Switching metal complexesviaintramolecular electron transfer: connections with solvatochromism

Abstract

Solvent-induced color-changing phenomena exhibited by some metal complexes can illuminate key aspects of their switchable behavior.

Chromic Ionic Liquids

“…Although it has not yet been investigated, ILs that undergo the VT or SCO equilibria upon thermal treatment have the potential to exhibit multichromic behavior because such equilibria could be driven not only by thermal treatment but also by other external stimuli such as light irradiation − and pressure application , in the solid state. In addition, some VT complexes are known to show marked solvatochromism in solution because the solvent polarity significantly affects the stability of the redox isomers with different charge distributions (or polarities) in the complex.…”

A Convenient DFT-Based Strategy for Predicting Transition Temperatures of Valence Tautomeric Molecular Switches

“…The range of metal–ligand combinations and the intrinsic redox-activity suggests avenues for multifunctional materials that are not available with SCO compounds. For example, the difference in charge distributions between valence tautomers confers possibilities involving polarization switching and spin-dependent conductivity and electrical properties. − …”

Rich redox-activity and solvatochromism in a family of heteroleptic cobalt complexes

“…Dipole stabilising interactions are particularly relevant to charge transfer excitations; the large change in dipole moment that typically accompanies charge transfer can often lead to solvatochromism. 4,39,90 The stabilisation of a dipole in a dielectric medium is proportional to the magnitude of the dipole, and hence, if the magnitude of the excited state dipole differs from that of the ground state, a change in solvent dielectric properties will change the relative energies between the ground and excited state, thereby altering the excitation energy. To capture these purely electrostatic effects, the Onsager function, f O (ε) = (ε − 1)/(2ε + 1), which is proportional to the energetic stabilisation of a dipole in a dielectric medium, is often applied.…”

“…31,34,37,38 Solvatochromic analysis is a particularly valuable tool for understanding environmental effects on valence tautomeric systems, as the combination of a redox-active ligand and redox-active metal often leads to solvatochromic charge transfer bands. 39,40 In previous studies, we have focussed on variation of the ancillary ligand in cobalt-dioxolene systems as a way of tuning valence tautomerism. 20,28,29,41,42 In this work, we have instead sought to combine a cobalt metal centre with a family of redox-active ligands that has been relatively underutilised in this context: bis(aryl)iminoacenaphthene (BIAN).…”