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

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2025-01, Vol.13 (1), p.16-176
• Main Authors: 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
• Format: Article
• Language: English
• Subjects: Benzothiophene; Coupling (molecular); Cross coupling; Crystallography; Deoxygenation; Electrical measurement; Electrical properties; Electrochemical analysis; Electronic structure; Electrons; Emitters; Fluorescence; Inkjet printing; Organic chemistry; Oxidation; Photoluminescence; Quenching; Spin coating; Structural analysis; X ray analysis
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d4tc03239j

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 BTBTOx 4 as the acceptor unit A. Three donor units D were selected and coupled with BTBTOx 4 , using a straightforward synthetic protocol based on microwave-assisted Buchwald-Hartwig cross-coupling, to yield three organic luminescent molecules labelled PTz 2 -BTBTOx 4 , MPA 2 -BTBTOx 4 and POCz 2 -BTBTOx 4 . 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. MPA 2 -BTBTOx 4 was selected as the reference molecule for X-ray analysis, which revealed torsion angles of −59° and 86° between the donor (MPA) and acceptor (BTBTOx 4 ) 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 PTz 2 -BTBTOx 4 and MPA 2 -BTBTOx 4 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 PTz 2 -BTBTOx 4 and MPA 2 -BTBTOx 4 and a minimal self-quenching for POCz 2 -BTBTOx 4 , which maintains a high Φ PL (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, POCz 2 -BTBTOx 4 , 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. [1]Benzothieno[3,2- b ]benzothiophene as a straightforward electron-acceptor building block to fabricate thermally activated delayed fluorescence (TADF) emitters.