Influence of Sulfur Atoms on TADF Properties from Through‐Space Charge Transfer Excited States

Abstract

The harnessing of heavy atom effect of chalcogen elements offers a way for boosting the thermally activated delayed fluorescence (TADF) of purely organic luminescent materials that can harvest triplet excitons. However, the conformational and electronic variations induced by the heavy and large atoms may also have adverse effects on the TADF properties. Herein, the design, synthesis, and structures of a new type of through‐space charge transfer (TSCT) emitters containing benzothiazino[2,3,4‐kl]phenothiazine (DPTZ) as the donor unit are reported. The influences of S atoms on the emission properties have been systematically investigated by means of theoretical simulations, electrochemical and spectroscopic studies. Although the presence of π‐stacking interactions and calculated spin‐orbit coupling (SOC) values are beneficial for TSCT‐TADF properties, the triplet TSCT states are uplifted to above the locally excited (LE) state of the acceptor moieties. As a result, the new emitters display longer delayed fluorescence lifetimes (τDF) of 255.0–114.3 μs and lower PLQYs of 45–61 % in comparison with the O‐containing congeners (τDF=26.9–6.8 μs; PLQYs=74–71 %). This work highlights that a full consideration of various effects is essential when making use of heavy chalcogen atoms for the design of TADF emitters.

Regulating the Distance Between Donor and Acceptor in Space‐Confined Through‐Space Charge Transfer Emitters for Fast Radiative Decays and High‐Efficiency Organic Light‐Emitting Diodes With Low Efficiency Roll‐Offs

“…previously reported double‐decker TSCT molecules featuring donor/acceptor/donor or acceptor/donor/acceptor sandwich structures, which show strong through‐space electronic interactions and noticeable 1 CT absorption bands. [ 37–39 ] It is worth noting that emitters 1–3 with a donor/acceptor sandwich structure also show 1 CT absorption bands, indicating the molecular design presented here is effective to promote through‐space electronic interactions.…”

“…Emitter R was synthesized and characterized in a previous report. [54] various bridges, such as 9,9-dimethyl-9,10-dihydroacridin or phenoxazine, [32] carbazole, [33][34][35][36][37][38][39] triptycene, [24] acenaphthene, [40] [2.2]paracyclophane, [41] dithia [3.3]paracyclophane, [42] and aromatic macrocycle, [43] have been employed to develop intramolecular TSCT emitters with cofacially aligned donor/acceptor. In these emitters, neither the donor nor the acceptor is fixed, which would cause non-radiative deactivation of the emissive 1 CT state by intramolecular rotation or vibration.…”

Deep Learning-Based Chemical Similarity for Accelerated Organic Light-Emitting Diode Materials Discovery

“…The first one is a set of chromophores reported in Joung et al’s database . The second one is comprised of TADF molecules that have been reported in several research papers. ,,,− …”

Peripheral halogen atoms in multi-resonant thermally activated delayed fluorescence emitters: the role of heavy atoms in intermolecular interactions and spin orbit coupling

“…19,20 Further examples of HAE investigations of D–A TADF materials are summarised in the (ESI†). 21–31…”

“…19,20 Further examples of HAE investigations of D-A TADF materials are summarised in the (ESI †). [21][22][23][24][25][26][27][28][29][30][31] In contrast to D-A TADF materials, multi-resonant TADF emitters (MR-TADF) are rigid polycyclic aromatic compounds containing a combination of p-and n-dopants, which usually show larger DE ST (40.10 eV) and slower k RISC (B10 4 s À1 ). 32 RISC is typically enabled through an upper-state crossing mechanism rather than the vibronic coupling of the lower energy triplet states in D-A TADF emitters.…”