Influences of fluorination on homoleptic iridium complexes with C∧N=N type ligand to material properties, ligand orientation and OLED performances

Abstract

Two new iridium complexes with C^N=N type ligand (i.e., Ir(BFPPya) 3 {tris[3,6-bis(4-fluorophenyl)pyridazine]iridium(III)} and Ir(BDFPPya) 3 {tris[3,6-bis (2,4-di-fluorophenyl)pyridazine]iridium(III)}) attaching with fluorine atoms, were synthesized and the effects of fluorination on the material properties and device performance were investigated. Compared with our previously reported fluorine-free analogue material, that is Ir(BPPya) 3 {tris[3,6-bis(phenyl)pyridazine]iridium(III)}, blue shifts in the emission spectra as well as in the long wavelength region of the absorptions were observed. The photoluminescence quantum yield (PLQY) (0.44 and 0.84 vs 0.29), phosphoresces lifetime (0.88 and 1.31 vs 0.66 s), and oxidation potential (1.10 and 1.37 vs 0.95 V) increased obviously after fluorinating the ligand. In contrast, the thermal stability of the iridium complexes decreased slightly (Td: 435 and 402 vs 440 °C). In the density functional theory (DFT) calculations, by comparing the steric shape of the three ligands within one optimized molecule, orientational differences among the complexes were observed. In OLED device studies, bluish green electroluminescence with peak emission of 500 nm, using the electron-transporting host of TPBI [2,2',2''-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)] and the most fluorinated dopant of Ir(BDFPPya) 3 , was achieved with maximum efficiency of 20.3 cd/A. On one hand this efficiency is not satisfactory considering a high PLQY of 0.84. On the other hand with the similar device structure, that the (HOMO-LUMO)s of all the dopants are wrapped within that of the host TPBI, and all the triplet energies of the dopants are smaller than that of the host TPBI, it is abnormal that the ordering of device efficiencies is contradictory to that of PLQY. Assisting with the phosphorescent spectrum of TPBI and the absorption spectra of the dopant, the contradiction was interpreted reasonably.

Supramolecular Orange-Red- and Yellow-Emitting Ir(III) Complexes with TFSI and PF6 Counteranions and Production of LEC Devices

“…The thermal stabilities of all complexes were analyzed by thermogravimetric analysis (TGA). It can be clearly seen that all complexes have good thermal stability above 200 °C (Figures S13 and S14), and these results are compatible with similar studies in the literature. , It is proposed that the presence of strong Ir–N bond in the structure increases the stability of complex . Furthermore, in the present study, the complexes with TFSI counterion were found to show higher thermal stability (350–435 °C) than those of complexes with PF 6 counterion as expected.…”

“…36,37 It is proposed that the presence of strong Ir−N bond in the structure increases the stability of complex. 38 Furthermore, in the present study, the complexes with TFSI counterion were found to show higher thermal stability (350−435 °C) than those of complexes with PF 6 counterion as expected. Previous studies have shown that the TFSI anion has higher thermal stability than the PF 6 anion.…”

Structure–Property Study on Two New D–A Type Materials Comprising Pyridazine Moiety and the OLED Application as Host

“…Pyridazine and its derivatives have received arising attention these past few years, as building blocks in organic semiconductors for OFET, solvate-chromic/fluorescent sensors, and liquid crystal materials as well as efficient ligands for strong phosphorescent iridium complexes. − As a six-member heterocyclic aromatic ring, pyridazine comprises two adjacent sp 2 N. When compared with other monocyclic aromatic ring analogues of benzene without N atom and pyridine with one N atom, pyridazine is not only more electron accepting but also more polar, beneficial to its usage as electron acceptor in D–A type materials. However, for optoelectronic application, to the best of our knowledge, except for the compounds reported in ref , which were used as a semiconductor in the OFET device, pyridazine incorporated D–A bipolar materials are rare in the literature.…”

Recent advances in versatile pyridazine-cored materials: principles, applications, and challenges

“…PD-units, for example, have been used as ligands to coordinate with Ir, Pt, and other precious metal ions to create phosphorescent emitters for OLEDs, which emit blue light, red light, and nearinfrared (NIR) light. [70][71][72] PD-units can also be combined with -BF 2 -to construct pure organic complex-based blue fluorescent emitters, 73,74 or with arylamine groups to construct phosphorescent host materials 75,76 and thermally activated delayed fluorescence (TADF) luminescent materials. 77,78 Scheme 3 and Fig.…”