Organic Long‐Persistent Luminescence from a Thermally Activated Delayed Fluorescence Compound. Issue 45 (7th October 2020)

• Record Type: Journal Article
• Authors: Li, Wenbo; Li, Zhaoning; Si, Changfeng; Wong, Michael Y.; Jinnai, Kazuya; Gupta, Abhishek Kumar; Kabe, Ryota; Adachi, Chihaya; Huang, Wei; Zysman‐Colman, Eli; Samuel, Ifor D. W.
• Is Part Of: Advanced materials. Volume 32:Issue 45(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-10-07
• Subjects: afterglow -- charge recombination -- charge separation -- long‐persistent luminescence (LPL) -- organic long‐persistent luminescence (OLPL) -- thermally activated delayed fluorescence (TADF); Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adma.202003911
• Languages: English
• ISSNs: 0935-9648

Abstract

Abstract: Organic long‐persistent luminescence (OLPL) is one of the most promising methods for long‐lived‐emission applications. However, present room‐temperature OLPL emitters are mainly based on a bimolecular exciplex system which usually needs an expensive small molecule such as 2, 8‐bis(diphenyl‐phosphoryl)dibenzo[b, d]thiophene (PPT) as the acceptor. In this study, a new thermally activated delayed fluorescence (TADF) compound, 3‐(4‐(9H‐carbazol‐9‐yl)phenyl)acenaphtho[1, 2‐b]pyrazine‐8, 9‐dicarbonitrile (CzPhAP), is designed, which also shows OLPL in many well‐known hosts such as PPT, 2, 2′, 2″‐(1, 3, 5‐benzinetriyl)‐tris(1‐phenyl‐1‐H‐benzimidazole) (TPBi), and poly(methyl methacrylate) (PMMA), without any exciplex formation, and its OLPL duration reaches more than 1 h at room temperature. Combining the low cost of PMMA manufacture and flexible designs of TADF molecules, pure organic, large‐scale, color tunable, and low‐cost room‐temperature OLPL applications become possible. Moreover, it is found that the onset of the 77 K afterglow spectra from a TADF‐emitter‐doped film is not necessarily reliable for determining the lowest triplet state energy level. This is because in some TADF‐emitter‐doped films, optical excitation can generate charges (electron and holes) that can later recombine to form singlet excitons during the phosphorescence spectrum measurement. The spectrum taken in the phosphorescence time window at low temperature may consequently consist of both singlet and triplet emission. Abstract : Organic long‐persistent luminescence from an organic thermally activated delayed fluorescence (TADF) compound is demonstrated. It is also shown that this phenomenon can occur in a number of chemically distinct host matrices. Furthermore, this work reveals the important role that photoinduced charges play in TADF‐emitter‐doped films, which has a significant impact on their photophysical properties.