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Switching between TADF and RTP: anion-regulated photoluminescence in organic salts and co-crystals.

ABSTRACT: Thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) are two photophysical phenomena which utilize triplet excitons. In this work, we demonstrate how variation of the anion in organic salts with carbazole and phenothiazine-5,5-dioxide donors and pyridinium and quinolinium acceptors may be used to switch between TADF and RTP. These compounds adopt similar molecular structures and packing modes with different anions and exhibit different types of photophysical behavior due to the electronic effects of the anions. With bromide anions, the salts exhibit TADF with some RTP. These compounds show fast reverse intersystem crossing and a short delayed lifetime, which is key to application in efficient and robust OLEDs. With BF₄ ^- and PF₆ ^- anions, RTP with long-lived lifetimes and afterglow are observed by eye. This behavior can be utilized for data encryption and anti-counterfeiting applications. Emission wavelengths and lifetimes are also anion-dependent. These results open up an avenue for developing novel luminescent materials through anion tuning and present a molecular model to understand the interplay of RTP and TADF.

SUBMITTER: Xu Z

PROVIDER: S-EPMC8406714 | biostudies-literature | 2021 Aug

REPOSITORIES: biostudies-literature

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Switching between TADF and RTP: anion-regulated photoluminescence in organic salts and co-crystals.

Xu Zhen Z Hean Duane D Climent Clàudia C Casanova David D Wolf Michael O MO

Materials advances 20210813 17

Thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) are two photophysical phenomena which utilize triplet excitons. In this work, we demonstrate how variation of the anion in organic salts with carbazole and phenothiazine-5,5-dioxide donors and pyridinium and quinolinium acceptors may be used to switch between TADF and RTP. These compounds adopt similar molecular structures and packing modes with different anions and exhibit different types of photophysical ...[more]

PMID: 34527950

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Project description:Engineering the electronic excited state manifolds of organic molecules can give rise to various functional outcomes, including ambient triplet harvesting, that has received prodigious attention in the recent past. Herein, we introduce a modular, non-covalent approach to bias the entire excited state landscape of an organic molecule using tunable 'through-space charge-transfer' interactions with appropriate donors. Although charge-transfer (CT) donor-acceptor complexes have been extensively explored as functional and supramolecular motifs in the realm of soft organic materials, they could not imprint their potentiality in the field of luminescent materials, and it still remains as a challenge. Thus, in the present study, we investigate the modulation of the excited state emission characteristics of a simple pyromellitic diimide derivative on complexation with appropriate donor molecules of varying electronic characteristics to demonstrate the selective harvesting of emission from its locally excited (LE) and CT singlet and triplet states. Remarkably, co-crystallization of the pyromellitic diimide with heavy-atom substituted and electron-rich aromatic donors leads to an unprecedented ambient CT phosphorescence with impressive efficiency and notable lifetime. Further, gradual minimizing of the electron-donating strength of the donors from 1,4-diiodo-2,3,5,6-tetramethylbenzene (or 1,2-diiodo-3,4,5,6-tetramethylbenzene) to 1,2-diiodo-4,5-dimethylbenzene and 1-bromo-4-iodobenzene modulates the source of ambient phosphorescence emission from the 3CT excited state to 3LE excited state. Through comprehensive spectroscopic, theoretical studies, and single-crystal analyses, we elucidate the unparalleled role of intermolecular donor-acceptor interactions to toggle between the emissive excited states and stabilize the triplet excitons. We envisage that the present study will be able to provide new and innovative dimensions to the existing molecular designs employed for triplet harvesting.

Dataset Information

Switching between TADF and RTP: anion-regulated photoluminescence in organic salts and co-crystals.

Publications

Switching between TADF and RTP: anion-regulated photoluminescence in organic salts and co-crystals.

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