Investigations on spectra and orientation of dipole moments of uracil and thymine by electrochromism

The direction of the ground stale dipole moment with respect to the transition moment to the lowest excited singlet state as well as the dipole moment in this excited state could be determined from the influence of an electric field on the light absorption of uracil and thymine in solution. By making use of results on the orientation of the transition moment in the molecular framework, the orientation of the ground‐and excited‐state dipole moments can also be fixed and compared with theoretical predictions. The agreement is fair. The measurements show that in both compounds a weak band is hidden under the longest‐wavelength absorption band.