Design and performance of sulfur and selenium-substituted triarylboron D3-A TADF emitters for OLED applications

• Published in: Organic electronics 2024-11, Vol.134, p.107130, Article 107130
• Main Authors: Karakurt, Oguzhan, Demirgezer, Elif Fatma, Dastemir, Murat, Cakmaktepe, Semih Can, Miranda-Salinas, Hector, Aksoy, Erkan, Danos, Andrew, Monkman, Andrew, Yildirim, Erol, Cirpan, Ali
• Format: Article
• Language: English
• Subjects: OLED; Phenoselenazine; Phenothiazine; TADF; Triaryl-boron
• ISSN: 1566-1199
• DOI: 10.1016/j.orgel.2024.107130

This study presents the design, synthesis, and comprehensive theoretical and photophysical analysis of two new D3-A type thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diode (OLED) applications. Utilizing a triarylboron core as the electron-accepting group and phenothiazine (PTZ) or phenoselenazine (PSZ) as electron-donating units, the molecules BTP-S and BTP-Se were developed. The D3-A structure supports the separation of frontier molecular orbitals (FMOs), leading to minimized singlet-triplet energy gaps (ΔEST), which are crucial for the TADF mechanism. Density functional theory (DFT) calculations presented that BTP-S and BTP-Se exhibit band gaps (Eg) of 2.52 and 3.23 eV, respectively, with BTP-S showing an ΔEST value as low as 0.007 eV for the S1-T1 transition at the lowest energy conformation. Photophysical studies revealed high photoluminescence quantum yields (PLQYs) for both compounds, with BTP-S achieving up to 85 % in mCP films and BTP-Se up to 59 %. In vacuum-processed OLEDs, BTP-S achieved a maximum external quantum efficiency (EQE) of 25.3 %, a current efficiency (ηc) of 195.8 cd/A, and a maximum luminance (Lmax) of 17356 cd/m2, while BTP-Se reached an EQE of 7.5 %, an ηc of 132.19 cd/A, and an Lmax of 16826 cd/m2 likely limited by the contributions of a folded-donor conformer enabled by the Se substitution. These findings underscore the impact of donor unit selection and conformation on the TADF characteristics, and provide valuable insights for designing high-performance OLED materials. [Display omitted] •Two novel D3-A type TADF emitters, BTP-S and BTP-Se, were designed and synthesized.•Both theoretical and photophysical results are consistent with a thermally activated mechanism of delayed fluorescence.•High photoluminescence quantum yields: BTP-S up to 85 %, BTP-Se up to 59 % in mCP films.•BTP-Se reached EQE of 7.5 %, ηc of 132.19 cd/A, and Lmax of 16826 cd/m2.•BTP-S achieved EQE of 25.3 %, ηc of 195.8 cd/A, and Lmax of 17356 cd/m2.