Electroabsorption (Stark effect) spectroscopy of monomeric purine and pyrimidine bases

Electronic charge distribution in individual purine and pyrimidine bases and in their systems is an important parameter useful for characterization of their molecular interactions. This paper describes experiments devoted to determination of changes in dipole moments and polarizabilities of DNA bases which take place on electronic excitation, using the Stark effect in absorption spectra of glassy solutions at low temperature (80-100 K). Dipole moment differences of 2-3 D and polarizability changes about 30-60 Å3 were obtained for electronic transitions corresponding to the ≈260 nm absorption band. The comparison of experimental data on difference dipoles with the results of semiempirical calculations allows for assignment of their directions within molecular structures.