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

Kurakula, Uma and Ekka, Akansha and Dutta, Basudeb and Mir, Mohammad Hedayetullah and Halcovitch, Nathan R. and Medishetty, Raghavender (2024) Photoreactive Zn(II) Coordination Compounds : Exploring Biomimetic Mechanical Motion and Photosalient Behavior. Crystal Growth and Design, 24 (17). pp. 7066-7074. ISSN 1528-7483

Text (Zinc_Halide_manuscript_R1_Final)
Zinc_Halide_manuscript_R1_Final.pdf - Accepted Version
Available under License Creative Commons Attribution.
Download (1MB)

Abstract

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.