Introduction of Twisted Backbone: A New Strategy to Achieve Efficient Blue Fluorescence Emitter with Delayed Emission

Abstract

By introducing an acceptor which contains double sulfonyl groups and a twisted biphenyl core, an efficient blue thermally activated delayed fluorescence emitter is successfully developed. Comparative study and analysis are carried out on it with an analogous molecule, which also imports two sulfonyl groups as acceptors and exactly same donor units but shows stretched shape and displays green emission. Results of quantum chemistry computation estimate that the introduction of such a twisted backbone is beneficial to increase energies of both singlet and triplet states. As a contrast to its counterpart, the newly developed blue emission compound with contorted structure enables a desirable emission with a peak wavelength of 460 nm and superior photoluminescence quantum yield up to 82%. Moreover, remarkable external quantum efficiency over 24% and Commission International de l'Eclairage coordinates with total (x + y) value <0.4 are achieved from the electroluminescent device based on the blue emitter, while this value is almost twice to that of the green emission device based on its analog.

Thioxanthone-based thermally activated delayed fluorescence emitters showing fast reverse intersystem crossing for efficient organic light-emitting diodes with small efficiency roll-off

“…The value is thirty times larger than that of the molecule which has the same chemical structure as MCz-TXO except that the oxygen atom is replaced with sulfur, con rming the effectiveness of our design concept. We believe that this concept, namely, good matching of 1 CT, 3 CT, and 3 LE, together with the incorporation of heavier organic atoms (such as S, Se), can be applied to various TADF materials, for further improvement of k RISC and thus the enhancement of TADF e ciency. Moreover, a higher radiative decay rate constant is also of vital importance to shorten the delayed lifetime and realize a small e ciency roll-off for OLEDs.…”

“…Most of the TADF materials were composed of electron donor (D) and acceptor (A) moieties with a large torsion angle between them, which causes well separated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distributions on the D and A moieties, respectively. 2,3 This kind of molecular design leads to a considerably small energy gap (ΔE ST ) between the lowest excited singlet and the lowest excited triplet states (S 1 and T 1 , respectively). [4][5][6] Theoretically, TADF materials in OLEDs can utilize all electro-generated triplet excitons for luminescence via a reverse intersystem crossing (RISC) process 7,8 and realize unity internal quantum e ciencies (IQE).…”

“…[18][19][20][21] According to the Femi's golden rule, as shown in equation 1, 22 k RISC depends on the magnitude of the spin-orbit coupling (SOC) and inversely depends on ΔE ST . between 1 CT and 3 CT has been often negligible. Therefore, according to the well-known El-Sayed's rule, 23 fast spin inversion cannot be expected.…”

Development of Red Exciplex for Efficient OLEDs by Employing a Phosphor as a Component

“…Organic light-emitting devices (OLEDs) based on thermally activated delayed fluorescence (TADF) emitters are considered the new generation of OLEDs (Adachi, 2014) and have drawn great attention in recent years (Goushi et al, 2012; Uoyama et al, 2012; Zhang et al, 2014b, 2016; Ban et al, 2015; Hirata et al, 2015; Liu M. et al, 2015, 2017; Liu W. et al, 2015; Chen et al, 2016, 2017; Gómez-Bombarelli et al, 2016; Li et al, 2016, 2017, 2018; Xie et al, 2016; Miwa et al, 2017; Moon et al, 2017; Shiu et al, 2017; Wang K. et al, 2017a; Yang et al, 2017). The TADF emitters can utilize both singlet and triplet excitons for emission by up-converting non-radiative (NR) triplet excitons to radiative singlet excitons via an efficient reverse intersystem crossing (RISC) process from lowest triplet state (T 1 ) to lowest singlet state (S 1 ) (Uoyama et al, 2012).…”

Suppressing Efficiency Roll-Off of TADF Based OLEDs by Constructing Emitting Layer With Dual Delayed Fluorescence

“…Recently, thermally activated delayed fluorescence (TADF) materials based on pure organic aromatic molecules have drawn great attention for their nature to achieve 100% exciton utilization in organic light emitting diodes (OLEDs) (Uoyama et al, 2012; Tao et al, 2014; Zhang et al, 2014a; Kaji et al, 2015; Liu et al, 2015, 2017; Cho et al, 2016; Data et al, 2016; Li et al, 2016; Chen et al, 2017). TADF-OLEDs with high external quantum efficiencies (EQEs) of over 20% have been reported within the visible light spectrum region.…”