title: Control of intramolecular π-π stacking interaction in cationic iridium complexes via fluorination of pendant phenyl rings.
abstract: Intramolecular π-π stacking interaction in one kind of phosphorescent cationic iridium complexes has been controlled through fluorination of the pendant phenyl rings on the ancillary ligands. Two blue-green-emitting cationic iridium complexes, [Ir(ppy)(2)(F2phpzpy)]PF(6) (2) and [Ir(ppy)(2)(F5phpzpy)]PF(6) (3), with the pendant phenyl rings on the ancillary ligands substituted with two and five fluorine atoms, respectively, have been synthesized and compared to the parent complex, [Ir(ppy)(2)(phpzpy)]PF(6) (1). Here Hppy is 2-phenylpyridine, F2phpzpy is 2-(1-(3,5-difluorophenyl)-1H-pyrazol-3-yl)pyridine, F5phpzpy is 2-(1-pentafluorophenyl-1H-pyrazol-3-yl)-pyridine, and phpzpy is 2-(1-phenyl-1H-pyrazol-3-yl)pyridine. Single crystal structures reveal that the pendant phenyl rings on the ancillary ligands stack to the phenyl rings of the ppy ligands, with dihedral angles of 21°, 18°, and 5.0° between least-squares planes for complexes 1, 2, and 3, respectively, and centroid-centroid distances of 3.75, 3.65, and 3.52 Å for complexes 1, 2, and 3, respectively, indicating progressively reinforced intramolecular π-π stacking interactions from complexes 1 to 2 and 3. Compared to complex 1, complex 3 with a significantly reinforced intramolecular face-to-face π-π stacking interaction exhibits a significantly enhanced (by 1 order of magnitude) photoluminescent efficiency in solution. Theoretical calculations reveal that in complex 3 it is unfavorable in energy for the pentafluorophenyl ring to swing by a large degree and the intramolecular π-π stacking interaction remains on the lowest triplet state.
authors.affiliation: Key Laboratory of Organic Optoelectronics and Molecular Engineering, Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, PR China.
authors.forename: Lei
authors.initials: L
authors.lastname: He
authors.forename: Dongxin
authors.initials: D
authors.lastname: Ma
authors.forename: Lian
authors.initials: L
authors.lastname: Duan
authors.forename: Yongge
authors.initials: Y
authors.lastname: Wei
authors.forename: Juan
authors.initials: J
authors.lastname: Qiao
authors.forename: Deqiang
authors.initials: D
authors.lastname: Zhang
authors.forename: Guifang
authors.initials: G
authors.lastname: Dong
authors.forename: Liduo
authors.initials: L
authors.lastname: Wang
authors.forename: Yong
authors.initials: Y
authors.lastname: Qiu
mesh_terms: D001554:Benzene / Q000737:chemistry*; D018360:Crystallography, X-Ray; D054879:Halogenation; D007495:Iridium / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D009942:Organometallic Compounds; D007495:Iridium; D001554:Benzene