Solid-State Effect Induced Thermally Activated Delayed Fluorescence with Tunable Emission: A Multiscale Study

Abstract

Thermally activated delayed fluorescence (TADF) molecules with tunable solid-state luminescence have shown great application potential in organic light-emitting diodes. However, theoretical studies on luminescence properties of organic emitters with consideration of solid-state effect are limited. In this work, the photophysical properties of a difluoroboron β-diketonate-based molecule (M1) in liquid, crystal, and amorphous states are studied using multiscale methods combined with the thermal vibration correlation function theory. Our results indicate that the geometric structures of M1 in liquid with toluene and crystal state are all in straight-chain form. However, M1 in amorphous state is subjected to form bending deformation at the triphenylamine unit under collaboration between intramolecular π-hydrogen bond and disordered intermolecular interactions. Moreover, in the amorphous state, the energy gap between the first singlet excited state (S 1 ) and the first triplet excited state (T 1 ) (ΔE ST ) of M1 is significantly reduced, and the spin−orbit coupling constant is remarkably increased in comparison with those of M1 in liquid with toluene and crystal state. As a result, the up-conversion of T 1 → S 1 in the amorphous state is favored, and remarkable TADF is thus observed. Besides, M1 in the solid state gives fluorescence in red shift emission compared to that in liquid with toluene. On the basis of the results above, we further theoretically design a new molecule noted as M2 which emits fluorescence in the near-infrared region in the solid state. Our theoretical results help in understanding the light-emitting mechanism induced by the solid-state effect and provide information for designing new-type TADF emitters with tunable solid-state emission.

Host‐Dopant Interaction between Organic Thermally Activated Delayed Fluorescence Emitter and Host Material: Insight into the Excited State

“…However, theoretical studies of TADF molecules taking into account the solid-state environment have so far been limited. [77,78,98,[115][116][117][118][119][120] In addition, among those theoretical investigations, little emphasis has been put on the host-guest amorphous state that is widely adopted for highly efficient TADF OLEDs. In this regard, theoretical investigations focusing on a host-guest amorphous state are highly desired to get insights into the interactions between the host materials and TADF emitters.…”

Red Thermally Activated Delayed Fluorescence in Dibenzopyridoquinoxaline-Based Nanoaggregates

“…Previous reports indicated the enhanced rate of RISC leading to delayed fluorescence in molecular aggregates. 53 We observed a gradual increase in the rate of RISC from 3.2 × 10 5 to 16.7 × 10 5 s −1 for PQACz-T aggregates with increasing water fraction from 50 % to 99 %, respectively (Figure 5, SI, Table S14). The enhanced rate of RISC could be attributed to the lowering of ΔE ST in the nanoaggregates at higher water fractions facilitating the delayed fluorescence (SI, Figure S27, Table S15).…”

“…54 The perturbation of the electronic states due to the intermolecular interactions in nanoaggregates results in the reduction of ΔE ST . 53,54 The rate of RISC in PQCz-T nanoaggregates at 99 % water fraction was found to be 5.5 × 10 5 s −1 (SI, Table S14). The self-assembly of PQACz-T and PQCz-T towards nanoaggregate formation was probed through field-emission scanning electron microscopy (FESEM) of the drop-casted dispersions.…”

“…54 The perturbation of the electronic states due to the intermolecular interactions in nanoaggregates results in the reduction of ΔEST. 53,54 The rate of RISC in PQCz-T nanoaggregates at 99% water fraction was found to be 5.5  10 5 s -1 (SI, Table S14).…”

Theoretically elucidating high photoluminescence performance of dimethylacridan-based blue-color thermally activated delayed fluorescent materials

“…In order to facilitate the comparison and verification, we calculate both the Huang-Rhys factor and reorganization energy as in previous studies. [60][61][62][63] The Huang-Rhys factor S can be written as: S ¼ o 2 h D 2 ; where D is the normal coordinate displacement. The reorganization energy l reorg can be written as: [60][61][62][63] The low-frequency vibration modes with larger HR factors and reorganization energies are shown in Fig.…”