The changes of the electronic structure of molecules in the columnar discotic liquid crystal 2,3,6,7,10,11-hexaheptyloxytriphenylene were studied by using the polarized electronic absorption measurements. The detailed analysis of the spectral data showed that a mixing of electronic excitations is present in discotics and that it affects the measured values of the optical density and the oscillator strength of the electronic absorption bands. The changes in the oscillator strength of the long-wavelength electronic transition and the conformation of the aromatic molecular cores have been discovered experimentally upon the isotropic-columnar phase transition.