Intramolecular Noncovalent Interactions Facilitate Thermally Activated Delayed Fluorescence (TADF)

Abstract

In the conventional molecular design of thermally activated delayed fluorescence (TADF) organic emitters, simultaneously achieving a fast rate of reverse intersystem crossing (RISC) from the triplet to the singlet manifold and a fast rate of radiative decay is a challenging task. A number of recent experimental data, however, point to TADF emitters with intramolecular π–π interactions as a potential pathway to overcome the issue. Here, we report a comprehensive investigation of TADF emitters with intramolecular π···π or lone-pair···π noncovalent interactions. We uncover the impact of those intramolecular noncovalent interactions on the TADF properties. In particular, we find that folded geometries in TADF molecules can trigger lone-pair···π interactions, introduce a n → π* character of the relevant transitions, enhance the singlet–triplet spin–orbit coupling, and ultimately greatly facilitate the RISC process. This work provides a robust foundation for the molecular design of a novel class of highly efficient TADF emitters in which intramolecular noncovalent interactions play a critical function.

Charge‐Transfer Exciton Manipulation Based on Hydrogen Bond for Efficient White Thermally Activated Delayed Fluorescence

“…The key transition constants of DBFDPO: x % TArDFTPPO films are estimated with Equations to quantitatively figure out the influence of intermolecular interactions on TADF performance:1c in which k PF , k DF , k ISC , k RISC, and are rate constants of PF and DF8, intersystem crossing (ISC) and RISC processes, and singlet radiation, respectively; η PF and η DF are PF and DF quantum efficiencies, respectively (Figure d and Table S2, Supporting Information). It indicates that the k RISC and k DF of the films are in direct proportion to x % in the range of 1–80%, owing to the Δ E ST reduction and multichannel RISC process induced by the intermolecular CT effect . Differently, k PF and rapidly decrease when x % increasing from 1% to 10%, but shapely increase when x % further increasing to 80%.…”

Thermally Activated Delayed Fluorescence Sensitization for Highly Efficient Blue Fluorescent Emitters

“…Recent studies have shown that this type of linkage disfavors intermolecular π-π stacking among TADF molecules, and simultaneously enhances spinorbit couplings between the S 1 and T 1 states. [48,51,52] These molecular features of ortho-linked donor/acceptor TADF molecules can help not only improve the rates of RISC processes for fast singlet-exciton generation in TADF molecules, but also suppress the formation of intermolecular aggregate states as well as the need for a host material, which all can improve IQEs in hyperfluorescence-based devices. Excitation energy-transfer calculations show that the Förster mechanism leads to efficient energy transfer from 4CzDPO to TBPe.…”

Molecular Engineering of Isomeric Benzofurocarbazole Donors for Photophysical Management of Thermally Activated Delayed Fluorescence Emitters

“…In each of the materials, the HOMO was seen to be dispersed over the benzofurocarbazole electron‐donating group, with the LUMO predominantly dispersed over the diphenyltriazine electron‐acceptor moiety. The n‐π* electron interaction between the triazine moiety and the non‐bonding electron of nitrogen in benzofurocarbazole is also similar in all three TADF phenyl linkers . The dihedral angles between the phenyl linker and diphenyltriazine moiety in the three compounds were calculated to lie in the narrow range of 35–38°.…”

“…In each of the materials, the HOMO was seen to be dispersed over the benzofurocarbazole electron-donatingg roup, with the LUMO predominantly dispersed over the diphenyltriazine electron-acceptor moiety.T he n-p*e lectron interaction between the triazine moiety andt he non-bonding electron of nitrogen in benzofurocarbazole is also similar in all three TADF phenyll inkers. [40] The dihedrala ngles betweent he phenyl linker and diphenyltriazine moiety in the three compounds were calculated to lie in the narrow range of 35-388.T he LUMO energy levels were also calculated to be similar in the three compounds. On the other hand, the dihedrala ngles be- DFT calculation results obtained by using the Gaussian 16 softwarea re basedo nt he B3LYP 6-31G* basis set.…”