New [1]benzothieno[3,2- b]benzothiophene-tetraoxide-based TADF emitters with a D–A–D structure for OLED applications

Montrone, Maria; Maggiore, Antonio; Moliterni, Anna; Pander, Piotr; Pugliese, Marco; Capodilupo, Agostina Lina; Gambino, Salvatore; Prontera, Carmela Tania; Valenzano, Vitantonio; Mariano, Fabrizio; Accorsi, Gianluca; Sibillano, Teresa; Giannini, Cinzia; Gigli, Giuseppe; Cardone, Antonio; Maiorano, Vincenzo

Abstract

Luminescent organic molecules showing thermally activated delayed fluorescence (TADF) are appealing materials for high-efficiency OLEDs. Here, we report a new class of organic luminescent materials with TADF properties, and a D–A–D electronic structure based on [1]benzothieno[3,2-b]benzothiophene-tetraoxide BTBTOx4 as the acceptor unit A. Three donor units D were selected and coupled with BTBTOx4, using a straightforward synthetic protocol based on microwave-assisted Buchwald–Hartwig cross-coupling, to yield three organic luminescent molecules labelled PTz2-BTBTOx4, MPA2-BTBTOx4 and POCz2-BTBTOx4. Chemico-physical and structural properties were investigated by cyclic voltammetry, electrical measurements, crystallographic analysis, theoretical study and photophysical characterization. All three emitters showed high electrochemical stability with reversible oxidation waves. MPA2-BTBTOx4 was selected as the reference molecule for X-ray analysis, which revealed torsion angles of −59° and 86° between the donor (MPA) and acceptor (BTBTOx4) units supporting their appropriate structural configuration to have TADF properties. Photophysical studies highlighted a noteworthy increase in PL efficiency upon deoxygenation for all three compounds. The oxygen-induced quenching of delayed fluorescence and time-resolved photoluminescence studies supported the presence of the TADF properties, further corroborated for PTz2-BTBTOx4 and MPA2-BTBTOx4 by DFT studies. Preliminary steady-state photophysical studies were also carried out on neat films of all three emitters, revealing a pronounced self-quenching of photoluminescence for PTz2-BTBTOx4 and MPA2-BTBTOx4 and a minimal self-quenching for POCz2-BTBTOx4, which maintains a high ΦPL (22%) comparable to that in Zeonex and half of that in PMMA. As a proof of concept, the three emitting molecules were tested as neat films in simple-structure OLED devices. In accordance with the photoluminescence data, POCz2-BTBTOx4, thanks to its sterically bulky structure, retains a good emission capacity even in a neat film and was also selected as an active matrix to build OLED devices by using two different deposition techniques: inkjet-printing and spin coating.

Citation

Montrone, M., Maggiore, A., Moliterni, A., Pander, P., Pugliese, M., Capodilupo, A. L., Gambino, S., Prontera, C. T., Valenzano, V., Mariano, F., Accorsi, G., Sibillano, T., Giannini, C., Gigli, G., Cardone, A., & Maiorano, V. (online). New [1]benzothieno[3,2- b]benzothiophene-tetraoxide-based TADF emitters with a D–A–D structure for OLED applications. Journal of Materials Chemistry C Materials for optical and electronic devices, https://doi.org/10.1039/d4tc03239j

• Journal Article Type: Article
• Acceptance Date: Oct 16, 2024
• Online Publication Date: Oct 17, 2024
• Deposit Date: Nov 5, 2024
• Publicly Available Date: Nov 5, 2024
• Journal: Journal of Materials Chemistry C Materials for optical and electronic devices
• Print ISSN: 2050-7526
• Electronic ISSN: 2050-7534
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• DOI: https://doi.org/10.1039/d4tc03239j
• Public URL: https://durham-repository.worktribe.com/output/3043984