Pyrazolate-Bridged NHC Cyclometalated [Pt₂] Complexes and [Pt₂Ag(PPh₃)]⁺ Clusters in Electroluminescent Devices

Area of Science:

• Coordination Chemistry
• Materials Science
• Photophysics

Background:

• Ionic transition metal complexes (iTMCs) offer tunable electronic and photophysical properties.
• Platinum-based complexes are of interest for optoelectronic applications due to their luminescence.
• Bridging ligands can influence the structure and properties of multinuclear metal complexes.

Purpose of the Study:

• To synthesize and characterize novel ionic platinum-silver complexes with imidazole-2-ylidene ligands.
• To investigate the structural, photophysical, and electroluminescent properties of these iTMCs.
• To evaluate the potential of selected complexes as active materials in organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs).

Main Methods:

• Synthesis and full characterization of neutral and ionic platinum-silver complexes.
• X-ray diffraction analysis to determine solid-state structures.
• Nuclear Magnetic Resonance (NMR) spectroscopy (195Pt and 31P) to confirm solution structures.
• Photoluminescence spectroscopy and theoretical calculations.
• Fabrication and testing of OLEDs and LECs.

Main Results:

• Novel iTMCs, [{Pt(C^C*)(μ-Rpz)}2Ag(PPh3)]X, were successfully synthesized and characterized.
• X-ray diffraction revealed a unique 'open book' structure with Pt-Ag donor-acceptor bonds (dPt-Ag ≈ 2.78 Å).
• NMR studies confirmed the retention of these structures in solution.
• Diphenylpyrazolate derivatives exhibited the highest photoluminescence quantum yield (PLQY) in the solid state.
• OLEDs fabricated with precursor C showed promising performance: turn-on voltage 3.2 V, peak luminance 21,357 cd m⁻², peak current efficiency 28.8 cd A⁻¹ (9.5% EQE), and lifetime t50 of 15.7 h.
• OLEDs with iTMC 2c achieved a maximum luminance of 114 cd m⁻², while LECs showed a maximum luminance of 20 cd m⁻² and a current efficiency of 0.2 cd A⁻¹ with a t50 of 50 min.

Conclusions:

• The synthesized ionic platinum-silver complexes possess stable structures in both solid and solution states.
• The diphenylpyrazolate derivatives are highly emissive, making them suitable for optoelectronic applications.
• The neutral precursor C demonstrates excellent performance in OLED devices, highlighting its potential for practical applications.