Giant Near-Infrared Induced Polarization Change via a Long-Lived Hidden Phase of a Valence Tautomeric Complex

Light-induced polarization change has attracted significant attention due to its rapid response and nondestructive nature, positioning it as a promising candidate for next-generation molecular storage devices and energy harvesting. However, achieving substantial photoconversion that results in giant polarization changes via a hidden phase under near-infrared light irradiation remains a formidable challenge. In this study, we successfully synthesized a novel [CrCo] complex with an enantiopure ligand. Unlike previously reported Co valence tautomeric (VT) complexes, this complex exhibits light-induced VT (LIVT) with nearly complete photoconversion ratio upon irradiation with a 1340 nm laser. Additionally, the molecules pack in the P2₁ polar space group with an optimized arrangement, leading to a giant NIR-induced polarization change (1.71 μC cm^-2), which surpasses that of other nonferroelectric crystals. Importantly, electric measurements and single-crystal X-ray analysis after irradiation revealed that the induced polarization change is related to not only the directional electron transfer but also the displacement of anions, which render a distinct hidden metastable phase compared to the thermally approachable one. Moreover, pyroelectric measurement was first used to characterize relaxation kinetics after light irradiation.