AUTHOR=Keshri Sudhir K. , Liu Guanting , Yasuda Takuma 

TITLE=Ultrafast spin-flip exciton conversion and narrowband sky-blue luminescence in a fused polycyclic selenaborin emitter

JOURNAL=Frontiers in Chemistry

VOLUME=12

YEAR=2024

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2024.1375552

DOI=10.3389/fchem.2024.1375552

ISSN=2296-2646

ABSTRACT=<p>Thermally activated delayed fluorescence (TADF) materials with high photoluminescence quantum yields and fast reverse intersystem crossing (RISC) capabilities are highly desirable for applications in high-efficiency organic light-emitting diodes. Herein, we report the synthesis as well as structural and photophysical properties of 5,9-diselena-13b-boranaphtho[3,2,1-<italic>de</italic>]anthracene (<bold>SeBSe</bold>) as a narrowband-emissive TADF material. The incorporation of two selenium atoms into the boron-fused pentacyclic π-core results in a small singlet–triplet energy gap (Δ<italic>E</italic><sub>ST</sub>) and thereby significant TADF properties. Moreover, theoretical calculations revealed a noticeable spin-orbit coupling enhancement between the singlet and triplet manifolds in <bold>SeBSe</bold> by virtue of the heavy-atom effect of selenium atoms. Consequently, <bold>SeBSe</bold> allows ultrafast spin-flip RISC with the rate constant surpassing 10<sup>8</sup> s<sup>−1</sup>, which far exceeds the corresponding fluorescence radiative decay rate (∼10<sup>6</sup> s<sup>−1</sup>), enabling an ideal singlet–triplet superimposed excited state.</p>