Homochiral Coordination Polymers Exhibiting Second-Harmonic Generation and Photo-Induced Structural Transformation

Two homochiral coordination polymers, [Zn2(RIAP)2(dpe)4(H2O)4]·6H2O (1R) and [Zn2(SIAP)2(dpe)4(H2O)4]·6H2O (1S), were synthesized via solvothermal reactions using enantiomeric amino acid-derived ligands (H2RIAP or H2SIAP) and the photosensitive coligand 1,2-di(4-pyridyl)ethylene (dpe). Both compounds crystallize in the noncentrosymmetric (NCS) polar space group P21, forming square-wave one-dimensional chain-like structures stabilized by π-π stacking and hydrogen bonding interactions. Powder second-harmonic generation (SHG) measurements revealed modest SHG responses, approximately 1.5 times that of α-SiO2, consistent with their NCS character. Notably, the slip-stacked arrangement of olefinic bonds enables photoinduced [2 + 2] cycloaddition reactions under ultraviolet light. Structural transformations were systematically monitored by in situ single-crystal and ex situ powder X-ray diffraction, alongside quantitative 1H NMR spectroscopy, which confirmed progressive formation of cyclobutene moieties with maximum conversion ratios of ca. 71%. These findings highlight the dual functionality of 1R and 1S as NCS materials that integrate SHG activity with solid-state photoreactivity.