Intramolecular locking and coumarin insertion: a stepwise approach for TADF design

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Thermally activated delayed fluorescence (TADF) emitters are crucial for efficient organic light-emitting diodes (OLEDs).
• The Qx-Ph-DMAC fluorophore serves as a foundational structure for developing new TADF materials.
• Optimizing TADF performance requires careful molecular design to control excited state energy levels.

Purpose of the Study:

• To design and synthesize novel TADF emitters based on the Qx-Ph-DMAC scaffold.
• To investigate the impact of structural modifications on the photophysical properties and TADF performance.
• To understand the relationship between molecular structure, excited state dynamics, and emission characteristics.

Main Methods:

• Synthesis of three novel TADF emitters: BQx-Ph-DMAC, ChromPy-Ph-DMAC, and DBChromQx-DMAC.
• Theoretical and experimental studies of photophysical properties, including absorption, emission, and excited state lifetimes.
• Fabrication of thin films (1 w/w% in zeonex) to evaluate TADF performance.

Main Results:

• BQx-Ph-DMAC showed increased conjugation length.
• ChromPy-Ph-DMAC and DBChromQx-DMAC exhibited red-shifted emission due to coumarin incorporation and further conjugation.
• The coumarin unit significantly reduced the singlet-triplet energy gap, enhancing TADF efficiency.
• 'Locking' the molecular structure in DBChromQx-DMAC further decreased the energy gap, improving reverse intersystem crossing.

Conclusions:

• Structural modifications, including extending conjugation and incorporating electron-deficient units, significantly enhance TADF emitter performance.
• Decreasing the singlet-triplet energy gap is key to improving TADF efficiency through enhanced reverse intersystem crossing.
• The developed emitters demonstrate promising potential for advanced OLED applications.