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Title: Highly luminescent palladium(II) complexes with sub-millisecond blue to green phosphorescent excited states. Photocatalysis and highly efficient PSF-OLEDs
Authors: Chow, PK
Cheng, G
Tong, GSM
Ma, C
Kwok, WM 
Ang, WH
Chung, CYS
Yang, C
Wang, F
Che, CM
Issue Date: 2016
Publisher: Royal Society of Chemistry
Source: Chemical science, 2016, v. 7, no. 9, p. 6083-6098 How to cite?
Journal: Chemical science 
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 80000 h, have been realized.
ISSN: 2041-6520 (print)
2041-6539 (online)
DOI: 10.1039/c6sc00462h
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