Blue-Green Electroluminescence in Copolymer Based on Poly(1,4-phenylene ethynylene)

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Abstract
Optical characteristics of poly(2,5-dialkoxy-1,4-phenylene diethynylene- co-2,5-pyridinylene) (ROPPE-Py) were investigated. Intense blue-green electroluminescence (EL) emission was observed in light emitting diode (LED) with Al/ROPPE-Py/indium-tin-oxide (ITO) structure. This result suggests that triple bonds in the main chain are resopnsible for the blue shift and enhancement of EL, due to the shortening the effective conjugation length and effective confinement of excitons or exciton-polarons. However, the effects of triple bonds were suppressed by the introduction of electron-rich moieties in the main chain such as poly(2,5-dialkoxy-1,4-phenylene diethynylene- co-9,10-anthracenylene) (ROPPE-An). Electronic energy structures obtained from optical absorption spectra and cyclicvoltammetry measurements confirmed the effect of the electron-rich moieties, which is due to the delocalization of π-electrons and the enhancement of interchain interactions.