Small molecular guest dye emitters

These compounds provided the source material for the first blue OLEDs.72 However, these devices were short-lived. Yet devices fabricated with improved blue-emitting amino oxadiazole fluorene did exhibit greater efficiency and stability,9 although their performance was still inferior to that of polyfluorene-based PLEDs (see below). 

These generally blue-emitting materials were studied extensively by Hosokawa and coworkers.73 Among them, 4,4 -bis(2,2 -diphenylvinyl)-l,l -biphenyl (DPVBi) (see Figs. 1.1 and 1.3) has proven to be a particularly promising material for blue OLEDs. The degradation of OLEDs based on this material is apparently due to its crystallization, which results from its relatively low Tg 64° C. Indeed, the related spiro-DPVBi, with Tg 100° C, yields considerably more stable devices.70 

Other widely-used electron-transporting materials include 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-l,3,4-oxadiazole (butyl-PBD), which is essentially nonemis-sive and often introduced between the cathode and the emitting layer precisely for that reason, and 3-(4-Biphenylyl)-5-(4-tert-butylphenyl) l-phenyl-l,2,4-triazole (TAZ-1).6,74 

4-dicyanomethylene-6-(p-dimethylaminostyryl)-2-methyl-4H-pyran (DCM) and 3-(2-benzothiazolyl)-7-diethylaminocoumarin (C540) 

As mentioned above, rubrene is a prominent red-emitting molecule, as its PL quantum yield is 100% in dilute solution, but that emission is strongly suppressed in the solid state due to fission of the l1 to two triplets. Hence, it yields bright red OLEDs when incorporated as a guest in hosts such as TPD.69 

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