Phosphorescent Platinum(II) Complexes with a Spiro-fused Xanthene Unit: Synthesis and Photophysical Properties

Area of Science:

• Organometallic Chemistry
• Materials Science
• Photophysics

Background:

• Platinum(II) complexes are crucial in developing advanced luminescent materials.
• Spiro[fluorene-9,9'-xanthene] (SFX) derivatives offer unique structural and electronic properties for optoelectronic applications.
• Tuning the electronic structure of metal complexes influences their photophysical behavior and emission characteristics.

Purpose of the Study:

• To synthesize and characterize novel platinum(II) complexes incorporating the SFX motif.
• To investigate the photophysical properties, including emission spectra and quantum yields, of these new complexes.
• To explore the relationship between the SFX motif's regioisomerism and the emissive state character.

Main Methods:

• Synthesis of platinum(II) complexes with SFX and various auxiliary ligands (acetylacetonate, mesacac, dihydrobis(3,5-dimethylpyrazole-1-yl) borate).
• Characterization using Nuclear Magnetic Resonance (NMR), X-ray diffraction, and combustion analysis.
• Photoluminescence measurements to determine emission spectra, Commission Internationale de l'Éclairage (CIExy) coordinates, photoluminescence quantum yields (PLQYs), and emission lifetimes.
• Density Functional Theory (DFT) calculations (B3LYP/6-311++G**) to elucidate the nature of the emissive states.

Main Results:

• Successful synthesis of platinum(II) complexes derived from the SFX motif in yields up to 36%.
• Observed structured green-blue emission spectra with CIExy coordinates of (0.21;0.46).
• Achieved excellent photoluminescence quantum yields (PLQYs) between 87% and 91%, with emission lifetimes from 33 μs to 43 μs.
• Computational analysis revealed that the emissive state nature depends on the SFX regioisomerism: 2-SFX complexes show ligand-centered (3LC) emission, while 2 '-SFX complexes with mesacac exhibit significant metal-to-ligand charge transfer (3MLCT) character.

Conclusions:

• The synthesized platinum(II)-SFX complexes are promising candidates for efficient light-emitting applications.
• The regioisomerism of the SFX motif plays a critical role in determining the photophysical properties and the nature of the excited state.
• Understanding the structure-property relationships allows for the rational design of novel phosphorescent materials with tailored emission characteristics.