Impact of π-Linkers Modifications on Tuning Nonlinear Optical Amplitudes of Pyridoquinazolinone-Based Aromatic Dyes: A Rational Entry to Novel D-π-A NLO Materials

Developing efficient nonlinear optical (NLO) materials is a cutting-edge field of study. The desirability of promising NLO materials for optoelectronic applications drove us to investigate the pyridoquinazolinone-based D-π-A architectured chromophores for predicting proficient NLO compounds. Pyridoquinazolinone-based dye (WL-O) is chosen as a reference and its nine derivatives (ASH1-ASH9) are quantum chemically modeled by inserting variously reported π-linkers into the D-π-A framework. Simulations using DFT and TD-DFT provide insight into how π-linker alteration affects the NLO properties. The potential use of investigated dyes for NLO response applications is confirmed by evaluating photophysical aspects, frontier molecular orbital (FMO), natural population analysis (NPA), molecular electrostatic potential (MEP), the density of state (DOS), transition density matrix (TDM) analysis, and static, frequency-dependent NLO response properties. FMO analysis shows that all dyes’ energy gaps are lower when compared to the reference, resulting in a strong NLO response. The highest absorption wavelength of the studied dyes was found to be in the visible spectrum, as determined by UV-Vis analysis. NPA-based findings demonstrated the movement of the electrons from D to A through π-linkers resulting in the formation of a charge separation state and active NLO sensitivity of the proposed dyes. Moreover, MEP, LOL, and ELF topological investigations are performed to appraise the charge transfer inside ASH1-ASH9 and high NLO characteristics. The robust NLO response revealed the eye-catching linear polarizability(α 0), first-hyperpolarizability (β), particularly ASH3, with the highest α 0 and β 0 computed to be 520.44 a.u. and 26166.79 a.u., respectively. Additionally, frequency-dependent hyperpolarizability SHG β(−2ω,ω,ω) and EOPE β(−ω,ω,0) calculations for commonly used lasers were performed at 1907.21, 532, and 1064 nm. ASH3 with terthiophene linker exhibits a striking EOPE β(−ω,ω,0) and SHG β(−2ω,ω,ω) response of 2.94 × 10⁴ a.u. and 3.80 × 10⁴ a.u. respectively at 1907.21 nm. This theoretical framework confirmed that the investigated dyes have fine NLO potential and are recommended for future NLO applications.