Electrochemistry, Electrogenerated Chemiluminescence, and Electropolymerization of Oligothienyl-BODIPY Derivatives

Abstract

We report the electrochemistry, electrogenerated chemiluminescence, and electropolymerization of a series of oligothienyl boron dipyrromethene (BODIPY) compounds in acetonitrile (MeCN) solution. For each compound, 1-5, the first oxidation wave was attributed to the first one electron (1e) oxidation of the BODIPY core. For 1, the second oxidation wave at Ep = 0.8V vs. the ferrocene/ferrocenium couple (Cp2Fc0/+), attributed to the oxidation of the first thienyl substituent, is irreversible. In the case of 2-5, the oxidation of the first thiophene is reversible, suggesting stability of the radical dication. In each case of 1-5, the first BODIPY reduction peak was irreversible due to the instability of the radical anion, which is due to the lack of complete substitution in the β’ and meso positions on the indacene periphery. ECL was detected for each compound; however, only 1 displayed enough light capable of generating an ECL spectrum (λECL = 674.5nm) with the aid of a co-reactant, tripropylamine (TPrA). This wavelength is bathochromically shifted compared to the fluorescence spectrum of the compound (λFL = 654nm). Compounds 1 and 2 showed evidence of electropolymerization. Each of these polymers, when deposited on a glassy carbon electrode and put into a fresh solution of MeCN and supporting electrolyte, showed peak currents increasing linearly with scan rate, which is indicative of an adsorption process on the electrode surface. Further, the electropolymerization product of 1 showed stable ECL in MeCN and produced a similar spectrum as observed with the free molecules. The polymer also produced ECL in water, which quickly decayed to zero due to the aqueous environment.