A New Family of Homoleptic Ir(III) Complexes: Tris‐Pyridyl Azolate Derivatives with Dual Phosphorescence

Homoleptic Tris(Pyridyl Pyrazolate) IrIII Complexes: En Route to Highly Efficient Phosphorescent OLEDs

“…Moreover, treatment of either the cis or trans complexes 2 a, 3 a and 2 b, 3 b had afforded a reasonable amount of the anticipated Ir III complexes 1 a and 1 b, confirming the previous observation. [8] However, for executing scale-up preparation, it is best to bypass the isolation of 2 and 3 and employ at least three equivalents of pyrazole in a higher-boiling-point solvent such as diethylene glycol monoethyl ether (DGME). Similarly, the related isoquinolinyl derivatives 4 a and 4 b were obtained in good yields, without the prior isolation of respective dichloride intermediates.…”

“…[8] Although these Ir III complexes failed to exhibit the anticipated bright phosphorescence at room temperature, we serendipitously observed a unique case of dual emission, of which the intensity ratio and the associated relaxation dynamics of each peak show remarkable temperature dependence. This result highlights an unusual intraligand chargetransfer (ILCT) to ligand-to-ligand charge-transfer (LLCT) conversion, that is, an electron-transfer-like excited-state process (see below) for which the LLCT has not only lowered the emission efficiency but also resulted in an unwanted bathochromatic shift.…”

“…As for the emission spectra, unlike the rather weak, dual phosphorescence of 1 a and 1 b observed in degassed CH 2 Cl 2 solution at room temperature, [8] complexes 4 a and 4 b all show unique, bright luminescence (e.g., F 4a % 0.86 and F 4b % 0.50) consisting of a notable vibronic progression (500-800 nm) with the first peak appearing at 567 and 545 nm, respectively (see Figure 4). The poor overlap between the emission signals and the lowest-energy absorption band for both 4 a and 4 b can be attributed to the origin of emission possessing excessive ligand-centered pp* and relatively low MLCT character.…”

“…This result highlights an unusual intraligand chargetransfer (ILCT) to ligand-to-ligand charge-transfer (LLCT) conversion, that is, an electron-transfer-like excited-state process (see below) for which the LLCT has not only lowered the emission efficiency but also resulted in an unwanted bathochromatic shift. [8] Herein, we report the mechanistic details that gave the formation of both 1 a and 1 b, which is highlighted by the isolation of two reaction intermediates (cis-2 a and cis-2 b and trans-3 a and trans-3 b) upon treatment of IrCl 3 ·nH 2 O with only two equivalents of (bppz)H and (fppz)H chelates. Their role in the transformation is also established.…”

“…The whole assignment is well supported by the well-matched absorption spectral patterns versus those of 1 a and 1 b (see Figure 5), [8] except that all peaks appear at relatively longer wavelengths, due to the greater p conjugation of the isoA C H T U N G T R E N N U N G quinA C H T U N G T R E N N U N G olinyl than that of the pyridyl moieties. [a] The emission properties were resolved in an CH 2 Cl 2 matrix at 77 K. [b] See Ref.…”