The azo-hydrazone tautomerism, solvatochromism and halochromism in diphenylamine based azo dye ((E)-1-(4-((4-(phenylamino)phenyl)diazenyl)phenyl)ethanone, DPA) were examined. The absorption wavelengths of the dye in different solvents were in the range 429-544 nm. The compound exhibits positive solvatochromism as the absorption band is red shifted with increasing solvent polarity. In addition, the absorption properties of the dye change drastically upon acidification, as the protonation of beta-nitrogen atom of the azo group increases the donor-acceptor interplay of the pi system. The experimental results are fully supported by DFT and TD-DFT calculations. Moreover, nonlinear optical properties (NLO) were also obtained by the theoretically predicted values of dipole moment (mu), polarizability (alpha) and first hyperpolarizability (beta). (C) 2015 Elsevier B.V. All rights reserved.