Thiophene materials for unconventional and advanced electroluminescent applications

7 Thiophene materials for unconventional and advanced electroluminescent applications 

Among other unconventional applications of PTs as light-emitting materials, it is necessary to mention microcavity LEDs prepared with PTs 30 and 24 [180] and nano-LEDs which were fabricated with a patterned contact structure and PT 30 blended in a PMMA matrix and shown to emit from 50-200 nm phase-separated domains [181]. 

An interesting application of the self-assembly properties of the oligomer 135 in LEDs was reported recently. This compound readily forms nanowires of diameter 10-100 nm [186]. Uniformly distributed 

One of the first reports of thiophene-based OLETs described red light emission from the film of oligomer 136, which can be controlled by the applied gate voltage [188]. The low electron mobility, a common drawback of polythiophenes, shifts the hole-electron recombination area close to the cathode, where the excitons can be quenched by the metal. As a result, the observed EL efficiency was rather low. 

Yamashita and co-workers introduced electron-deficient benzothiadiazole and related units into thiophene oligomers 137a-c, which allowed for ambipolar transport and thus yielded more efficient OLETs [189]. The devices with oligothiophene 137a showed intense red emission at 661 mn, a high electron mobility of 0.04-0.19 cm V s and an on/off ratio of 10 -10 . WeU-balanced ambipolar transport was also demonstrated for layered-structure OLETs using an a,(o-dihexyl-quaterthiophene oligomer (as p-type semiconductor) and A,A -ditridecylperylene-3,4,9,10-tetracarboxylic diimide [190] (see also Chapter 16). 

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