Symmetry-Guided Theoretical Study on Photoexcitation Characteristics of CdSe Quantum Dots Hybridized with Graphene and BN

This study employs density functional theory (DFT) and time-dependent DFT (TD-DFT) to systematically investigate the ground- and excited-state properties of hybrid systems composed of CdSe quantum dots (QDs) with graphene and boron nitride (BN). Through Multiwfn wavefunction analysis, we calculated the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gaps and density of states (DOS), revealing distinct symmetry-dependent electronic characteristics. The HOMO–LUMO gap analysis demonstrates graphene’s superior charge transfer capability compared to BN, attributed to its higher structural symmetry enabling more efficient orbital overlap. DOS analysis further confirms the enhanced electrical conductivity in symmetry-matched graphene hybrids. The independent gradient model (IGM) and reduced density gradient (RDG) analyses reveal fundamentally different interfacial interaction patterns: the graphene hybrid exhibits uniform van der Waals interactions, consistent with its hexagonal symmetry, while the BN system shows heterogeneous interactions with localized hydrogen bonding due to symmetry reduction from heteroatomic composition. Binding energy calculations indicate greater stability in the graphene-based hybrid, reflecting optimal symmetry matching at the interface. UV–Vis spectra analysis shows that graphene dominates the optical response in its hybrid system, maintaining its symmetric spectral characteristics, while CdSe QDs govern the BN hybrid’s absorption. Electrostatic potential distributions remain essentially unchanged post-hybridization, preserving the intrinsic charge symmetry of components. Two-photon absorption (TPA) characterization reveals significant nonlinear optical properties in CdSe QDs, particularly at the first excited state. This work provides the first systematic comparison of charge transfer dynamics in CdSe QDs hybridized with graphene versus BN, demonstrating how material symmetry governs optoelectronic modulation mechanisms. The findings establish symmetry–property relationships that inform the design of low-dimensional hybrid materials for photonic applications.