EFFECTS OF SOLVENT AND IONIC-STRENGTH ON THE ELECTROCHEMILUMINESCENCEOF 9,10-DIPHENYLANTHRACENE

The steady-state electrochemiluminescence (ECL) from the annihilation reaction of the radical anion and cation of 9,10-diphenylanthracene (D PA) was examined at a double-band microelectrode in acetonitrile, prop ylene carbonate, 1,2-dimethoxyethane, acetonitrile-toluene, and propyl ene carbonate-toluene mixtures, all containing 0.1 M tetrabutylammoniu m hexafluorophosphate. In each solvent, the ECL efficiency was found t o be greatest at large DPA concentration due to the effect of competin g side reactions. The ECL efficiencies extrapolated to infinite DPA co ncentrations were found to be solution dependent and were correlated t o the separation of the half-wave potentials for the generation of the radical anion and cation. In acetonitrile-toluene mixtures, the ECL e fficiency was also found to increase as the ionic strength of the solu tion was decreased. In 50:50 acetonitrile-toluene the ECL efficiency i ncreased from 6.3 to 8.8% as the concentration of supporting electroly te was lowered from 100 to 1 mM. This increase was found to correlate with changes in the rate constant for dissociation of the reaction enc ounter complex as the ionic strength of the solution was lowered.