Differently substituted benzonitriles for non-doped OLEDs

Abstract

Towards highly efficient doping-free organic light-emitting diodes, five benzonitrile-based emitters with different substitution pattern were designed exploiting symmetrical donor-acceptor-donor and asymmetrical donoracceptor-donor* structures. As it was predicted by theoretical calculations, different thermally activated delayed fluorescence of different energy with relatively high absolute quantum yields (11-42%) was detected for nondoped films of the studied compounds. The smallest singlet-triplet energy splitting of 0.05 eV thus the most efficient TADF was estimated for the film of compound with the asymmetrical donor-acceptor-donor* structure containing carbazole and acridan donor moieties. Thermogravimetry revealed sublimation of the materials with the onset temperatures in the range of 350-383°C. Glass transition temperatures of the molecular materials were in the range of 82-94°C. Tuning of hole injection properties of these compounds in solid-state was demonstrated. Their ionization potential was in range from 5.8 to 6.0 eV. Strong effect of different substitutions was observed on hole mobilities of the layers of compounds. They were found to be in the wide range from 3 × 10 −7 cm 2 V −1 s −1 to 1 × 10 −4 cm 2 V −1 s −1 . Electron mobility values of the compounds were found to be comparable and ranged from 1.5 × 10 −4 cm 2 V −1 s −1 to 3 × 10 −4 cm 2 V −1 s −1 at electric field of 6.9 × 10 5 Vcm −1 . Reflecting effect of substitution pattern of benzonitrile on electroluminescent properties of OLEDs, maximum external quantum efficiencies in the range from 1.6 to 5% as well as maximum brightness in the wide range from 1200 to 22600 cd/m 2 were observed for the devices based on the doping-free light-emitting layer.

Bipolar 1,8-naphthalimides showing high electron mobility and red AIE-active TADF for OLED applications

“…The TADF efficiencies of compounds 1–3 can be represented by their rate constants k RISC , the highest value of which (1.13 × 10 6 s −1 ) was obtained for compound 3 (Table 2). The lowest k RISC of 2.08 × 10 5 s −1 is for 2 confirming the suggestion made previously 46,49 of phenothiazine causing ICT suppression in the solid mixture of 2 and a host. This k RISC value of 3 is, however, among the best for state-of-the-art TADF emitters, displaying the potential of the synthesized compounds (especially of compound 3 ) for practical applications.…”

“…The bathochromic shift of emission spectrum of 2 is apparently determined by the stronger donor attached. 46 PL spectra of the solid samples of 1–3 had maxima at 658, 638, and 646 nm, respectively. Hypsochromically shifted PL spectra relative to those of the films of the net compounds were recorded for 10 wt% solid solutions of 1–3 in 1,3-bis( N -carbazolyl)benzene (mCP) (Fig.…”

“…As it was shown before, the phenothiazine-based compound can be characterized by a blue shift of the emission spectra in the solid state when compared to solutions due to the effects of aggregation, arguably caused by phenothiazine-driven aggregation-caused suppression of ICT states in neat and doped films. 46,49…”

Not the sum of their parts: understanding multi-donor interactions in symmetric and asymmetric TADF emitters

“…A plethora of multicolour TADF emitters have been developed using this approach. [36][37][38][39][40][41][42][43][44] Even a number of white emitters with D-A-D 0 structure have been reported, [45][46][47] although it remains unclear how to correlate the properties of the D-A-D 0 materials from those of the individual D-A and D 0 -A analogues. 48 An early advance in the D-A-D approach was made by Adachi et al, who introduced multiple donors with mutual steric interactions.…”

Selective Expression of a Carbazole‐Phenothiazine Derivative Leads to Dual‐mode AIEE, TADF and Distinctive Mechanochromism

“…[11] If both PTZ and Cz are linked together by a acceptor, what will happen? [12] Can we observe the dual-mode AIEE phenomena arising from both PTZ and Cz? Dual-mode AIEE from a single component will give a deep insight into the mechanism of AIEE, which has not been achieved yet.…”