Electrogenerated chemiluminescence of 9,10-substituted Benzo(k)fluoranthenes and of surface bound Ru(bpy)₃²⁺ on platinum silicide

Abstract

Three aspects of electrogenerated chemiluminescence (ECL) were studied. First, the effect of substitution on the photochemical, electrochemical and ECL properties of 7,12-diphenylbenzo[k]fluoranthene was investigated. Upon the addition of methyl groups, both of which are weak electron donors, and the subsequent addition of sulfone, an electron withdrawing group, onto the 9,10 positions of 7,12-diphenylbenzo[k]fluoranthene, only small changes in the photophysical and electrochemical properties were observed. This was not the case for the rate of radical cation-radical cation coupling or dimerization, which occurs during the electrochemical oxidation of these compounds. Upon addition of the electron donating methyl groups, the rate decreased to 195 M -1 while the addition of the electron withdrawing sulfone group increased the rate to 20,000 M -1 . As a result, the amount of dimer emission that was observed in the ECL spectrum of these two benzo[k]fluoranthene derivatives correlated directly with these rates. Second, by using these differences in the rate of dimerization, one reaction that is responsible for the formation of the emitting excited state upon electrochemical reduction of polycyclic aromatic hydrocarbons in the presence of the ECL coreactant, peroxydisulfate, was determined. Specifically, the formation of the radical cation through the homogeneous oxidation of the neutral hydrocarbon by sulfate radical anions was confirmed by emission from the dimer during electrochemical reduction in the presence of this coreactant. Therefore, emission under these electrochemical conditions most likely occurs through a radical ion annihilation reaction between the electrochemically generated radical anion and the chemically generated radical cation. Finally, platinum silicide (PtSi) was evaluated as a potential platform for ECL based assays. Through cyclic voltammetry and scanning electrochemical microscopy (SECM), the oxide layer on PtSi, which was shown to be stable upon extensive potential cycling, did not interfere with heterogeneous rate of electrochemical oxidation of the ECL label, Ru(bpy)3 2+. Upon modifying the oxidized PtSi surface with an aminosilane, Ru(bpy)3 2+, either directly or as a label bound to DNA, was chemically attached to the surface. In both cases, ECL of this bound label was detected showing the viability of using this surface as a platform for chemical and biological assays involving ECL detection.