Stimuli‐Responsive Homochiral Coordination Polymers Undergoing Single‐Crystal‐to‐Single‐Crystal [2+2] Photodimerization

ABSTRACT The development of homochiral coordination polymers (HCPs) that combine structural robustness with stimuli‐responsive functionality remains a significant challenge. Herein, we report two Zn‐based HCPs, Zn(R) and Zn(S), constructed from alanine‐derived chiral ligands and the photosensitive coligand 1,2‐di(4‐pyridyl)ethylene (dpe). Both compounds crystallize in the polar noncentrosymmetric (NCS) space group P 2 1 and exhibit second‐harmonic generation (SHG) activity arising from their chirality‐induced NCS structures. Temperature‐dependent in situ powder x‐ray diffraction analyses reveal reversible dehydration–rehydration phase transitions, demonstrating the remarkable adaptability of the framework. Notably, the frameworks enforce a slip‐stacked arrangement of dpe ligands that aligns neighboring olefinic bonds in accordance with Schmidt's criterion, thereby enabling UV‐induced single‐crystal‐to‐single‐crystal [2+2] cycloaddition. Site‐selective photodimerization to rctt ‐tetra(4‐pyridyl)cyclobutane ( rctt ‐tpcb) is achieved within 8 h of UV irradiation. Kinetic analyses yield Avrami exponents close to 2, indicating a predominantly two‐dimensional solid‐state transformation mechanism. Importantly, the mirror‐image circular dichroism signals are retained throughout the photoreaction, confirming preservation of homochirality, while the SHG response persists after photoconversion. Quantitative analyses reveal a maximum rctt ‐tpcb conversion of 97%, accompanied by approximately 10% thermal cycloreversion in polycrystalline samples. These results establish a multifunctional HCP platform that combines reversible phase transformation, solid‐state photoreactivity, and NCS optical functionality within a single framework.