The Critical Role of nπ* States in the Photophysics and Thermally Activated Delayed Fluorescence of Spiro Acridine-Anthracenone

Gomes Franca, Larissa; Long, Yun; Li, Chunyong; Danos, Andrew; Monkman, Andrew

doi:10.1021/acs.jpclett.0c03314

The Critical Role of nπ* States in the Photophysics and Thermally Activated Delayed Fluorescence of Spiro Acridine-Anthracenone

Gomes Franca, Larissa; Long, Yun; Li, Chunyong; Danos, Andrew; Monkman, Andrew

Authors

Larissa Franca larissa.gomes-franca@durham.ac.uk
PGR Student Doctor of Philosophy

Yun Long

Dr Chunyong Li chunyong.li@durham.ac.uk
Laser Science Experimental Officer

Dr Andrew Danos andrew.danos@durham.ac.uk
Senior Experimental Officer

Professor Andrew Monkman a.p.monkman@durham.ac.uk
Professor

Abstract

The molecular photophysics and thermally activated delayed fluorescence (TADF) in spiro compounds are distinct because of the rigid orthogonal C–C bridging bond between donor and acceptor. The photophysics is found to be highly complex, with unprecedented multiple anti-Kasha emissions from three different singlet states, two of which are one-photon forbidden. The TADF mechanism is critically controlled by local acceptor nπ* states; the singlet nπ* state undergoes rapid intersystem crossing populating an energetically close acceptor ππ* triplet state. The acceptor triplet nπ* state couples nonadiabatically to a CT triplet state mediating reverse intersystem crossing. When the nπ* and CT states are energetically close, TADF is greatly enhanced with rISC rate reaching 107 s–1. We observe neither DF from the singlet nπ* state nor electron transfer (ET) to form the 1CT because there is no ET driving force; however, ET from the higher-energy donor singlet ππ* state readily occurs along with donor emission.

Citation

Gomes Franca, L., Long, Y., Li, C., Danos, A., & Monkman, A. (2021). The Critical Role of nπ* States in the Photophysics and Thermally Activated Delayed Fluorescence of Spiro Acridine-Anthracenone. Journal of Physical Chemistry Letters, 12(5), 1490-1500. https://doi.org/10.1021/acs.jpclett.0c03314

Journal Article Type	Article
Acceptance Date	Jan 28, 2021
Online Publication Date	Feb 3, 2021
Publication Date	2021
Deposit Date	Apr 8, 2021
Publicly Available Date	Jun 3, 2021
Journal	Journal of Physical Chemistry Letters
Electronic ISSN	1948-7185
Publisher	American Chemical Society
Peer Reviewed	Peer Reviewed
Volume	12
Issue	5
Pages	1490-1500
DOI	https://doi.org/10.1021/acs.jpclett.0c03314