Electron transfer-mediated synergistic nonlinear optical response in the Ag_n@C₁₈ (n = 4-6) complexes: A DFT study on...

Seeking highly efficient and stable non-linear optical (NLO) materials is crucial yet challenging, given their promising applications in laser diodes and photovoltaics. In this study, we employ the excess electron and charge transfer strategies to theoretically design three novel complexes, namely Ag_n@C₁₈ (n = 4-6), by adsorbing silver clusters onto the cyclo[18]carbon ring (C₁₈). Our aim is to investigate the NLO characteristics of these complexes using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The results reveal that the adsorption of Ag clusters onto C₁₈ leads to a decrease in excitation energy and an increase in dipole moment and oscillator strengths, thereby significantly enhancing the hyperpolarizability of the complexes. Strikingly, among all these complexes, Ag₆@C₁₈ exhibits the highest first hyperpolarizability value of approximately 109496.2620 au calculated at the B3LYP/cc-PVDZ-pp level of theory, which is about 1.3 × 10⁶ times higher than that of pure C₁₈. This finding validates the effectiveness of the proposed strategies in enhancing the NLO response of the species. Moreover, the calculated UV-Vis absorption spectrum demonstrates that the Ag_n@C₁₈ complexes with excess electrons exhibit absorption at longer wavelengths (ranging from 385 to 731 nm) compared to C₁₈. In addition, the stability, chemical bonding, and charge transfer characteristics of the Ag_n@C₁₈ (n = 4-6) complexes were also discussed. These findings highlight the potential of these complexes for the development of highly efficient NLO devices.