Chemiluminescence and Electroluminescence

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. 

A review of chemiluminescent and bioluminescent methods in analytical chemistry has been given by Kricka and Thorpe. A two-phase flow cell for chemiluminescence and bioluminescencc has been designed by Mullin and Seitz. The chemiluminescence mechanisms of cyclic hydrazides, such as luminol, have been extensively analysed. " Fluorescence quantum yields of some phenyl and phenylethynyl aromatic compounds in peroxylate systems have been determined in benzene. Excited triplet states from dismutation of geminate alkoxyl radical pairs are involved in chemiluminescence from hyponitrite esters. Ruorophor-labelled compounds can be determined by a method based on peroxyoxalate-induced chemiluminescence. Fluorescence and phosphorescence spectra of firefly have been used to identify the multiplicity of the emitting species. " The chemiluminescence and e.s.r. of plasma-irradiated saccharides and the relationship between lyoluminescence and radical reaction rate constants have also been investigated. Electroluminescence from poly(vinylcarbazole) films has been reported in a series of four... 

Other types of luminescence are defined by the source of the energy that causes the light emission. These include chemiluminescence, bioluminescence, electroluminescence, sonoluminescence, triboluminescence, and thermoluminescence. 

Emitters can be classified in terms of those which emit in the gas phase, the solution phase, or the solid state, and also by mode of excitation, i.e. electroluminescence, thermoluminescence, chemiluminescence, radioluminescence and photoluminescence. We are most concerned with photoluminescent materials, but thermoluminescence and electroluminescence, in both gas and solid phases, are important technologies. 

Hydrogen peroxide is produced by the activity of oxidases and determining its intracellular concentration provides assays of the activity of the corresponding enzyme or of substrates such as glucose. It can be detected with high sensitivity by chemiluminescence or electroluminescence, however only at relatively high pH values. A lanthanide-based analytical procedure was proposed in 2002 by O. Wolfbeis and collaborators,... 

Luminescence covers all emissions of light in the near IR, VIS and near UV spectral regions. The origin of the luminescence can be specified as photoluminescence , electroluminescence , chemiluminescence , or bioluminescence for example. These definitions depend on the mode of formation of the excited molecule which eventually emits the luminescence. 

Refs. [i] Ivey F (1963) Electroluminescence and related effects. Academic Press, New York [ii] Miyata S, Nalwa HS (eds) (1997) Organic electroluminescent materials and devices. Gordon and Breach, Amsterdam [iii] Bard AJ (ed) (2004) Electrogenerated chemiluminescence. Marcel Dekker, New York, p 21 [iv] Ouyang J, Fan FRF, Bard AJ (1989) J Elec-trochem Soc 136 1033... 

The emission properties of a fluorophore in a single nanoaperture have been theoretically studied (41, 46). These calculations do not depend on the excitation mechanism, and are therefore valid for chemiluminescence, electroluminescence, and photoluminescence, making the conclusions relevant to a number of biotechnology applications. 

Electrogenerated chemiluminescence, also known as electroluminescence or electrochemiluminescence, has been studied for many years and extensively reviewed... 

The octahedral Ru complex [Ru(bipy)3] (bipy=2,2 -bipyridyl) exhibits efficient photoluminescence, electroluminescence, and also electrochemically-generated chemiluminescence (quantum yields up to 5-7%) through the reactions shown in Eqs. 2.18a and 2.18b, respectively (excited states are labelled ) [68-70]. These properties have led to a range of studies on polymers with appended polypyridyl and related complexes. 

To date, there have been no data on electroluminescent thin film devices with spirothiophenes available, but BSuerle et al. examined the appUcability of these compounds by electrogenerated chemiluminescence experiments. They found for the quaterthiophene 98 an intense but unstable electrochemiluminescence because of the instabihty of the radical anion. On the other hand, the sexithiophene 99 showed a more intense and more stable electrochemiluminescence. The emission spectra center around 506 nm and 560 nm for 98 and 99, respectively. 

Chemiluminescence can also be produced by electrochemical oxidation or reduction (electrogenerated chemiluminescence). Ruthenium and osmium chelates show the ability to emit light when undergoing an electrochemical process. Based on this phenomenon, an electroluminescence immunoassay has been developed using a ruthenium(II) tris(bipyridyl) chelate as a label. 

The strongly exothermic transfer of electrons between fluorescent organic molecules represents one of the most general mechanisms in chemiluminescence [50, 51]. It can be found in electroluminescence, radical ion annihilation and peroxide decomposition. The basic concept was introduced by Hercules [39] following the general theory of Marcus [52]. The reaction co-ordinate can be roughly indicated by the potential energy curves shown. 

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