Quantum chemical study of structures, electronic spectrum, and nonlinear optical properties of polynuclear lithium compounds

A theoretical study of polynuclear lithium compounds has shown that these species display large calculated nonlinear optical (NLO) responses. These compounds are based on aromatic subunits connected through polyhedral inorganic core (Li7O6 or Li8O6). These compounds show the calculated first hyperpolarizabilities (β) ranging from 262.55 to 16336.35 × 10−33 esu. The results show that subtle structural modification can substantially enhance the first hyperpolarizability. A basis for understanding the origin of these large NLO responses is proposed based on consideration of the molecular orbitals and electronic transition features of the compounds and the two-state model. Charge transfer from central core to the peripheral phenyl groups plays a key role in the nonlinear optical response. Moreover, the effects of different functionals and basis sets on first hyperpolarizability were systemically investigated.