Electro-Chemiluminescence Reactions

The application of the Woodward-Hoffmann theory 22> of electro-cyclic reactions to chemiluminescence has proved a very useful and productive approach, suggested independently by E. H. White and M. J. C. Harding 23>, F. Me Capra, D. G. Richardson, and Y. C. Chang u> 24>, and M. M. Rauhut and coworkers 25>. 

The simplest systems where electron-transfer chemiluminescence occurs on interaction of radical ions are radical-anion and radical-cation recombination reactions in which the radical ions are produced from the same aromatic hydrocarbon (see D, p. 128) by electrolysis this type of chemiluminescence is also called electro-chemiluminescence. The systems consisting of e.g. a radical anion of an aromatic hydrocarbon and some other electron acceptor such as Wurster s red are more complicated. Recent investigations have concentrated mainly on the energetic requirements for light production and on the primary excited species. 

Furthermore, although in this chapter we will mainly deal with photoluminescence (i.e., luminescence arising from an excited state created by the absorption of light), it is important to underline at this point that (electro-)chemiluminescence (luminescence arising from an excited state generated by an (electro-)chemical reaction), has made analytical potentials even stronger. 

The electrogenerated radical anions of aromatic hydrocarbons, e.g. DPA, rubrene, fluorene, can also act as reductants towards electro-chemically obtained radical cations which are derivatives of other aromatic compounds such as N,N-dimethyl-/>-phenylenediamine (Wurster s red) 150> (see Section VIII. B.). When a mixture of DPA and a halide such as 99 (DPACI2) or 100 is electrolysed, a bright chemiluminescence is observed the quantum yields are about two orders of magnitude higher than that of the DPA radical anion-radical cation reaction 153>. 

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