Vibrational spectroscopic characterization, electronic absorption, optical nonlinearity computation and terahertz investigation of (2E) 3-(4-ethoxyphenyl)-1-(3-bromophenyl) prop-2-en-1-one for NLO device fabrication

Abstract The present study spotlights the key structure-property features of a chalcone derivative (2E) 3-(4-ethoxyphenyl)-1-(3-bromophenyl) prop-2-en-1-one (E3BC) for future applications in nonlinear optical devices through dual approach involving experimental and theoretical techniques. The sample has been characterized by 1H NMR, FT-IR, FT-Raman and terahertz spectroscopies. The experimental results are supported by computational studies using density functional theory. To analyse the 1H NMR spectra, theoretical calculations on chemical shifts were done by GIAO method. Complete vibrational assignments of the vibrational modes have been made on the basis of the potential energy distribution in terms of internal coordinates. The low frequency vibrational modes between 0.2 and 1.8 THz were examined via terahertz time domain spectroscopy. The UV–vis spectrum was recorded in methanol solution. The energies, absorption wavelengths and oscillator strengths of electronic singlet-singlet transitions were determined by time dependent density functional theory. The calculated HOMO-LUMO energy gap is small which reveals that the charge transfer takes place within the molecule and it can be exploited for the nonlinear optical applications. Information about the charge density distribution and the sites of chemical reactivity of the molecule has been obtained by mapping electron density with molecular electrostatic potential. The MEP surface around the bromine atom exhibited the dual nature. Along the C-Br axis the positive electrostatic potential (the σ-hole) is present while the remainder of the surface is negative. Hence bromine atom can interact electrostatically with both nucleophiles and electrophiles. For other atoms no atom-specific effects are found. The stability of the molecule arising from hyper conjugative interactions and charge delocalization has been interpreted using natural bond orbital analysis. The study indicates that the intramolecular charge transfer (n → σ∗, n → π∗ and π → π∗) can induce nonlinearity in the molecule and validates E3BC's candidature to be used as a nonlinear optical active material. In order to understand the nonlinear optical activity of the molecule the calculations of electronic dipole moment, polarizability, anisotropy of polarizability as well as first and second hyperpolarizabilities are performed using finite field approach implemented in the DFT method. The findings suggested that the first order hyperpolarizability of titled molecule is 139 times greater than the value of urea. The high value of first order hyperpolarizability shows that E3BC can be a potential candidate in the nonlinear optical applications. The vibrational contribution to the above properties has also been computed using the self-consistent field wave functions within the double harmonic oscillator approximation.