Systematic designing of efficient dipolar tetrasubstituted pyrene-based chromophores to tune the frequency dependent nonlinear optical response: A DFT/TD-DFT approach.

Recently, pyrene-based compounds have attracted significant attention for designing advanced organic NLO materials. Herein, a series of pyrene-based derivatives (PyD1–PyD5) was designed with donor–π–acceptor (D–π–A) framework, tailored for potential non-linear optical materials. Structural modeling was performed by introducing end-capped oxazole-based acceptors into the reference molecule (PyR). Quantum chemical calculations were carried out at the M06 functional with 6-311G (d, p) basis set to obtain detailed insights into optical, structural, and electronic properties of designed chromophores. Therefore, various analyses including non-linear optical (NLO), natural bond orbitals (NBOs), transition density matrix (TDM), density of states (DOS), and frontier molecular orbitals (FMOs) analyses were performed. The structural modifications significantly influence on the HOMO and LUMO energies of the derivatives, resulting in reduced energy gaps and enhanced spectral absorption. Among all the designed compounds, PyD4 chromophore exhibited the narrowest energy gap (2.963 eV) with the highest chemical softness (0.337 eV− 1) and maximum absorption (λmax = 504.124 nm in the gas phase and 499.694 nm in dichloromethane), highlighting its remarkable optical performance. All derivatives exhibited significant NLO responses, with PyD4 showing the highest first hyperpolarizability (βtotal = (5.182 × 10⁴ a.u.) and second hyperpolarizability value (γtotal = 7.73 × 10⁶ a.u.). The above findings highlight the key role of end–capped acceptor tailoring in enhancing NLO response, indicating the potential of these derivatives as efficient NLO materials.