Organic Long-Persistent Luminescence from a Thermally Activated Delayed Fluorescence Compound

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Organic long-persistent luminescence (OLPL) is crucial for long-lived emission applications.
• Current OLPL emitters often rely on expensive bimolecular exciplex systems.
• There is a need for cost-effective and efficient OLPL materials.

Purpose of the Study:

• To design and synthesize a novel thermally activated delayed fluorescence (TADF) compound for room-temperature OLPL.
• To investigate the OLPL properties of the designed compound in various host materials.
• To explore the potential for low-cost, large-scale OLPL applications.

Main Methods:

• Synthesis of the TADF compound CzPhAP (3-(4-(9H-carbazol-9-yl)phenyl)acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile).
• Fabrication of OLPL devices using CzPhAP in hosts like PPT, TPBi, and PMMA.
• Characterization of OLPL properties, including emission duration and spectral analysis at room temperature and 77 K.

Main Results:

• CzPhAP exhibits stable room-temperature OLPL exceeding 1 hour in various hosts, including inexpensive PMMA.
• The compound functions without forming exciplexes, overcoming a limitation of previous OLPL emitters.
• Analysis revealed that low-temperature afterglow spectra onset may not reliably indicate the lowest triplet state energy due to charge recombination effects.

Conclusions:

• The designed TADF molecule CzPhAP offers a promising pathway for developing pure organic, cost-effective, and color-tunable room-temperature OLPL devices.
• The findings challenge the conventional method of determining triplet state energy from low-temperature afterglow spectra in certain TADF systems.
• This research paves the way for scalable and affordable long-lived emission technologies.