DFT exploration of solvation and lone pair effects on the second harmonic generation of circular π-conjugated macrocycles

This study investigates four series of dibenzothiophene-based cyclic systems (AZ-S1-S3, AZ-O1-O3, AZ-Se1-Se3, and AZ-N1-N3) that follow a D–π–D structure, having 1,2-bis(diazenyl)benzene as π bridges. The research employs density functional theory (DFT) and time-dependent DFT (TD-DFT) at D3-B3LYP, M06-2X, CAM-B3LYP and ωB97XD level to analyze electronic, optical, and nonlinear optical characteristics of these molecules in gas phase and DMF solvent. Frontier molecular orbital (FMO) analysis revealed that all designed molecules possess E gap range 0.97 eV (AZ-Se1) to 2.79 eV (AZ-O2) with smallest energy gap exhibited by AZ-Se1 showing efficient intramolecular charge transfer (ICT). Electrostatic potential (ESP),electron localization function (ELF) and localized orbital analysis (LOL) were performed to investigate electronic properties of designed molecules. AZ-Se1 demonstrates the highest first hyperpolarizability ( β tot = 66,947.17 a.u.), indicating superior second harmonic generation (SHG) and stronger electro-optic (EOPE) responses, making it suitable for electro-optic applications. Dynamic hyperpolarizability in solvent phase at 1460 nm and 1907 nm show frequency-dependent behavior, with AZ-Se1 displaying the maximum values of γ(ω, ω, 0) and γ(− 2ω, ω, ω) at 9.3 × 10 8 a.u. and 1.4 × 10 9 a.u., respectively, making it the most promising candidate for dc-SHG and other third-order nonlinear optical applications. Light harvesting efficiency (LHE up to 0.99), and radiative lifetime (τ r = 40.82 ns for AZ-Se1) further highlight the potential of these derivatives in optoelectronic applications. This thiophene based cyclic D–π–D system enable efficient light harvesting and the rational design of optoelectronic materials with enhanced NLO properties.