Electrochemiluminescence system emission

Most electrochemiluminescent systems rapidly decay with time (cf. Fig. 6), even when strenuous efforts are made to exclude impurities and when applied voltages are minimal. Some unusual temporary increases in emission intensity with time have also been noted.63 These have not yet been satisfactorily explained. 

By media variables we mean the solvent, electrolyte, and electrodes employed in electrochemical generation of excited states. The roles which these play in the emissive process have not been sufficiently investigated. The combination of A vV-dimethylformamide, or acetonitrile, tetra-n-butylammonium perchlorate and platinum have been most commonly reported because they have been found empirically to function well. Despite various inadequacies of these systems, however, relatively little has been done to find and develop improved conditions under which emission could be seen and studied. Electrochemiluminescence emission has also been observed in dimethyl sulfite, propylene carbonate, 1,2-dimethoxyethane, trimethylacetonitrile, and benzonitrile.17 Recently the last of these has proven very useful for stabilizing the rubrene cation radical.65,66 Other electrolytes that have been tried are tetraethylam-monium bromide and perchlorate1 and tetra-n-butylammonium bromide and iodide.5 Emission has also been observed with gold,4 mercury,5 and transparent tin oxide electrodes,9 but few studies have yet been made1 as to the effects of electrode construction and orientation on the emission character. 

The influence of impurities on electrochemiluminescence emission behavior has been difficult to ascertain. The best quantum yield of emission under annihilative conditions thus far achieved is about 1 %.63 The preannihilative emission is one to two orders of magnitude less intense.11 As the concentration of fluorescer in emitting systems is ca. 10 3M, as low a concentration of impurity as 10 7M may be responsible for the entire emission. Investigations thus far conducted have tacitly accepted such impurity levels in these solutions and have concentrated on inferring their action by observing the effects of additives... 

The emission intensity of electrochemiluminescence has been measured as a function of a number of system variables. These include... 

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