From Molecular Structure to Optical Functionality: Tailoring Nonlinear Optical Behavior in Phosphorus‐Doped g‐C₃N₄

ABSTRACT Phosphorus (P)–doped graphitic carbon nitride (g‐C 3 N 4 ) represents a significant advancement in nonlinear optical (NLO) materials, where subtle atomic modifications induce notable changes in electronic behavior. In this study, we conduct a comprehensive quantum‐chemical and wavefunction‐based investigation into the electronic and NLO properties of both pristine and P‐doped g‐C 3 N 4 , under static and dynamic regimes. Using advanced real‐space function analyses, we reveal complex patterns of electronic excitation and charge redistribution, highlighting P‐doping's pivotal role in enhancing van der Waals attractions and exchange‐repulsion forces, which are essential for the material's binding interactions. The modulation of molecular (hyper)polarizabilities is systematically explored through sophisticated tools such as unit sphere representation and second‐order NLO spectra. Our findings show that P‐doping significantly enhances polarization anisotropy. Notably, the second‐order hyperpolarizability exhibits pronounced optical anisotropy, particularly in the xy ‐plane, with a remarkable dispersion effect at 589 nm ( γ yyyy = 3.55 × 10 10 a.u.), demonstrating unprecedented control over optical properties. The selected S2 and S4 structures exhibit strong octupolar behavior, with the octupolar molecular tensor contributing up to 80% of the NLO response. This study not only positions P‐doped g‐C 3 N 4 at the forefront of high‐performance NLO material design but also paves the way for further exploration of heteroatom‐engineered carbon‐based nanostructures. These materials offer versatile platforms for advanced photonic and optoelectronic devices. Future directions could delve into the synergistic integration of P‐doped g‐C 3 N 4 within hybrid architectures, broadening its potential for tunable NLO systems in fields such as quantum optics, telecommunications, and molecular sensing.