The characteristic feature of bichromophore is the fact, that along with the excited states localized on separate bichromophore fragments, there are states, delocalized on the whole molecule, including wave functions of atoms of the donor and acceptor fragments. In bichromophore the different from F rster mechanism for intramolecular transfer energy may be realized. Recognizing the mixed character of the electronic states of the test bichromophores and treating them as a unified molecular system we have assumed the following scheme for photophysical processes in the bichromophore molecules. Thus the energy transfer from the donor fragment to the acceptor may be interpreted as the internal conversion process. The rate constants k ic increase by an order of magnitude due to fluorination the donor fragment.
Bold lines show mixed states.
Bold lines show mixed states. Bold lines show mixed states. Fluorination of the energy donor decreases the energies of the mixed states and, consequently, these states come to play a more important role in the photoprocesses involved in the bichromophores. The fluorescence yield of this bichromophore does not change as compared to that of UC 17. In our opinion this channel is able to compete with the process of the internal conversion and it is responsible for the reduced fluorescence efficiency.