The electrogenerated chemiluminescence (ECL) of Ru(bpy)3 2+ and tripropylamine, tributylamine, triethylamine, trimethylamine, or sodium oxalate encapsulated within sol-gel-derived silica monoliths have been investigated using an immobilized ultramicroelectrode assembly. The major purpose of this study was to investigate the role of the reductant on the magnitude and stability of the ECL in this solid host matrix. For gel-entrapped Ru(bpy)3 2-/tertiary amines, the shape and intensity of the ECL-potential curves were highly dependent on scan rate. At 10 mV/s, the ECL intensity was ca. 6-fold higher relative to that observed at 500 mV/s. When the ECL acquired at low scan rates was normalized by that obtained in solution under similar conditions, a value of 0.03-0.06 was obtained. In direct contrast, the ECL of the Ru(bpy)3 2+-oxalate system showed little dependence on scan rate, and the ECL was ca. 65-75% of that measured in solution. These differences can be attributed to differences in rotational and translational mobility between the reductants (amines vs oxalate) trapped in this porous solid host For both systems, the ECL was found to be stable upon continuous oxidation or upon drying the gels in a high-humidity environment for over 10 days.
A novel approach for the electrogeneration of stable light emission in a solid host structure under room conditions is described. In this work, the chemiluminescent precursors, ruthenium(II) tris(bipyridine) (Ru(bpy) 3 2+ ) and tripropylamine (TPA), were trapped in a porous silicate host matrix along with an electrode assembly. When the electrode potential was scanned or stepped to a potential sufficient to oxidize gel-entrapped TPA and Ru(bpy) 3 2+ , electrochemiluminescence (ECL) was observed. The solid-state ECL spectrum was identical to the fluorescence spectrum of gel-entrapped Ru(bpy) 3 2+ . The intensity of the emission depends on the amount of TPA and Ru(bpy) 3 2+ in the gel as well as the size of the electrode. When an ultramicroelectrode (microband or microdisk) was used to generate the ECL, the resultant emission was found to be remarkably stable. Little drop in intensity was observed upon continuous application of ca. 1.2 V for 2-12 h. In direct contrast, the ECL dropped significantly at a large electrode (e.g., r ) 1.1 mm) in a relatively short period of time. The improved stability of the ECL at ultramicroelectrodes can be attributed not only to their small size, which results in a decreased consumption of TPA, but also to the steady-state flux of reagents to the electrode surface.
Stable solid-state electrogenerated chemiluminescence has been achieved by trapping the chemiluminescent precursors, ruthenium(ii) tris(bipyridine) and tripropylamine, in a porous silicate host matrix prepared by the sol-gel process and exciting them electrochemically via an immobilized microelectrode assembly.
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