Intramolecular Charge Transfer Controls Switching Between Room Temperature Phosphorescence and Thermally Activated Delayed Fluorescence

Abstract

Chemical modification of phenothiazine-benzophenone derivatives tunes the emission behavior from triplet states by selecting the geometry of the intramolecular charge transfer (ICT) state.Afundamental principle of planar ICT (PICT) and twisted ICT (TICT) is demonstrated to obtain selectively either room temperature phosphorescence (RTP) or thermally activated delayed fluorescence (TADF), respectively.T imeresolved spectroscopya nd time-dependent density functional theory (TD-DFT) investigations on polymorphic single crystals demonstrate the roles of PICT and TICT states in the underlying photophysics.This has resulted in aRTP molecule OPM,w here the triplet states contribute with 89 %o ft he luminescence,a nd an isomeric TADF molecule OMP,w here the triplet states contribute with 95 %ofthe luminescence.

Dual emission in purely organic materials for optoelectronic applications

“…However, unlike other types of DE, dual DF is often hard to distinguish and unambiguously identify, as the emission spectra for each process are often very similar. Different types of DF can be identified by analysis of time-resolved photoluminescence decay kinetics and laser fluence experiments (dependence of DF intensity on the excitation pulse power) 21,90,120,122,123 However, even though TADF and TTA can often coexist in a single molecule, 90 not many studies thoroughly analyse the dual DF case. Therefore, in this section we focus on the handful of well-documented cases of dual DF.…”

Recent Advancements in and the Future of Organic Emitters: TADF‐ and RTP‐Active Multifunctional Organic Materials

“…The influence of the different conformers allowed both RTP and TADF to be observed, but no correlation between a particular structure and the emissions was presented . The influence of conformation on the photophysical properties of organic molecules and their stabilization through steric hindrance was presented by Bryce and co‐workers, in which the analysis of different phenothiazine‐benzophenone compounds was demonstrated. By adding a methyl group to the phenothiazine donor ( OPM ), the molecules adopted a quasi‐axial conformation in the crystal (Figure ), which enhanced the RTP process.…”

Bond Rotations and Heteroatom Effects in Donor–Acceptor–Donor Molecules: Implications for Thermally Activated Delayed Fluorescence and Room Temperature Phosphorescence

“…Stericallysubstituted D−A−D molecules with substituents on the donor often favor different conformers compared to the unsubstituted analogs leading to different HOMO/LUMO levels, which are critical to electrical device performance. 22,23 Substitution of the donor in sterically-hindering positions was avoided in the present work to prevent the formation of undesirable axial conformers, which are detrimental to TADF performance. 24 In the case of III, the structure was also anticipated to be more twisted on average due to the presence of the methyl substituents on the 9,9-dimethyl-thioxanthene-S,S-dioxide acceptor unit.…”