First ligand-driven light-induced spin change at room temperature in a transition-metal molecular compound

Applied to the new iron(II) compound Fe(t-msbpy)(2)(NCS)(2) (t-msbpy = 4-me thyl-4'-trans-styryl-2,2'-bipyridine) a novel strategy based on the so-call ed "ligand-driven light-induced spin change" (or LD-LISC) effect, which con sists in triggering the metal ion electronic spin-state crossover in a comp lex by a photochemical modification of the ligand, allowed this photomagnet ic effect to be observed for the first time at room temperature. The compou nd, 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 th e photostationary state with lambda(exc) = 334 nm was shown, by using UV-VI S 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.