title: Supramolecular photomagnetic materials: photoinduced dimerization of ferrocene-based polychlorotriphenylmethyl radicals.
abstract: New ferrocenyl Schiff-base polychlorotriphenylmethyl radicals have been synthesized and characterized. The imino group of one such radical undergoes an irreversible trans to cis structural isomerization induced by light. Such photoinduced isomerization has been monitored by UV/Vis and ESR spectroscopy and also monitored by HPLC. ESR frozen solution experiments at low temperature revealed that the cis isomer dimerizes, showing a strong antiferromagnetic interaction. Although numerous photochromic supramolecular systems have been described, such a photoinduced self-assembly process represents the first example of a one-way photoswitchable magnetic system in which a conversion between a doublet and a singlet ground state species is promoted by a photoinduced dimerization process driven by the formation of hydrogen bonds. DFT calculations on the minimized structure and on the rotational barriers have been performed to establish the origin of such behavior. The effect of the substituents and the media polarity on the photoisomerization of this imine chromophore have also been studied. It has been observed that the efficiency of the process is markedly dependent on the presence and characteristics of electron-donor and electron-acceptor substituents of the ferrocenyl Schiff-base polychlorotriphenylmethyl radicals as well as on the polarity of the solvent.
authors.affiliation: Institut de Ciència de Materials de Barcelona (CSIC), Campus Universitari de Bellaterra, 08193-Cerdanyola, Spain.
authors.forename: Imma
authors.initials: I
authors.lastname: Ratera
authors.forename: Daniel
authors.initials: D
authors.lastname: Ruiz-Molina
authors.forename: José
authors.initials: J
authors.lastname: Vidal-Gancedo
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Novoa
authors.forename: Klaus
authors.initials: K
authors.lastname: Wurst
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Letard
authors.forename: Concepció
authors.initials: C
authors.lastname: Rovira
authors.forename: Jaume
authors.initials: J
authors.lastname: Veciana