TY - JOUR
T1 - Multifunctional Cationic Iridium(III) Complexes Bearing 2-Aryloxazolo[4,5-f][1,10]phenanthroline (N^N) Ligand
T2 - Synthesis, Crystal Structure, Photophysics, Mechanochromic/Vapochromic Effects, and Reverse Saturable Absorption
AU - Zhu, Xiaolin
AU - Cui, Peng
AU - Kilina, Svetlana
AU - Sun, Wenfang
N1 - Funding Information:
We would like to thank Dr. A. Ugrinov at North Dakota State University for his help in the X-ray crystallographic measurements. We acknowledge the financial support from the National Science Foundation (DMR-1411086 and CNS- 1229316) for materials synthesis, characterization, and computational simulation of the optical spectra. For computational resources and administrative support, authors thank the Center for Computationally Assisted Science and Technology (CCAST) at North Dakota State University. S.K. thanks the National Energy Research Scientific Computing Center (NERSC) allocation award 86678, supported by the Office of Science of the Department of Energy under Contract No. DE-AC02-05CH11231. For partial financial support of the quantum chemistry software, S.K. acknowledges Sloan Research Fellowship BR2014-073.
Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/11/20
Y1 - 2017/11/20
N2 - 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-NO2-phenyl (1), 4-Br-phenyl (2), Ph (3), 4-NPh2-phenyl (4), 4-NH2-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 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 11ILCT (intraligand charge transfer) transitions, mixed with 1LLCT (ligand-to-ligand charge transfer)/1MLCT (metal-to-ligand charge transfer) transitions. At the range of 350-570 nm, all complexes exhibited moderately strong 1ILCT/1LLCT/1MLCT transitions at 350 450 nm, and broad but very weak 3LLCT/3MLCT 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 NO2 or NPh2 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.
AB - 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-NO2-phenyl (1), 4-Br-phenyl (2), Ph (3), 4-NPh2-phenyl (4), 4-NH2-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 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 11ILCT (intraligand charge transfer) transitions, mixed with 1LLCT (ligand-to-ligand charge transfer)/1MLCT (metal-to-ligand charge transfer) transitions. At the range of 350-570 nm, all complexes exhibited moderately strong 1ILCT/1LLCT/1MLCT transitions at 350 450 nm, and broad but very weak 3LLCT/3MLCT 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 NO2 or NPh2 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.
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U2 - 10.1021/acs.inorgchem.7b01472
DO - 10.1021/acs.inorgchem.7b01472
M3 - Article
AN - SCOPUS:85034599285
SN - 0020-1669
VL - 56
SP - 13715
EP - 13731
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 22
ER -