Enormously high second-order nonlinear optical response of single alkali atom decorated hexalithiobenzene

Abstract

We have studied C6Li6−M (M = Li, Na, and K) complexes by decorating hexalithiobenzene with an alkali atom using density functional theory. These aromatic complexes are stabilized by charge transfer from M to C6Li6 such that they possess non-vanishing dipole moment and high polarizability (609.3–852.2 a.u.). More interestingly, the first-order static hyperpolarizability of C6Li6−M becomes enormously high, up to 5.4 × 105 a.u. for M = K, which suggests its exceptionally large second-order nonlinear optical (NLO) response. Furthermore, the large hyperpolarizabilities are related to the aromaticity of C6Li6−M complexes. Our TD-DFT calculations explain that the large NLO response of C6Li6−M results due to its smaller transition energy in the crucial excited state. This work demonstrates a suitable path for the enhancement of NLO response and establishes C6Li6−M complexes as potential candidates for NLO materials.