Tetradentate Pt(II) Complexes with Peripheral Hindrances for Highly Efficient Solution-Processed Blue Phosphorescent OLEDs.

Two tetradentate Pt(II) complexes with peripheral bulky-group hindrances [Pt(pzpyOczpy-B1) and Pt(pzpyOczpy-B2)] were synthesized and fully investigated for their structural and blue phosphorescent properties. Both X-ray crystallography and computational simulation revealed that bulky substituents incorporated into the C-pyrazolyl and C-pyridinyl positions lie out of the cyclometallated plane, thus alleviating the intramolecular distortions as well as reducing the intermolecular interaction in the solid state. In dichloromethane, their emission peaks at 460 nm with a narrow full width at half-maximum (FWHM) of less than 50 nm, and the photoluminescent quantum yields are over 95% with short decay lifetimes (<5 µs). Solution-processed blue devices are fabricated based on the two complexes. Device A based on Pt(pzpyOczpy-B1) shows excellent electroluminescent performances with the maximum current efficiency, power efficiency, and external quantum efficiency of 47.0 cd/A, 24.6 lm/W, and 22.9%, respectively. The understanding on inert peripheral hindrances provides an effective approach to designing Pt(II) complexes for high-quality blue phosphorescent emitters.

Structural modulation induced by cobalt-based ionic liquids for enhanced thermoelectric transport in PEDOT:PSS.

Poly(3,4ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) has been intensively studied for its thermoelectric applications. Structural modulation to improve crystalline ordering, chain conformation and film morphology is a promising way to decouple the trade-off between conductivity and Seebeck coefficient and thus improve the thermoelectric power factor. Post treatment with ionic liquid ([CoCl2 ⋅ 6H2 O]:[ChCl]) bearing cobalt-containing anions resulted in a remarkable enhancement of the power factor to 76.8 µW m-1 K-2 . This IL combines the influence of a high-boiling polar organic solvent and diffusing ions. A high σ mainly resulted from the efficient removal of PSS chains, ordering of the structure and delocalization of bipoloran-dominant transport after conformational change. The increase in S was not due to dedoping of PEDOT chains, but rather the sharp feature of the density of states at the Fermi level induced by ion-exchange with unconventional anions.