Organic light-emitting diodes (OLEDs) based on heavy transition-metal complexes are playing a pivotal role in next generation of, for example, flat panel displays and solid-state lighting.[1] The readily available, Os II -, Pt II -, and in particular Ir III -based phosphorescence complexes grant superior advantage over fluorescent materials.[2] This is mainly due to heavyatom-induced spin-orbit coupling, giving effective harvesting of both singlet and triplet excitons. However, tuning of phosphorescence over the entire visible spectrum still remains a challenge. Particularly, designing new materials to show higher energy, such as deep-blue emission-with an ideal CIE x,y coordinate (CIE = Commission Internationale de LEclairage) of (0.14, 0.09)-encounters more obstacle than the progress made for obtaining green and red colors. Representative blue phosphors are a class of Ir III complexes possessing at least one cyclometalated 4,6-difluorophenyl pyridine {(dfppy)H} ligand, known as FIrpic, FIr6, FIrtaz, and others.[3] The majority of blue phosphors showed inferior color chromaticity with a sum of CIE x+y values being much greater than 0.3 or with single CIE y coordinate higher than 0.25.[4] Such inferior chromaticity, in part, has been improved upon adoption of carbene-, [5] triazolyl-, [6] and fluorine-substituted bipyridine (dfpypy) based chelates. [7] The above urgency prompted us to search for better and new blue phosphors. We produced a class of 2-pyridylazolate chelates possessing very large ligand-centered p-p* energy gap, as evidenced by the blue-emitting Os II complexes.[8]Subsequently, room-temperature blue phosphorescence was also visualized for the respective heteroleptic Ir III complexes, [9] particularly for those dubbed "nonconjugated" ancillary chelate(s). The nonconjugated ligands so far comprise a benzyl substituted pyrazole, [10] an N-heterocyclic carbene, [11] phosphines, [12] and other ingenious molecular designs.[13]Herein, we report the preparation of a novel class of heteroleptic Ir III complexes by incorporation of tripodal, facially coordinated phosphite (or phosphonite), [14] denoted as the P^C 2 chelate, for serving as the ancillary, together with the employment of 2-pyridyltriazolate acting as blue chromophore.[15] The reaction intermediate, which possesses an acetate chelate, was isolated and characterized to establish the synthetic pathway. The tridentate P^C 2 ancillary chelate offers several advantages: 1) Good stabilization of complex and necessary long-term stability in application of for example, emitting devices. 2) The strong bonding of phosphorous donors is expected to destabilize the ligand field d-d excited state, thus minimizing its interference to the radiative process from the lower lying excited state. 3) P^C 2 inherits profound and versatile functionality (see below) capable of fine-tuning the electronic character. As a result, highly efficient blue phosphorescence is attained with good OLED performance.Treatment of a mixture of [IrCl 3 (tht) 3 ] (tht = tetrahydrothioph...
