A Remarkable Ligand Orientational Effect in Osmium‐Atom‐Induced Blue Phosphorescence

Abstract

A new series of Os(II)-based carbonyl complexes cis(CO),trans(Npy,Npy),cis(Ntz,Ntz)-[Os(CO)2(bptz)2] (1), cis(CO),cis(Npy,Npy),trans(Ntz,Ntz)-[Os(bptz)2(CO)2] (2), and cis(CO),trans(Npy,Npy),cis(Ntz,Ntz)-[Os(CO)2(fptz)2] (3), where bptz and fptz denote 3-tert-butyl-5-(2-pyridyl)- and 3-trifluoromethyl-5-(2-pyridyl)-1,2,4-triazolate, respectively, have been designed and synthesized in an effort to achieve high efficiency, room-temperature blue phosphorescence. Although 1 and 2 are geometric isomers, remarkably different excited-state relaxation pathways were observed. Complex 1 exhibits strong phosphorescence in CH3CN (Phi(p) approximately 0.47) and as a single crystal at room temperature, whereas complex 2 is nearly nonemissive under similar conditions. The associated relaxation dynamics have been comprehensively investigated by spectroscopic and relaxation dynamics as well as by theoretical approaches. Our results lead us to the conclusion that for complex 2, the "loose bolt" effect of metal-ligand bonding interactions plays a crucial role in the fast radiationless deactivation of this type of geometrical isomer. Fine adjustment can also be achieved by functionalizing the ligands so that the electron-withdrawing nature of the CF3 group in 3 stabilizes the HOMO of the triazolate moiety, thus moving the emission further into the pure "blue" region; this results in highly efficient phosphorescence and renders 3 particularly attractive for application in blue OLED devices.

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

“…[12] Recent reports indicated that both the cyclometalated ligand (C^N)H and pyridyl azole ligand (N^N)H are capawww.chemeurj.org ble of reacting with reagents M 3 (CO) 12 , M= Ru and Os, to afford good yields of octahedral complexes [MA C H T U N G T R E N N U N G (C^N) 2 (CO) 2 ] and [MA C H T U N G T R E N N U N G (N^N) 2 (CO) 2 ], respectively. [13,14] This implies that the (N^N)H ligand could react with IrCl 3 ·nH 2 O to afford trisubstituted [IrA C H T U N G T R E N N U N G (N^N) 3 ] in a fashion akin to the previously men-…”

Arresting “Loose Bolt” Internal Conversion from −B(OH)2 Groups is the Mechanism for Emission Turn-On in ortho-Aminomethylphenylboronic Acid-Based Saccharide Sensors

“…The “loose bolt effect” is an example of Dexter energy transfer (also known as exchange or collisional energy transfer), and is a dynamic quenching mechanism . It is simply another term for vibrational coupling to an electronic excited state that leads to radiationless relaxation, i.e., internal conversion. − On a Jablonski diagram the S 1 to S 0 transition is horizontal, where the ZPE (zero-point energy) of S 1 transitions to an equal energy n-vibrational level of S 0 , followed by Kasha’s rule vibrational relaxation of S 0 . Because the probability of the transition depends upon vibrational overlap it is sensitive to any isotopic substitution in the molecules that modifies the vibrational frequencies involved, and this is the basis of the deuterium substitution experiment presented above .…”

Osmium‐ and Ruthenium‐Based Phosphorescent Materials: Design, Photophysics, and Utilization in OLED Fabrication

“…Treatment of 3‐trifluoromethyl‐5‐(2‐pyridyl)pyrazole (fppz)H and Os 3 (CO) 12 afforded only one complex, 20 , in moderate yield 28. For reactions with the related triazole chelate, two isomeric complexes, 21 and 22 , were observed for the direct treatment of 3‐ tert ‐butyl‐5‐(2‐pyridyl)triazole (bptz)H with Os 3 (CO) 12 29. Separation of products was achieved by using their marked solubility differences in acetone, where the less soluble isomer 21 , which is structurally related to complex 20 , can readily be obtained as a crystalline solid, while isolation of the second complex 22 required repeated extraction and slow diffusion of hexane vapor into a saturated acetone solution at room temperature.…”