Controlling the intersystem crossing/reverse intersystem crossing (ISC/RISC) competition to achieve efficient red...

Area of Science:

• Materials Science
• Organic Chemistry
• Photophysics

Background:

• Tuning photophysical properties of organic molecules is crucial for advanced optoelectronic devices.
• Achieving efficient room-temperature phosphorescence (RTP) in metal-free organic materials remains a challenge.
• Controlling intersystem crossing/reverse intersystem crossing (ISC/RISC) is key to managing emission pathways.

Purpose of the Study:

• To systematically modulate emission properties from fluorescence to RTP in D-A-D organic molecules.
• To investigate the effect of incorporating chalcogen atoms (O, S, Se) on photophysical behavior.
• To develop efficient metal-free red-emitting phosphorescent materials for organic light-emitting diodes (OLEDs).

Main Methods:

• Synthesis of D-A-D molecules (PhODCB, PhSDCB, PhSeDCB) with varying chalcogen atoms.
• Systematic modulation of intersystem crossing/reverse intersystem crossing (ISC/RISC) competition.
• Photophysical characterization including quantum yield and lifetime measurements.
• Fabrication and testing of organic light-emitting diodes (OLEDs).

Main Results:

• Incorporating O, S, and Se atoms shifted emission from fluorescence to thermally activated delayed fluorescence (TADF) and then to RTP.
• Enhanced heavy-atom effect and n → π* transitions correlated with improved quantum yield and radiative decay.
• PhSeDCB demonstrated unprecedented red-emitting RTP with a high photoluminescence quantum yield (PLQY) of 0.48 and short lifetime (14.7 µs).
• Red OLEDs fabricated with PhSeDCB achieved a high electroluminescence efficiency of 18.9%.

Conclusions:

• Chalcogen substitution effectively controls photophysical pathways in D-A-D organic molecules.
• Metal-free PhSeDCB is a promising red-emitting RTP material for high-performance OLEDs.
• This strategy offers significant potential for developing novel phosphorescent organic materials.