Photochromic Hybrid Organic-Inorganic Metal Halide Glasses

Melt-quenching provides an effective route to glass formation while reconfiguring the atomic and electronic structures of materials. Despite the accompanying changes in mechanical and optical properties, how the resulting disorder can be exploited to enable functionalities beyond those of crystalline phases remains insufficiently understood. Here, we show that a hybrid organic-inorganic metal halide (OIMH) glass, g-4-MeOBPP₂ZnBr₄ (4-MeOBPP⁺ = 4-methoxybenzyltriphenylphosphonium), exploits vitrification-induced disorder to deliver a sub-second UV-triggered photochromic response absent in its crystalline counterpart, together with pronounced x-ray-induced photochromism. Upon UV irradiation, the initially colorless glass rapidly turns red, reaching 50% of the saturation absorbance within 0.5 s. Reverse Monte Carlo modeling combined with time-dependent density functional theory indicates that medium-range structural disorder generates locally perturbed environments that can serve as photoactive motifs. These motifs can host energetically proximate singlet and triplet states (ΔE_ST ∼ 0.02 eV), favoring intersystem crossing and intermolecular charge separation between adjacent cations. Guided by this design rationale, two glass analogs, g-4-MeOBPP₂CdBr₄ and g-3-MeOBPP₂ZnBr₄ (3-MeOBPP⁺ = 3-methoxybenzyltriphenylphosphonium cation), are also found to exhibit vitrification-induced photochromism. These findings identify medium-range disorder as an effective design lever in OIMH molecular glasses, providing a conceptual framework for creating turn-on optical responses in disordered materials.