Theoretical Investigation of Substitution Effect on the First Position of Coumarin Derivatives

Density functional theory (DFT) and time-dependent DFT (TD-DFT) were used to investigate the linear and nonlinear optical properties of 1-substituted coumarins. The molecular electrostatic potential plot, frontier molecular orbitals, and natural bond order analysis were used to study charge transfer properties. The bandgap exhibited an inverse relationship with the chemical potential (µ) and electrophilicity index (ω), while the chemical hardness (η) and hyperhardness (Γ) showed a direct relationship. First-order hyperpolarizability (β₀) and second-order hyperpolarizability (γ) were directly correlated with the global reactivity descriptors μ and ω and inversely correlated with η and Γ.