A centrosymmetric crystal structure has been determined by single crystal X-ray diffraction analysis of Hydroxyethylammonium Picrate (HEAP) crystals. It is mentioned for the first time in the literature for its monoclinic structure crystallizing in centrosymmetrical space group P2(1)/c which is basically a donor acceptor organic material grown by slow evaporation solution growth technique. We used Fourier Transform Infra Red and Raman spectroscopy to study the intermolecular interactions present in the 1:1 combination of picric acid and ethanolamine. Optical, mechanical and thermal stabilities of the title crystal were carried out to propose the material for useful applications. Z-scan is used to measure the effective third-order nonlinear optical susceptibility, which is found to be 3.24 x 10(-3) esu. The negative sign of the nonlinear refractive index n(2) = -9.2 x 10(-5) cm(2) W-1, indicates that this material exhibits self-defocusing optical nonlinearity. We also report the details of theoretical studies of the macroscopic nonlinear optical properties and molecular orbital calculations by quantum chemical calculations. (c) 2012 Elsevier B.V. All rights reserved.