Issue 44, 2005

Novel distyrylcarbazole derivatives as hole-transporting blue emitters for electroluminescent devices

Abstract

We have synthesized three novel distyrylcarbazole derivatives for use as simultaneously hole-transporting and light-emitting layers in blue light-emitting diodes. Each compound, which contains a rigid carbazole core and two 2,2-diphenylvinyl end groups substituted through either the 3,6- or the 2,7- position, forms films satisfactorily and exhibits a blue emission with its PL maximum in the range 459–470 nm. Photophysical measurements indicate that twisting of the adjacent C–C bonds in the 3,6-position of the carbazole core in dilute solutions causes an efficient nonradiative relaxation to occur, yielding a much smaller quantum yield for fluorescence in 3,6-linked carbazoles. As intense emissions of 2,7-linked carbazoles are observed, such deactivation from an excited-state is inefficient therein. Electrochemical studies revealed that incorporation of the carbazole core increased the HOMO energy effectively; this feature facilitates hole injection. These distyrylcarbazole derivatives are promising bifunctional, blue-emitting, hole-transporting molecules for use in simple double-layer devices of a general structure ITO/emitting layer/TPBI/Mg : Ag, in which TPBI—1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene—serves as a hole-blocking and electron-transporting material. The devices prepared using 2,7-distyrylcarbazole as the emitter produced bright blue emissions having activating voltages below 3.0 V. A DPVTCz-based device attained a luminance efficiency of 3.11 cd A−1 at 5 V, a brightness of 3062 cd m−2, and CIE color coordinates of (0.14, 0.22).

Graphical abstract: Novel distyrylcarbazole derivatives as hole-transporting blue emitters for electroluminescent devices

Supplementary files

Article information

Article type
Paper
Submitted
14 Jul 2005
Accepted
13 Sep 2005
First published
30 Sep 2005

J. Mater. Chem., 2005,15, 4753-4760

Novel distyrylcarbazole derivatives as hole-transporting blue emitters for electroluminescent devices

F. Wu, P. Shih, M. Yuan, A. K. Dixit, C. Shu, Z. Chung and E. W. Diau, J. Mater. Chem., 2005, 15, 4753 DOI: 10.1039/B510035F

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