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Strongly Phosphorescent Transition-Metal Complexes with N-Heterocyclic Carbene Ligands as Cellular Probes

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Luminescent and Photoactive Transition Metal Complexes as Biomolecular Probes and Cellular Reagents

Part of the book series: Structure and Bonding ((STRUCTURE,volume 165))

Abstract

The development of functionalized luminescent transition-metal complexes that selectively target specific cellular structures (proteins, organelles, or nucleic acids) has been and continues to be an area of burgeoning interest in the design of luminescent probes and/or anticancer agents. The prevalence of deriving phosphorescent probes is owing to their long emission lifetimes (100 ns to ms), tunable emission wavelength, and fairly large Stokes shifts (hundreds of nm). However, metal complexes often suffer from the obstacles including low stability, inadequate water solubility, and low cellular uptake. The charge neutral and strong σ donor properties of N-heterocyclic carbene (NHC) ligands render NHCs as excellent ancillary ligands to form cationic metal complexes with high stability. More importantly, coordination of transition-metal ion with NHC ligand leads to the destabilization of the strongly antibonding metal (ndx2 -y2)-ligand orbital; consequently the non-radiative decay of the emissive excited state is strongly suppressed with concomitant enhancement of both the emission quantum yield and emission lifetime. In this review, we highlight recent works on luminescent transition-metal complexes with NHC ligands and their applications as cellular probes and bio-imaging reagents. In particular, examples of luminescent transition-metal complexes with planar d8 (e.g., Pt2+, Au3+), linear d10 (e.g., Au+), and octahedral d6 (e.g., Ir3+) metal centers are focused. The structural features of luminescent metal complexes in relation to their cellular uptake, localization properties, and designated biomolecular interactions for specific analytical and biological applications are discussed.

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Acknowledgments

We thank the National Key Basic Research Program of China (2013CB834802) and the University Grants Committee (Area of Excellence Scheme AoE/P-03/08, HKSAR, China) for financial support.

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Authors and Affiliations

  1. Department of Chemistry, State Key Laboratory of Synthetic Chemistry, Institute of Molecular Functional Materials, Chemical Biology Centre, The University of Hong Kong, Pokfulam Road, Hong Kong, China

    Taotao Zou, Faan-Fung Hung, Chen Yang & Chi-Ming Che

  2. HKU Shenzhen Institute of Research and Innovation, Shenzhen, 518053, China

    Taotao Zou, Chen Yang & Chi-Ming Che

Authors
  1. Taotao Zou
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  2. Faan-Fung Hung
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  3. Chen Yang
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  4. Chi-Ming Che
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Correspondence to Chi-Ming Che .

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Editors and Affiliations

  1. City University of Hong Kong, City University of Hong Kong, Hong Kong, China

    Kenneth Kam-Wing Lo

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Zou, T., Hung, FF., Yang, C., Che, CM. (2015). Strongly Phosphorescent Transition-Metal Complexes with N-Heterocyclic Carbene Ligands as Cellular Probes. In: Lo, KW. (eds) Luminescent and Photoactive Transition Metal Complexes as Biomolecular Probes and Cellular Reagents. Structure and Bonding, vol 165. Springer, Berlin, Heidelberg. https://doi.org/10.1007/430_2015_173

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