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Tuning Emission Lifetimes of Ir(C^N)2(acac) Complexes with Oligo(phenyleneethynylene) Groups
Ross Davidson1, Yu-Ting Hsu1, Mark A Fox1
1Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, England, U.K.
Inorganic Chemistry
|January 27, 2023
Summary
New iridium complexes with oligo(para-phenyleneethynylene) (OPE3) motifs exhibit extended emission lifetimes up to 625 μs. This is achieved through reversible electronic energy transfer (REET), enabling potential applications in oxygen sensing and cellular imaging.
Area of Science:
- Coordination Chemistry
- Photophysics
- Materials Science
Background:
- Long emission lifetimes (μs to ms) in visible light are crucial for applications like oxygen sensing and cellular imaging.
- Iridium(III) complexes, specifically Ir(ppy)2(acac), are known for their emissive properties.
- Oligo(para-phenyleneethynylene) (OPE3) motifs possess long-lived triplet states accessible for energy transfer.
Purpose of the Study:
- To synthesize and investigate the photophysical properties of nine novel Ir(ppy)2(acac) complexes functionalized with OPE3 units.
- To explore the impact of OPE3 motif integration (at acac, ppy, or via a durylene linker) on emission lifetimes and mechanisms.
- To evaluate the potential of these complexes for oxygen sensing and cellular imaging applications.
Main Methods:
- Synthesis of nine Ir(ppy)2(acac) complexes featuring OPE3 units at different positions (aOPE3, pOPE3, dOPE3).
- Spectroscopic analysis, including excitation wavelength-dependent and time-dependent emission spectra.
- Lifetime measurements to quantify emission durations and investigate energy transfer processes.
Main Results:
- Decoupled aOPE3 and dOPE3 complexes exhibited significantly longer emission lifetimes (50-625 μs) compared to conjugated pOPE3 complexes (0.69-32.8 μs) and non-OPE3 controls (1.00-23.1 μs).
- The extended lifetimes in aOPE3 and dOPE3 complexes are attributed to intramolecular reversible electronic energy transfer (REET) between triplet-state metal-to-ligand charge transfer (3MLCT) and OPE3 states.
- dOPE3 complexes showed visible emission maxima (524-526 nm) and photoluminescent quantum yields (0.44-0.60), suitable for practical applications.
Conclusions:
- The strategic incorporation of OPE3 motifs, particularly when decoupled from the Ir(ppy)2(acac) core, enables significantly prolonged emission lifetimes via REET.
- The observed long lifetimes, emission wavelengths, and quantum yields make dOPE3 complexes promising candidates for advanced sensing and imaging technologies.
- Understanding the REET mechanism provides a pathway for designing next-generation emissive materials with tailored photophysical properties.
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