Effects of systematic methyl substitution of metal (III) tris(n-methyl-8-quinolinolato) chelates on material properties for optimum electroluminescence device performance
Effects of systematic methyl substitution of metal (III) tris(n-methyl-8-quinolinolato) chelates on material properties for optimum electroluminescence device performance
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DOI：
10.1021/ja010120m
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发表时间：
2001-07-04
影响因子：
15
通讯作者：
Forrest, SR
中科院分区：
文献类型：
--
作者：
Sapochak, LS;Padmaperuma, A;Forrest, SR
我们将一系列甲基 (Me) 取代的第 III 族金属三(8-quinofinolato) 螯合物 (nMeq(3)M: n = 0, 3, 4, 5; M = Al3+, Ga3+) 的化学结构与其光致发光 (PL)、电致发光和热性质联系起来。 8-羟基喹啉配体在 3 或 4 位（吡啶环）的甲基化导致 PL 量子效率 (phi (PL)) 提高 1.4 和 3.0 倍。相对于未取代的类似物，5号位（氧化环）的甲基化导致 phi (PL) 降低约 3.0 倍。对于未取代的5-、4-和3-甲基-8-羟基喹啉配体，使用三(8-羟基喹啉)铝螯合物的未掺杂有机发光器件的电致发光量子效率分别为1%、0.45%、1.4%和0.80%。用后两种配体制成的器件具有更高的工作电压以产生相同的电流密度。三(8-羟基喹啉)镓螯合物的甲基化也观察到类似的趋势。我们将这些结果与通过同步差示扫描量热法和热重分析测量的化合物的热性质联系起来。 C-4 甲基化衍生物的晶体熔点比所有其他衍生物低约 60 摄氏度，表明分子之间的内聚力最弱。与 Alq(3) 不同，C-4 和 C-5 甲基化衍生物在低于 500 摄氏度时不会出现玻璃态重结晶，并且表现出类似于 20-25 摄氏度的较高玻璃化转变温度。我们推断 8-羟基喹啉配体的甲基化减少了分子间相互作用，从而阻碍了通过薄膜的电荷传输。
We relate the chemical structure of a series of methyl (Me) substituted group III metal tris(8-quinofinolato) chelates (nMeq(3)M: n = 0, 3, 4, 5; M = Al3+, Ga3+) to their photoluminescence (PL), electroluminescence, and thermal properties. Methylation of the 8-quinolinol ligand at the 3 or 4 position (pyridyl ring) results in a factor of 1.4 and 3.0 enhancement of PL quantum efficiency (phi (PL)). respectively, whereas methylation at the 5 position (phonoxide ring) results in a factor of similar to3.0 decrease in phi (PL) relative to the unsubstituted analogue. Electroluminescent quantum efficiencies of undoped organic light-emitting devices using the aluminum tris(8-quinolinolato) chelates are 1, 0.45, 1.4, and 0.80% for unsubstituted 5-, 4-, and 3-methyl-8-quinolinol ligands, respectively. Devices made with the latter two ligands have a higher operating voltage to generate the same current density. Similar trends were observed for methylation of gallium tris(8-quinolinolato) chelates. We relate these results to the thermal properties of the compounds measured by simultaneous differential scanning calorimetry and thermal gravimetric analysis. The C-4 methylated derivatives exhibit similar to 60 degreesC lower crystalline melting points than all other derivatives, indicating the weakest cohesive forces between molecules. Unlike Alq(3), both the C-4 and C-5 methylated derivatives show no recrystallization of the glassy state below 500 degreesC and exhibit similar to 20-25 degreesC higher glass transition temperatures. We infer that methylation of the 8-quinolinol ligand reduces intermolecular interactions and consequently impedes charge transport through the film.