Synthesis photophysical characterization and DFT Study of triazine benzothiazole hybrid azo dyes as π conjugated materials for organic photovoltaic and nonlinear optical applications

In the search for sustainable alternatives to silicon-based photovoltaics, π-conjugated organic materials that combine electron-donor and electron-acceptor heterocycles are attracting increasing interest. In this work, hybrid azo dyes built from a 3-amino-5,6-dimethyl-1,2,4-triazine core and 2-aminobenzothiazole derivatives were synthesized via diazotization/coupling reactions, affording three azo compounds ( 4a – 4c ) and a bis-triazine derivative ( 5 ). Structures were established by IR, 1 H/13 C NMR, HSQC, COSY, and mass spectrometry, and the regioselectivity of each coupling was determined from proton coupling constants. The electronic, optoelectronic, nonlinear optical (NLO), and thermodynamic properties of the four compounds were investigated using DFT and TD-DFT calculations at the B3LYP/6-311 + G(d, p) level in the gas phase and with the polarizable continuum model (PCM/SMD) in methanol and DMSO. Compounds 4a and 4c s how energy gaps of ~ 2.95 eV in polar solvents and hole/electron reorganization energies of 0.61–0.67 eV, markedly lower than compound 4b (> 1 eV) though still higher than the reference p-type semiconductor pentacene (0.08–0.12 eV), pointing to comparatively favourable, but not optimal, charge-transport characteristics. Their first-order hyperpolarizability in polar solvents (~ 171 × 10⁻³⁰ esu) exceeds that of para-nitroaniline by a factor of 7–8. Compound 4b , bearing a nitro substituent, is electronically the most stable and shows the highest electrophilicity index, consistent with an electron-acceptor character, but its high reorganization energies suggest limited intrinsic mobility. On the basis of these computed descriptors, compounds 4a and 4c , and to a lesser extent 5 , display electronic and optical profiles compatible with organic dye, NLO and charge-transport applications; experimental and device-level validation will be required to confirm their suitability for OPV, OLED or photonic technologies.