Spectroscopic and computational study on Azobenzene
S. Xavierab*, S. Periandyc,
aDepartment of Physics, St. Joseph’s College of Arts and Science, Cuddalore, Tamil Nadu, India.
bResearch scholar, Bharathiyar University, Coimbatore,Tamil Nadu, India
cDepartment of Physics, Tagore Arts College,Puducherry, India.

A research study has been made on Azobenzene using the FT-IR, FT-Raman, NMR and UV spectra obtained through various spectroscopic techniques. The theoretical vibrational frequencies and optimized geometric parameters have been calculated by using HF and density functional theory with the hybrid methods B3LYP, B3PW91and 6-311+G(d,p)/6-311++G(d,p) basis sets.

Keywords: Azobenzene, chemical shifts; NBO, HOMO-LUMO, Fukui function.

*Corresponding author E-mail address: [email protected]
Tel & Fax- +91 9443428971

1. Introduction
The properties of azobenzene chromophore containing organized films have attracted increasing interests recently, partially due to their potential applications in the fields of nonlinear materials and high-density memory device , etc. We have been paying particular and continuous attention to the azobenzene functionalized monolayer assemblies for both its fundamental and technological perspectives.

2. Experimental details
The spectra compound azobenzene is purchased from Sigma–Aldrich Chemicals, USA, which is of spectroscopic grade and hence used for recording the spectra as such without any further purification. The FT-IR spectrum of the compound is recorded using a Bruker IFS 66V spectrometer in the range of 4000–400 cm���1.
[insert Fig. 1&2 here]

3. Methodology
In the present work, HF and some of the hybrid methods, B3LYP and B3PW91, are carried out using the basis sets 6-31+G(d,p) and 6-311+G(d,p). All these calculations are performed using the GAUSSIAN 09W[2] program package on an i7 processor in a personal computer. In DFT methods, Becke’s three-parameter hybrid function, combined with the Lee–Yang–Parr correlation function (B3LYP)[3,4] and Becke’s three parameter exact exchange-function (B3)[5] combined with the gradient-corrected correlational functional of Lee, Yang and Parr (LYP)[6,7] and Perdew and Wang (PW91)[8,9] predict the best results for molecular geometry and vibrational frequencies of moderately larger molecules. The calculated frequencies are scaled down to give up the rational with the observed frequencies.
[Insert Table 1& 2 here]

4. Results and discussion
The bond length values between C1–C2 and C2–C3 differed by 0.0790 Å; C13-C18 and C13-C14 are differed by 0.011 Å since further weighted by N=N bond. The bond angle of C2–C3–C4 is 0.26º elevated than C1–C6–C5; C13-C18-C17 is elevated 0.1595º than C14-C15-C16 in the ring, which also confirms the deformation of the hexagonal shield.
[Insert Fig. 3& 4]

4.2. Vibrational assignments
In order to obtain the spectroscopic signature of azobenzene, the computational calculations are performed using frequency analysis. On the basis of C2H symmetry, the 66 fundamental vibrations of the molecule can be distributed as 39 in-plane vibrations of A species and 18 out-of-plane vibrations of A species, i.e., vib = 49 A + 17 A. [Insert Table 3 & 4 here]
[Insert Figure 5 & 6 here]

5. Conclusion
In the present investigation, FT-IR, FT-Raman and 13C NMR and 1H NMR spectra of azobenzene are recorded and the observed vibrational frequencies are assigned depending upon their expected region.

We remain grateful to the Administration of St. Joseph’s college of Arts and Science (Autonomous), Cuddalore for providing us the Quantum Computational Research Lab for all the computational works of the compound.

Reference to a Journal
[1] L. Burgio, P.J. Gibbs, Spectrochim. Acta A 57 (2001) 1491-1521.

Reference to a book:
[2] W. Strunk Jr., E.B. White, The Elements of Style, third ed., Macmillan, New York, 1979.

Reference to a chapter in an edited book:
[3] G.R. Mettam, L.B. Adams, in: B.S. Jones, R.Z. Smith (Eds.), Introduction to the Electronic Age, E-Publishing, Inc., New York, 1994, pp. 281-304.