期刊
CHEMICAL SCIENCE
卷 7, 期 9, 页码 6083-6098出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c6sc00462h
关键词
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资金
- National Key Basic Research Program of China [2013CB834802]
- Hong Kong Research Grants Council [HKU 700812P, HKU17300614]
- Hong Kong UGC Special Equipment Grant [SEG HKU09]
- Guangdong Special Project of the Introduction of Innovative RD Teams, China
- [T23-713/11]
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 ms, 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 T-1 excited state is more ligand-localized and has smaller structural distortion, leading to slower non-radiative decay as well as radiative decay of T-1 -> S-0 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.
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