Density functional theory studies on 2,5-bis(4-hydroxy-3-methoxybenzylidene)- cyclopentanone H. Saleem a,⇑ , Akhil R. Krishnan a , Y. Erdogdu b , S. Subashchandrabose a , V. Thanikachalam c , G. Manikandan c a Department of Physics, Annamalai University, Annamalainagar, Chidambaram 608 002, India b Department of Physics, Ahi Evran University, Kirsehir 40100, Turkey c Department of Chemistry, Annamalai University, Annamalainagar, Chidambaram 608 002, India article info Article history: Received 16 November 2010 Received in revised form 19 February 2011 Accepted 20 February 2011 Available online 24 February 2011 Keywords: DFT HOMO LUMO Curcumin NBO MEP abstract The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments of 2,5-bis(4-hydroxy-3-methoxybenzylidene)cyclopentanone (BHMBC) have been investigated by using density functional theory (B3LYP) methods at 6-311G(d,p) basis set. The energy and oscillator strength calculated by Time Dependent Density Functional Theory (TD-DFT) results almost compliments with experimental findings. Then, gauge-including atomic orbital (GIAO) 13 C NMR and 1 H NMR chemical shifts calculations of the BHMBC molecule were carried out by using B3LYP functional with 6-311G(d,p) basis sets. The mass spectrum is also recorded. Moreover, we have not only simulated highest occupied molec- ular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) but also determined the transition state and energy band gap. The stability of the molecule arising from hyperconjugative interaction and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Besides, molecular electrostatic potential (MEP) were performed by the DFT method and the infrared and Raman intensities have also been reported. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction The title compound 2,5-bis(4-hydroxy-3-methoxybenzyli- dene)cyclopentanone (BHMBC) is a curcumin derivative. Curcu- mins have several biological activities, such as anti-inflammatory, antioxidative, antibacterial, antihepatotoxic, hypertensive and hypocholesterolenic properties [1–5]. Curcumin inhibits in vitro li- pid peroxide formation by liver homogenates of endemic mice [6]. It is used for the synthesis of bioactive pyrimidine compounds [7] and also find applications in the preparation of liquid–crystalline polymers [8]. Thermo tropic liquid crystalline behavior of poly- meric materials containing cyclopentanone moiety linked with polyethylene spacers is of considerable current interest, not only because of their potential as high-strength fibers, plastics, mol- dings, etc. [9–11], but also their applications in non-linear optical materials [12]. The benzylidene derivatives are intermediates in various pharmaceuticals, agrochemicals and perfumes [13]. Curcu- min demonstrated a great ability in chelating essential metal ions such as Cu (II) [14] and the complexes showed a higher scavenging ability than curcumin. The theoretical study on physicochemical properties of curcu- min has been reported [15]. Spectroscopic and theoretical study of the electronic structure of curcumin and related fragment mol- ecules were carried out [16]. Density functional theory investiga- tion of Cu (I) and Cu (II) curcumin complexes were reported [17]. A theoretical study based on comparison of calculated spectro- scopic properties with NMR, UV–visible and IR experimental data is done [18]. A combined theoretical and experimental approach to the study of the structure and electronic properties of curcumin as a function of solvent is also reported [19]. Literature reveals that to the best of our knowledge DFT cal- culations and experimental studies on BHMBC molecule have not been reported so far. Therefore, the present work deals with FT-IR, FT-Raman, Mass spectra, UV and NMR spectroscopic inves- tigation of BHMBC utilizing DFT (B3LYP) method with 6- 311G(d,p) as basis set. Vibrational spectrum of the molecule sup- ported by using the Scaled Quantum Mechanical (SQM) force field technique based on density functional theory (DFT). All pos- sible conformers of BHMBC molecule have been optimized at B3LYP levels at 6-311G(d,p) level. The redistribution of electron density (ED) in various bonding and antibonding orbitals and E2 energies have been calculated by natural bond orbital (NBO) analysis using DFT method to give clear evidence of stabilization originating from the hyper conjugation of various intra-molecular interactions. The HOMO and LUMO analysis have been used to elucidate information regarding charge transfer within the molecule. 0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2011.02.039 ⇑ Corresponding author. Tel.: +91 9443879295. E-mail address: saleem_h2001@yahoo.com (H. Saleem). Journal of Molecular Structure 999 (2011) 2–9 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc