Intramolecular charge delocalization and nonlinear opticalproperties of Methyl 3-(4-methoxy phenyl) prop-2-enoate fromvibrational spectra

Abstract

The density functional computations of MMP areperformed at B3LYP/6-31G (d,p) level to derive equilibriumgeometry, vibrational wavenumbers and intensities, and firsthyperpolarizability. Large NLO efficiency predicted for the firsttime in this new class of compounds has been confirmed by powderefficiency experiments. DFT calculation reveals that endocyclicangle at the junction of the propenoate group and the phenyl ringis decreased from 120° by 2.5°, whereas twoneighbouring angles around the ring are increased by 2.1°and 1.2° respectively, associated with intramolecularcharge transfer interaction. The vibrational spectra confirm thecharge transfer interaction between -COOCH3 group and phenylring through the ethylenic bridge with simultaneous infrared andRaman activation of C7=C18 stretching and ring modes 8and 19. The large intensity differences observed between 8aand 8b modes in both IR and Raman spectrum due to the algebraicdifference of the electronic effects of the substitutents havebeen discussed. The charge transfer interaction between -COOCH3group and phenyl ring through the ethylenic bridge resulting inπ-electron cloud movement from donor to acceptor can make themolecule highly polarized and must be responsible for the NLOactivity of MMP.