Open AccessThe Critical Role of nπ* States in the Photophysics and Thermally Activated Delayed Fluorescence of Spiro Acridine-Anthracenone
Author(s) -
Larissa Gomes Franca,
Yun Long,
Chunyong Li,
Andrew Danos,
Andrew P. Monkman
Publication year - 2021
Publication title -
the journal of physical chemistry letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.563
H-Index - 203
ISSN - 1948-7185
DOI - 10.1021/acs.jpclett.0c03314
Subject(s) - intersystem crossing , singlet state , photochemistry , acceptor , triplet state , fluorescence , singlet fission , chemistry , acridine , excited state , atomic physics , molecule , physics , organic chemistry , quantum mechanics , condensed matter physics
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 10 7 s -1 . We observe neither DF from the singlet nπ* state nor electron transfer (ET) to form the 1 CT because there is no ET driving force; however, ET from the higher-energy donor singlet ππ* state readily occurs along with donor emission.