Regulating photosalient behaviour in dynamic metal-organic crystals

Abstract

Dynamic photoactuating crystals have become a sensation due to their potential applications in developing smart medical devices, molecular machines, artificial muscles, flexible electronics sensing and probes. Here we report the synthesis of two iso-structural metal-organic crystals, [Zn(4-ohbz)2(4-nvp)2] (1) and [Cd(4-ohbz)2(4-nvp)2] (2) {H4-ohbz = 4-hydroxy benzoic acid; 4-nvp = 4-(1-naphthylvinyl)pyridine} which undergo topochemical [2 + 2] cycloaddition under UV as well as sunlight to generate a dimerized product of discrete metal-complex[Zn(4-ohbz)2(rctt-4-pncb)] {rctt-4-pncb = 1,3-bis(4'-pyridyl)-2,4-bis(naphthyl)cyclobutane} (1') and one-dimensional coordination polymer (1D CP) [Cd(4-ohbz)2(rctt-4-pncb)] (2') respectively, in a single-crystal to single-crystal (SCSC) manner. The Zn-based compounds demonstrate photosalient behaviour, wherein crystals show jumping, splitting, rolling, and swelling upon UV irradiation. However, the Cd crystals do not show such behaviour maintaining the original unit cell. Thus the photomechanical behaviour can be induced by choosing a suitable metal ion. The above findings are well validated by quantitative density functional theory (DFT) calculations which show that the Zn-based crystal shifts towards an orthorhombic structure to resolve the anisotropic UV-induced mechanical strain.

A Practical Synthesis and X-Ray Crystal Structure of (E)-4-(1-naphthylvinyl)pyridine and Related Compounds

“…License: CC BY-NC-ND 4.0 utilize photochemical [2 + 2] cycloadditions of neighbouring (E)-4-1-nvp molecules, including a Zn(II) based 2D metal-organic framework, [Zn2(suc)2((E)-4-1-nvp)2] (H2suc = succinic acid), [14] and the metal organic compound [Zn(4-ohbz)2((E)-4-1-nvp)2] (H-4-ohbz = 4-hydroxy benzoic acid). [15] Central to the architecture of these complexes is the extensive supramolecular network imposed by hydrogen bonding, CH•••π, and π•••π interactions through the incorporation of the (E)-4-1-nvp moiety. [16,17] These intermolecular interactions can assist with olefin stacking between neighboring molecules and increase the potential of photochemical transformations in the solid-state.…”