Energy-deficient ECL

The enthalpy of the ECL redox process thus either must be sufficient to populate the Si state energy sufficient ECL , or, if it is not ( energy deficient ECL ) there must exist an alternative mechanism to provide for the Si-energy. 

An example of an energy-deficient system is the 9,10-diphenyl"-anthracene (DPA) and A,A,A, A -tetra"-methyl"-p-phenylene"-diamine (TMPD) ECL system ... 

ECL can also be obtained when the reactants in the redox reaction arise from different parent molecules (so-called mixed systems). The system N,N,N ,N -tetramethyl p-phenylene-diamine/DPA is an example. This is an energy-deficient system. Another very efficient mixed system is that of 9,10-dimethyl-anthracene radical anion (1) and tri-p-tolylaminium perchlorate (2). 

However, the ECL-intensity of energy-deficient systems is increased as paramagnetic quenchers, particularly molecular oxygen, are prevented from reacting with the triplet species leading to ECL by the T-route [3]. 

Triplet quenchers cause a decrease of ECL in energy-deficient systems, and trans-stilbene can be transformed into the cisisomer. This type of quenching is especially efficient when the energy of the triplet state of the primary excited product is ca. 0.2 eV higher than that of trans-stilbene [15]. 

As in energy-deficient systems in ECL, an external magnetic field influences the emission spectrum, as is demonstrated in the Wurster s Blue/4,4 -dimethyl-biphenyl system (Fig. 18). 

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