Theoretical study on thermally activated delayed fluorescent molecules based on space charge transfer

Area of Science:

• Materials Science
• Organic Electronics
• Quantum Chemistry

Background:

• Thermally Activated Delayed Fluorescent (TADF) molecules are crucial for efficient organic light-emitting diodes (OLEDs).
• Through-space charge transfer (TSCT) is a key mechanism influencing TADF properties.
• Understanding structure-property relationships is vital for designing novel TADF emitters.

Purpose of the Study:

• To investigate the impact of electron-withdrawing groups on TSCT-TADF molecules.
• To quantitatively analyze the TSCT character in TPA-ace based systems.
• To elucidate the factors governing TADF efficiency in these materials.

Main Methods:

• Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations.
• Polarizable Continuum Model (PCM) for solvent effects (Methylcyclohexane, Toluene, Dichloromethane).
• Analysis of charge transfer ratios, energy gaps (ΔE_ST), spin-orbit coupling, and intersystem crossing rates.

Main Results:

• Stronger electron-withdrawing groups induce redshift in emission and decrease the singlet-triplet energy gap (ΔE_ST).
• Quantitative analysis confirmed the significant TSCT character in TPA-ace-TRZ.
• Calculated spin-orbit coupling and intersystem crossing rates provide insights into TADF mechanisms.

Conclusions:

• The electron-withdrawing ability of acceptors directly influences the optoelectronic properties of TSCT-TADF molecules.
• The findings support the TSCT mechanism as a viable strategy for developing efficient TADF emitters.
• This study provides a computational basis for designing next-generation OLED materials.