Electrochemistry and Electrogenerated Chemiluminescence of (dppy)BTPAsa Bipolar, Solvatochromic Boron Compound

We investigated the electrochemistry and electrogenerated chemiluminescence (ECL) of the highly solvatochromic emitter (dppy)BTPA, which consists of a 2,6-diphenolpyridine (dppy) boron moiety linked to a triphenylamine moiety (BTPA). At 0.72 V versus a saturated calomel electrode (SCE), in pure MeCN, the triphenylamine moiety of (dppy)BTPA is oxidized to form a stable radical cation. At -1.72 V versus SCE, in pure MeCN, the diphenolpyridine boron moiety is reduced to form a radical anion that dimerizes with kf ) 1.8 × 104 M-1 s-1. Annihilation between the two radical ions generates an ECL spectrum in the same region as the photoluminescence (PL) spectrum, but with an additional shoulder at a longer wavelength. Both the PL and the ECL exhibit a strong bathochromic shift and quenching as solvent polarizability increases (for different solvents or for mixtures of MeCN and benzene). This effect is enhanced by the presence of the supporting electrolyte, Bu4NClO4.