Charge-Transfer Complexes in Organic Semiconductor Systems

Charge-transfer complexes (CTCs) in organic semiconductor systems arise from the reversible interaction between electron-donating and electron-accepting molecules, leading to partial electron transfer and the formation of delocalised states. These assemblies exhibit tuneable optical absorption, narrow electronic band gaps and enhanced charge mobility owing to π-stacking and co-crystal engineering. Research spans molecular design, supramolecular assembly, photophysics and device integration, with demonstrated applications in organic field-effect transistors, photovoltaics, photodetectors, optical waveguides and sensors. The global significance of CTCs lies in their low-temperature solution processing, structural versatility and the ability to combine semiconducting functionality with emergent properties such as thermally activated delayed fluorescence and near-infrared responsiveness. Current challenges include predictive control of solid-state packing, ambient stability and scalable fabrication of uniform films for practical devices.

Research from Nature Portfolio

Recent studies have demonstrated the molecular engineering of donor–acceptor π-conjugated systems to produce co-crystals with highly efficient, colour-tunable emission. By modulating acceptor strength and molecular geometry, researchers achieved thermally activated delayed fluorescence in hydrocarbon-based co-crystals and identified polymorphs exhibiting superior photoluminescence quantum yields. Innovations in growth techniques have enabled precise control over one-dimensional and two-dimensional mixed-stack CTC morphologies, yielding anisotropic optical waveguiding in microrod and plate-like crystals. Detailed in situ observations and energy calculations have clarified how kinetic and thermodynamic factors govern co-crystal habit, guiding the deliberate tuning of charge delocalisation and optical anisotropy. Further work has harnessed strong intermolecular charge-transfer interactions in two-photon excited near-infrared co-crystals, extending absorption into the NIR-II region for potential deep-tissue imaging and advanced optoelectronic applications.

Charge-Transfer Complexes in Organic Semiconductor Systems publication trend

The graph below shows the total number of articles in charge-transfer complexes in organic semiconductor systems across all publications each year (not limited to Nature Index journals).

Technical terms

Charge-transfer complex: A molecular assembly of electron-rich donors and electron-deficient acceptors that facilitates partial electron transfer and delocalised electronic states.

Donor–acceptor pairing: The spatial arrangement of molecules with complementary electronic character to promote charge-transfer interactions.

Co-crystal: A single crystalline phase comprising two or more different compounds in a defined stoichiometry bound by non-covalent forces.

π-stacking: The non-covalent overlap of aromatic π-orbitals between adjacent molecules, critical for effective charge delocalisation and transport.

Band gap: The energy difference between the highest occupied and lowest unoccupied electronic states, determining optical absorption and charge injection thresholds.

Thermally activated delayed fluorescence (TADF): A process where triplet excitons are thermally upconverted to singlet states, enhancing luminescence efficiency.

Optical waveguiding: The confinement and directed propagation of light within a structured medium, enabled by controlled morphology and refractive index contrast in co-crystals.

References

1. Charge-Transfer Complexes: Fundamentals and Advances in Catalysis, Sensing, and Optoelectronic Applications.. Advanced Materials (2024).
2. Highly efficient color-tunable organic co-crystals unveiling polymorphism, isomerism, delayed fluorescence for optical waveguides and cell-imaging. Nature Communications (2023).
3. Organic Photothermal Cocrystals: Rational Design, Controlled Synthesis, and Advanced Application. Advanced Science (2023).
4. 1D versus 2D cocrystals growth via microspacing in-air sublimation. Nature Communications (2019).
5. Two-photon excited deep-red and near-infrared emissive organic co-crystals. Nature Communications (2020).