Minimization of solid-state conformational disorder in donor-acceptor TADF compounds

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Flexible donor-acceptor structures in TADF compounds lead to conformational disorder in solid-state.
• This disorder negatively impacts emission properties and OLED performance.
• Predictable solid-state emission properties are crucial for advanced TADF materials.

Purpose of the Study:

• To investigate the relationship between molecular rigidity and solid-state TADF properties.
• To understand how molecular structure influences conformational disorder and emission characteristics.
• To guide the design of TADF materials for improved OLED applications.

Main Methods:

• Systematic study of two TADF compounds (PTZ-mPYR and 4CzPN) with varying molecular rigidity.
• Comparative analysis with a related compound (PXZ-PYR) featuring a more constrained donor unit.
• Evaluation of conformational disorder in diluted polymer films and its effect on TADF properties.

Main Results:

• Conformational disorder extent is directly dependent on molecular structure.
• Less rigid PTZ-mPYR exhibited prolonged TADF lifetime due to dispersed energy gaps.
• Rigid 4CzPN showed rapid TADF decay with reduced conformational disorder.
• Sterically constrained planar donor units were found to be preferable for minimizing disorder.

Conclusions:

• Molecular rigidity is a key factor in determining solid-state TADF properties.
• Minimizing conformational disorder through structural design enhances TADF efficiency.
• Findings are vital for designing efficient solid-state TADF materials for OLEDs with reduced efficiency roll-off.