Determining the excited‐state substituent constants σCCex of meta‐substituent from 3,4'‐disubstituted stilbenes

In this paper, 61 samples of 3,4'-disubstituted stilbenes and 18 samples of 3,3'-disubstituted stilbenes were synthesized, and their UV data were measured in anhydrous ethanol. Based on the UV absorption energy (wavenumber) of 3,4'-disubstituted stilbenes, the excited-state substituent constants sCCmex of meta-substituent were determined by means of curve-fitting. The availability of sCCmex was confirmed by the good correlation with the UV absorption energy of 3,4'-disubstituted stilbenes and 4,4'-disubstituted stilbenes. Further, using the obtained constants sCCmex and the correlation equation, we calculated the UV wavenumbers of 3,3'-disubstituted stilbenes, and the calculated wavenumbers are in good agreement with the experimental values. These results verified that the excited-state substituent constants sCCmex of meta-substituent are reliable parameter to scale the effect of meta-substituent on the UV absorption energy. Copyright (c) 2012 John Wiley & Sons, Ltd.