DOI: 10.1002/cphc.200700216 Confocal Microscopy Imaging of Electrochemiluminescence at Double Band Microelectrode Assemblies: Numerical Solution of the Inverse Optical Problem Christian Amatore,* [a] Alexander Oleinick, [a, b] Oleksiy V. Klymenko, [b] Laurent Thouin, [a] Laurent Servant, [c] and Irina Svir* [b] 1. Introduction Studies of electrochemical processes leading to light emission are of interest at least for two reasons. First, light-emitting electrochemical processes provide a spectroscopic means of probing the molecular aspects of homogeneous and heteroge- neous electron transfer. Second, it has been shown that elec- trochemiluminescence (ECL) [1–8] could lead to the possibility of display and lighting applications in, for example, organic light- emitting diodes (OLEDs). For such devices, the possible asym- metry in the location of the emissive zone has been investigat- ed, and there is a need for the development of original ap- proaches to image in situ, the light field emitted. Recently, [5] we investigated the mapping of light generated in a two-band microelectrode assembly using a confocal microscope; the key idea was to take advantage of the true three-dimensional (3D) optical resolution provided by confocal microscopy obtained by actively suppressing any signal coming from out-of-focus planes using a pinhole in front of the detector. Using such a set-up allows light originating from an in-focus plane to be imaged by the microscope objective as it freely passes the pin- hole, whereas the light coming from out-of-focus planes is largely blocked by the pinhole. With this technique, a signifi- cant improvement in the spatial resolution is obtained: the sampling volume (so called “confocal volume”) lies in the mi- crometric range when the visible light signal is captured. Indeed in ECL, the light sources are dispersed into the solu- tion and emit on their own, so that light may transit through the confocal diaphragm even when the emitting sources are located outside the sampling microscopic volume. Further- more, under the particular circumstances where polished elec- trodes are used, a significant light contribution may be trans- mitted after its attenuated specular reflection from the elec- trode surfaces. In the case of ECL [1–8] generated in a two-band microelectrode assembly [2,4–7] probed with a confocal micro- scope (see Figure 1a), one would expect a direct in situ moni- toring of the distribution of light sources free from significant distortions owing to the high spatial resolution of such micro- scopes. According to theory, [2,4–7] the ECL light intensity distri- bution should exhibit a Gaussian-type shape, with a maximum located over the middle of the interelectrode gap and decreas- ing rapidly and monotonically to the left and right from this central point so as to reach negligible values when—or even before—the scanning point passes above each inner electrode edge. The width of this ECL intensity peak is expected to in- A realistic theoretical model describing the outcome of confocal microscopic imaging of electrochemiluminescence (ECL) light emission is derived for a two parallel band microelectrodes as- sembly operated under steady state. The model takes into ac- count the experimental distortions ensuing from a) the specific finite shape of the sampling volume in confocal microscopy, b) the light arising directly from out-of-focus area but transmitted through the microscope diaphragm or c) transmitted after reflec- tion from the polished platinum band electrodes. The model is based on a detailed optical, physico-mathematical and numerical analysis of the problem at hand, and on simulations of the con- centration distribution of the species giving rise to the ECL gener- ation. Its outcome allows the reconstruction of the real spatial distribution of ECL light emission based on the confocal micro- scopy measurements upon correcting for the effect of experimen- tal distortions using numerical fitting procedure. [a] Prof. C. Amatore, Dr. A. Oleinick, Dr. L. Thouin Ecole Normale SupØrieure, Departement de Chimie UMR CNRS 8640 “PASTEUR’’, 24 rue Lhomond 75231 Paris Cedex 05 (France) Fax: (+ 33)1-4432-3863 E-mail: christian.amatore@ens.fr [b] Dr. A. Oleinick, Dr. O. V. Klymenko, Prof. I. Svir Kharkov National University of Radioelectronics Mathematical and Computer Modelling Laboratory 14 Lenin Avenue, Kharkov, 61166 (Ukraine) Fax: (+ 38)057-702-1013 E-mail: irina.svir@kture.kharkov.ua irina.svir@ens.fr [c] Prof. L. Servant UniversitØ Bordeaux I, Institut des Sciences MolØculaires UMR 5255 CNRS, 351 Cours de la LibØration 33405 Talence (France) 1664 # 2007 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim ChemPhysChem 2007, 8, 1664 – 1676