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

Pui Keong Chow, Gang Cheng, Glenna So Ming Tong, Chensheng Ma, Wai Ming Kwok, Wai Hung Ang, Clive Yik Sham Chung, Chen Yang, Feng Wang, Chi Ming Che

Research output: Journal article publicationJournal articleAcademic researchpeer-review

77 Citations (Scopus)

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 T1excited state is more ligand-localized and has smaller structural distortion, leading to slower non-radiative decay as well as radiative decay of T1→ S0transition 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.
Original languageEnglish
Pages (from-to)6083-6098
Number of pages16
JournalChemical Science
Volume7
Issue number9
DOIs
Publication statusPublished - 1 Jan 2016

ASJC Scopus subject areas

  • Chemistry(all)

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