Abstract
The discovery that a number of cobalt-dioxolene complexes undergo photoswitchable behavior was reported in the recent past. This phenomenon is always associated with valence tautomeric interconversion processes involving low-spin cobalt(III) and high-spin cobalt(II) species. Herein is stressed the strong formal correlation existing between these processes and the LIESST (Light-Induced Excited Spin State Trapping) effect shown by several iron(II) complexes undergoing spin crossover interconversion. The dynamics of the relaxation of the photoinduced metastable species to the ground state is discussed in terms of non-adiabatic processes within the Jortner theory of radiationless multiphonon relaxation.
Highlights
The study of molecular systems whose physical properties can be reversibly changed and controlled following a variation of an external parameter constitutes an appealing perspective for the realization of molecular scale electronic devices.[1,2] In particular molecules showing photoreactivity or photochromic properties are of potential interest as materials for optical data storage.[3]
A dramatic extension of the perspectives of photochromism was given by the discovery that the change of magnetic properties of a molecule and long-range magnetic order effects can be induced by photoexcitation.[4,5,6,7]
The discovery that some cobalt-dioxolene complexes may undergo valence tautomeric interconversion in the solid state by optical perturbation was independently reported by Hayami, Sato et al and Varret et al in 2001.38-40 The irradiation of the LMCT band of [CoIII(phen)(DBCat)(DBSQ)]·C H CH complex at 5 K, 65 3 induced a significant increase of the magnetisation value of the sample
Summary
The study of molecular systems whose physical properties can be reversibly changed and controlled following a variation of an external parameter constitutes an appealing perspective for the realization of molecular scale electronic devices.[1,2] In particular molecules showing photoreactivity or photochromic properties are of potential interest as materials for optical data storage.[3]. It is currently believed that the possibility of obtaining long lived metastable state at low temperature is strictly connected with large Detailed reviews concerning this topic have been reported in the past.[15,16,17,18,19,20,21,22] Among all the metal dioxolene complexes undergoing valence tautomerism, cobalt derivatives are undoubtedly the most attractive. In all of the reported examples the interconversion involves an intramolecular electron transfer from a coordinated dioxolene ligand to a six-coordinate diamagnetic, low spin (ls) CoIII (t2g6 (Oh)), yielding a CoII coordinated to the one electron oxidized dioxolene species (Scheme 1) In this species the metal ion is in the high-spin (hs) electronic configuration (t 5e 2, S = 3/2) with a large. Compounds of potential technological interest as candidates for molecular switches, is here emphasized
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