Spectral and density functional studies on the absorbance and fluorescence spectra of 2-R-5-phenyl-1,3,4-oxadiazoles and their conjugate acids

Alexander Gaenko, Ajitha Devarajan, Rostislav E Trifonov, Vladimir A Ostrovskii

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5 Citations (SciVal)

Abstract

Absorption and fluorescence spectra of 2-R-5-phenyl-1,3,4-oxadiazoles (R = H, methyl, tert-butyl, trifluoromethyl, amino, phenyl, benzyl) were studied experimentally and by time dependent density functional theory (TDDFT) methods. In acidic media a substantial red shift is observed due to the presence of conjugate acid forms. Two conjugate acid forms (3H and 4H) are possible for unsymmetrically substituted oxadiazoles. Relative basicities of the two basic centers of oxadiazole ring at the S-0 and S-1 geometries were calculated using the local density descriptors approach. Substituent effects were studied by analyzing the electron density distribution in the ground and excited states. Analyzing the absorption spectra and local descriptors results, we predict 4H forms to be the dominant acid forms. Calculated emission peaks of 4H forms agree well with experimental observations. An abnormal red shift in the case of the 3H forms is attributed to the increased stabilization of the N-H bond in the 3H forms compared to the 4H forms.
Original languageEnglish
Pages (from-to)8750-8757
JournalThe Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory
Volume110
Issue number28
DOIs
Publication statusPublished - 2006

Bibliographical note

The information about affiliations in this record was updated in December 2015.
The record was previously connected to the following departments: Theoretical Chemistry (S) (011001039)

Subject classification (UKÄ)

  • Theoretical Chemistry

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