Experimental and computational investigation of novel dihydrated organic single crystal of 2,4,6-triaminopyrimidine and 3,5-dintrobenzoic acid: Linear and nonlinear optical response with limiting performance Mohd Faizan a, b , Mohd Mehkoom a , Ziya Afroz c, ** , Vítor Hugo Nunes Rodrigues d , S.M. Afzal a , Shabbir Ahmad a, * a Department of Physics Aligarh Muslim University, Aligarh, UP, 202002, India b Department of Physics, Mirza Ghalib College, Gaya, Bihar, 823001, India c Department of Chemistry Aligarh Muslim University, Aligarh, UP, 202002, India d CFisUC, Department of Physics, Universidade de Coimbra, Rua Larga, 3004-516, Coimbra, Portugal ARTICLE INFO Keywords: Dihydrated organic crystal SCXRD FTIR Z-Scan technique DFT calculation Hirshfeld surface analysis ABSTRACT Newly synthesized dihydrated organic crystal (TAP þ DNB  .2H 2 O) of 2,4,6-triaminopyrimidine (TAP) with 3,5- dinitrobenzoic acid (DNB) was grown by slow evaporation technique and this crystal belongs to monoclinic P- 1 space group. Infrared spectroscopy combined with DFT calculation has been used to confirm the presence of the expected functional group of the titular crystal. Further, the UV–Vis absorption spectroscopy has been utilized to determine various optical parameters such as excitation wavelength, optical band gap, and extinction coefficient from the point of view of optical application. In addition to this, TD-DFT/B3LYP computational theory was also applied to simulate the UV–Vis absorption spectrum for supporting the experimental result. The effect of complex formation from its constituents has been explored using frontier molecular orbitals analysis. Furthermore, the mapping of the 3D Hirshfeld surface and its related fingerprint plots were used for qualitative and quantitative analysis of the intermolecular interactions which involve among different molecular moiety in the synthesized crystal. The third-order nonlinear optical response of this molecular complex (TAP þ DNB  .2H 2 O) have been investigated in detail using the z-scan technique with CW diode laser (520 nm). Also, theoretical nonlinear optical parameters have been investigated by the DFT method. The thermal characteristic of the growth dihydrate crystal has been studied by thermal gravimetric-differential thermal analysis (TG-DTA). 1. Introduction In recent decades, the design and development of new promising organic single crystals (co-crystal, salt and hydrated salt) with high nonlinear susceptibility and ultrafast response time have gained much interest due to their potential optical applicability in the field of nonlinear optics, photonics and optoelectronics [1,2]. The organic mo- lecular crystal generally has specific properties such as high charge mobility, high nonlinear response and photochemical stability due to the delocalization of the π-electron system and presence of intermolecular hydrogen bond interactions [3]. During the formation of crystals, when a proton is completely shifted from one molecule to another. This type of crystals are generally referred to as organic salt which shows the advantage for second and third-order nonlinearity due to its asymmetric charge distribution in the ground state [4]. These properties make the organic crystals propitious materials for the application in the field of optical devices for the transfer and storage of data, optical modulation, optical switching and optical logic for developing technologies in the areas of signal processing, communication and second harmonic gener- ation (SHG) [5,6]. Due to high third order nonlinear optical suscepti- bilities and a high potential for frequency shifting, the organic crystals have been used for the optical frequency mixing [5,7]. Hence, the research and development of organic crystals with these crucial charac- teristics have been becoming more and more important to create future for the community. At a glance, pyrimidine and its derivative are most imperative * Corresponding author., ** Corresponding author. E-mail addresses: zia19a@gmail.com (Z. Afroz), ahmad.shhabir@redifmail.com (S. Ahmad). Contents lists available at ScienceDirect Journal of Solid State Chemistry journal homepage: www.elsevier.com/locate/jssc https://doi.org/10.1016/j.jssc.2021.122255 Received 22 November 2020; Received in revised form 2 May 2021; Accepted 3 May 2021 Available online 13 May 2021 0022-4596/© 2021 Elsevier Inc. All rights reserved. Journal of Solid State Chemistry 300 (2021) 122255