Thermally activated delayed fluorescence materials with aggregation-induced emission properties: a QM/MM study

Area of Science:

• Materials Science
• Organic Chemistry
• Photophysics

Background:

• Organic molecules with TADF and AIE properties are key for OLEDs.
• Multicolor mechanochromic luminescence (MCL) is a desired feature.
• Understanding aggregation effects on TADF emitters is crucial.

Purpose of the Study:

• To theoretically investigate the luminescence characteristics of DMAC-CNQ, an organic emitter with TADF and AIE properties.
• To quantify the relationship between TADF properties and aggregation states.
• To explore the impact of aggregation on photophysical properties.

Main Methods:

• Quantum mechanics and molecular mechanics (QM/MM) method.
• Calculation of photophysical properties in gas, solid, and amorphous states.
• Analysis of molecular stacking and geometric torsion effects.

Main Results:

• Aggregation states significantly enhance reverse intersystem crossing rates and transition dipole moments.
• Aggregation suppresses non-radiative decay rates from the lowest excited singlet state (S1) to the ground state (S0).
• Molecular stacking restricts DMAC moiety torsion (decreasing non-radiative decay) and CNQ moiety torsion (increasing reverse intersystem crossing).

Conclusions:

• The study quantifies how aggregation states influence TADF properties.
• Calculated fluorescence efficiencies (67% crystal, 26% amorphous) align with experimental data.
• Theoretical insights aid in designing efficient TADF emitters for OLED applications.