ORIGINAL PAPER Optimized geometry, spectroscopic characterization and nonlinear optical properties of carbazole picrate: a density functional theory study C¸ Arıog˘lu, O ¨ Tamer*, D Avcı and Y Atalay Department of Physics, Art and Science Faculty, Sakarya University, 54187 Sakarya, Turkey Received: 12 December 2017 / Accepted: 27 April 2018 Abstract: The molecular modeling of carbazole picrate (CP) was carried out by using B3LYP and HSEH1PBE levels of density functional theory and 6-311??G(d,p) basis set by means of Gaussian 09 revision D.01 program. These methods have been used to determine the optimized molecular geometries, vibrational frequencies, electronic transitions and bonding features of the title compound. The computed small energy gap between HOMO and LUMO energies shows that the charge transfer occurs within the investigated compound. Additionally, the intensive interactions characterized by high stabilization energies were the powerful indicators of intra- and intermolecular charge transfer interactions. The obtained molecular dipole moment (l), polarizability ( a hi) and hyperpolarizability ( b hi) indicates that CP exhibits considerable nonlinear optical characteristic. The theoretical structural parameters such as bond lengths and bond angles are in a good agreement with the experimental values of the title compound. Additionally, the hydrogen bonding interactions were visualized via molecular electrostatic potential surface. Keywords: Carbazole picrate; Density functional theory; IR and NMR; Nonlinear optics; Natural bond orbital PACS Nos.: 33.15.Dj; 31.15.E-; 33.20.Tp; 67.30.er; 33.20.Lg; 42.65. - k 1. Introduction Carbazole alkaloids presented in the genus Clausena (Ru- taceae) possess a number of biological activities, such as antibacterial, neuroprotective, cytotoxicity, and antimalar- ial activities [1–4]. Clausena emarginata Huang, a bush commonly distributed in the southern part of China, was historically used as a folk medicine for the treatment of coughs, headache, gastrointestinal diseases, and rheumatic arthritis [4, 5]. Additionally, ellipticine class is a well- known carbazole compounds, which are used as a chemotherapeutic agent [6–8]. Carbazoles exhibit good photorefractive, photoconductive, and light emitting prop- erties, so they are also used as an efficient organic material. So, a number of studies concerning the structural, spec- troscopic and electronic properties of these molecules have been reported [8, 9]. Organic materials have received much attention due to the increasing requirement for potentially active compounds for the wide range of electronic and optoelec- tronic devices [8, 10–15]. Picric acid which has three electron withdrawing nitro groups and an electron donating hydroxyl group is an important class of organic ligand [8, 16]. It is well known that the substitution of organic ligands with electron donating and electron withdrawing groups induces the linear and nonlinear optical properties of organic materials. Organic nonlinear optical materials have been found applications in frequency shifting, laser technology, telecommunication, optical data storage and optical modulation [17]. Compared to inorganic counter- parts, organic NLO materials have some advantages such as high degree of nonlinearity, low dielectric constants, natural synthetic flexibility and rapid response in electro- optic effect [18–21]. Saravanabhavan et al. [8] has synthesized the title compound and reported its structural parameters, FT–IR and UV–Vis spectra as well as 1 H and 13 C NMR chemical shift values. However, to the best of our knowledge, there is no theoretical study concerning the structural, spectro- scopic and nonlinear optical properties of the title com- pound. In order to eliminate this deficiency, we have performed a series of density functional theory (DFT) *Corresponding author, E-mail: omertamer@sakarya.edu.tr Indian J Phys https://doi.org/10.1007/s12648-018-1258-5 Ó 2018 IACS