Theoretical study of tautomeric structures and fluorescence spectra of Hoechst 33258

Various tautomers of Hoechst 33258 have been studied in this work, and their UV absorption and fluorescence spectra calculated theoretically. These have been compared with the experimental spectra and the likely species in the ground and excited states have been discussed. The results indicate that proton transfer takes place in the excited state, yielding a highly conjugated species that fluoresces at long wavelengths. The findings explain the two kinds of fluorescence observed in DNA-bound Hoechst 33258 in terms of two binding modes involving different tautomers. (C) 2002 Elsevier Science B.V. All rights reserved.