Switching the Luminescence between TADF and RTP for Organic D‐A‐D Emitters: The Role of D‐A Connection Modes

Abstract

The impact of the connection modes between donor (D) and acceptor (A) on the luminescence properties is revealed for organic D‐A‐D emitters based on triphenylamine (TPA) and 9,10‐phenanthroquinone (PAQ). When TPA and PAQ are linked via a single bond, the emitters exhibit small energy difference between the lowest singlet and triplet excited states (∆EST) due to the separated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distributions, thus featuring thermally activated delayed fluorescence (TADF). Interestingly, for the emitters with TPA and PAQ sharing a benzene ring, the ∆EST are significantly increased because of the enhanced overlap between the HOMO and LUMO, which is beneficial to realize room temperature phosphorescence (RTP). Moreover, upon changing the connection from β to γ‐position, high‐lying triplet states can become energetically lower than the lowest singlet excited state, thus affording additional channels to facilitate TADF and RTP. This work sheds some light on controlling of the excited state energy level alignments via modulating the D‐A connection modes to tune molecular emission from TADF to RTP.

Theoretical exploration of the bromine substitution effect and hydrostatic pressure responsive mechanism for room temperature phosphorescence

“…[18][19][20][21][22][23][24] At the same time, many theoretical research groups have performed a lot of research to detect the inner RTP mechanisms and design new efficient RTP molecules. [25][26][27][28][29][30][31][32] Ma et al revealed the dual RTP emission source based on first-principles calculations, and the T 1 state and the upper-lying triplet excited state (T 2 ) were responsible for the dual RTP mechanism. 33 Shuai and Peng et al used molecular dynamics simulations, and the combined quantum mechanics and molecular mechanics (QM/MM) coupled with thermal vibration correlation function (TVCF) theory to propose a mechanism for the induction of RTP by intermolecular electrostatic interactions at the molecular level.…”