Theoretical Study on the Nonlinear Optical Property of Boron Nitride Nanoclusters Functionalized by Electron Donating and Electron Accepting Groups.

The influence of donor-acceptor (D-A) groups on the nonlinear optical (NLO) property of BN functionalized nanocluster has been investigated by density functional theory. We study the effect of bonding of three electron acceptor ligands (CN, COOH, and NO) and three donor ligands (NH, N(CH), and PhNH) positioned at opposite ends of BN nanocluster in the gas phase. The result reveals that the complexation of D-A groups on the BN nanocluster is energetically favorable and significantly narrowed the HOMO-LUMO gaps. The functionalization of D-A groups lead to an extremely large first hyperpolarizability value. Our survey reports the strongest NLO responses found in PhNH-BN-PhCN cluster (1882.47 × 10 esu), whereas centrosymmetric BN cluster yields a zero hyperpolarizability value. Designed systems are analyzed through the HOMO-LUMO gap, frontier molecular orbital, hyperpolarizability, Δ index, transition dipole moment density, density of states (DOS), and molecular electrostatic potential. The obtained results are well correlated with the computed absorption spectra of the molecule. The results demonstrate that phenyl ring incorporated D-A groups amplify the NLO response to a larger extent. The significant first hyperpolarizability arises due to charge transfer from the donor to the acceptor moiety. As a whole, this theoretical work provides a direction to researchers that the right choice of substitution can considerably impact the nonlinear optical property of BN nanoclusters.