Tang Xiangyang, Shan Tong, Bai Qing, Ma Hongwei, He Xin, Lu Ping
Department of Chemistry, Jilin University, State Key Laboratory of Supramolecular Structure and Materials, 2699 Qianjin Avenue, Changchun, 130012, P. R. China.
Chem Asian J. 2017 Mar 2;12(5):552-560. doi: 10.1002/asia.201601626. Epub 2017 Feb 2.
Developing efficient deep-blue materials is a long-term research focus in the field of organic light-emitting diodes (OLEDs). In this paper, we report two deep-blue molecules, PITO and PISF, which share similar chemical structures but exhibit different photophysical and device properties. These two molecules consist of phenanthroimidazole and dibenzothiophene analogs. The distinction of their chemical structures lies in the different oxidation states of the S atom. For PITO, the S atom is oxidized and the resulting structure dibenzothiophene S,S-dioxide becomes electron deficient. Therefore, PITO displays remarkable solvatochromism, implying a charge-transfer (CT) excited state formed between the donor (D) phenanthroimidazole and acceptor (A) dibenzothiophene S,S-dioxide. For PISF, it is constituted of phenanthroimidazole and dibenzothiophene in which the S atom is not oxidized. PISF displays locally excited (LE) emission with little solvatochromism. Compared with PISF, the D-A molecule PITO with an electron-deficient group shows a much lower LUMO energy level, which is in favor of electron injection in device. In addition, PITO exhibits more balanced carrier transport. However, PISF is capable of emitting in the shorter wavelength region, which is beneficial to obtain better color purity. The doped electroluminescence (EL) device of the D-A molecule PITO manifests deep-blue emission with CIE coordinates of (0.15, 0.08) and maximum external quantum efficiency (EQE) of 4.67 %. The doped EL device of the LE molecule PISF, however, reveals an even bluer emission with CIE coordinates of (0.15, 0.06) and a maximum EQE of 4.08 %.
开发高效的深蓝色材料是有机发光二极管（OLED）领域的长期研究重点。在本文中，我们报道了两种深蓝色分子，PITO和PISF，它们具有相似的化学结构，但表现出不同的光物理和器件性能。这两种分子由菲并咪唑和二苯并噻吩类似物组成。它们化学结构的区别在于S原子的氧化态不同。对于PITO，S原子被氧化，生成的二苯并噻吩S,S-二氧化物结构变得缺电子。因此，PITO表现出显著的溶剂化变色现象，这意味着在供体（D）菲并咪唑和受体（A）二苯并噻吩S,S-二氧化物之间形成了电荷转移（CT）激发态。对于PISF，它由菲并咪唑和未被氧化的二苯并噻吩组成。PISF表现出局部激发（LE）发射，几乎没有溶剂化变色现象。与PISF相比，具有缺电子基团的D-A分子PITO的最低未占分子轨道（LUMO）能级要低得多，这有利于器件中的电子注入。此外，PITO表现出更平衡的载流子传输。然而，PISF能够在更短的波长区域发射，这有利于获得更好的色纯度。D-A分子PITO的掺杂电致发光（EL）器件表现出深蓝色发射，国际照明委员会（CIE）坐标为（0.15, 0.08），最大外量子效率（EQE）为4.67%。然而，LE分子PISF的掺杂EL器件显示出更蓝的发射，CIE坐标为（0.15, 0.06），最大EQE为4.08%。
