Green emitters, chemical structures

Because luciferyl adenylate emitted a red chemiluminescence in the presence of base, coinciding with the red fluorescence of 5,5-dimethyloxylucferin, the keto-form monoanion Cl in its excited state is considered to be the emitter of the red light. Thus, the emitter of the yellow-green light is probably the enol-form dianion C2 in its excited state, provided that the enolization takes place within the life-time of the excited state. Although the evidence had not been conclusive, especially on the chemical structures of the light emitters that emit two different colors, the mechanism shown in Fig. 1.12 was widely believed and cited until about 1990. 

SCHEME 3.1 Chemical structures of anthracene, a hole transport triarylamine, an electron transport and a green emitter Alq3, and a phosphorescent dopant PtOEP. 

The optical properties can be tuned by variations of the chromophores (e.g. type of side-chains or length of chromophore). The alkyl- and alkoxy-substituted polymers emit in the blue-green range of the visible spectrum with high photoluminescence quantum yields (0.4-0.8 in solution), while yellow or red emission is obtained by a further modification of the chemical structure of the chromophores. For example, cyano substitution on the vinylene moiety yields an orange emitter. 

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