Fluorescence quenching between strong pi-electron donor-acceptors of carbazolocarbazole and tetranitrofluorenone leading to electron transfer

Singlet energies and fluorescence quantum yields of synthesized dihydrocarbazolocarbazole, 1, dimethylcarbazolocarbazole, 2, dibenzylcarbazolocarbazole, 3, were measured to be between 76.5-74.3 kcal/mol and 0.07-0.02 respectively. A Stern-Volmer plot of fluorescence quenching of dihydrocarbazolocarbazole, 1, with 2,4,5,7-tetranitrofluorenone, 4, has given a rate constant of quenching of k(q) = 7.4 x 10(12) M(-1)s(-1). The free energies of the exothermic electron transfer reaction are calculated to be -33.6 kcal/mol for dihydrocarbazolocarbazole, 1, and -26.8 kcal/mol for dimethylcarbazolocarbazole, 2. High values for the rate of fluorescence quenching and the free energies are the evidence for an electron transfer process between these strong pi-electron donor-acceptor complexed molecules.