Chemiluminescence electrogenerated

Electrogenerated Chemiluminescence. In electron transfer processes light can participate as a reactant (Eq. (15)), or it can be generated as a product (Eq. (16)) [16]  

In both cases, of course, the involvement of light takes place via the formation of electronically excited states. 

The processes described by Eq. (16) are called chemiluminescence processes. A special case of chemiluminescence is that in which one or both of the redox reactants of Eq. (16a) are produced by electrochemical methods (electrochemiluminescence, eel) [116]. 

Studies in these fields [16] have shown that transition metal complexes may play the role of sensitizers both in the photoinduced processes schematized by Eq. 15 and in the light generating processes schematized by Eq. (16). In the first case, the complex can be called a light absorption sensitizer (LAS), while in the second case it can be called a light emission sensitizer (LES). High luminescence efficiency is a useful property for a LAS, and a necessary requirement for a LES. 

Most of the electrochemiluminescence investigations involving transition metal complexes have been performed on Ru(bpy) + or its derivates [15,16]. Because of its strong luminescence [117], stability towards photodecomposition (in the absence of oxygen and of halogenated solvents [117]), and reversible reduction behavior [118] Pt(tpy)2 is also a good candidate for eel experiments. 

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Nowadays all over the world considerable attention is focused on development of chemical sensors for the detection of various organic compounds in solutions and gas phase. One of the possible sensor types for organic compounds in solutions detection is optochemotronic sensor - device of liquid-phase optoelectronics that utilize effect of electrogenerated chemiluminescence. In order to enhance selectivity and broaden the range of detected substances the modification of working electrode of optochemotronic cell with organic films is used. Composition and deposition technique of modifying films considerably influence on electrochemical and physical processes in the sensor. 

Electrogenerated chemiluminescence (ECL) has proved to be useful for analytical applications including organic analysis, ECL-based immunosensors, DNA probe assays, and enzymatic biosensors. In the last few years, the electrochemistry and ECL of compound semiconductor nanocrystallites have attracted much attention due to their potential applications in analytical chemistry (ECL sensors). 

Zou G, Ju H (2004) Electrogenerated chemiluminescence from a CdSe nanocrystal film and its sensing application in aqueous solution. Anal Chem 76 6871-6876... 

Fang YM, Sun JJ, Wu AH, Su XL, Chen GN (2009) Catalytic electrogenerated chemiluminescence and nitrate reduction at CdS nanotubes modified glassy carbon electrode. Langmuir 25 555-560... 

Zhou B, Liu B, Jiang LP, Zhu JJ (2007) Ultrasonic-assisted size-controllable synthesis of Bi2Te3 nanoflakes with electrogenerated chemiluminescence. Ultrason Sonochem 14 229-234... 

Yang X, Jiang X, Zhao C, Chen R, Qin P, Sun L (2006) Donor-acceptor molecules containing thiophene chromophore synthesis, spectroscopic study and electrogenerated chemiluminescence. Tetrahedron Lett 47 4961 -964... 

The current trends toward miniaturization and the need of massively parallel measurements led to the development of biochips. In this area, biocatalyzed and electrogenerated chemiluminescence reactions appear attractive and represent an alternative to fluorescence detection which is still widespread used despite the numerous problems of quantitative measurements and interference fluorescence emission. 

As it was indicated above, the main optical interrogation methods include absorbance, reflectance, fluorescence, chemiluminescence (CL), or electrogenerated chemiluminescence (ECL)9,41"42. 

H. Qi and C. Zhang, Homogeneous electrogenerated chemiluminescence immunoassay for the determination of digoxin. Anal. Chim. Acta 501, 31-35 (2004). 

There is experimental evidence that triplet states indeed play an important role in radical ion reactions. The formation of excimers has been suggested on the basis of chemiluminescence emission spectra, e.g. in the case of N-phenylcarbazole 15> and in some other experiments 18>. Other authors 19>20> have observed that the excimer fluorescence reported is probably produced by decomposition products of the radical ions or other impurities, as is very probably the so-called preannihilation chemiluminescence which occurs in electrogenerated chemiluminescence (see 21>). 

In electrogenerated chemiluminescence, light emission occurs not on the electrode surface but in the solution. Oxygen has to be excluded 5>. In the usual form a one-electrode technique is applied the potential of the electrode is changed periodically. At cathodic potential the radical anion is produced, at anodic potential the radical cation. These two radical ions react in the diffusion layer near the electrode surface the electron transfer from the radical anion to the radical cation causes the light emission 5>2°). 

The intensity of electrogenerated chemiluminescence is influenced by an external magnetic field 148,150,152)... 

Chemiluminescence also occurs during electrolysis of mixtures of DPACI2 99 and rubrene or perylene In the case of rubrene the chemiluminescence matches the fluorescence of the latter at the reduction potential of rubrene radical anion formation ( — 1.4 V) at —1.9 V, the reduction potential of DPA radical anion, a mixed emission is observed consisting of rubrene and DPA fluorescence. Similar results were obtained with the dibromide 100 and DPA and/or rubrene. An energy-transfer mechanism from excited DPA to rubrene could not be detected under the reaction conditions (see also 154>). There seems to be no explanation yet as to why, in mixtures of halides like DPACI2 and aromatic hydrocarbons, electrogenerated chemiluminescence always stems from that hydrocarbon which is most easily reduced. A great number of aryl and alkyl halides is reported to exhibit this type of rather efficient chemiluminescence 155>. 

Hetero-excimer chemiluminescence yields were measured by A. Weller and K. Zachariasse 214) the system dimethylanthracene anion radical/tri-p-tolylaminium perchlorate in tetrahydrofurane exhibits particularly strong chemiluminescence with quantum yields of about 7.5 x 10-2 215>. A. J. Bard and coworkers 216> very thoroughly investigated the influence of several parameters, e.g. supporting electrolyte concentration, on the efficiency of electrogenerated chemiluminescence. 

Electrochemiluminescence Emission occurring in solution, from an electronically excited state produced by high-energy electron transfer reactions Electrogenerated chemiluminescence Emission produced at an electrode surface Oxyluminescence Emission from polymers caused by oxidative processes (presence of oxygen is required)... 

This discussion will be confined to strictly chemical reactions and will not include electrogenerated chemiluminescence. 

Electrogenerated chemiluminescence (ECL) is the process whereby a chemiluminescence emission is produced directly, or indirectly, as a result of electrochemical reactions. It is also commonly known as electrochemiluminescence and electroluminescence. In general, electrically generated reactants diffuse from one or more electrodes, and undergo high-energy electron transfer reactions either with one another or with chemicals in the bulk solution. This process yields excited-state molecules, which produce a chemiluminescent emission in the vicinity of the electrode surface. 

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