Separating triplet exciton diffusion from triplet-triplet annihilation by the introduction of a mediator.

Triplet-triplet annihilation photon upconversion (TTA-UC) combines the energy of two photons to provide one of higher energy that can be used to drive photochemical or photophysical processes. TTA-UC proceeds at high efficiencies in dilute solution, but in solid state the efficiency drastically reduces. This is because exciton diffusion, compared to molecular diffusion in solid annihilator films, suffers concentration induced quenching, undermining efficient emission.

Rigid and planar π-conjugated molecules leading to long-lived intramolecular charge-transfer states exhibiting thermally activated delayed fluorescence.

Intramolecular charge transfer (ICT) occurs when photoexcitation causes electron transfer from an electron donor to an electron acceptor within the same molecule and is usually stabilized by decoupling of the donor and acceptor through an orthogonal twist between them. Thermally activated delayed fluorescence (TADF) exploits such twisted ICT states to harvest triplet excitons in OLEDs. However, the highly twisted conformation of TADF molecules results in limited device lifetimes.

Influence of Multiple rISC Channels on the Maximum Efficiency and Roll-Off of TADF OLEDs.

In this work, we look into the detailed photophysical characterization of a multidonor-acceptor () family of thermally activated delayed fluorescent (TADF) emitters to find correlations with their device performance. Increasing the number of closely packed s around the core leads to changes in dihedral angles between s and affecting the highest occupied molecular orbital (HOMO)/lowest unpccupied molecualar orbital (LUMO) separation and impacting the singlet-triplet energy gaps. Moreover, dihedral angles change molecular conjugation affecting the spread of charge-transfer state energies as well as the energy of local triplet states.

Aryl-Substituted Acridine Donor Derivatives Modulate the Transition Dipole Moment Orientation and Exciton Harvesting Properties of Donor-Acceptor TADF Emitters.

Thermally activated delayed fluorescence (TADF) compounds are highly attractive as sensitizing and emitting materials for organic light-emitting diodes (OLEDs). The efficiency of the OLED depends on multiple parameters, most of which rely on the properties of the emitter including those that govern the internal quantum and outcoupling efficiencies. Herein, we investigate a series of aryl substituted acridine donor derivatives of the donor-acceptor TADF emitter , with the objective of correlating their properties, such as triplet harvesting efficiency and transition dipole moment orientation, with their corresponding device efficiency.

Exciplex, Not Heavy-Atom Effect, Controls the Triplet Dynamics of a Series of Sulfur-Containing Thermally Activated Delayed Fluorescence Molecules.

The efficiency of thermally activated delayed fluorescence (TADF) in organic materials relies on rapid intersystem crossing rates and fast conversion of triplet (T) excitons into a singlet (S) state. Heavy atoms such as sulfur or selenium are now frequently incorporated into TADF molecular structures to enhance these properties by increased spin-orbit coupling [spin orbit coupling (SOC)] between the T and S states. Here a series of donor-acceptor (D-A) molecules based on 12-benzo[4,5]thieno[2,3-]carbazole and dicyanopyridine is compared with their nonsulfur control molecules designed to probe such SOC effects.