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Modifying Emission Spectral Bandwidth of Phosphorescent Platinum(II) Complexes Through Synthetic Control
journal contribution
posted on 2017-06-26, 11:48 authored by Guijie Li, Alicia Wolfe, Jason Brooks, Zhi-Qiang Zhu, Jian LiThe design, synthesis,
and characterization of a series of tetradentate
cyclometalated Pt(II) complexes are reported. The platinum complexes
have the general structure Pt(ppz-O-CbPy-R), where
a tetradentate cyclometalating ligand is consisting of ppz (3,5-dimethyl-1-phenyl-pyrazole), CbPy (carbazolylpyridine) components,
and an oxygen bridging group. Variations of the R group on the pyridyl
ring with various electron withdrawing and donating substituents are
shown to have profound effects on the photophysical properties of
Pt complexes. Electrochemical analysis indicates that reduction process
occurs mainly on the electron-accepting pyridyl group, and the irreversible
oxidation process is primarily localized on the metal-phenyl portions.
The studies of their photophysical properties indicate that the lowest
excited state of the platinum complexes is a ligand-centered 3π–π* state with minor to significant 1MLCT/3MLCT character and are strongly dependent
on the nature of the electron-accepting pyridyl moiety. A systematic
study of the substituent effects on the pyridyl ring demonstrates
that the T1 state properties can be tuned by altering the
functionality and positions of substituents. Importantly, it is revealed
that how the emission spectra of the Pt(II) complexes can be significantly
narrowed and why it can be achieved by incorporating an electron-donating
group on the 4-position of the pyridyl ring. Most of the Pt(II) complexes
reported here are highly emissive at room temperature in dichloromethane
solutions (Φ = 1.1–95%) and in doped PMMA films (Φ
= 29–88%) with luminescent lifetimes in the microsecond range
(τ = 0.6–13.5 μs in solution and 0.9–11.3
μs in thin film respectively) and λmax = 442–568
nm and 440–544 nm in solution and thin film, respectively.
Moreover, these complexes are neutral and thermally stable for sublimation,
indicating that they can be useful for display and solid-state lighting
applications.