Zhu Xiaolin, Cui Peng, Kilina Svetlana, Sun Wenfang
Department of Chemistry and Biochemistry, North Dakota State University , Fargo, North Dakota 58108-6050, United States.
Materials and Nanotechnology Program, North Dakota State University , Fargo, North Dakota 58105, United States.
Inorg Chem. 2017 Nov 20;56(22):13715-13731. doi: 10.1021/acs.inorgchem.7b01472. Epub 2017 Oct 30.
A series of 2-aryloxazolo[4,5-f][1,10]phenanthroline ligands (N^N ligands) and their cationic iridium(III) complexes (1-11, aryl = 4-NO-phenyl (1), 4-Br-phenyl (2), Ph (3), 4-NPh-phenyl (4), 4-NH-phenyl (5), pyridin-4-yl (6), naphthalen-1-yl (7), naphthalen-2-yl (8), phenanthren-9-yl (9), anthracen-9-yl (10), and pyren-1-yl (11)) were synthesized and characterized. By introducing different electron-donating or electron-withdrawing substituents at the 4-position of the 2-phenyl ring (1-5), or different aromatic substituents with varied degrees of π-conjugation (6-11) on oxazolo[4,5-f][1,10]phenanthroline ligand, we aim to understand the effects of terminal substituents at the N^N ligands on the photophysics of cationic Ir(III) complexes using both spectroscopic methods and quantum chemistry calculations. Complexes with the 4-R-phenyl substituents adopted an almost coplanar structure with the oxazolo[4,5-f][1,10]phenanthroline motif, while the polycyclic aryl substituents (except for naphthalen-2-yl) were twisted away from the oxazolo[4,5-f][1,10]phenanthroline motif. All complexes possessed strong absorption bands below 350 nm that emanated from the ligand-localized π,π*/ILCT (intraligand charge transfer) transitions, mixed with LLCT (ligand-to-ligand charge transfer)/MLCT (metal-to-ligand charge transfer) transitions. At the range of 350-570 nm, all complexes exhibited moderately strong ILCT/LLCT/MLCT transitions at 350-450 nm, and broad but very weak LLCT/MLCT absorption at 450-570 nm. Most of the complexes demonstrated moderate to strong room temperature phosphorescence both in solution and in the solid state. Among them, complex 7 also manifested a drastic mechanochromic and vapochromic luminescence effect. Except for complexes 1 and 4 that contain NO or NPh substituent at the phenyl ring, respectively, all other complexes exhibited moderate to strong triplet excited-state absorption in the spectral region of 440-750 nm. Moderate to very strong reverse saturable absorption (RSA) of these complexes appeared at 532 nm for 4.1 ns laser pulses. The RSA strength followed the trend of 7 > 11 > 9 > 3 > 2 ≈ 4 > 5 ≈ 10 ≈ 6 ≈ 8 > 1. The photophysical studies revealed that the different 2-aryl substituents on the oxazole ring impacted the singlet and triplet excited-state characteristics dramatically, which in turn notably influenced the RSA of these complexes.
合成并表征了一系列2-芳基恶唑并[4,5-f][1,10]菲咯啉配体（N^N配体）及其阳离子铱(III)配合物（1-11，芳基 = 4-NO-苯基(1)、4-Br-苯基(2)、苯基(3)、4-NPh-苯基(4)、4-NH-苯基(5)、吡啶-4-基(6)、萘-1-基(7)、萘-2-基(8)、菲-9-基(9)、蒽-9-基(10)和芘-1-基(11)）。通过在2-苯环的4-位引入不同的供电子或吸电子取代基（1-5），或在恶唑并[4,5-f][1,10]菲咯啉配体上引入具有不同程度π共轭的不同芳基取代基（6-11），我们旨在使用光谱方法和量子化学计算来了解N^N配体上末端取代基对阳离子Ir(III)配合物光物理性质的影响。具有4-R-苯基取代基的配合物与恶唑并[4,5-f][1,10]菲咯啉基序几乎共面，而多环芳基取代基（萘-2-基除外）则偏离恶唑并[4,5-f][1,10]菲咯啉基序。所有配合物在350 nm以下都有强吸收带，这些吸收带源于配体局部的π,π*/ILCT（配体内电荷转移）跃迁，并与LLCT（配体间电荷转移）/MLCT（金属到配体电荷转移）跃迁混合。在350-570 nm范围内，所有配合物在350-450 nm处表现出中等强度的ILCT/LLCT/MLCT跃迁，在450-570 nm处表现出宽但非常弱的LLCT/MLCT吸收。大多数配合物在溶液和固态中都表现出中等至强的室温磷光。其中，配合物7还表现出剧烈的机械变色和气相变色发光效应。除了分别在苯环上含有NO或NPh取代基的配合物1和4外，所有其他配合物在440-750 nm光谱区域表现出中等至强的三重态激发态吸收。对于4.1 ns激光脉冲，这些配合物在532 nm处出现中等至非常强的反向饱和吸收（RSA）。RSA强度遵循7 > 11 > 9 > 3 > 2 ≈ 4 > 5 ≈ 10 ≈ 6 ≈ 8 > 1的趋势。光物理研究表明，恶唑环上不同的2-芳基取代基极大地影响了单重态和三重态激发态特性，进而显著影响了这些配合物的RSA。
