Modulation in Nonlinear Optical (NLO) Properties of Tryptanthrin and Quinazolinedione Using Acceptor and Donor Substitution: DFT Approach

Abstract Trans form of tryptanthrin exhibits greater stability than the cis form of quinozolinedione, supported by its smaller energy gap, longer vertical excitation, and higher first‐order hyperpolarizability. The reduced highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap in tryptanthrin promotes enhanced charge transfer. Compared to tryptanthrin (3.64 eV in B3LYP, 6.20 eV in CAM‐B3LYP), quinozolinedione shows slightly higher energy gaps (3.92 and 6.47 eV, respectively). Among the derivatives, nitro (NO 2 ) substitutions significantly lower energy gaps. The 3‐NO 2 ‐8‐N(CH 3 ) 2 tryptanthrin ( SD36 ) stands out with the smallest energy gap, highest dipole moment, and exceptional hyperpolarizability, alongside vertical excitation above 600 nm. In the quinozolinedione group, 7‐NO 2 quinozolinedione ( SD79 ) is the most active. Other 8‐N(CH 3 ) 2 tryptanthrin derivatives also show vertical excitations above 600 nm. Overall, NO 2 ‐substituted derivatives from both families display excellent density functional theory (DFT)‐based properties, making them strong candidates for NLO applications. Future efforts will focus on synthesizing these derivatives and evaluating their potential in real‐world photonic and optoelectronic devices.