From Metal-Centered Catalysis to Organic Orbital Programming in Photoelectrocatalysis

Photoelectrocatalysis has traditionally relied on inorganic metals and compounds, where activity is optimized through crystal field regulation, band alignment, and defect engineering. However, periodic lattice structures intrinsically constrain orbital degeneracy, energy-level reconstruction, and molecular-scale control of intermediate adsorption, electron transfer, and reaction flux. Purely organic photoelectrocatalytic materials offer a distinct paradigm based on π-conjugated frameworks, in which frontier orbitals, energy-level splitting, electron delocalization, and polarization can be precisely programmed through molecular design. Donor-acceptor architectures, orbital overlap, and electronic asymmetry regulate exciton binding, charge separation, interfacial coupling, and intermediate electronic occupation, thereby linking photocarrier dynamics directly with reaction barriers and pathway selection. In water splitting, CO₂ reduction, N₂ reduction, and photoelectrochemical organic synthesis, such orbital-level tunability enables refined control over proton-coupled electron transfer, transition-state stabilization, and selectivity beyond conventional metal-centered descriptors. This review analyzes the principles of electronic structure control and interfacial reaction mechanisms in purely organic photoelectrocatalytic materials from atomic and orbital perspectives, highlights their distinctions from inorganic systems in energy level construction and reaction pathway regulation, and outlines a theoretical foundation for developing organic-inorganic cooperative platforms that combine orbital programmability with structural stability.