Selective Photochromismof 2,6-Di(1,6-naphthyridin-2-yl)pyridine-BasedZinc(II)-Complexes by Varying the Tethers of Dicarboxylate Coligands:Significance of Anion−π Interactions on Photo-InducedElectron Transfer

Photochromic inorganic–organic hybrids with reversible color transitions under photoirradiation have exhibited promising applications in a wide variety of fields. However, the decisive factors for the photochromism assisted by metal coordination are still unclear and are a great challenge. Herein, to explore the preferred geometries between the electron donor (D) and acceptor (A) facilitating the photoinduced electron transfer (PIET), four crystalline 2,6-di(1,6-naphthyridin-2-yl)pyridine (DNP)-based Zn(II)-complexes have been designed and prepared solvothermally by varying the tethers of dicarboxylate coligands. Four anionic carboxylate pairs connected by length- and flexibility-adjustable tethers have significantly dominated the twisted carboxylate-Zn(II)-chelating DNP substructures and overall dimensionality of the resultant hybrids (three-dimensional pillared layered framework, bent and helical one-dimensional chains, and zero-dimensional binuclear entity), resulting in selective photochromism under UV lamp irradiation. More importantly, the accurate structural comparisons and theoretical calculations at the molecular level have demonstrated that the anion−π interactions within the local COO^–-Zn(II)-DNP substructures strongly correlate with the through-space PIET, resulting in selective photochromism. These findings are highly informative for the rational design and skillful manipulation of crystalline redox-type photochromic materials.