Issue 9, 2016

Highly luminescent palladium(ii) complexes with sub-millisecond blue to green phosphorescent excited states. Photocatalysis and highly efficient PSF-OLEDs

Abstract

Palladium(II) complexes supported by tetradentate [N^C^C^N] and [O^N^C^N] ligand systems display sky blue to red phosphorescence with emission quantum yields and emission lifetimes up to 0.64 and 272 μs, respectively. Femtosecond time-resolved fluorescence (fs-TRF) measurements on these Pd(II) complexes reveal a fast intersystem crossing from singlet to triplet manifolds with time constants of 0.6–21 ps. DFT/TDDFT calculations revealed that, as a result of the spiro-fluorene and bridging tertiary amine units of the ligands, the T1 excited state is more ligand-localized and has smaller structural distortion, leading to slower non-radiative decay as well as radiative decay of T1 → S0 transition and thereby highly emissive, long-lived triplet excited states. The Pd(II) complexes have been found to be efficient catalysts for visible light-driven, reductive C–C bond formation from unactivated alkyl bromides with conversions and yields of up to 90% and 83%, respectively. These complexes have also been employed as photosensitizers for [2 + 2] cycloaddition of styrenes, with conversions and yields comparable to those of the reported Ir(III) complexes. Both green and sky blue organic-light emitting devices (OLEDs) have been generated with these Pd(II) complexes as guest emitters. Maximum external quantum efficiencies (EQE) of up to 16.5% have been achieved in the sky blue OLEDs. The long emission lifetimes render the Pd(II) complexes good sensitizers for phosphor-sensitized fluorescent OLEDs (PSF-OLEDs). By utilizing these phosphorescent Pd(II) complexes as sensitizers, highly efficient green and yellow PSF-OLEDs having high EQE (up to 14.3%), high colour purity and long operation lifetimes, with 90% of initial luminance (LT90) for more than 80 000 h, have been realized.

Graphical abstract: Highly luminescent palladium(ii) complexes with sub-millisecond blue to green phosphorescent excited states. Photocatalysis and highly efficient PSF-OLEDs

Supplementary files

Article information

Article type
Edge Article
Submitted
29 Jan 2016
Accepted
23 May 2016
First published
15 Jun 2016
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2016,7, 6083-6098

Highly luminescent palladium(II) complexes with sub-millisecond blue to green phosphorescent excited states. Photocatalysis and highly efficient PSF-OLEDs

P. Chow, G. Cheng, G. S. M. Tong, C. Ma, W. Kwok, W. Ang, C. Y. Chung, C. Yang, F. Wang and C. Che, Chem. Sci., 2016, 7, 6083 DOI: 10.1039/C6SC00462H

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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