A novel phosphonate substituted 4,4â²-bis(N-carbazolyl)biphenyl (CBP), namely PCBP, has been designed and successfully synthesized by an indirect palladium catalyzed SuzukiâMiyaura reaction. X-Ray crystallography analysis from a PCBP single crystal demonstrates that there is a hydrogen bond interaction between the two adjacent molecules due to the presence of phosphonate, which promotes their one-dimensional line arrangement along the c-axis. Compared with the prototype CBP (â5.55 eV), in addition, the highest occupied molecular orbital (HOMO) level of PCBP is reduced to â6.00 eV, leading to a large hole injection barrier. On the other hand, the introduction of phosphonate substitutes can endow PCBP with excellent electron injection/transport ability. As a result, PCBP shows an electron-dominated behaviour observed in single carrier devices, which is different from the hole-dominated one for CBP. Such a transition is then used to tune the single-layer device performance of a self-host phosphorescent dendrimer, and the peak luminous efficiency significantly increases from 1.7 cd Aâ1 of CBP to 31.4 cd Aâ1 of PCBP.
一种新型
膦酸酯取代的4,4²-双(N-
咔唑基)
联苯(CBP),即PCBP,已经通过间接
钯催化铃木-宫浦反应设计并成功合成。对PCBP单晶的X射线晶体学分析表明,由于
膦酸酯的存在,两个相邻分子之间存在氢键相互作用,从而促进它们沿c轴的一维线排列。此外,与原型CBP(△5.55eV)相比,PCBP的最高占分子轨道(HOMO)
水平降低到△6.00eV,导致形成较大的空穴注入势垒。另一方面,
膦酸酯取代物的引入可以使PCBP具有优异的电子注入/传输能力。因此,PCBP表现出在单载流子器件中观察到的电子主导行为,这与CBP的空穴主导行为不同。这种转变随后被用来调节自宿主
磷光树状大分子的单层器件性能,峰值发光效率从CBP的1.7 cd A△1显着提高到PCBP的31.4 cd A△1。