Synthesis, growth, structural, thermal, linear and nonlinear optical properties of a new organic crystal: Dimethylammonium picrate G. Anandha Babu a,n , S. Sreedhar b , S. Venugopal Rao b , P. Ramasamy a a Centre for Crystal Growth, SSN College of Engineering, SSN Nagar, Tamilnadu 603 110, India b Advanced Centre of Research in High Energy Materials, University of Hyderabad, Hyderabad 500 046, India article info Article history: Received 5 January 2010 Received in revised form 23 February 2010 Accepted 15 March 2010 Communicated by M. Schieber Available online 30 March 2010 Keywords: A1. X-ray diffraction A2. Growth from solutions B1. Organic compounds B2. Nonlinear optic materials abstract Single crystal of dimethylammonium picrate (DMAP) was successfully grown for the first time by the slow evaporation method with dimensions 25  15  10 mm 3 . 1 H NMR was recorded to elucidate the molecular structure. The cell parameters were determined from single crystal X-ray diffraction studies. The crystal has eight developed facets with major ones (0 0 1) and (0 0 1). The structural perfection of the grown crystals has been analyzed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements. Fourier transform infrared (FTIR) spectral studies have been performed to identify the functional groups. Thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study its thermal properties. Powder test with Nd:YAG laser radiation shows second harmonic generation. The proton donor (–OH) group and proton acceptor amine (–NH) group in the DMAP structure provide infrastructure to introduce the charge asymmetry. The optical transmittance window and the lower cutoff wavelength of the DMAP have been identified by UV–vis–NIR studies. The laser induced surface damage threshold for the grown crystal was measured using Nd:YAG laser. The dielectric properties of DMAP from 323 to 373 K were investigated by the impedance analysis. The microhardness test was carried out and the load dependent hardness was measured. & 2010 Elsevier B.V. All rights reserved. 1. Introduction In recent years, an intense worldwide effort has been focused on the design and development of highly efficient organic nonlinear optical (NLO) materials [1]. The nonlinearity of organic compounds having a p-electron conjugated system is caused by nonlinear polarization that occurs due to the interaction between laser light which comprises a strong electromagnetic wave and the delocalized p-electrons in the organic molecule of interest. In order to increase the magnitude of nonlinear polarization of the molecule, an electron donating group (donor) or an electron withdrawing group (acceptor) is introduced into the p-electron conjugated system as a common technique for molecular design. Organic nonlinear materials have the advantage that they are less costly and can be synthesized fairly easily. However, the absorption wavelength range of such organic materials, if they have a high SHG efficiency, extends to visible region and their crystals show a yellow or orange color, which makes them useless to wavelength conversion of semiconductor lasers. Finding ways to ensure that a bulk material is acentric has been a serious hurdle in the design of new organic materials for NLO uses. Various strategies have been proposed to get noncentrosymmetric pack- ing. These include chirality, hydrogen bonding [2], reduced dipole–dipole interaction [3], etc. The proton transfer between two separate NLO organic compounds takes place and results in a noncentrosymmetric organic salt, then this could increase the hyperpolarizability of both species, provided one is an acid and the second is a base. The first purposeful utilization of this strategy (proton transfer) to increase the hyperpolarizabilities of the organic compounds was proposed. Picric acid derivatives are interesting candidates, as the presence of phenolic OH favors the formation of salts with various organic bases. The conjugated base, picrate, thus formed has increased molecular hyperpolariz- ability because of the proton transfer. On the basis of this, in the present investigation we report for the first time, the growth, crystal morphology, structural, electrical, thermal, laser damage threshold, linear and NLO studies of the title compound dimethylammonium picrate. 2. Experimental procedures 2.1. Material synthesis The title compound was synthesized by reacting equimolar quantities of dimethylamine and picric acid in acetone. When a ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2010.03.017 n Corresponding author. Tel./fax: + 91 4427475166. E-mail address: anandcgc@gmail.com (G. Anandha Babu). Journal of Crystal Growth 312 (2010) 1957–1962