Ultrafast Spectroscopic Investigation of the Aggregation Induced TADF from High-Level Reversed Intersystem Crossing.

Area of Science:

• Materials Science
• Photophysics
• Organic Electronics

Background:

• Thermally activated delayed fluorescence (TADF) offers efficient utilization of triplet excitons.
• High-level intersystem crossing (hRISC) is a key mechanism for TADF generation.
• Understanding aggregation effects is crucial for optimizing optoelectronic materials.

Purpose of the Study:

• To investigate the influence of aggregation on the luminescence properties of DPA-FBP and TPA-FBP.
• To elucidate the role of doping concentration in enabling TADF via hRISC.
• To explore aggregation-induced changes in excited-state dynamics.

Main Methods:

• Doping DPA-FBP and TPA-FBP into PMMA films at varying weight fractions (1 wt % and 50 wt %).
• Photoluminescence spectroscopy to analyze emission properties.
• Femtosecond transient absorption (fs-TA) spectroscopy to probe excited-state dynamics.

Main Results:

• TADF via hRISC was observed only in the 50 wt % doped film.
• The 1 wt % doped film exhibited only prompt fluorescence.
• fs-TA spectroscopy revealed charge transfer species formation in the 50 wt % film, lowering the energy gap.
• The 1 wt % film showed rapid transition to the lowest triplet state due to unfavorable energy splitting.

Conclusions:

• Aggregation plays a critical role in facilitating TADF from hRISC in DPA-FBP and TPA-FBP.
• Concentration-dependent aggregation can tune excited-state pathways, enabling efficient reverse intersystem crossing.
• This work provides insights into aggregation effects on hot exciton materials for solid-state photodynamic applications.