Distortion-engineered C1-symmetric inorganic molecular cages enable tunable chiroptical nonlinear optics with broad infrared transparency

Chiroptical materials combining chirality with second-harmonic generation are attractive for polarization-resolved photonics, yet examples integrating strong chiroptical nonlinear activity, broad infrared transparency and inorganic robustness remain limited. Here we report a purely inorganic strategy in which molecular-level geometric distortion of intrinsically C1-symmetric phosphorus–chalcogen cages tunes second-harmonic generation circular dichroism (SHG-CD). Site-selective homologous substitution yields enantiopure molecular cage crystals, S/R-P4S5, S/R-AsP3S5, S/R-P4S4Se and S/R-AsP3S4Se, spanning a controlled distortion series. These crystals exhibit pronounced SHG-CD, with $${{\mbox{g}}}_{{\mbox{SHG}}-{\mbox{CD}}}$$ = 0.48–1.70 under 1064 nm excitation, strong SHG outputs of 1.1–2.8 × AgGaS2 at 2050 nm, broad infrared transparency and high laser-induced damage thresholds. Across this series, SHG-CD correlates with distortion-driven molecular asymmetry, indicating that the cage dipole moment can serve as a practical descriptor for chiroptical nonlinear response within this isostructural molecular cage family. These results establish inorganic molecular cages as a tunable chiroptical nonlinear platform for infrared-transparent chiroptical nonlinear materials. Chiroptical materials that combine chirality with nonlinear optics are prized for photonics, but robust infrared-transparent examples are rare. Here, authors show that distorting inorganic phosphorus–chalcogen cages tune strong chiroptical second-harmonic generation across a crystal series.