Dynamic Olefinic Bond Restructuring in Coordination Polymers Enables Precision Photocycloaddition

Biological systems adapt their conformations and reactivities in response to diverse external cues, inspiring the development of synthetic materials with similar responsiveness for controlled chemical transformations. Here we report a flexible coordination polymer, [{Cd₄(OCH₃-BPEB)₄(OBA)₄}·7DEF]_n (CP1, OCH₃-BPEB = 4,4'-((1E,1'E)-(2,5-dimethoxyl-1,4-phenylene)bis(ethene-2,1-diyl))dipyridine, H₂OBA = 4,4'-oxybis(benzoic acid), DEF = N,N-diethylformamide), capable of multistimuli-induced restructuring of otherwise inactive olefinic bond pairs to achieve regioselective [2+2] photocycloadditions. Sequence exposure to solvent vapours and visible light drives stepwise structural transformations, producing two monocyclobutane isomers-4,4'-((1S,3R)bis(2,5-dimethoxyl-4-((E)-2-(pyridin-4-yl)vinyl)phenyl)cyclobutane-1,2-diyl)dipyridine (OCH₃-PCDP) and 4,4'-((1R,2R,3S,4S)-2,4-bis(2,5-dimethoxy-4-((E)-2-(pyridin-4-yl)vinyl)phenyl)cyclobutane-1,3-diyl)dipyridine, (2,4-OCH₃-PCDP)-from their respective photoirradiated derivatives [{Cd₄(OCH₃-PCDP)₂(OBA)₄}·3DEF]_n (CP2) and [{Cd₄(2,4-OCH₃-PCDP)₂(OBA)₄}·3MeOH]_n (CP3, MeOH = methanol). Single-crystal X-ray diffraction captures five intermediate structures, and density functional theory (DFT) calculations elucidate how stimuli-mediated realignment of olefinic pairs dictates regioselectivity. This work demonstrates precise photochemical cyclobutane synthesis within a coordination polymer single-crystal platform, offering mechanistic insights applicable to the broader design of stimuli-controlled photoreactions and functional materials.