Investigation of photocatalytic performance of GQD/Ir(III) complex nanocomposite: Effect of π-conjugation

Abstract

This study explores the photophysics of graphene quantum dots (GQDs) and iridium complexes, and their nanocomposites using density functional theory calculations. We evaluate the electronic structures and energy conversion efficiencies of the nanocomposites as a function of the π-conjugation of the 2-aryl substituents. Our results indicate that the GQD primarily influences the occupied frontier molecular orbitals of the nanocomposite, while the unoccupied frontier molecular orbitals are mainly determined by the Ir(III) complex. The dipolar interaction between GQD and the Ir(III) complex causes a redistribution of charge between the two molecules, resulting in enhanced delocalization of electrons in the nanocomposite. The nanocomposite's unique electronic configuration results in enhanced charge separation, leading to improved electron injection into the semiconductor. Moreover, the high-energy absorption is determined by GQD, while the Ir(III) complex primarily contributes to low-energy absorption. Furthermore, increasing the π-conjugation of the 2-aryl substituent increases the nanocomposite's LUMO levels and open-circuit voltage, but decreases its light harvesting ability. However, the electron-hole recombination time increases, leading to improved short-circuit current and energy conversion efficiency. Our computational results provide valuable insight into the photophysical properties of GQD/Ir(III) complex nanocomposites, specifically the important elements affecting their photocatalytic performance.