Spectroscopic and Nonlinear Optical Insights of Picolinaldehyde-Based Materials: Experimental and DFT Approach

Herein, a series of picolinaldehyde-based materials (DMeP-TFMP) were synthesized, via the decarboxylative Suzuki coupling reaction using readily accessible 2-formyl-6-pyridinoic acid, to investigate their nonlinear optical (NLO) properties. Various spectroscopic techniques like UV–vis, FT-IR, ¹H-NMR, and ¹³C-NMR were employed to elucidate the molecular structures of synthesized chromophores. Further, the density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations at M06/6-311G (d,p) level were conducted to assess their frontier molecular orbitals (FMOs), absorption properties, and nonlinear optical (NLO) insights. The DMeP displayed the minimal band gap (4.390 eV) among the studied compounds with the highest bathochromic shift (340.476 nm). The density of states (DOS) and transition density matrix (TDM) analyses validated the charge transitions from valance to conduction band. All compounds exhibited enhanced exciton dissociation rates because of low binding energy values (E_b = 0.525 to 0.572 eV). Furthermore, electron-hole analysis revealed the distribution of electron and hole densities across different atoms in the compounds, indicating significant electron-hole creation at specific atomic sites. All synthesized compounds exhibited notable linear polarizability that is, (⟨α⟩ = 2.59 × 10⁻²³-3.62 × 10⁻²³ esu), first hyperpolarizability (β_tot = 2.87 × 10⁻³⁰−16.4 × 10⁻³⁰ esu), and second hyperpolarizability (γ_tot = 1.93 × 10⁻³⁵-8.44 × 10⁻³⁵ esu), highlighting their potential as efficient materials for advanced NLO applications.