Electrogenerated Chemiluminescence XI. Electrochemistry and Electrogenerated Chemiluminescence in Scintillator Dye Melts

Melts of sc int i l la tor compounds which are solid at room tempera ture , such as 2 ,5-diphenyloxazole (PPO) and 2 ,5-diphenyloxadiazole (PPD) conta ining severa l qua te rna ry ammonium salts as suppor t ing electrolytes , were examined as solvents for e lec t rochemical and e lec t rogenera ted chemi luminescence (ECL) studies. Al though the resistance of these solutions was high, cyclic vo l t ammet ry of 9 ,10-diphenylanthracene and rubrene in PPO showed the product ion of s table radica l anions and cat ions for both compounds, and the ECL emission was essent ia l ly the same as the fluorescence emission of these compounds in PPO. ECL of rubrene was also observed in mol ten phenanthrene, PPD, th ianthrene , and p te rpheny l , as wel l as in mix tu res of PPO wi th 1or 2 -methy lnaphtha lene . There has been much interest in recent years in the appl icat ion of nonaqueous solvents in e lec t rochemis t ry (1). Many of these solvents have the advan tage of r a the r wide potent ia l l imits before the solvent i tself or the suppor t ing e lec t ro ly te undergoes reduct ion or oxidat ion at an iner t electrode; these solvents are also often less l ike ly to react wi th e lec t rogenera ted species. Most solvents employed are l iquid at room t empera tu re [e.g., N,N-d ime thy l fo rmamide (DMF), acetoni t r i le (ACN)] while severa l l iquefy at low tempera tu res (SO2, NH3). Only a few studies of organic systems have employed as solvents compounds which are solid at room tempera tu re ; these include d imethylsu l fone (rap 127~ (1,2) , mol ten e thy lammonium chloride (3), and the A1CI~-KC1 mol ten salt sys tem (4). Recent studies involving aprot ic solvents include e lec t rogene ra ted chemiluminescence (ECL) of aromat ic compounds, whe re e lec t rogenera ted radica l anions (R T)