chargetransfer

Chargetransfer, often written as charge transfer, is the movement of electronic charge from a donor region to an acceptor region within a molecular system, between molecules, or across a material interface. This process can be driven by chemical redox potential, photonic excitation, or electrochemical potential, and it underpins many noncovalent interactions and electronic functions. In chemistry, a charge-transfer interaction yields a donor–acceptor complex in which partial electron density shifts toward the acceptor. The resulting charge-transfer state often features a characteristic absorption in the ultraviolet-visible spectrum, giving CT complexes their distinctive colors.

Mechanisms and scope: Charge transfer can occur without changes to covalent bonding (outer-sphere electron transfer) or may involve bridging ligands or bonds (inner-sphere electron transfer). In solid-state and polymeric systems, charge transfer occurs between donor and acceptor materials across interfaces and can give rise to electronic conductivity, ambipolar transport, or photoinduced charge separation in devices such as organic solar cells and photodetectors.

The rate and feasibility of charge transfer are described by theories such as Marcus theory, which relates transfer rate to the free-energy change, reorganization energy, and electronic coupling. In electrochemistry, applied potentials drive redox couples toward electron transfer, with kinetics influenced by diffusion, solvent reorganization, and overpotential.

Examples and applications: Classic charge-transfer salts, such as donor–acceptor stacks of tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ), exhibit partial oxidation states and enhanced conductivity. In organic electronics, donor–acceptor interfaces enable light absorption, exciton dissociation, and charge separation in solar cells. Charge transfer is also relevant to biological electron transfer cascades and redox chemistry in enzymes.