The emission of circularly-polarized light is central to many applications, including data storage, quantum computation, biosensing, environmental monitoring and display technologies. An emerging method to induce (chiral) circularly-polarized (CP) electroluminescence from the active layer of polymer light emitting diodes (polymer OLEDs; PLEDs) involves blending achiral polymers with chiral small molecule additives, where the handedness/sign of the CP light is controlled by the absolute stereochemistry of the small molecule. Through the in-depth study of such a system we report an interesting chiroptical property: the ability to tune the sign of CP light as function of active layer thickness for a fixed enantiomer of the chiral additive. We demonstrate that it is possible to achieve both efficient (4.0 cd/A) and bright (8000 cd/m 2) CP-PLEDs, with high dissymmetry of emission of both left handed (LH) and right handed (RH) light, depending on thickness (thin films, 110 nm: g EL = 0.51, thick films, 160 nm: g EL = −1.05, with the terms "thick" and "thin" representing the upper and lower limits of the thickness regime studied), for the same additive enantiomer. We propose that this arises due to an interplay between localized CP emission originating from molecular chirality and CP light amplification or inversion through a chiral medium. We link morphological, spectroscopic, and electronic characterization in thin films and devices with theoretical studies in an effort to determine the factors that underpin these observations. Through the control of active layer thickness and device architecture, this study provides insights into the mechanisms that result in CP luminescence from CP-PLEDs, opportunities in CP photonic device design, and demonstrate high performance CP-PLEDs.

We report a strategy for positively influencing the conformation of thermally activated delayed fluorescence (TADF) molecules containing phenothiazine and dibenzothiophene-S,S-dioxide units.

Molecules and materials that absorb and/or emit light form a central part of our daily lives. Consequently, a description of their excited-state properties plays a crucial role in designing new molecules and materials with enhanced properties. Due to its favorable balance between high computational efficiency and accuracy, time-dependent density functional theory (TDDFT) is often a method of choice for characterizing these properties. However, within standard approximations to the exchangecorrelation functional, it remains challenging to achieve a balanced description of all excited states, especially for those exhibiting charge-transfer (CT) characteristics. In this work, we have applied two approaches, namely, the optimal tuning and triplet tuning methods, for a nonempirical definition of range-separated functionals to improve the description of excited states within TDDFT. This is applied to study the CT properties of two thermally activated delayed fluorescence emitters, namely, PTZ-DBTO 2 and TAT-3DBTO 2 . We demonstrate the connection between the two methods, the performance of each in the presence on multiple excited states of different characters and the geometry dependence of each method especially relevant in the context of developing size-consistent potential energy surfaces.

If you like brighter TADF then you should put a ring on it. We report rotaxanes containing a carbazole-containing TADF luminophore in which the mechanical bond improves key photophysical properties, including the photoluminescence quantum yield and the singlet-triplet energy gap (DEST). Computational simulations, supported by X-ray crystallography, suggest this is due to weak interactions between the axle and macrocycle, enforced by the mechanical bond.