Polar Phosphorus Chalcogenide Cage Molecules: Enhancement of Nonlinear Optical Properties in Adducts

Inorganic adducts are an emerging class of infrared nonlinear optical (NLO) materials. However, although the reported NLO adducts have sufficient birefringences and significant laser-induced damage thresholds (LIDTs), they commonly suffer from weak second harmonic generation (SHG) responses. In this work, a series of polar phosphorus chalcogenide cage molecules with strong hyperpolarizabilities were theoretically screened out to enhance the SHG responses of adducts. Accordingly, (CuI)₃ (P₄ S₄ ), (CuI)₃ (P₄ Se₄ ), (CuBr)₇ (P₄ S₃ )₃ and (CuBr)₇ (P₄ Se₃ )₃ with target polar cage molecules were successfully synthesized. As expected, they exhibit enhanced SHG responses while keeping moderate birefringences and high LIDTs. Notably, (CuBr)₇ (P₄ Se₃ )₃ possesses the largest SHG response (3.5×AGS@2.05 μm) among the known inorganic NLO adducts. Our study confirms that introducing NLO-active cage molecules into adducts is an efficient strategy for high-performance NLO materials.