AbstractThere are mainly three kinds of substituent electronic effects derived from aromatic rings: ground‐state, radical‐state, and excited‐state effect. However, excited‐state substituent constants of ortho‐substituents have not been reported up to now. In this paper, a method for extracting the excited‐state substituent constant of ortho‐substituents was provided. Forty‐nine 2,4’‐disubstituted stilbenes were synthesized, and the ultraviolet absorption spectra of the synthesized stilbenes were determined. The values of ortho‐substituents involving MeO, Me, F, Cl, Br, CF3, and CN were quantified by curve fitting method based on the measured ultraviolet absorption spectra. The rationality of the values were further experimentally confirmed by measuring the ultraviolet absorption spectra of other 10 samples of synthesized 2,3’‐disubstituted stilbenes and by applying these values in regression analysis of the ultraviolet absorption spectra for a complicated data set of 284 organic compounds.