Suppressing dimer formation by increasing conformational freedom in multi-carbazole thermally activated delayed fluorescence emitters

Abstract

Twisted carbazoles and shallow dihedral angles provide a defence against dimer formation that adversely affects OLED performance.

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

“…This surprising result was explained in terms of the DMAC donor self-regulating its steric environment with the C-H bonds at the 1-and 8-positions. This final conclusion stands in contrast to other more compact donors such as carbazole, 34,35 with dihedral angles that are more susceptible to external influences. This property also makes DMAC an ideal donor for comparing more subtle aspects of molecular design, with the influence of dihedral angle variation largely controlled.…”

“…56 However, this comparison is complicated by the potential for steric interactions between neighbouring carbazoles. 34 Such steric interactions can be disregarded for the well-spaced and intrinsically perpendicular DMAC donors in the present materials though, giving clearer insight into the purely electronic effects associated with different substituent positions.…”

“…We also suggest that much of the complex photophysics of 4CzIPN is more likely attributable to the presence of persistent dimer species. 34,50,51 Although based on well-established principles of molecular orbital theory, much of the previous explanation is speculative. Nonetheless some evidence for the existence of the proposed D-D states can be found in the experimental absorption spectra (Fig.…”

“…Such a dihedral effect allowed for a degree of control over the energy gap and a rISC rate, resulting in OLEDs with correlated efficiencies and roll-offs. While significant attention in this work was dedicated to the investigation of the steric effects (which dominate dihedral angles for carbazole donors 34,35 ), many questions regarding the electronic communication in multi-donor TADF emitters remained unanswered.…”

Data-driven machine learning models for the quick and accurate prediction of thermal stability properties of OLED materials

“…Furthermore, these compounds were not included In order to clarify the reasons for this large prediction error, 3CzCNPyz was compared with two other compounds that appear in the same literature. 49 The TGA curve of 3CzCNPyz is shown in Fig. S2 and the TGA curves of 2Cz2CNPyz and 4CzPyz are shown in Fig.…”