Achieving large thermal hysteresis in an anthracene-based manganese(II) complex via photo-induced electron transfer

Abstract

Achieving magnetic bistability with large thermal hysteresis is still a formidable challenge in material science. Here we synthesize a series of isostructural chain complexes using 9,10-anthracene dicarboxylic acid as a photoactive component. The electron transfer photochromic Mn2+ and Zn2+ compounds with photogenerated diradicals are confirmed by structures, optical spectra, magnetic analyses, and density functional theory calculations. For the Mn2+ analog, light irradiation changes the spin topology from a single Mn2+ ion to a radical-Mn2+ single chain, further inducing magnetic bistability with a remarkably wide thermal hysteresis of 177 K. Structural analysis of light irradiated crystals at 300 and 50 K reveals that the rotation of the anthracene rings changes the Mn1–O2–C8 angle and coordination geometries of the Mn2+ center, resulting in magnetic bistability with this wide thermal hysteresis. This work provides a strategy for constructing molecular magnets with large thermal hysteresis via electron transfer photochromism.

From Weak to Strong Antiferromagnetism: Tuning the Magnetic Properties of a Mononuclear Fe3+ Complex via Electron Transfer Photochromism

“…These phenomena should be attributed to the stronger AF coupling of photogenerated radicals with metal ions or/and larger magnetic contribution of Fe 3+ ions in 1 than that of the photogenerated radicals in 1a, similar to the other Fe 3+ -based photochromic complexes. 24 Meanwhile, the isothermal magnetization curves of 1 at 2 K were measured before and after light irradiation (Figure 4b). The saturated magnetization value was 4.63 Nβ at 5 T before irradiation; this slightly lower value than the theoretical one (5.0 Nβ) should be due to weak AF coupling interactions.…”

“…In this way, the photochromic materials derived from electron transfer (ET) attract much attention because the photogenerated stable radicals can not only be readily available and induce detectable colorations at room temperature but also influence the ligand field strength and tune the magnetic properties of pristine materials through magnetic couplings between the photogenerated radicals and paramagnetic metal centers. 24,25 On the basis of the aforementioned strategy, oxalic acid (H 2 C 2 O 4 ) and 1,3,5-tris(4-pyridyl)benzene (TPB) ligands were, respectively, selected as electron donors (EDs) and acceptors (EAs) to construct a novel photochromic complex ( provide more opportunities for tuning the magnetic coupling interactions. As a result, the optical analyses including ultraviolet−visible (UV−vis), fluorescence, infrared (IR), and Mossbauer spectra showed that photochromism derived from ET appeared for 1 after a photostimulus, accompanied with coloration from light green to dark brown, parts of Fe 3+ centers reduced to Fe 2+ , and parts of oxalate groups photodecomposed to CO 2 .…”

105 K Wide Room Temperature Spin Transition Memory Due to a Supramolecular Latch Mechanism

“…It is interesting to note that the known ST and non-ST molecular materials with robust thermal bistability in the range extending over 70 K near RT can be divided into two groups according to the amplitude of lattice structural rearrangements they undergo. Simple highly symmetric frameworks, such as c h a r g e -t r a n s f e r P r u s s i a n b l u e a n a l o g u e s (Rb x Mn II [Fe III (CN) 6 ] (x+2)/3 •zH 2 O, ΔT h = 86−138 K), 65,66 the abovementioned 3D polymer [Fe II (1,2,3-triazolate) 2 ] 0 (ΔT h = 110 K), 17 simple small planar heterocyclic (1,3,5trithia-2,4,6-triazapentalenyl, ΔT h = 75 K), 67 and metal− organic radicals ([Mn II (ADC • )(H 2 O) 2 (DMF) 2 ] 1D∞ , ΔT h = 177 K) 68 undergo structural hysteresis with relatively moderate lattice rearrangements, consisting in contraction/extension of the lattice and minor relative shifts/rotations/tilts of the lattice components. These are incomparable to the amplitude of the rearrangement of compounds with dynamic coordination environments, such as the bistable Ni II −porphyrin complex capable of switching the coordination environment of the Ni II ion between planar N 4 (S = 0) and square pyramidal N 5 (S = 1), which requires sufficient free space for the grafted cis-trans photoisomerizable pendant group, ending with an N-donor pyridine fragment, to switch between the two conformations.…”

Photoactive Anthracene-9,10-dicarboxylic Acid for Tuning of Photochromism in the Cd/Zn Coordination Polymers

“…Photochromic materials, with reversible color change and diverse physicochemical properties between two forms, have been increasingly employed for constructing smart materials with potentialities in anticounterfeiting, displays, energy conversion, and information storage. − Typical photochromic materials include structural variations with trans / cis and ring closing/opening photoisomerization, such as spiropyrans, azobenzenes, imidazole dimers, diarylethenes, and fulgides, or changes in electron configuration, including spin transition complexes, electron transfer of valence tautomerism, polyoxometalates, , naphthalenediimide, and viologens . Among them, viologen derivatives with intra/intermolecular electron transfer between donors and acceptors have drawn much attention due to their easy preparation, better system stability, and high fatigue resistance. − Especially, metal–organic photochromic complexes based on viologens and polypyridines have advantages in resolving structures via the formed single crystals and easily tuning photoresponsive behaviors by the organization of D–A blocks, prompting chemists to create more opportunities and provide more strategies for designing and expanding radical-actuated photochromic materials. − Furthermore, the photo-triggered stable radicals enable these photochromic species to reversibly tune the diverse physical properties, such as conductance of semiconductors, proton conductivities, fluorescence, single-molecule magnetism, and nonlinear optical signals. − …”