Photophysical and electroluminescence properties of bis(2′,6′-difluoro-2,3′-bipyridinato-N,C4′)iridium(picolinate) complexes: effect of electron-withdrawing and electron-donating group substituents at the 4′ position of the pyridyl moiety of the cyclometalated ligand

Abstract

†Electronic Supplementary Information (ESI) available: X-ray crystallographic data in CIF format for the complexes Ir2 and Ir4 [CCDC 973778 (Ir2) and 1005716 (Ir4)], NMR and MASS spectra of ligands and complexes, TGA−DSC thermal curves, cyclic voltammograms, lifetime curves, selected bond lengths and angles, intermolecular interactions, calculated transitions of Ir1-Ir5 in CH2Cl2 media and composition of the MOs and the assignment of different fragments. CIF files. See Herein, we have synthesized a series of 2',6'-difluoro-2,3'-bipyridine cyclometalating ligands by substituting electronwithdrawing (-CHO, -CF3, -CN) and electron-donating (-OMe, -NMe2) groups at the 4′ posiƟon of the pyridyl moiety and utilized for the construction of five new iridium(III) complexes (Ir1-Ir5) in the presence of picolinate as an ancillary ligand. The photophysical properties of the developed iridium(III) compounds were investigated with a view to understand the substituent effects. The strong electron-withdrawing (-CN) group containing iridium(III) compound (Ir3) exhibits highly efficient genuine green phosphorescence (λmax= 508 nm) at room temperature in solution and in thin film, with an excellent quantum efficiency (ΦPL) of 0.90 and 0.98, respectively. On the other hand, the -CF3 group substituted iridium(III) compound (Ir2) displays a sky-blue emission (λmax = 468 nm) with a promising quantum efficiency (ΦPL = 0.88 and 0.84 in solution and in thin film, respectively). The -CHO substituted iridium(III) complex (Ir1) showed greenishyellow emission (λmax = 542 nm). Most importantly, the strong electron-donating -NMe2 substituted iridium(III) complex (Ir5) gives a structureless and a broad emission profile in the wavelength region 450 to 700 nm (λmax = 520 nm) with a poor quantum efficiency. An intense blue phosphorescence with impressive quantum efficiency, especially in thin-film noted in the case of -OMe substituted iridium(III) complex (Ir4). Comprehensive density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches have been performed on the ground and excited states of the synthesized iridium(III) complexes, in order to obtain information about the absorption and emission processes and to gain deeper insights into the photophysical properties. The combinations of a smaller ΔES1-T1 and higher contribution of 3 MLCT in the emission process result in the higher quantum yields and lifetime values for complexes Ir1-Ir3. Multi-layered Phosphorescence Organic Light Emitting Diodes (PhOLEDS) were designed using the phosphorescent dopants Ir2, Ir3 and Ir4 and evaluated their elecroluminescence properties. The compound Ir4 at a doping level of 5 wt% shows the best performance with an external quantum efficiency of 4.7% , in nonoptimized device, and power efficiency of 5.8 lm W −1 , together with a true-blue chromacity CIEx,y = 0.15, 0.17 recorded at maximum brightness of 33,180 cd/m 2 . 28,[45][46][47][48][49][50][51] Accordingly, several groups have demonstrated that phosphorescence emission wavelengths can be tuned in t...

Mesomorphism and Photophysics of Some Metallomesogens Based on Hexasubstituted 2,2′:6′, 2′′‐Terpyridines

“…In second‐ and third‐row transition metal complexes, emission from the triplet state, normally formally forbidden, is promoted through high spin‐orbit coupling of the metal ions, the extent of which depends on the participation of metal orbitals in the excited state . The broad emission bands exhibited by the Ir III complexes without vibronic structure indicates that they originate from the 3 MLCT transition state . This contrasts with the behaviour of the unsubstituted complex [Ir(terpy)Cl 3 ] where emission is from a 3 LC excited state.…”

“…Complexes 13 ‐16 and 15 ‐16 give long excited‐state lifetimes ( τ ) in degassed solutions and lifetimes of 0.7 and 0.8 μs in DCM, and 1.5 and 1.2 μs in hexane, respectively, were obtained. In second‐ and third‐row transition metal complexes, emission from the triplet state, normally formally forbidden, is promoted through high spin‐orbit coupling of the metal ions, the extent of which depends on the participation of metal orbitals in the excited state . The broad emission bands exhibited by the Ir III complexes without vibronic structure indicates that they originate from the 3 MLCT transition state .…”

Towards deep‐blue phosphorescence: molecular design and property prediction of iridium complexes with pyridinylphosphinate ancillary ligand

“…These complexes are the octahedral structures in which two N atoms in dfppy are located at the trans position as depicted in the structure of 1 in Figure . Such geometrical structures are verified to be the most stable configurations by the crystal structure of 1 and previous theoretical calculations . The optimized ground‐state structures of 2 – 5 are shown in Figure S1 in the SI.…”

Theoretical Investigation and Design of Highly Efficient Blue Phosphorescent Iridium(III) Complexes Bearing Fluorinated Aromatic Sulfonyl Groups

“…[4] Thus,significant efforts need to be done to develop blue phosphorescent Ir III complexesw ith high efficiency. [5] Recently,aromatic sulfonyl groups have received much interest in the field of OLEDs owing to their inherent electronic features. [6] In the past decades, somen ovel host materials with phenylsulfonyl groups have been developedt om ake highly efficient phosphorescent OLEDs( PhOLEDs) with good electron injection/transporting (EI/ET) abilities.…”

“…Relative to stable and high‐efficiency red and green phosphorescent Ir III complexes, the application of blue phosphorescent emitters in OLEDs is still limited and challenging . Thus, significant efforts need to be done to develop blue phosphorescent Ir III complexes with high efficiency …”