Ab initio calculations of the absorption spectrum of chalcone

The excitation energies and excited states of trans-chalcone (trans-(s-cis) -1,3-diphenylpropenone), and several related molecules (trans-(s-cis)-3-phe nylpropenal, s-cis-1-phenylpropenone, propenal, trans-(s-cis)-1-(4-hydroxyp henyl)-3-phenylpropenone, trans-(s-cis)3-(4-hydroxyphenyl)-1-phenyl) have b een calculated using single reference ab initio molecular orbital methods, and characterized by attachment-detachment density analysis. The results su ggest assignments for the lowest three electronic transitions observed expe rimentally for trans-(s-cis)-chalcone in solution. The extent of localizati on of the electronic transitions is established by calculations on the exci ted states of trans-(s-cis)-3-phenylpropenal, s-cis-1-phenylpropenone and p ropenal, as well as analysis of the chalcone calculations. Contrary to some previous work, none of these excitations are strongly delocalized over the entire molecule. Calculated substituent shifts for the hydroxy chalcones a re in qualitative agreement with experimental data, and support the localiz ed interpretation of the main pi-->pi* transition. (C) 1999 Elsevier Scienc e B.V. All rights reserved.