Solution‐Processible Phosphorescent Blue Dendrimers Based on Biphenyl‐Dendrons and Fac‐tris(phenyltriazolyl)iridium(III) Cores

Abstract

Solution‐processible saturated blue phosphorescence is an important goal for organic light‐emitting diodes (OLEDs). Fac‐tris(5‐aryltriazolyl)iridium(III) complexes can emit blue phosphorescence at room temperature. Mono‐ and doubly dendronized fac‐tris(1‐methyl‐5‐phenyl‐3‐n‐propyl‐1H‐[1,2,4]triazolyl)iridium(III) 1 and fac‐tris{1‐methyl‐5‐(4‐fluorophenyl)‐3‐n‐propyl‐1H‐[1,2,4]triazolyl}iridium(III) 4 with first generation biphenyl‐based dendrons were prepared. The dendrimers emitted blue light at room temperature and could be solution processed to form thin films. The doubly dendronized 3 had a film photoluminescence quantum yield of 67% and Commission Internationale de l'Eclairage (CIE) coordinates of (0.17, 0.33). OLEDs comprised of a neat film of dendrimer 3 and an electron transport layer achieved a brightness of 142 cd m−2 at 3.8 V with an external quantum efficiency of 7.9%, and CIE coordinates of (0.18, 0.35). Attachment of the fluorine atom to the emissive core had the effect of moving the luminescence to shorter wavelengths but also quenched the luminescence of the mono‐ and doubly dendronized dendrimers.

Solution‐Processed Highly Efficient Blue Phosphorescent Polymer Light‐Emitting Diodes Enabled by a New Electron Transport Material

“…[ 9 ] In contrast to the considerable progress in developing highly effi cient PhOLEDs using vacuum deposition, reports on solution-processed devices are still relatively few. [10][11][12][13] Surprisingly, nearly all prior reports on solutionprocessable PhOLEDs, are multilayered structures that included a vacuum deposited electron-transport layer (ETL)/hole-blocking layer (HBL). [ 10 , 11 ] High-performance polymer-based PhOLEDs without a vacuum-deposited ETL/HBL still included a vacuumdeposited thin layer of low work function metals (e.g., Ba, Ca) [ 12 ] or interfacial materials (e.g., LiF, CsF) [ 13 , 14 ] inserted between the EML and cathode metals such as Al or Ag.…”

Molecular hosts for triplet emitters in organic light-emitting diodes and the corresponding working principle

“…An example of backward energy transfer from the triplet of the guest to that of the host was demonstrated by the triplet emission from the host at low temperature in BAlq (bis(2-methyl-8-quinolinato)4-phenylphenolate aluminum(III))-Ir(ppy) 3 (3) [tris(2-phenylpyridine)iridium(III)] system [20]. Tsuboi et al also investigated the energy transfer in phosphorescent emitters based host-guest system by analyzing the changes of the PL spectra under different temperatures and obtained similar results [21].…”

“…The efficiencies of Ir(ppy) 3 (3) based devices are highly dependent on the host and device configuration, with the maximum efficiencies of 105 cd/A (29%, or 133 lm/W) [ (20.2%, or 59.3 lm/W) [28], for high performances, 27.4 cd/A (4.5 lm/W) [42] and 20 cd/A [44] for relatively low performances. Utilizing suitable host and the optimizing of device structure according to device mechanism are very significant toward improving PhOLED performance.…”

“…Taking Ir(ppy) 3 (3), the most intensively studied phosphorescent material in PhOLEDs, as an example, the variations of performance are demonstrated in Table 1, the features of host materials and different devices characteristics, together with device performance are compared, and the related references are listed for further survey [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44].…”

“…Non-doped PhOLEDs for blue [3], green [4,5], orange [6], and red [7,8] were demonstrated. However, those devices usually face the problem of luminescence quenching from the condensed state of emitters.…”