Chemiluminescence energy acceptors

Addition of fluorescent energy acceptors such as 9,10-dibromoanthracene substantially increases chemiluminescence intensity by transferring excitation energy (132,133), as is the case with dioxetanes. 

Despite the clear implication of the involvement of intramolecular electron transfer in the chemiluminescence of certain dioxetanes, there have been no clear examples of intermolecular electron exchange luminescence processes with dioxetanes. In a recent note, however, Wilson (1979) reports the observation of catalysis of the chemiluminescence of tetramethoxy-1,2-dioxetane by rubrene and, most surprisingly, by 9,10-dicyanoanthracene. While catalysis by the added fluorescers was not kinetically discernible, a lowering of the activation energy for chemiluminescence was observed. These results were interpreted not in terms of an actual electron transfer with the formation of radical ions, but rather in terms of charge transfer interactions between fluorescer and dioxetane in the collision complex. In any event, these results certainly emphasize the need for caution in considering the fluorescer as a passive energy acceptor in dioxetane chemiluminescence. 

In the case of fluorescence, that is, chemienergized by energy transfer, an energy acceptor is chosen that exhibits efficient fluorescence, for example, polycyclic aromatic hydrocarbons and, particularly, 9,10-disubstituted anthracene derivatives. Consequently, in the presence of such fluorescers (FI), the feeble direct chemiluminescence emission intensity is significantly enhanced. Such a phenomenon is commonly referred to as enhanced chemOuminescence (EC). 

Huang XY, Li L, Qian HF, Dong CQ, Ren CJ (2006). A resonance energy transfer between chemiluminescent donors and luminescent quantum-dots as acceptors (CRET). Angew. Chem. Int. Ed. 45 5140-5143. 

The sensitization of fluorescence of an acceptor molecule is considered a concentration-dependent process. The enhancement of chemiluminescence with the Coumarin C337 content was observed in the range of concentration studied. This result would indicate that energy transfer is a diffusion-controlled process. The requirement for donor and acceptor to diffuse to near or actual physical contact with... 

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