CuIn-ethylxanthate, a “Versatile Precursor” for Photosensitization of Graphene-Quantum Dots and Nanocatalyzed Synthesis of Imidazopyridines with Ideal Green Chemistry Metrics

Abstract

Recently, the development of hybrid nanocatalysts involving Earth-abundant transition metals for photosensitization and multicomponent reactions in industry and academia has been a matter of intense study. Such hybridized catalytic systems minimize the production cost and act as a bridged system by diversifying the application in different areas. In the present study, copper indium ethylxanthate was used as a versatile precursor for the synthesis of colloidal chalcopyrite phase copper indium sulfide nanoparticles (C-CIS NPs) in photosensitization of graphene quantum dots and reusable powdered wurzite phased copper indium sulfide nanoparticles (PW-CIS500 NPs) for selective and efficient single-pot sustainable synthesis of substituted imidazopyridines via an A3 coupling strategy of an aldehyde, amine, and alkyne. The material was characterized by various spectroscopic techniques viz. high-resolution transmission electron microscopy, powder X-ray diffraction, field emission scanning electron microscopy, elemental mapping studies, UV visible spectroscopy, photoluminescence, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller analysis, inductively coupled plasma optical emission spectroscopy/mass spectrometry, etc. Quenching of photoluminescence intensity of colloidal CuInS2 on anchoring the graphene quantum dots (GQDs) was confirmed by photosensitization of GQDs via efficient charge transfer in the CIS-GQD interface. On the other hand, the PW-CIS500 nanocomposites (NCs) catalyzed A3 coupling strategy demonstrates the high catalytic efficiency for the A3 coupling reaction giving substituted imidazopyridines without losing its activity and could be recycled with a total turnover (TOF) number of >210, good E-factor of 0.13, and high RME of 88%.