Harnessing carbazole based small molecules for the synthesis of the fluorescent gold nanoparticles: A unified experimental and theoretical approach to understand the mechanism of synthesis.

Six structurally different carbazoles (1-6) were explored as the green reducing agents for the synthesis of the fluorescent Au nanoparticles with tailor-made morphology in anionic (sodium dodecyl sulphate, SDS), cationic (cetyltrimethylammonium bromide, CTAB) and neutral (polyvinylpyrrolidone, PVP) micelle medium. Structure of the carbazoles played an important role in controlling the morphology, rate of formation and fluorescent activity of the Au nanoparticles. The Au nanoparticles formed in-situ also simultaneously catalyzed the intermolecular CC and NN couplings between the carbazoles, leading to the corresponding bis-carbazole derivatives. The free and bis-carbazole derivatives functionalized the surface of the synthesized Au nanoparticles and thereby controlling their morphology and fluorescence activity. A computational study was also made to determine the origin of the absorption and emission bands of the synthesized nanoparticles. The combined experimental and theoretical studies unraveled the nanoparticle formation process and mechanistic pathway of this green and easily implementable synthetic protocol of Au nanoparticles.