Efficiency Boost in Through Space Charge Transfer Emitters: Insights from Spiro Lateral Rocking Confinement

Area of Science:

• Materials Science
• Organic Chemistry
• Photophysics

Background:

• Intramolecular through-space charge-transfer (TSCT) excited states are key for thermally activated delayed fluorescence (TADF) emitters.
• Tuning excited state dynamics is crucial for efficient exciton utilization in TADF materials.
• Conformational engineering presents challenges but offers opportunities for performance enhancement.

Purpose of the Study:

• To develop a strategy for enhancing TSCT-TADF molecule performance by controlling conformational dynamics.
• To investigate the impact of restricted molecular motion on excited state properties.
• To design and synthesize novel TSCT-TADF emitters for high-efficiency organic light-emitting diodes (OLEDs).

Main Methods:

• Synthesized two TSCT-TADF emitters, 8PhDM-B and 8PyDM-B, utilizing a rigid spiro-fluorene bridge.
• Incorporated immobilizing groups to restrict the lateral rocking of the spiro unit.
• Fabricated OLED devices using the synthesized emitters to evaluate their performance.

Main Results:

• The immobilization strategy effectively restricted the lateral rocking of the spiro unit, influencing donor-acceptor conformations.
• OLED devices incorporating 8PhDM-B and 8PyDM-B achieved high maximum external quantum efficiencies of 33.1% and 31.0%, respectively.
• Demonstrated a clear correlation between restricted molecular motion and improved emitter performance.

Conclusions:

• Restricting molecular rocking via immobilizing groups is an effective strategy to enhance TSCT-TADF emitter performance.
• This approach allows for fine-tuning of excited state dynamics, leading to improved exciton utilization.
• The findings provide valuable insights for the rational design of next-generation, highly efficient OLED emitters.