Silicon https://doi.org/10.1007/s12633-018-9837-9 ORIGINAL PAPER Synthesis, Characterization, Physico-Chemical and DFT Studies of Potential Organic NLO Materials: Experimental and Theoretical Combined Study I. Manikandan 1 · M. Venkatesh Perumal 2 · K. Jayamoorthy 3 Received: 6 December 2017 / Accepted: 27 March 2018 © Springer Science+Business Media B.V., part of Springer Nature 2018 Abstract 1-(2,4-difluorobenzyl)-2-(2,4-difluorophenyl)-6-methyl-1H -benzo[d ]imidazole(1) and 1-(3-(tri fluoromethyl)benzyl)2-(4- (trifluoromethyl)phenyl)-6-methyl-1H -benzo[d ]imidazole (2) were synthesized and characterized using FT-IR, 1 H- NMR, 13 C-NMR and mass spectral studies. UV-Vis absorption and emission spectral studies were studied in hexane and ethanol medium. In addition to these, density functional theory studies (DFT/B3LYP/6-31G(d,p)) has also been carried out to compute the relevant electronic properties of the molecules and the observed theoretical results of the non-zero dipole moments, polarizability and hyper polarizability values which show that these types of molecules are promising candidates for applications in various non-linear optical (NLO) devices because of their significant values of the molecular hyperpolarizabilities and fine microscopic NLO behaviour. The high NLO responses of the donor-acceptor π -conjugated molecules are related to the intramolecular charge transfer excited state. The results confirmed that the synthesized benzimidazoles can act as a non-linear optical material and changing the substituents in the aldehydic phenyl ring will change the energy gap in the molecule. Keywords Benzimidazoles · DFT · Organic NLO materials · π -conjugated molecules 1 Introduction Imidazole compound plays an imperative role in chemistry as mediators for synthetic reactions [1], primarily for preparing functionalized materials and also in analytical applications due to their unique optical properties. The imidazole ring can be easily designed to accommodate Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12633-018-9837-9) contains sup- plementary material, which is available to authorized users.  M. Venkatesh Perumal venkatkumar.ac@gmail.com 1 Department of Chemistry, Bannari Amman Institute of Technology, Sathyamangalam 638 401, Tamilnadu, India 2 Department of Chemistry, Ramco Institute of Technology, Rajapalayam 626117, India 3 Department of Chemistry, St. Joseph’s College of Engineering, Chennai 600119, India functional groups, which permits the covalent embodiment of the NLO chromophores into polyamides leading to NLO side chain polymers [2, 3]. Due to their optoelectronic properties, imidazole derivative plays an important role in material science and supramolecular chemistry [4–6]. The optimization of these materials for NLO devices involves the understanding of NLO processes as a function of electronic and geometrical molecular structure. An imidazole derivative with the nitrogen substituent removes the tautomerism possibility and announces a new potentially suitable chemical variable for the optimization of NLO activity of the chromophore. For the practical application of second-order nonlinear optical materials, not only a large hyperpolarizability but also good thermal stability is required. Benzimidazole [7] based chromophores have established increasing attention due to their distinctive linear, non- linear optical properties, thermal stability in guest–host systems and also in materials chemistry [8]. These benzimidazoles can be used as a chromophore, because of their high extinction coefficient, readily tunable absorption