Piotr Pander

Dibenzo[a,j]phenazine‐Cored Donor–Acceptor–Donor Compounds as Green‐to‐Red/NIR Thermally Activated Delayed Fluorescence Organic Light Emitters

A new family of thermally activated delayed fluorescence (TADF) emitters based on U-shaped D-A-D architecture with a novel accepting unit has been developed. All investigated compounds have small singlet-triplet energy splitting (ΔEST ) ranging from 0.02 to 0.20 eV and showed efficient TADF properties. The lowest triplet state of the acceptor unit plays the key role in the TADF mechanism. OLEDs fabricated with these TADF emitters achieved excellent efficiencies up to 16 % external quantum efficiency (EQE).

Multicolor Luminescence Switching and Controllable Thermally Activated Delayed Fluorescence Turn on/Turn off in Carbazole–Quinoxaline–Carbazole Triads

We report a series of thermally activated delayed fluorescence (TADF) molecules with mechanochromic luminescence properties and reversible TADF turn on/off properties in solid state that are induced by the transition between amorphous and crystalline states. Additionally, multicolor altering through external stimulus is demonstrated. All of the studied compounds exhibited recovery of the initial states associated with narrower emission spectra. TADF organic light-emitting diodes fabricated by solution processing rendered high external quantum efficiency up to 10.9% and luminance of 16 760 cd m-2.

Thermally activated delayed fluorescence with a narrow emission spectrum and organic room temperature phosphorescence by controlling spin–orbit coupling and phosphorescence lifetime of metal-free organic molecules

This work presents a study of two organic molecules with a very similar, large singlet–triplet energy gap, one of which is a thermally activated delayed fluorescence (TADF) emitter and the other is a room temperature phosphorescence (RTP) emitter. By investigating their photophysical properties we are able to explain their distinct behavior. The molecules are studied in non-polar polymers and OLED hosts. Furthermore, this work presents a CT TADF emitter that shows a narrow and resolved electroluminescence spectrum (FWHM = 53 nm). The study shows an efficient RTP emitter based on a D–D–D structure and also the first acridone-based TADF emitter with a D–A–D structure.

Triphenylamine disubstituted naphthalene diimide: elucidation of excited states involved in TADF and application in near-infrared organic light emitting diodes

It is demonstrated that a naphthalene diimide core disubstituted with triphenylamine can be used as a thermally activated delayed fluorescence emitter in organic light emitting diodes. Detailed spectroscopic studies demonstrated unusual host effects on the photophysical properties of this material. In particular, we were able to deduce recombination pathways and the role of the host and temperature in increasing/decreasing the TADF contribution in overall emission. Furthermore, stemming from these host effects on the geometry of the emitter we discover different local triplet states involved in the TADF mechanism. We elucidate this confusing situation to show that simply measuring low-temperature phosphorescence does not always give the energy of the local triplet involved in TADF. The studies carried out in a non-polar polymer and the OLED host were completed by NIR OLED fabrication showing promising characteristics.

Intermolecular Interactions in Molecular Crystals and Their Effect on Thermally Activated Delayed Fluorescence of Helicene-Based Emitters

Here, we discuss the influence of the crystal structure on the photophysical properties of two new TADF emitters containing a non-planar helical moiety. The presence of solvent in the crystal lattice of a diaza[5]helicene-based compound alters molecular packing significantly and suppresses aggregation. This results in more intense TADF emission and an increase in PLQY. Solution-processed OLED devices gave a maximum external quantum efficiency of 7.1%.

Thermally-activated delayed fluorescence in polymer-small molecule exciplex blends for solution-processed organic light-emitting diodes.

The photophysics of an exciplex state formed between a small molecule and a polymer is investigated in this work. The results obtained with this blend show the strong potential of polymer-small-molecule blends for triplet harvesting in organic light-emitting diodes (OLEDs) via thermally activated delayed fluorescence. The exciplex formed between poly( N-vinylcarbazole) (PVK) and 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T) shows yellow-green emission and is applied in solution-processed OLEDs. The excellent film-forming properties in this blend allow easy spin coating and potential use in other solution-processing techniques, such as slot die coating. In this work, we critically address the reverse intersystem crossing mechanism in the presented exciplex system, including the role of local triplet states. Moreover, we bring a clear physical meaning to the decay components of the exciplex emission, including the decay occurring in a power-law fashion that is often ignored in the literature.