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

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 n?* states; the singlet n?* state undergoes rapid intersystem crossing populating an energetically close acceptor ??* triplet state. The acceptor triplet n?* state couples nonadiabatically to a CT triplet state mediating reverse intersystem crossing. When the n?* and CT states are energetically close, TADF is greatly enhanced with rISC rate reaching 10⁷ s^-1. We observe neither DF from the singlet n?* state nor electron transfer (ET) to form the ¹CT because there is no ET driving force; however, ET from the higher-energy donor singlet ??* state readily occurs along with donor emission.

SUBMITTER: Franca LG 

PROVIDER: S-EPMC7886023 | biostudies-literature | 2021 Feb

REPOSITORIES: biostudies-literature