The charge transfer anion-radical alkali-metal salts M+TCNQ− (M = Li, Na, K): The structures and static hyperpolarizabilities

The structures and nonlinear optical (NLO) properties of the charge transfer anion-radical salts without excess electron, M+TCNQ− (M = Li, Na, K) are studied for the first time. These anion-radical salts exhibit large first (β0) and second (γ0) hyperpolarizabilities, which are related to the ligand-to-metal charge transfer (LMCT) transitions. The largest β0 and γ0 values for K+TCNQ− are 2.8 × 104 and 2.0 × 106 a.u., respectively. In addition, the effect of alkali-metal doping and monotonous dependence on the alkali atomic number of both β0 and γ0 are observed. These results may be beneficial to design high-performance NLO materials.