Excited-State Engineering toward Accelerated Reverse Intersystem Crossing in Diindolocarbazole-Embedded...

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Developing efficient, pure-colored blue organic light-emitting diodes (OLEDs) is challenging.
• Diindolocarbazole emitters offer narrow emission but suffer from slow reverse intersystem crossing (RISC) rates (10^2 s^-1).
• Slow RISC limits the practical application of these promising emitters.

Purpose of the Study:

• To accelerate the RISC process in diindolocarbazole-based emitters.
• To improve the efficiency of blue OLEDs without compromising emission properties.
• To provide a design strategy for high-performance emitters.

Main Methods:

• Decorating diindolocarbazole emitters with electron-withdrawing groups (TPT) to modulate excited states.
• Inducing long-range charge transfer states to decrease energy gaps (ΔE_ST).
• Enhancing spin-orbital coupling (SOC) matrix elements.

Main Results:

• Achieved a significantly accelerated RISC rate (k_RISC) of 1.11 × 10^4 s^-1 for pICz-TPT.
• Retained narrowband blue emission (peak at 449 nm, FWHM of 44 nm, CIE (0.15, 0.10)).
• Demonstrated high maximum external quantum efficiencies (EQE_max) of 14.4% in non-sensitized OLEDs and 24.2% in hyperfluorescent OLEDs.

Conclusions:

• Acceptor decoration effectively accelerates RISC by tuning excited states and SOC.
• The developed pICz-TPT emitter achieves high efficiency and good color purity in blue OLEDs.
• This approach offers a powerful strategy for designing efficient, pure-colored emitters.