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(mu-Cl](2), [(fpiq)(2)Ir(mu-Cl](2), and [(fppy)(2)Ir(mu-Cl](2) with diphenyl(1-naphthyl)phosphine (dronH) in decalin at 100 degrees 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 boolean AND 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 la revealed existence of two trans-NW cyclometalates, with both chloride and dpnH donors located at the positions opposite to the phenyl substituents. Subsequent heating of la-lc at higher tempo rature afforded the second isomer (2a-2c), showing formation of cis-NW orientation for the aforementioned cyclometalatos. Further thermolysis of either trans or cis-Ir(111) 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 rlrans-N,N'-[(C boolean AND N)(2)Ir(dpn)] (3a-3c) and cis-N,N'-[(C boolean AND 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 CAN cyclometalates from quinazolinyl, isoquinolinyl, and, finally, to pyridyl fragment, the lowest unoccupied molecular orbitals (LUM0s) 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 thy usefulness of relevant molecular architecture in designing triplet OLED emitters.