donoracceptor

In chemistry and materials science, donor-acceptor (D–A) refers to a system consisting of an electron donor moiety and an electron acceptor moiety that can interact through electronic coupling to enable charge transfer. D and A can be discrete molecules, functional groups within a single molecule, or alternating units in a conjugated polymer.

In the ground state, D and A interact weakly via noncovalent forces or π–π stacking; upon excitation, often by light, an electron may transfer from the donor to the acceptor, forming a charge-transfer state or a radical ion pair. The efficiency of this process depends on factors such as the relative energies of the frontier molecular orbitals (HOMO of the donor and LUMO of the acceptor), the strength of electronic coupling, and the reorganization energy. Marcus theory is frequently used to describe the energetics of electron transfer in these systems.

Common examples include electron-rich donors such as alkoxy- or amino-substituted aromatic rings and electron-poor acceptors such as nitro-substituted aromatics, cyano groups, or fullerenes. In polymer chemistry, donor-acceptor copolymers alternate donor and acceptor units to achieve narrowed band gaps and strong intramolecular charge transfer. Push-pull chromophores are typical D–A dye structures employed in spectroscopy and photovoltaic contexts.

Applications of donor-acceptor systems span organic electronics and energy conversion, including organic solar cells, organic light-emitting devices, and photodetectors. Donor–acceptor interactions are also exploited in supramolecular chemistry, sensing, and nonlinear optical materials, where charge-transfer effects influence absorption, emission, and electronic properties.

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