and HRMS spectra. For the SM reaction, the catalytic performance of the monometallic Pd@rGO and bimetallic Pd–Ni@rGO and Pd–Cu@rGO catalysts were studied with various metal loadings. In comparison to the monometallic Pd@rGO and bimetallic Pd–Ni@rGO catalysts, the bimetallic Pd–Cu@rGO heterogeneous catalyst (L3) demonstrated improved catalytic performance with yields of up to 98%. The material exhibits excellent recyclability and can be reused up to five times without experiencing any decline in its effectiveness. The electronic structure modification offered by the Pd–Cu ensemble on rGO may be responsible for its higher catalytic efficiency. UV and fluorescence spectra were used to investigate the optoelectronic properties of the produced carbazole compounds. Among the compounds studied, 5f, 5n, and 5h exhibited superior UV absorption and fluorescence emission due to the presence of auxochromes and extended conjugation. This study explores the efficacies of the reduced graphene oxide-supported Pd–Cu bimetallic system with different weight% for milder SM reactions.