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, holetransporting 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 2,7distyrylcarbazole 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 21 at 5 V, a brightness of 3062 cd m 22 , and CIE color coordinates of (0.14, 0.22).

Highly Efficient Non‐Doped Blue‐Light‐Emitting Diodes Based on an Anthrancene Derivative End‐Capped with Tetraphenylethylene Groups

“…4) through sequential vapor deposition of the materials onto ITO glass under vacuum (3 × 10 -6 Torr); the fabrication and characterization of these EL devices are similar to techniques we have reported previously. [38] Device I was designed as our standard blue-light-emitting device having the following configuration: indium tin oxide (ITO)/4,4′-bis[N-(1-naphthyl)-Nphenylamino] biphenyl (NPB) (30 nm)/(TPVAn) (40 nm)/ 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) (40 nm)/ Mg:Ag (100 nm)/Ag (100 nm). NPB and TPBI were employed as the hole-transporting layer (HTL) and the electron-transporting layer (ETL), respectively.…”

Ambipolar Conductive 2,7‐Carbazole Derivatives for Electroluminescent Devices

“…A comparison is also made between the compounds in this study and compounds with a similar carbon skeleton: 2,7-carbazole derivatives without arylamines, 4,4′-bis(diarylamine)-biphenyl, and 2,7-bis(diarylamino)-9,9-dimethylfluorene. Although compound 7 has a lower solution quantum yield (U = 0.25 in toluene) than 2,7-bis(2,2-diphenylvinyl)-9-isopropyl-9H-carbazole (U = 0.37 in toluene) and 2,7-bis(2,2-diphenylvinyl)-9-tolyl-9H-carbazole (U = 0.51 in toluene), [28] the type I device for 7 has a much better performance than the devices of similar structure for the other two. It is possible that the presence of the two peripheral arylamines in 7 results in a smaller energy gap between the Fermi level of ITO and the HOMO of 7, and in a better balance of carriers mobilities.…”

Excitation Energy Transfer in Organic Materials: From Fundamentals to Optoelectronic Devices

“…Various combinations of hosts and dopants have been studied and examples are summarized in Figure 15. [162][163][164][165][166][167][168][169][170][171][172][173][174][175][176][177][178][179][180] Important factors in selecting a host and a dopant are the overlap of the emission spectrum of the host and the absorption spectrum of the dopant for energy transfer, charge transport properties of the host, and emission color (purity) and fluorescence efficiency of the dopant as well as the stability of the materials.…”