Yellow and Red Electrophosphors Based on Linkage Isomers of Phenylisoquinolinyliridium Complexes: Distinct Differences in Photophysical and Electroluminescence Properties

Abstract

We report the synthesis and organic light‐emitting devices (OLEDs) made from a series of 1‐phenyl‐ and 3‐phenylisoquinolinyliridium complexes in which the phenyl group is linked to the C1 and C3 carbons of isoquinoline, respectively. These linkage isomers show distinct differences in their photophysical and electroluminescence (EL) properties, including the magnitude of phosphorescent lifetimes and photoluminescence (PL) and EL emission wavelengths, as well as the phenomenon of triplet–triplet (T–T) annihilation. Complexes of these two families show a strong absorption band in the region 440–490 nm assignable to spin‐forbidden 3MLCT (metal–ligand charge‐transfer) bands. The extinction coefficients of these bands are similar to those of spin‐allowed 1MLCT bands, indicative of an anomalously strong spin–orbital coupling. Upon excitation, 1‐phenylisoquinolinyliridium complexes exhibit a single phosphorescent emission band in the red region (595–631 nm). All of these red phosphors show outstanding EL performance with negligible T–T annihilation because of short phosphorescent lifetimes (1.04–2.46 μs in CH2Cl2) and good emission quantum yields. One representative, [Ir(5‐f‐1piq)2(acac)] (acac = acetylacetonate) (3) (5‐f‐1piqH = 5‐fluoro‐1‐phenylisoquinoline), is not only the brightest at low voltages (1883 cd m–2 at 7.1 V; 8320 cd m–2 at 9.0 V) but also shows a ηext value of. 6.50 % at high current (J = 400 mA cm–2). The maximum brightness is 38 218 cd m–2 (x = 0.68, y = 0.31) with the full width at half maximum (FWHM) only 50 nm at 8 V. In contrast, 3‐phenylisoquinolinyliridium complexes show phosphorescent emissions in the yellow region (534–562 nm) but with a long phosphorescent lifetime (3.90–15.6 μs in CH2Cl2). Most of these yellow phosphors suffer T–T annihilation in the EL performance. The exception is [Ir(3‐piq)2(acac)] (5) (3‐piqH = 3‐phenylisoquinoline), which has a relatively short lifetime 3.90 μs in CH2Cl2. Complex 5 achieves an external efficiency (ηext) value of 5.27 % at J = 20 mA cm–2 and maintains a ηext value of 3.58 at J = 400 mA cm–2 with a maximum brightness of 65 448 cd m–2 (x = 0.49, y = 0.51).

Versatile Benzimidazole/Triphenylamine Hybrids: Efficient Nondoped Deep‐Blue Electroluminescence and Good Host Materials for Phosphorescent Emitters

“…Finally, we also fabricated red phosphorescent devices D and E by doping 1 or 2 with 6 wt % bis(1-phenylisoquinolinato-N,C2')iridium(acetylacetonate) ([(piq) 2 IrA C H T U N G T R E N N U N G (acac)]) (E T = 2.0 eV) [22] in the same device structures as devices B and C. Devices D and E emit deep red light with CIE chromaticity coordinates of (0.68, 0.32). Device E hosted by 2 shows a maximum luminance of 11 446 cd m À2 at 12.7 V, a maximum current efficiency of 6.5 cd A À1 , and a maximum power efficiency of 5.1 lm W À1 ; whereas device D hosted by 1 exhibits much better EL performance (23 616 cd m À2 at 13.7 V, 11.5 cd A À1 , and 9.8 lm W À1 ).…”

The Role of Substituent Effects in Tuning Metallophilic Interactions and Emission Energy of Bis‐4‐(2‐pyridyl)‐1,2,3‐triazolatoplatinum(II) Complexes

“…[1] Foro rganic LEDs (OLEDs), innovations have been spurred along by the discovery of new molecules with good stability and high emission intensity, followed through by intense engineering efforts.H eavymetal-containing complexes are potent molecular emitters as aresult of their high quantum efficiencies (QEs, f)related to facile intersystem crossing (ISC) between excited-state manifolds (efficient spin orbit coupling (SOC)) and resultant efficient emission from the triplet state (phosphorescence). [2] Rational tuning of the emission wavelengths based on structural modifications of the ligands, [3] with concomitant control of the QE, has been demonstrated in an umber of octahedral complexes of d 6 metals [4] including predominantly iridium, [4a,b] rhodium, [4c] and ruthenium [4d] and with al arge range of structurally diverse ligands.T he square-planar d 8 complexes have also received considerable interest since the seminal work of Gray,V lcek, Miskowski, and co-workers. [5] Square-planar platinum complexes present excellent emissive properties and allow for am ore minimal planar structural motif with less diasteromeric diversity.However, anticipated deleterious excitonic self-quenching of planar complexes brought on by enhanced intermolecular electronic coupling through p-p stacking interactions implies considerable design difficulties for this class of phosphors.N onetheless,f or Pt II complexes this negative aspect is largely offset by the propensity of these systems to engage in metallophilic Pt-Pt interactions.T hese interactions give rise to new and interesting photophysics involving transitions between metallophilic bonds and ligands,d enoted metal-metal-to-ligand charge transfer (MMLCT), providing supramolecular design potential for further property tunability.…”

Polymer light-emitting devices based on europium(III) complex with 11-bromo-dipyrido[3,2-a:2′,3′-c]phenazine

“…Compared to Eu(DBM) 3 (DBrPhen), Eu(DBM) 3 (BrDPPz) as a dopant can trap carriers from PFO more efficiently, which results in efficient EL in the corresponding devices [17,41]. However, compared with Eu(DBM) 3 (DPPz) [11], Eu(DBM) 3 (BrDPPz) possesses a higher LUMO energy level by 0.05 eV [42]. This implies that Eu(DBM) 3 (BrDPPz) is poorer at trapping electrons than Eu(DBM) 3 (DPPz), which would decrease the EL efficiency of the Eu(DBM) 3 (BrDPPz)-doped PFO-PBD devices [12,43].…”