RESUMO
A green method to synthesize cyclobutane derivatives has been developed over the past three decades in the form of solid-state [2+2] photochemical reactions. These solid-state reactions also play a major role in the structural transformation of hybrid materials. In this regard, crystal engineering has played a major role in designing photoreactive molecular systems. Here, we report three novel binuclear Cd(II) complexes with the molecular formula [Cd2(4spy)4L4], where 4spy = 4-styryl pyridine and L = p-toluate (1); 4-fluorobenzoate (2); and 3-fluorobenzoate (3). Although three different benzoates are used, all three complexes are isostructural, as corroborated through SCXRD experiments. Structural analysis also helped in identifying two potential photoreactions. These are both intra- and intermolecular in nature and are driven by the head-to-head (HH) and head-to-tail (HT) alignment of 4spy linkers within these metal complexes. 1H NMR spectroscopy studies showed evidence of a quantitative head-to-head photoreaction in all these three complexes, and SCXRD analysis of the recrystallization of the photoproducts also provided confirmation. TGA studies of these photoreactive complexes showed an increase in the thermal stability of the complexes due to the solid-state photoreaction. Photoluminescence studies of these complexes have been conducted, showing a blue shift in emission spectra across all three cases after the photoreaction.
RESUMO
Single crystals of coordination complexes that show mechanical motion under the influence of external stimuli are of great interest due to their applications in photoactuators, sensors and probes. The solid-state [2+2] cycloaddition reaction has been one of the most prominent chemical reactions for photoresponsive materials in recent years. However, a relatively limited number of compounds have been reported, and most of these compounds have only shown destructive photosalient effects. Here, we report two photoreactive Zn(II) metal complexes with a thiophene-based photoreactive linker, 2tpy (4-(2-(thiophen-2-yl)vinyl)pyridine). In addition, under photoirradiation these complexes showed flagella-like bending, first towards and subsequently away from the excitation light source. This is the first report of metal-complexes and the solid-state [2+2] cycloaddition reaction that presents flagella-like motion in single crystals.
RESUMO
A Zn(II) based one-dimensional (1D) coordination polymer (CP), [Zn(cis-1,4-chdc)(4-nvp)] (1) {cis-1,4-H2chdc = cis-1,4-cyclohexanedicarboxylic acid and 4-nvp = 4-(1-naphthylvinyl)pyridine}, undergoes a solid-state photochemical [2+2] cycloaddition reaction, accompanied by mechanical motion, wherein crystals show swelling, jumping, splitting and bursting upon UV irradiation, whereas the analogous Cd(II) CP [Cd(cis-1,4-chdc)(4-nvp)] (2) does not show any such response under UV light, although it undergoes [2+2] photodimerization. The present study can certainly provide the fundamental understanding for designing smart photoactuating materials.
RESUMO
Some special crystals respond to light by jumping, scattering or bursting just like popping of popcorn kernels on a hot surface. This rare phenomenon is called the photosalient (PS) effect. Molecular level control over the arrangement of light-responsive molecules in microscopic crystals for macroscale deformation or mechanical motion offers the possibility of using light to control smart material structures across the length scales. Photochemical [2+2] cycloaddition has recently emerged as a promising route to obtain photoswitchable structures and a wide variety of frameworks, but such reaction in crystals leading to macroscopic mechanical motion is relatively less explored. Study of chemistry of such novel soft crystals for the generation of smart materials is an imperative task. This minireview highlights recent advances in solid-state [2+2] cycloaddition in crystals to induce macroscale mechanical motion and thereby transduction of light into kinetic energy.