Photochromic diarylethene ligands featuring 2-(imidazol-2-yl)pyridine coordination site and their iron(II) complexes

Abstract

A new family of photochromic diarylethene-based ligands bearing a 2-(imidazol-2-yl)pyridine coordination unit has been developed. Four members of the new family have been synthesized. The photoactive ligands feature non-aromatic ethene bridges (cyclopentene, cyclopentenone, and cyclohexenone), as well as closely spaced photoactive and metal coordination sites aiming a strong impact of photocyclization on the electronic structure of the coordinated metal ion. The ligands with cyclopentenone and cyclohexenone bridges show good cycloreversion quantum yields of 0.20–0.32. The thermal stability of closed-ring isomers reveals half-lives of up to 20 days in solution at room temperature. The ligands were used to explore coordination chemistry with iron(II) targeting photoswitchable spin-crossover complexes. Unexpectedly, dinuclear and tetranuclear iron(II) complexes were obtained, which were thoroughly characterized by X-ray crystallography, magnetic measurements, and Mössbauer spectroscopy. The formation of multinuclear complexes is facilitated by two coordination sites of the diarylethene, acting as a bridging ligand. The bridging nature of the diarylethene in the complexes prevents photocyclization.

Molecular photoswitches in aqueous environments

“…333,[340][341][342] The aryl rings are often (benzo)thiophenes, resulting in dithienylethenes (DTEs), 3,328,331 as switching between the open and the closed form gives the best compromise between the loss of aromaticity and the gain in stabilization upon cyclization to result in bi-stable photoswitches. Furthermore, also other (hetero)aromatic systems such as pyridine, 343,344 benzene, 328 naphthalene, 345 indole, 333 (benzo)furan, 328,331,344 pyrrole, 328 oxazole, 346 imidazole, 347 and thiazole, 340,348 etc., have been employed.…”

Weak interactions in imidazole‐containing zinc(II)‐based metal–organic frameworks

“…[ 17–24 ] Although the synthesis and properties of a number of imidazole‐containing MOFs have been reported, [ 14–16,25–29 ] the integration of an imidazole group with two pyridine moieties in a coordinated ligand in an MOF has rarely been addressed. [ 30–33 ]…”

“…[17][18][19][20][21][22][23][24] Although the synthesis and properties of a number of imidazole-containing MOFs have been reported, [14][15][16][25][26][27][28][29] the integration of an imidazole group with two pyridine moieties in a coordinated ligand in an MOF has rarely been addressed. [30][31][32][33] Here, we report on the selection of a model ligand L (L = 2-(pyridin-4-yl)-3H-imidazo [4,5-c]pyridine), from which two MOFs, [Zn 2 (L)(bdc) 2 ]Á3MeOHÁ4H 2 O} n (1, H 2 bdc = 1,4-benzenedicarboxylic acid) and [Zn 2 (L) (bdc) 2 ]Á2DMFÁH 2 O} n (2) (Scheme 1), were synthesized. Interestingly, the coordination modes of the ligand L in the two products are completely different in each structure.…”

Reversible Shifting of a Chemical Equilibrium by Light: The Case of Keto–Enol Tautomerism of a β-Ketoester

“…Herein, we report an unprecedented reversible shifting of keto–enol equilibrium toward a thermally stable enol form upon photocyclization of diarylethene 2A (Scheme B), which has been achieved in polar and nonpolar solvents. Implementation of this approach allowed us to control a well-known keto–enol equilibrium of β-ketoesters (e.g., ethyl acetoacetate, Scheme B) by light irradiation only.…”

“…A simple combination of a β-ketoester and a diarylethene framework allowed us to control the tautomeric equilibrium in reversible manner in polar and nonpolar solvents with light at ambient conditions. Variation of heterocyclic moieties (e.g., application of azoles 21 instead of thiophene or incorporation of electronwithdrawing groups at the α-position of thiophenes 29b ) and ethene bridges (e.g., cyclopentenone 31 instead of cyclohexenone) should provide deeper insight into the nature of this phenomenon and improve the performance of reported here photoinduced tautomerism. Ultimately, these future efforts should afford new efficient photochromic molecules for manipulating various processes in materials chemistry and biology that utilize reversible switching between ketone and enol tautomers.…”