Determinating The Excited-state Substituent σ_CC^ex Of Meta-substituent From3,4-disubstituted Stilbenes

Substituent effect on UV absorption energy of compounds is an interesting field of QSPR researches. Researches showed that the UV absorption energy of compounds can be affected by the type and position of substituents in a narrow range, and knowledge of the correlation between molecular structure and UV absorption energy is helpful to design optical molecules. Therefore, considerable effort has been devoted to studying the correlation between substituent effect and UV absorption energy. Recently, Cao C. et al. proposed a new excited-state substituent parameter σCCex, and recommended it to correlate the UV absorption wavenumbers (νmax) of compounds. Comparing with polar constants (σp,σmb etc.) or radical substituent parameters (σJJ·,σ·Cetc), σCCex is more suitable for the quantitative researches of UV optical properties of compounds. Then, he and co-workers use this excited-state substituent parameter to study successfully the UV absorption energy of compounds, such as1,4-disubstituted benzenes,4,4’-disubstituted stilbenes and4,4’-disubstituted N-benzylidenebenzenamines, etc.Cao’s reported work focus mainly on the νmax of compounds with para-substituent varied, due to the lack of the σCCex of meta-substituent. Therefore, it is meaningful to get the excited-state substituent σCCex(m) of meta-substituent for extending the application of the σCCex in the optical materials.In this work, a set of trans-3,4’-disubstituted stilbenes are synthesized, their structures are determined with IR and1H NMR, and corresponding UV absorption wavelengths (λmax) are measured in anhydrous ethanol. With a series of UV absorption wavenumbers of3,4’-disubstituted stilbenes, by structuring suitable equation and making curve-fitting in MATLAB to obtain eight correlation equations and corresponding values of σCCex(m).Then, σCCex(m) is recommended to correlate the UV energy of86kinds of stilbenes including3,4’-disubstituted stilbenes and 4,4’-disubstituted stilbenes, the obtained equation shows an excellent correlation. The result indicates that σCCex(m) can successfully correlate with the UV absorption energy of meta-substituted stilbenes.In addition, using the correlation equation with σCCex(m) to calculate the UV absorption wavenumbers of newly-synthesized3,3’-disubstituted stilbenes, the plot shows that the calculated values are in good agreement with the experimental values.