A Deep Blue B,N-Doped Heptacene Emitter That Shows Both Thermally Activated Delayed Fluorescence and Delayed Fluorescence by Triplet-Triplet Annihilation

Subeesh Madayanad Suresh, Eimantas Duda, David Hall, Zhen Yao, Sergey Bagnich, Alexandra M.Z. Slawin, Heinz Bässler, David Beljonne, Manfred Buck, Yoann Olivier, Anna Köhler, Eli Zysman-Colman

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Abstract

An easy-to-access, near-UV-emitting linearly extended B,N-doped heptacene with high thermal stability is designed and synthesized in good yields. This compound exhibits thermally activated delayed fluorescence (TADF) at ambient temperature from a multiresonant (MR) state and represents a rare example of a non-triangulene-based MR-TADF emitter. At lower temperatures triplet-triplet annihilation dominates. The compound simultaneously possesses narrow, deep-blue emission with CIE coordinates of (0.17, 0.01). While delayed fluorescence results mainly from triplet-triplet annihilation at lower temperatures in THF solution, where aggregates form upon cooling, the TADF mechanism takes over around room temperature in solution when the aggregates dissolve or when the compound is well dispersed in a solid matrix. The potential of our molecular design to trigger TADF in larger acenes is demonstrated through the accurate prediction of ΔEST using correlated wave-function-based calculations. On the basis of these calculations, we predicted dramatically different optoelectronic behavior in terms of both ΔEST and the optical energy gap of two constitutional isomers where only the boron and nitrogen positions change. A comprehensive structural, optoelectronic, and theoretical investigation is presented. In addition, the ability of the achiral molecule to assemble on a Au(111) surface to a highly ordered layer composed of enantiomorphic domains of racemic entities is demonstrated by scanning tunneling microscopy.

Original languageEnglish
Pages (from-to)6588-6599
Number of pages12
JournalJournal of the American Chemical Society
Volume142
Issue number14
DOIs
Publication statusPublished - 8 Apr 2020

Funding

We thank the Leverhulme Trust (RPG-2016-047). This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska Curie grant agreement no. 838885 (NarrowbandSSL) and 812872 (TADFlife). We thank Umicore for their generous supply of catalysts. S.S. acknowledges support from the Marie Skłodowska-Curie Individual Fellowship. S.B. acknowledges support from the Bayrisches Staatsministerium für Wissenschaft und Kunst (Stmwk) in the framework of the initiative “SolTech” as well as from the German Science foundation (DFG) (no. 392306670). Z.Y. acknowledges support from the Chinese Scholarship Council (201606100044) and the University of St. Andrews through a stipend. Computational resources have been provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifiques de Belgique (F.R.S.-FNRS) under grant no. 2.5020.11, as well as the Tier-1 supercomputer of the Fédération Wallonie-Bruxelles, infrastructure funded by the Walloon Region under the grant agreement no. 1117545. The authors thank F. Rodella and Prof. P. Strohriegl from Bayreuth University for help with the thermogravimetric analysis.

FundersFunder number
Chinese Scholarship Council
Consortium des Equipements de Calcul Intensif
Federation Wallonie-Bruxelles
Fonds de la Recherche Scientifiques de Belgique2.5020.11
German Science foundation
Marie Sklodowska-Curie
Marie Skłodowska-Curie
University of St. Andrews
Walloon Region1117545
Horizon 2020 Framework Programme838885, 812872
Leverhulme TrustRPG-2016-047
University of St Andrews
Deutsche Forschungsgemeinschaft392306670
Fédération Wallonie-Bruxelles
China Scholarship Council201606100044
Bayerisches Staatsministerium für Wissenschaft, Forschung und Kunst
Sächsisches Staatsministerium für Wissenschaft und Kunst

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