Harvesting highly electronically excited energy to triplet manifolds: state-dependent intersystem crossing rate in Os(II) and Ag(I) complexes.

A series of newly synthesized Os(II) and Ag(I) complexes exhibit remarkable ratiometric changes of intensity for phosphorescence versus fluorescence that are excitation wavelength dependent. This phenomenon is in stark contrast to what is commonly observed in condensed phase photophysics. While the singlet to triplet intersystem crossing (ISC) for the titled complexes is anomalously slow, approaching several hundred picoseconds in the lowest electronic excited state (S(1) → T(1)), higher electronic excitation leads to a much accelerated rate of ISC (10(11)-10(12) s(-1)), which is competitive with internal conversion and/or vibrational relaxation, as commonly observed in heavy transition metal complexes. The mechanism is rationalized by negligible metal d orbital contribution in the S(1) state for the titled complexes. Conversely, significant ligand-to-metal charge transfer character in higher-lying excited states greatly enhances spin-orbit coupling and hence the ISC rate. The net result is to harvest high electronically excited energy toward triplet states, enhancing the phosphorescence.

Heteroleptic Ir(III) complexes containing both azolate chromophoric chelate and diphenylphosphinoaryl cyclometalates; reactivities, electronic properties and applications.

The synthesis of a new family of octahedral Ir(III) complexes with dual cyclometalating phosphine chelates, namely: 1-(diphenylphosphino)naphthalene (dpnaH) and isoquinoline (dppiH), is reported. Two series of intermediate complexes, [Ir(dpna)(tht)(2)Cl(2)] (1), [Ir(dpna)(2)(OAc)] (2), [Ir(dppiH)(dppi)Cl(2)] (3) and [Ir(dppi)(2)(OAc)] (4), which can be classified by the coexistence of either a pair of cis-chlorides or a single acetate chelate, were obtained from treatment of phosphine with [IrCl(3)(tht)(3)] (tht = tetrahydrothiophene). The in situ generated acetate complexes 2 and 4 could react with azolate chelates, namely: 5-(2-pyridyl)-3-trifluoromethyl pyrazole (fppzH) and 5-(1-isoquinolyl)-3-tert-butyl-1,2,4-triazole (iqbtzH), to afford a new series of luminescent complexes [Ir(dpna)(2)(fppz)] (5a and 5b), [Ir(dpna)(2)(iqbtz)] (6a and 6b), [Ir(dppi)(2)(fppz)] (7a) and [Ir(dppi)(2)(iqbtz)] (8a). The phosphorescence lifetime (τ(obs)) fell in the range of a few tens of µs, showing possession of excessive ligand-centered ππ* mixed in part with MLCT character. A density functional theory (DFT) study was also conducted in order to shed light on the origin of the transitions in the absorption and emission spectra and to predict emission energies for these complexes. Organic light emitting diodes (OLEDs) displaying bright orange emission and with maximum η(ext) up to 17.1% were fabricated employing complexes 6a and 8a as the phosphorescent dopants.

Diphenyl(1-naphthyl)phosphine ancillary for assembling of red and orange-emitting Ir(III) based phosphors; strategic synthesis, photophysics, and organic light-emitting diode fabrication.

Treatment of a series of dinuclear Ir(III) complexes [(fnazo)(2)Ir(µ-Cl](2), [(fpiq)(2)Ir(µ-Cl](2), and [(fppy)(2)Ir(µ-Cl](2) with diphenyl(1-naphthyl)phosphine (dpnH) in decalin at 100 °C afforded the simple adducts, trans-N,N'-[(fnazo)(2)Ir(dpnH)Cl] (1a), trans-N,N'-[(fpiq)(2)Ir(dpnH)Cl] (1b), and trans-N,N'-[(fppy)(2)Ir(dpnH)Cl] (1c), for which the C(∧)N cyclometalating reagents, that is, fnazoH, fpiqH and fppyH, stands for 4-(4-fluorophenyl)quinazoline, 1-(4-fluorophenyl)isoquinoline and 4-fluorophenylpyridine, respectively. Single crystal X-ray diffraction study on 1a revealed existence of two trans-N,N' cyclometalates, with both chloride and dpnH donors located at the positions opposite to the phenyl substituents. Subsequent heating of 1a-1c at higher temperature afforded the second isomer (2a-2c), showing formation of cis-N,N' orientation for the aforementioned cyclometalates. Further thermolysis of either trans or cis-Ir(III) complexes 1 or 2 in presence of sodium acetate, which serves as both activator and chloride scavenger, gave successful isolation of a mixture of two fully cyclometalated Ir(III) complexes trans-N,N'-[(C(∧)N)(2)Ir(dpn)] (3a-3c) and cis-N,N'-[(C(∧)N)(2)Ir(dpn)] (4a-4c). Structural and photophysical properties of complexes 3a-3c and 4a-4c were measured and compared. Time-dependent density functional theory (DFT) studies suggested that, upon changing the C(∧)N cyclometalates from quinazolinyl, isoquinolinyl, and, finally, to pyridyl fragment, the lowest unoccupied molecular orbitals (LUMOs) are gradually shifted from the cyclometalating nitrogen heterocycles to the 1-naphthyl group of the phosphine chelate and, concomitantly altered the photophysical properties. An organic light-emitting diode (OLED) using orange-red phosphors 4a and 4b has been successfully fabricated. At the practical brightness of 500 cd·m(-2), decent external quantum efficiency of 10.6% and 12.5% could be reached for 4a and 4b, respectively, revealing the usefulness of relevant molecular architecture in designing triplet OLED emitters.

Authentic-blue phosphorescent iridium(III) complexes bearing both hydride and benzyl diphenylphosphine; control of the emission efficiency by ligand coordination geometry.

Sequential treatment of IrCl(3) x nH(2)O with 2 equiv of benzyl diphenylphosphine (bdpH) and then 1 equiv of 3-trifluoromethyl-5-(2-pyridyl) pyrazole (fppzH) in 2-methoxyethanol gave formation to three isomeric complexes with formula [Ir(bdp)(fppz)(bdpH)H] (1-3). Their molecular structures were established by single crystal X-ray diffraction studies, showing existence of one monodentate phosphine bdpH, one terminal hydride, a cyclometalated bdp chelate, and a fppz chelate. Variation of the metal-ligand bond distances showed good agreement with those predicted by the trans effect. Raman spectroscopic analyses and the corresponding photophysical data are also recorded and compared. Among all isomers complex 1 showed the worst emission efficiency, while complexes 2 and 3 exhibited the greatest luminescent efficiency in solid state and in degassed CH(2)Cl(2) solution at room temperature, respectively. This structural relationship could be due to the simultaneously weakened hydride and the monodentate bdpH bonding that are destabilized by the trans-pyrazolate anion and cyclometalated benzyl group, respectively.

Reactions of the (2-pyridyl) pyrrolide platinum(II) complex driven by sterically encumbered chelation: a model for the reversible attack of alcohol at the coordinated carbon monoxide.

Treatment of 3,5-bis(trifluoromethyl)-2-(2'-pyridyl)pyrrole (fpyroH) with Pt(DMSO)2Cl2 and Na2CO3 in THF solution gave a light-yellow complex denoted as [Pt(fpyro)2] (1). A single-crystal X-ray diffraction study on 1 revealed a large conformational distortion around the platinum(II) center, which is attributed to interligand repulsion between the pyridyl groups and the CF3 substituents of the nearby pyrrolides. Reaction of 1 with N- and C-donor ligands such as acetonitrile, pyridine, isocyanide, and CO affords the adducts [Pt(fpyro)2(L)], L = NCMe (2), pyridine (3), CNBut (4), and CO (5), showing formation of one monodentate fpyro ligand by release of the strain energy. The variable-temperature 1H NMR studies showed a static structure for the N-substituted adducts 2 and 3, whereas the C-adducts 4 and 5 are shown to be more labile, displaying a pairwise exchange of bidentate and monodentate fpyro ligands in solution. Addition of ethanol to the coordinated CO in 5 during recrystallization is also established, affording an ethoxycarbonyl complex [Pt(fpyro)(fpyroH)(CO2Et)] (6), which was isolated as a crystalline solid and can be readily converted back to 5 and free ethanol upon dissolution at room temperature.