ANODIC COUPLING OF DIPHENYLBENZO[K] FLUORANTHENE - MECHANISTIC AND KINETIC-STUDIES UTILIZING CYCLIC VOLTAMMETRY AND ELECTROGENERATED CHEMILUMINESCENCE

Upon oxidation at a platinum electrode, (7,12-diphenyl)benzo[k]fluoran thene (1) undergoes intermolecular dehydrogenative coupling to form bi s-4,4'-(7, 12-diphenyl)benzo[k]fluoranthene (2). Further oxidation of this product results in a much slower intramolecular coupling reaction that yields etraphenyl)}diindeno[1,2,3-cd:1',2',3'-lm]perylene (3). 2 can be synthesized via bulk electrolysis of 1 and also by the chemica l coupling of 4-bromo-7,12-diphenylbenzo[k]fluoranthene (4) with a nic kel catalyst. Compounds 1-3 are capable of electrogenerated chemilumin escence (ECL), and their coupling reactions have been detected and fol lowed using this technique. Cyclic voltammograms of 1 have been digita lly simulated to provide mechanistic and kinetic insight into the init ial intermolecular oxidative coupling reaction. Evidence supports an E C(2)EE mechanism, in which the coupling of radical cations of 1 is the rate-limiting step. A second-order rate constant of k = 7500 M(-1) s( -1) has been determined for the dimerization process by fitting experi mental data to theoretical working curves.