Thermally Activated Delayed Fluorescence and Aggregation Induced Emission with Through-Space Charge Transfer

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Donor-acceptor molecules are crucial for optoelectronic applications.
• 9,9-dimethylxanthene serves as a rigid bridge to control molecular geometry.
• Spatial charge transfer is key for efficient light emission.

Purpose of the Study:

• To synthesize and characterize novel emissive molecules (XPT, XCT, XtBuCT) based on a 9,9-dimethylxanthene core.
• To investigate the relationship between molecular structure, solid-state packing, and photophysical properties.
• To evaluate the performance of these molecules in organic light-emitting devices (OLEDs).

Main Methods:

• Synthesis of XPT, XCT, and XtBuCT molecules.
• Photophysical characterization including quantum yield and fluorescence lifetime measurements.
• X-ray crystallography to determine solid-state structures.
• Fabrication and testing of OLED devices.

Main Results:

• Molecules exhibit cofacial donor-acceptor alignment (3.3-3.5 Å) facilitating charge transfer.
• Thermally activated delayed fluorescence (TADF) observed with microsecond lifetimes.
• Significantly higher quantum yields in the solid state compared to solution.
• Crystal structures reveal dominant C-H···π intermolecular interactions promoting aggregation-induced emission.
• OLEDs with XPT and XtBuCT dopants achieved external quantum efficiencies up to 10%.

Conclusions:

• The 9,9-dimethylxanthene bridge effectively promotes efficient emission through controlled molecular architecture.
• Aggregation-induced enhanced emission is a key factor for solid-state performance.
• These molecules represent promising materials for high-efficiency OLED applications.