TY - JOUR
T1 - Tuning the photophysical properties of cationic iridium(iii) complexes containing cyclometallated 1-(2,4-difluorophenyl)-1H-pyrazole through functionalized 2,2′-bipyridine ligands
T2 - Blue but not blue enough
AU - Baranoff, Etienne
AU - Bolink, Henk J.
AU - Constable, Edwin C.
AU - Delgado, Manuel
AU - Häussinger, Daniel
AU - Housecroft, Catherine E.
AU - Nazeeruddin, Mohammad K.
AU - Neuburger, Markus
AU - Ortí, Enrique
AU - Schneider, Gabriel E.
AU - Tordera, Daniel
AU - Walliser, Roché M.
AU - Zampese, Jennifer A.
PY - 2013/1/28
Y1 - 2013/1/28
N2 - Four new heteroleptic iridium(iii) complexes in the family [Ir(dfppz) 2(N^N)]+, where Hdfppz = 1-(2,4-difluorophenyl)-1H- pyrazole and N^N = 6-phenyl-2,2′-bipyridine (1), 4,4′-(di-tert- butyl)-6-phenyl-2,2′-bipyridine (2), 4,4′-(di-tert-butyl)-6, 6′-diphenyl-2,2′-bipyridine (3) and 4,4′-bis(dimethylamino)-2, 2′-bipyridine (4), have been synthesized as the hexafluoridophosphate salts and fully characterized. Single crystal structures of ligand 3 and the precursor [Ir2(dfppz)4(μ-Cl)2] have been determined, along with the structures of the complexes 4{[Ir(dfppz) 2(1)][PF6]}·3CH2Cl2, [Ir(dfppz)2(3)][PF6]·CH2Cl2 and [Ir(dfppz)2(4)][PF6]·CH2Cl 2. The role of inter- and intramolecular face-to-face π-stacking in the solid state is discussed. In the [Ir(dfppz)2(N^N)]+ (N^N = 1-3) cations, the phenyl substituent in ligands 1, 2 or 3 undergoes hindered rotation on the NMR timescale at 298 K in solution and the systems have been studied by variable temperature NMR spectroscopy. Acetonitrile solutions of [Ir(dfppz)2(N^N)][PF6] (N^N = 1-3) exhibit similar absorption spectra arising from ligand-based transitions; absorption intensity is enhanced on going to [Ir(dfppz)2(4)][PF6] and the spectrum extends further into the visible region. Acetonitrile solutions of the complexes are blue emitters with λem = 517, 505, 501 and 493 nm for N^N = 1, 2, 3 and 4, respectively (λexc = 280-310 nm). The redox behaviours of [Ir(dfppz)2(N^N)][PF6] (N^N = 1-3) are similar, and the introduction of the electron-donating NMe2 substituents onto the N^N ligand shifts the metal-centred oxidation to less positive potentials. Theoretical calculations predict a mixed metal-to-ligand/ligand-to-ligand charge transfer (MLCT/LLCT) character for the emitting triplet state in agreement with the broad and unstructured character of the emission bands. The NMe2 substituents enlarge the HOMO-LUMO gap and blue-shifts the emission of [Ir(dfppz)2(4)]+ that is centred on the ancillary ligand. These complexes, when processed into a thin film and sandwiched between two electrodes, lead to very low voltage operating electroluminescent devices. No additional components are needed, which demonstrates their electron and hole transport abilities in conjunction with the luminescent properties.
AB - Four new heteroleptic iridium(iii) complexes in the family [Ir(dfppz) 2(N^N)]+, where Hdfppz = 1-(2,4-difluorophenyl)-1H- pyrazole and N^N = 6-phenyl-2,2′-bipyridine (1), 4,4′-(di-tert- butyl)-6-phenyl-2,2′-bipyridine (2), 4,4′-(di-tert-butyl)-6, 6′-diphenyl-2,2′-bipyridine (3) and 4,4′-bis(dimethylamino)-2, 2′-bipyridine (4), have been synthesized as the hexafluoridophosphate salts and fully characterized. Single crystal structures of ligand 3 and the precursor [Ir2(dfppz)4(μ-Cl)2] have been determined, along with the structures of the complexes 4{[Ir(dfppz) 2(1)][PF6]}·3CH2Cl2, [Ir(dfppz)2(3)][PF6]·CH2Cl2 and [Ir(dfppz)2(4)][PF6]·CH2Cl 2. The role of inter- and intramolecular face-to-face π-stacking in the solid state is discussed. In the [Ir(dfppz)2(N^N)]+ (N^N = 1-3) cations, the phenyl substituent in ligands 1, 2 or 3 undergoes hindered rotation on the NMR timescale at 298 K in solution and the systems have been studied by variable temperature NMR spectroscopy. Acetonitrile solutions of [Ir(dfppz)2(N^N)][PF6] (N^N = 1-3) exhibit similar absorption spectra arising from ligand-based transitions; absorption intensity is enhanced on going to [Ir(dfppz)2(4)][PF6] and the spectrum extends further into the visible region. Acetonitrile solutions of the complexes are blue emitters with λem = 517, 505, 501 and 493 nm for N^N = 1, 2, 3 and 4, respectively (λexc = 280-310 nm). The redox behaviours of [Ir(dfppz)2(N^N)][PF6] (N^N = 1-3) are similar, and the introduction of the electron-donating NMe2 substituents onto the N^N ligand shifts the metal-centred oxidation to less positive potentials. Theoretical calculations predict a mixed metal-to-ligand/ligand-to-ligand charge transfer (MLCT/LLCT) character for the emitting triplet state in agreement with the broad and unstructured character of the emission bands. The NMe2 substituents enlarge the HOMO-LUMO gap and blue-shifts the emission of [Ir(dfppz)2(4)]+ that is centred on the ancillary ligand. These complexes, when processed into a thin film and sandwiched between two electrodes, lead to very low voltage operating electroluminescent devices. No additional components are needed, which demonstrates their electron and hole transport abilities in conjunction with the luminescent properties.
UR - http://www.scopus.com/inward/record.url?scp=84871962553&partnerID=8YFLogxK
U2 - 10.1039/c2dt32160b
DO - 10.1039/c2dt32160b
M3 - Article
AN - SCOPUS:84871962553
SN - 1477-9226
VL - 42
SP - 1073
EP - 1087
JO - Dalton Transactions
JF - Dalton Transactions
IS - 4
ER -