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.
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