© 2022In this study, three azo dyes bearing coumarin thiophene (6a-c) were synthesized, and their photophysical properties were studied via UV–vis spectroscopy in various solvents. Acidochromic properties were also investigated in DMSO/H2O, and all products showed acidochromic properties. The reversibility studies were carried out to investigate the reusability of the prepared compounds. Furthermore, products 6a-c were also investigated for their potential use as hydroxide sensors. The electric field-induced second harmonic generation (EFISH) technique was used to measure the second-order nonlinear optical properties. The thermal properties of the prepared compounds were investigated via thermogravimetric analysis (TGA). The results showed that the samples are thermally stable up to around 200 °C. The protonation of the compounds and their nonlinear optical (NLO) properties were investigated in the framework of Density Functional Theory (DFT) calculations.