Revealing resonance effects and intramolecular dipole interactions in the positional isomers of benzonitrile-core thermally activated delayed fluorescence materials

Abstract

Rather than donor–acceptor dihedral angles, the TADF performance of DMAC–BZN positional isomers is instead controlled by differences in acceptor strength arising from π-system electron density – along with a through-space dipole interaction.

Environmental Control of Triplet Emission in Donor–Bridge–Acceptor Organometallics

“…The result is that the photoluminescence peak of CMA1 can be increased in energy by 210 meV, into the blue color range, without altering its chemical structure. We determine that static electrostatic interactions are one of the most important parameters for these composites, whereas for organic TADF‐type emitters, the influence of the host is typically to redshift the emission through dynamic polarizability . Despite the significant change in emission energy achieved, we find that the low activation energy for delayed emission and short room‐temperature emission lifetimes are preserved.…”

Dual emission in purely organic materials for optoelectronic applications

“…52 Linking D-A units of balanced electron donating/accepting strength by an N-C bond gives rise to strong intramolecular CT states of n-p* origin, leading in turn to thermally activated delayed fluorescence (TADF). 30,53,54 However, if the chromophores possess a certain degree of conformational flexibility (especially the donor unit), 55 rotation around the N-C bond will inevitably lead to the equilibrium of at least two stable conformers, i.e. planar (quasi-axial) and twisted (quasiequatorial) ( Fig.…”

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

“…Towards this ultimate goal, in 2012, Uoyama et al 1 presented fluorescent OLEDs with superior external quantum efficiencies (EQEs) by virtue of triplet harvesting through a thermally activated delayed fluorescence (TADF) mechanism. [2][3][4][5] The TADF mechanism allows an emissive material to achieve an internal quantum efficiency (IQE) of unity without the need to incorporate heavy elements in the structures. It provides a counterpoint to the phosphorescent mechanism that predominates in emitters based around iridium or other heavy metal atoms.…”

“…Consequently, the optimization of TADFactive structures has stimulated significant research interest in the past few years. 4,[10][11][12][13][14] However, applying the TADF mechanism towards stable and efficient blue OLEDs has not been straightforward. Current state-of-the-art materials still struggle in terms of roll-off efficiency and device operational lifetime.…”