Allochroic thermally activated delayed fluorescence diodes through field-induced solvatochromic effect

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Allochroic organic light-emitting diodes (AOLEDs) show promise for intelligent applications due to their field-dependent color variation.
• Existing AOLEDs often suffer from limited repeatability, stability, and electroluminescence (EL) performance due to complex mechanisms like recombination zone changes or energy transfer.

Purpose of the Study:

• To develop a novel thermally activated delayed fluorescence (TADF) diode with an irreversible, voltage-driven emission color change.
• To leverage the solvatochromic effect and host polarity modulation for controlled color switching in AOLEDs.
• To achieve superior EL performance and explore applications in data storage and information security.

Main Methods:

• Design and synthesis of a novel TADF molecule and its host material, 3,6-di-tert-butyl-1,8-bis(diphenylphosphoryl)-9H-carbazole (tBCzHDPO).
• Investigation of the host material's field-dependent polarity reduction via hydrogen bond-induced conformational isomerization.
• Fabrication and characterization of the TADF diode, evaluating its electroluminescence properties and color-switching behavior.

Main Results:

• The TADF diode demonstrated a successive and irreversible emission color change from bluish green to deep blue upon increasing voltage.
• The host material exhibited a significant polarity reduction from 7.9 to 3.3 D, driven by conformational isomerization.
• The device achieved high external quantum efficiency (>15%), representing the best EL performance reported for AOLEDs to date.

Conclusions:

• The developed TADF diode offers a unique irreversible allochroic characteristic for visible data storage and information security.
• The study highlights the potential of host polarity modulation via solvatochromism for advanced AOLED functionalities.
• This work sets a new benchmark for EL performance in AOLEDs and opens avenues for novel electronic devices.