Enhancing Thermally Activated Delayed Fluorescence by Fine-Tuning the Dendron Donor Strength

Area of Science:

• Organic electronics
• Photophysics
• Materials science

Background:

• Thermally activated delayed fluorescence (TADF) enables efficient light emission by utilizing small energy gaps between singlet and triplet states.
• Achieving efficient TADF requires balancing reduced wavefunction overlap (for small singlet-triplet gaps) with sufficient overlap (for oscillator strength).

Purpose of the Study:

• To investigate a method for fine-tuning wavefunction overlap in TADF emitters using donor dendrons.
• To understand how varying donor dendron functionality impacts photoluminescence properties and TADF efficiency.

Main Methods:

• Synthesis of carbazole-phthalonitrile (2CzPN) based donor-acceptor emitters with progressively functionalized donor dendrons (carbazole, tert-butylphenylamine, phenoxazine).
• Photoluminescence studies and density functional theory (DFT) calculations to analyze singlet-triplet energy gap (ΔEST) and wavefunction overlap.

Main Results:

• A gradual decrease in ΔEST from 300 to 10 meV was achieved by modifying donor dendrons.
• Sufficient oscillator strength was maintained with carbazole and tert-butylphenylamine dendrons.
• Excessive wavefunction overlap reduction with the phenoxazine dendron diminished oscillator strength, hindering efficient emission.

Conclusions:

• Donor dendron extension is a viable strategy for precisely controlling the photoluminescence properties of TADF emitters.
• Optimizing TADF emitters requires a careful balance between minimizing the singlet-triplet gap and maintaining adequate wavefunction overlap for strong oscillator strength.