Photoreactive Zn(II) Coordination Compounds : Exploring Biomimetic Mechanical Motion and Photosalient Behavior

Locomotion plays a pivotal role in the survival of most organisms, enabling essential activities such as foraging, predator evasion, and reproduction. In the realm of biomimetics, seedpod explosion and bark peeling, well-established biological mechanisms employed by various plant species for defense and reproduction, offer a fascinating avenue for exploration. In this study, we present six novel photoreactive Zn(II)-based coordination compounds capable of significant mechanical motion, including explosion and a peeling effect under UV light irradiation. These compounds were synthesized using aryl derivatives of 4-vinylpyridines, namely, 4spy (4-styrylpyridine), 3tpy (4-(3-(thiophene-3-yl)vinyl)pyridine), and 2tpy (4-(2-(thiophene-2-yl)vinyl)pyridine), in conjunction with chloride or bromide colinkers. The resulting complexes, [ZnCl2(4spy)2] (1), [ZnCl2(3tpy)2] (2), [ZnCl2(2tpy)2] (3), [ZnBr2(4spy)2] (4), [ZnBr2(3tpy)2] (5), and [ZnBr2(2tpy)2] (6), were characterized as isostructural, with slight variations observed in compound 6’s structural packing. X-ray diffraction analysis confirmed the tetrahedral geometry of Zn(II) in all six complexes. Notably, compounds 1–5 exhibited coordination involving both planar and nonplanar linkers, leading to an expected 50% photoreaction. Interestingly, despite not meeting Schmidt’s criteria, the nonplanar linkers also exhibited photoreaction at slower rates. Furthermore, alongside the UV-induced photoreaction, these compounds displayed intriguing and vigorous mechanical motion reminiscent of a photosalient effect, characterized by rolling, cracking, jumping, and fragmentation. In contrast, compound 6 demonstrated complete photoreaction due to both coordinated linkers adopting planar configurations. Additionally, these crystals exhibited a peeling effect under UV irradiation, akin to the natural peeling of tree bark due to aging. These findings highlight the potential of Zn(II)-based coordination compounds as promising candidates for developing metal-based photoactuators and optical switches, with biomimetic applications

Solid-State [2+2] Photoreaction of Isostructural Cd(II) Metal Complexes and Solid-State Fluorescence

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

Influence of C-H⋯π interactions on the solid-state [2+2] cycloaddition reaction of a Ag(i) coordination complex in an inorganic co-crystal

Chemical Communications49576298-6300CHCO

Thermally reversible single-crystal to single-crystal transformation of mononuclear to dinuclear Zn(II) complexes by [2+2] cycloaddition reaction

10.1039/c3cc45706kChemical Communications49839567-9569CHCO

Multi-Photon Absorption in Metal–Organic Frameworks

Multi-photon absorption (MPA) is among the most prominent nonlinear optical (NLO) effects and has applications, for example in telecommunications, defense, photonics, and bio-medicines. Established MPA materials include dyes, quantum dots, organometallics and conjugated polymers, most often dispersed in solution. We demonstrate how metal–organic frameworks (MOFs), a novel NLO solid-state materials class, can be designed for exceptionally strong MPA behavior. MOFs consisting of zirconium- and hafnium-oxo-clusters and featuring a chromophore linker based on the tetraphenylethene (TPE) molecule exhibit record high two-photon absorption (2PA) cross-section values, up to 3600 GM. The unique modular building-block principle of MOFs allows enhancing and optimizing their MPA properties in a theory-guided approach by combining tailored charge polarization, conformational strain, three-dimensional arrangement, and alignment of the chromophore linkers in the crystal

Multiphotonenabsorption in Metall-organischen Gerüstverbindungen

Multiphotonenabsorption (MPA) ist eine der wichtigsten nichtlinear-optischen (NLO) Effekte und hat verschiedene Anwendungen, z. B. in Telekommunikation, Verteidigung, Photonik und Biomedizin. Bekannte MPA-Materialien sind Farbstoffe, Quantenpunkte, metallorganische Verbindungen und konjugierte Polymere, die oft als Dispersion in Lösung verwendet werden. Wir zeigen wie Metall-organische Gerüsteverbindungen (MOFs), eine neuartige NLO-Festkörpermaterialklasse, so entworfen werden können, dass sie außergewöhnlich starkes MPA-Verhalten zeigen. MOFs, die aus Zirconium- und Hafnium-Oxo-Clustern bestehen und einen Tetraphenylethen(TPE)-basierten Chromophor-Linker beinhalten, zeigen rekordverdächtig hohe Zweiphotonenabsoptionsquerschnitte mit bis zu 3600 GM. Das einzigartige, modulare Baukastenprinzip von MOFs erlaubt eine Optimierung und Verbesserung ihrer MPA-Eigenschaften, gestützt auf einen theoriebasierten Ansatz, durch die Berücksichtigung von maßgeschneiderter Ladungspolymerisation, konformativer Spannung, dreidimensionaler Anordnung und Ausrichtung der Chromophore im Kristall

Light-driven flagella-like motion of coordination compound single crystals

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

Second harmonic generation from the 'Centrosymmetric' crystals

10.1107/S2052252515002183IUCrJ2317-32