Exciplex-Forming Systems of Physically Mixed and Covalently Bonded Benzoyl-1H-1,2,3-Triazole and Carbazole Moieties for Solution-Processed White OLEDs

Abstract

Using the newly designed exciplex-forming 1,2,3-triazole-based acceptors with fast and efficient singlet → triplet intersystem crossing (ISC) processes, carbazole and benzoyl-1 H -1,2,3-triazole derivatives were synthesized by Dimroth-type 1,2,3-triazole ring formation and Ullmann–Goldberg C–N coupling reactions. Due to the exciplex formation between covalently bonded electron-donating (carbazole) and 1,2,3-triazole-based electron-accepting moieties with small singlet-triplet splitting (0.07–0.13 eV), the compounds exhibited ISC-assisted bluish–green thermally activated delayed fluorescence. The compounds were characterized by high triplet energy levels ranging from 2.93 to 2.98 eV. The most efficient exciplex-type thermally activated delayed fluorescence was observed for ortho-substituted carbazole-benzoyl-1 H -1,2,3-triazole which was selected as a host in the structure of efficient solution-processed white light-emitting diodes. The best device exhibited a maximum power efficiency of 10.7 lm/W, current efficiency of 18.4 cd/A, and quantum efficiency of 7.1%. This device also showed the highest brightness exceeding 10 thousand cd/m 2 . Usage of the exciplex-forming host allowed us to achieve a low turn-on voltage of 3.6 V. High-quality white electroluminescence was obtained with the close to nature white color coordinates (0.31, 0.34) and a color rendering index of 92.

Effects of Electron-Withdrawing Strengths of the Substituents on the Properties of 4-(Carbazolyl-R-benzoyl)-5-CF3-1H-1,2,3-triazole Derivatives as Blue Emitters for Doping-Free Electroluminescence Devices

“…All of the emission spectra were found to be Gaussian-shaped, which was indicative of charge transfer from donor to acceptor moieties and conformed with the results of computational studies. The emission maxima of the investigated compounds were found to be blue-shifted in comparison to those of our previously reported derivatives of benzoyl-1 H -1,2,3-triazole (λ max PL = 480 nm) . This observation can be attributed to the effect of different substitution patterns.…”

“…The TADF host achieved an EQE of 13.5% with a low roll-off value of 4.4% at a luminance of 1000 cd/m 2 . In our previous work, we reported the convenient synthesis of 1 H -1,2,3- triazole-based electroactive materials exhibiting TADF . They were used as hosts in efficient solution-processed hybrid white light-emitting diodes with a multilayer structure .…”

“…In our previous work, we reported the convenient synthesis of 1 H -1,2,3- triazole-based electroactive materials exhibiting TADF. 29 They were used as hosts in efficient solution-processed hybrid white light-emitting diodes with a multilayer structure. 29 However, to our knowledge, 1 H -1,2,3-triazole derivatives have not yet been used for the preparation of host-free emitting layers for OLEDs.…”

Fluorinated 1,2,3‐Triazoles: Terra Incognita in 1,2,3‐Triazoles Chemistry

“…Recently fluoroalkyl 1,2,3‐triazoles have been reviewed [5] and their wide application is presented. For example, we have used fluoroalkyl 1,2,3‐triazoles to prepare compounds for OLEDs [6] . On contrary, fluorinated 1,2,3‐triazoles are unfortunately presented in a much smaller number of works, although their valuable properties have been known for a long time.…”

Revealing the Origin of Fast Delayed Fluorescence in a Donor Functionalized Bisterpyridine

“…This donor molecule is typically based on carbazole and the most prominent candidate for exciplex formation is tris(N-carbazol)triphenylamine (TCTA). While several donor-acceptor combinations display TADF behaviour in covalently connected twisted configuration as well as in exciplexes, [11,12] oligopyridine compounds have not been covalently connected to a donor moiety for TADF emission. Both exciplex and covalently connected donor-acceptor systems entail a charge transfer (CT) excited state, for which the emission is bathochromically shifted compared with the fluorescence of the individual donor and acceptor units.…”