Single-exponential solid-state delayed fluorescence decay in TADF compounds with minimized conformational disorder

Abstract

Construction of rigid TADF compounds allows us to minimize the conformational disorder and obtain single-exponential DF in solid hosts with an exceptional RISC rate of nearly 6 × 106 s−1 and high emission yield.

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

“…[62,66] Similar results have also been reported in some very recent studies. [6,67] For instance, Hatakeyama and co-workers 6 found that the activation energy barriers are 8.9 and 24 meV, respectively, for the ISC and RISC process of the green TADF emitter of OAB-ABP-1. These above-mentioned results indicate that the real activation energy for RISC from T 1 to S 1 states is not necessarily equal to the ΔE ST values and that even the forward ISC process can be endothermic.…”

“…[49] Embedded in a rigid matrix (e.g., in doped film states), TADF emitters suffer from inhomogeneous conformer distribution due to the lack of free molecular motions (e.g., rotation), which is evidenced by the multiorder transient PL decays commonly observed in the doped films. [64,67,97] In addition, reorientation and relaxation of the emitting molecules in excited states are restricted in the rigid environment, which of course is related to the rigidity of host materials, leading to the differently stabilized CT states. For TADF emitters, conformers with a higher S 1 level (also a larger ΔE ST ) usually correspond to a higher oscillator strength, which will decay first with a short lifetime, leading to a gradual redshift of prompt fluorescence.…”

Spiro donor–acceptor TADF emitters: naked TADF free from inhomogeneity caused by donor acceptor bridge bond disorder. Fast rISC and invariant photophysics in solid state hosts

“…6 This conformational disorder, originating from the rotation around the C-N bond has also been investigated in other studies. [7][8][9][10] Furthermore, a molecular design which restricts this torsional motion was reported as an approach to avoid this disorder effect. [11][12][13] However, by using a spiro TADF emitter, the rigidity enforced by the tetrahedral spiro carbon atom gives potential immunity to external conformational distortion of the molecule caused by host interactions.…”

Low efficiency roll-off blue TADF OLEDs employing a novel acridine–pyrimidine based high triplet energy host

“…The synthesized compounds 2PPA, 1PPA, and 1MPA were purified by train sublimation in a Carbolite split tube furnace HZS 12/450. Characterization 1 H NMR and 13 C NMR spectra were recorded on a Bruker Avance III HD (500 MHz), the chemical shifts were referred to chloroform-d3 (7.26 ppm), and the J values are given in Hz. MS spectra were obtained on a Finningan MAT 8500 using electron impact ionization.…”

“…Acridine is often used as a donor (D) in emitter molecules because of its rigidity and strong donating feature. [10][11][12][13] Few cases report its use in hosts for red phosphorescence OLEDs. 14,15 Furthermore, what brought our attention to the acridine group is that it has a higher triplet energy than carbazole (due to less conjugation).…”