Theoretical investigation of the structures, stabilities, and NLO responses of calcium-doped pyridazine: Alkaline-earth-based alkaline salt electrides

•The described alkaline-earth-doped compounds exhibit unusual alkaline-earth-based alkaline salt electrides.•From the triplet to the singlet state, the chemical valence of the Ca atom changes from +1 to 0, and the μ0 of the molecule is reversed.•The β0 value increases 324-fold from 826 (Li-H3C4N2) to 268,679 (2.69 × 105) au (Li-H3C4N2⋯Ca).•Alkaline-earth-atom doping is an important method through which to enhance the NLO response.

Currently, whether alkaline-earth-doped compounds with electride characteristics are novel candidates for high-performance nonlinear optical (NLO) materials is unknown. In this paper, using quantum chemical computations, we show that: when doping calcium atoms into a family of alkaline-substituted pyridazines, alkaline-earth-based alkaline salt electrides M-H3C4N2⋯Ca (MH, Li, and K) with distended excess electron clouds are formed. Interestingly, from the triplet to the singlet state, the chemical valence of calcium atom changes from +1 to 0, and the dipole moment direction (μ0) of the molecule reverses for each M-H3C4N2⋯Ca. Changing pyridazine from without (H4C4N2⋯Ca) to with one alkaline substituent (M-H3C4N2⋯Ca, MLi and K), the ground state changes from the triplet to the singlet state. The alkaline earth metal doping effect (electride effect) and alkaline salt effect on the static first hyperpolarizabilities (β0) demonstrates that (1) the β0 value is increased approximately 1371-fold from 2 (pyridazine, H4C4N2) to 2745 au (Ca-doped pyridazine, H4C4N2⋯Ca), (2) the β0 value is increased approximately 1146-fold from 2 in pyridazine (H4C4N2) to 2294 au in an Li-substituted pyridazine (Li-H3C4N2), and (3) the β0 value is increased 324-(MLi) and 106-(MK) fold from 826 (MLi) and 2294 au (MK) to 268,679 (MLi) and 245,878 au (MK), respectively, from the alkalized pyridazine (M-H3C4N2) to the Ca-doped pyridazine (M-H3C4N2⋯Ca). These results may provide a new means for designing high-performance NLO materials.

Graphical abstractThese alkaline-earth-doped compounds exhibit not only unusual alkaline-earth-based electride features but also large static first hyperpolarizabilities (β0) up to 245,878 (∼2.46 × 105) au (K-H3C4N2⋯Ca), which suggests that alkaline earth atom doping is an important method through which to enhance NLO responses.Figure optionsDownload full-size imageDownload high-quality image (148 K)Download as PowerPoint slide