DFT based photophysical assessment of 2-substituted-3-(pyridin-2-yl)-benzo-[d][1,3]-azaphosphole P-oxide for organic optoelectronic applications.

P-containing heterocycles such as 1,3-benzazaphospholes offer a versatile platform for tunable organic semiconductors. This computational study demonstrates that replacing a terminal phenyl group with a pyridin-2-yl unit in 2-substituted benzo-[d][1,3]- azaphosphole P-oxides reconfigures the intramolecular charge-transfer pathway. Fragment orbital analysis quantifies this inversion: the pyridine (PY) ring contributes 52–75% of HOMO density, establishing it as the electron donor, while the opposing aryl (AR) substituent contributes 33–59% of LUMO density, functioning as the acceptor. This electronic reconfiguration creates a push-pull framework where the AR group dictates optoelectronic properties across three distinct classes. π-extended heteroacene derivatives (6–9) exhibit tunable emission (367–515 nm) with high oscillator strengths, enhanced nonlinear optical response (β up to 2621 a.u.), and favorable hole transport (λh = 0.20–0.28 eV). Thermal stability improves with π-extension (P-C BDE > 78 kcal/mol). Across the series, all properties scale with HOMO-LUMO spatial separation establishing a unified mechanistic framework where greater orbital separation systematically red-shifts emission, lowers reorganization energy, narrows ΔEST, and increases hyperpolarizability. Three compounds emerge with particularly favorable combinations: 6 (cyan emission, λh = 0.22 eV, β = 1871 a.u.), 7 (blue emission, highest f = 0.793, β = 2621 a.u.), and 8 (orange emission, balanced λh/λe, highest BDE = 80.3 kcal/mol). These computational predictions, provide a foundation for rational design of P-based organic semiconductors, with compounds 6–8 prioritized for experimental validation.