First ligand-driven light-induced spin change atroomtemperature in a transition-metal molecular compound

Abstract

Applied to the new iron(II) compound Fe(t-msbpy)₂(NCS)₂ (t-msbpy=4-methyl-4′-trans-styryl-2,2′-bipyridine), a novel strategy based on the so-called "‘ligand-driven light-induced spin change’' (or LD-LISC) effect, which consists in triggering the metal ion electronic spin-state crossover in a complex by a photochemical modification of the ligand, allowed this photomagnetic effect to be observed for the first time at room temperature. The compound, studied in CH₃CN or CD₃CN, was found to be initially nearly diamagnetic (S=0) by means of NMR experiments. Then, irradiation of a solution to the photostationary state with λ_exc=334 nm was shown, by using UV-VIS spectrometry, to result in the trans→cis isomerization of the styryl substituent of msbpy and in the subsequent S=0 (low spin)→S=2 (high spin) conversion of a significant fraction of the iron(II) ions.