Switching metal complexes via intramolecular electron transfer: connections with solvatochromism

Abstract

Metal complexes that can exist in two different charge distributions often exhibit dramatic color changes when switched between them. The underlying spectral changes are fundamentally related to the switchable behavior. In valence tautomeric (VT) systems, the transition is a stimulated, reversible intramolecular electron transfer between a metal center and a ligand, while in charge-transfer-induced-spin-transition (CTIST), also known as electron-transfer-coupled-spin-transition (ETCST), systems, the electron is transferred between two metal centers. We discuss, herein, the relationships between the switchable behavior of these systems and two related optical phenomena: charge transfer and solvatochromism. The insights gained from analyzing these phenomena can illuminate important aspects of VT or CTIST behavior, for example, the energetic relationship between the electromeric forms, or the effects of molecular environment on a VT or CTIST thermal equilibrium. Such insights may assist efforts to employ these compounds as molecular scale components in data storage, sensor and display devices.