Abstract
Electrogenerated chemiluminescence of 10-methylphenothiazine (10MP) is demonstrated using the radical cation of 10MP and a variety of radical anions which provided a range of energies from insufficient to form the triplet state of 10MP through sufficient to form the first excited singlet state. When naphthalene was used as the radical anion, the reaction was sufficiently energetic to populate the singlet state of 10MP and the expected spectrum was obtained. When benzophenone was used as the radical anion, the sufficiency of the reaction energy depended upon the dielectric constant of the solvent. At high values (ε = 20) the reaction was energy insufficient and no emission was observed, but at low values (ε = 7) the reaction was sufficiently energetic to populate the triplet and emission was observed at wavelengths significantly longer than that of the excited singlet. Identical emission from 10MP was formed with the radical anion of 1,6-diphenyl-1,3,5-hexatriene. The emission results were inconsistent with an exciplex but the available energetics from the radical ion reactions and the susceptibility to quenching suggest an excited triplet state of 10MP. Efforts to corroborate this state photochemically were inconclusive since phosphorescence could only be obtained at 77 K and the spectrum was not identical to the room-temperature electrogenerated chemiluminescence. When three different anthracene derivatives were employed (9,10-diphenylanthracene, 9-phenylanthracene, and 9,-10-dimethylanthracene) as the radical anion, the triplet-like emission was observed from 10MP and also singlet emission from the anthracenes, resulting in a bright, white or pale blue light. This mixed emission has been observed in solid-state systems, but never before in solution ECL.