Influence of solvents on the spectra of benzylidene malonitrile derivative and DFT calculations S. Hisaindee a, * , M.A. Rauf a , J.P. Graham b , M.J.S. Al Daweela a , M.A. Ali Ahmed a a Department of Chemistry, PO Box 15551, UAE University, Al-Ain, United Arab Emirates b Department of Life and Physical Sciences, Galway-Mayo Institute of Technology, Galway, Ireland article info Article history: Received 16 June 2018 Received in revised form 20 September 2018 Accepted 20 September 2018 Available online 22 September 2018 Keywords: Benzylidene malonitrile Solvatochromism UV/Vis spectra DFT Solvent mixture abstract The spectroscopic behavior of benzylidene malonitrile (BZM), a donor-p-conjugate-electron acceptor compound, is reported in various solvents. KamleteTaft and Catalan models were used to evaluate specific and non-specific solute-solvent interactions. Solvent polarizability (SP) was found to be the dominant factor affecting the absorption and fluorescence spectral shifts. The p /p* transitions was assigned between HOMO and LUMO, based on time-dependent density functional theoretical calcula- tions. The dipole moment of BZM in the ground and excited states were calculated using Stokes shift and solvent polarity functions. The experimental ground state dipole moment (m g ¼ 1.7 D) was found to be lower than that in the excited state (m e ¼ 5.5 D). In binary solvent mixtures, BZM showed both ideal (DMSO/ethanol) and non-ideal (DMSO/acetone and DMSO/dioxane) behaviors. The formation constants in DMSO/ethanol was much lower as compared to the other two mixtures. BZM also exhibited self- quenching fluorescence which is attributed to the primary inner filter effect. © 2018 Elsevier B.V. All rights reserved. 1. Introduction Donor-acceptor (D-p-A) compounds have intrinsic intra- molecular charge transfer (ICT), which is of interest in a variety of applications. These compounds have high molar absorptivity, and tunable color based on the extent of the donor-acceptor interaction [1e3]. D-p-A compounds have been applied in optoelectronics such as molecular electronic devices and sensors as well as for ultrahigh density data storage [1 ,4e8]. Malonitrile is an important compo- nent in the construction of D-p-A compounds, owing to the exceptional electron-withdrawing capacity of the cyanide group and therefore its electron acceptor ability [2]. Derivatives of malonitrile such as benzylidene malonitriles have been used in the synthesis of a new class of photo cross-linkable liquid crystalline polymers [3]. The conjugated link is responsible for ICT in these compounds. Their ground and excited state dipole moments are dependent on the charge of the donor-acceptor groups, the extent of p conjugation and solvent property. Thus, the structure and solvent polarity play- an important role on the spectral properties of such compounds. Therefore they have potential use inthe conversion of photo energy [7e9]. Malonitrile derivatives are organic non-linear optical compounds and have been reported in the literature for their potential optical applications [4e10]. In this paper, we report the spectral properties, with emphasis on sol- vatochromism, of a benzylidene D-p-A composed of a malonitrile acceptor and a dimethyl amino donor. The dimethylamino group is the strongest electron donating group according to the Hammett scale. The solute-solvent interactions of benzylidene malonitrile (BZM) were studied in various solvents and solvent mixtures using absorption and fluorescence spectroscopy. This was supplemented by computational studies using Gaussian and the time dependent density functional theory (TDDFT). 2. Experimental 2.1. Synthesis and characterization of BZM A mixture of 4-(Dimethylamino)benzaldehyde (3.0 mmol), malonitrile (3.3 mmol) and piperidine (0.1 mmol) in ethanol (4 mL) was heated for 15min, with stirring, in a microwave reactor at 110  C (dynamic power 50e60 W). The mixture was filtered and the residue was washed with coldwater, followed by recrystallization using hot ethanol and finally dried under vacuum to give an orange-red solid: m.p:184e186  C; 1 H NMR (400 MHz, DMSO‑d 6 ): v * Corresponding author. E-mail address: soleiman.hisaindee@uaeu.ac.ae (S. Hisaindee). Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc https://doi.org/10.1016/j.molstruc.2018.09.054 0022-2860/© 2018 Elsevier B.V. All rights reserved. Journal of Molecular Structure 1177 (2019) 160e167