Aggregation-assisted energy gap modulation controls delayed emission in hybrid charge-transfer emitters

Area of Science:

• Materials Science
• Photochemistry
• Organic Electronics

Background:

• Tailoring long-lived delayed emission in organic materials is crucial for applications like OLEDs and sensors.
• Understanding excited-state energy landscapes and the role of molecular aggregation is key to controlling photoluminescence pathways.

Purpose of the Study:

• To investigate how molecular aggregation influences the balance between delayed fluorescence (DF) and room-temperature phosphorescence (RTP).
• To demonstrate aggregation-assisted energy gap modulation in indole-based hybrid charge-transfer emitters.

Main Methods:

• Synthesis of indole-based hybrid charge-transfer emitters (HD and brominated BrD).
• Time-resolved spectroscopy to analyze excited-state dynamics.
• Theoretical calculations to elucidate excited-state evolution and energy landscapes.

Main Results:

• J-aggregation in HD reduced the singlet-triplet energy gap, enhanced reverse intersystem crossing (RISC), and favored DF.
• H-aggregation in BrD increased the singlet-triplet energy gap, suppressed RISC, and resulted in prominent RTP.
• Hybridization of local-excited and charge-transfer states mediated excited-state evolution, with aggregation type dictating photoluminescence pathway.

Conclusions:

• Molecular aggregation directly influences the choice between DF and RTP pathways in organic materials.
• Aggregation-assisted energy gap modulation provides a strategy for tuning delayed emission properties.
• This study establishes a structure-property relationship for designing organic emitters with desired delayed luminescence characteristics.