Document Detail

Spectral and density functional studies on the absorbance and fluorescence spectra of 2-R-5-phenyl-1,3,4-oxadiazoles and their conjugate acids.
MedLine Citation:
PMID:  16836437     Owner:  NLM     Status:  MEDLINE    
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 S0 and S1 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.
Alexander V Gaenko; Ajitha Devarajan; Rostislav E Trifonov; Vladimir A Ostrovskii
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  The journal of physical chemistry. A     Volume:  110     ISSN:  1089-5639     ISO Abbreviation:  J Phys Chem A     Publication Date:  2006 Jul 
Date Detail:
Created Date:  2006-07-13     Completed Date:  2007-11-28     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9890903     Medline TA:  J Phys Chem A     Country:  United States    
Other Details:
Languages:  eng     Pagination:  8750-7     Citation Subset:  IM    
Department of Theoretical Chemistry, Chemical Center, Lund University, P.O. Box 124, S-221 00 Lund, Sweden.
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MeSH Terms
Hydrogen-Ion Concentration
Models, Chemical*
Models, Molecular*
Molecular Structure
Oxadiazoles / chemistry*
Spectrometry, Fluorescence
Reg. No./Substance:

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