Synthesis, cyclic voltammetric studies, and electrogenerated chemiluminescence of a new donor-acceptor molecule: 3,7-[bis[4-phenyl-2-quinolyl]]-10-methylphenothiazine

We report here the synthesis of a novel compound that contains two electron -accepting phenylquinoline groups covalently attached to the 3,7-positions of a light-emitting electron donor, 10-methylphenothiazine. The optimized g eometry as determined from semiempirical MNDO calculations shows that the p henylquinoline moieties are twisted similar to 77.5 degrees from the phenot hiazine central ring. As a result, no molecular orbital overlap between the se two groups exists, inhibiting any delocalization of the charge upon elec trochemical oxidation or reduction. Comparison between cyclic voltammograms obtained of this compound as well as of the individual compounds, 10-methy lphenothiazine and 2-phenylquinonine, did indeed show no change in the elec trochemical behavior of these two groups upon the covalent attachment, conf irming the results obtained from the semiempirical calculations. A shift to lower energy wavelengths of phenothiazine was observed upon the addition o f the electron-deficient phenylquinoline moieties. Overall, this unique geo metry allows us to electrochemically produce the stable radical ions needed to generate the light-emitting excited state of phenothiazine within a pot ential window not obtainable with just 10-methylphenothiazine. ECL spectrum produced by annihilation between the radical cation of phenothiazine and t he radical anion of phenylquinoline shows good agreement with the fluoresce nce emission of 10-methylphenothiazine.