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Steric effect on excimer formation in planar Pt(ii) complexes.

Yang-Jin Cho1, So-Yoen Kim1, Ho-Jin Son1

  • 1Department of Advanced Materials Chemistry, Korea University (Sejong), Sejong, 30019, South Korea. hjson@korea.ac.kr sangok@korea.ac.kr.

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Steric hindrance from bulky triphenylsilyl groups influences excimer formation in platinum(II) complexes. This interaction, specifically between pyridine moieties, is key to understanding luminescence in these square planar metal complexes.

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Area of Science:

  • Materials Science
  • Photochemistry
  • Coordination Chemistry

Background:

  • Square planar metal complexes are investigated for their luminescent properties.
  • Excimer formation, a phenomenon where excited molecules interact, influences luminescence intensity and lifetime.
  • Steric effects play a crucial role in molecular packing and intermolecular interactions.

Purpose of the Study:

  • To investigate the steric influence of bulky substituents on excimer formation in platinum(II) complexes.
  • To understand the relationship between molecular structure, steric hindrance, and luminescent properties.
  • To elucidate the mechanism of excimer formation in these Pt(II) systems.

Main Methods:

  • Synthesis of three platinum(II) complexes with varying substituents: Pt(ii)(dfppy)(acac), Pt-2 (with Ph3Si on pyridine), and Pt-3 (with Ph3Si on phenyl).
  • Photoluminescence spectroscopy to analyze emission spectra, lifetimes, and concentration dependence.
  • Stern-Volmer analysis to determine intrinsic emission lifetimes.
  • X-ray crystallography to determine the crystal structures of Pt-1 and Pt-3.

Main Results:

  • Pt(ii) complexes exhibited sky-blue emission around 460 nm.
  • Pt-1 and Pt-3 showed excimer emission around 600 nm in concentrated solutions and solid states.
  • Pt-2, with a bulky group on the pyridine, did not exhibit excimer emission.
  • Emission lifetimes and intensities of monomeric Pt-1 and Pt-3 were concentration-dependent, with reduced monomer lifetimes in concentrated solutions.
  • X-ray crystallography revealed close overlap of LUMO moieties in Pt-1 and Pt-3.

Conclusions:

  • The bulky triphenylsilyl group's steric hindrance significantly impacts excimer formation.
  • LUMO-LUMO interaction between the pyridine moieties of the main ligand is the primary driver for excimer formation.
  • Strategic placement of substituents can control or prevent excimer formation in Pt(II) complexes.