Synthesis, photophysical, linear, and non-linear optical properties of 4-methoxyphenyl dicyanovinylene dyes: DFT and TD-DFT studies.

Dyes were synthesized via Knoevenagel condensation using various aldehydes of julolidine, n-hexylcarbazole, n-hexylphenothiazine, triphenylamine, and 7-N, N-diethylaminocoumarin named as MB1, MB2, MB3, MB4, and MB5. The dyes were characterized using FT-IR, H NMR, C NMR, and HRMS, which provided detailed structural information. Significant absorption, emission, and Stokes shift properties were observed through spectroscopic analysis. Notably, MB2, MB3, and MB4 exhibited solid-state and aggregation-induced emission (AIE) properties. MB1, MB3, and MB4 showed high viscosity sensitivity in polar solvents. Dyes containing nitrogen donors (MB1, MB2, and MB3) demonstrated acidochromism, responding to trifluoroacetic acid, while MB4 and MB5 remained neutral. Solvatochromic analysis indicated enhanced hyperpolarizabilities (α, β and γ) in polar solvents, with MB1 exhibiting the highest linear and second-order hyperpolarizability, making it ideal for non-linear optical (NLO) applications. MB5 also showed a notable solvent polarity response. Computational studies using B3LYP and CAM-B3LYP functionals confirmed increased hyperpolarizabilities in polar environments. All dyes displayed solvatochromism and promising NLO properties, with MB3 and MB5 showing lower band gaps and higher dipole moments in polar solvents, indicating their potential for photonics, bioimaging, and sensors.