Incorporation of switchable donors into an acceptor core led to tricolor luminescence and thermally activated delayed fluorescence.

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).

Chemical modification of phenothiazine-benzophenone derivatives tunes the emission behavior from triplet states by selecting the geometry of the intramolecular charge transfer (ICT) state.Afundamental principle of planar ICT (PICT) and twisted ICT (TICT) is demonstrated to obtain selectively either room temperature phosphorescence (RTP) or thermally activated delayed fluorescence (TADF), respectively.T imeresolved spectroscopya nd time-dependent density functional theory (TD-DFT) investigations on polymorphic single crystals demonstrate the roles of PICT and TICT states in the underlying photophysics.This has resulted in aRTP molecule OPM,w here the triplet states contribute with 89 %o ft he luminescence,a nd an isomeric TADF molecule OMP,w here the triplet states contribute with 95 %ofthe luminescence.

The investigation of non-doped exciplex blends of 2,4,6-Tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T), working as the one-electron acceptor molecule, with different electron donors is reported. The emissions of these exciplexes span from the blue to orange-red regions, showing clear contribution from thermally activated delayed fluorescence (TADF) and delayed fluorescence originated from non-geminate recombination of charge carriers created by the dissociation of optically generated exciplexes. We focus our

The light-emitting efficiency of luminescent materials is invariably compromised on moving to the red and near infrared regions of the spectrum, due to the transfer of electronic excited state energy into vibrations. We describe how this undesirable "energy gap law" can be side-stepped for phosphorescent organometallic emitters through the design of a molecular emitter that incorporates two platinum(II) centres. The dinuclear cyclometallated complex of a substituted 4,6-bis(2-thienyl)pyrimidine emits very brightly in the red region of the spectrum (λ max = 610 nm, Φ = 0.85 in deoxygenated CH 2 Cl 2 at 300 K). The lowest-energy absorption band is extraordinarily intense for a cyclometallated metal complex: at λ = 500 nm, ε = 53800 M-1 cm-1. The very high efficiency of emission achieved can be traced to an unusually high rate constant for the T 1 → S 0 phosphorescence process, allowing it to compete effectively with non-radiative vibrational decay. The high radiative rate constant correlates with an unusually large zero-field splitting of the triplet state, which is estimated to be 40 cm-1 by means of variable-temperature time-resolved spectroscopy over the range 1.7 < T < 120 K. The compound has been successfully tested as a red phosphor in an organic light-emitting diode (OLED) prepared by solution processing. The results highlight a potentially attractive way to develop highly efficient red and NIR-emitting devices through the use of multinuclear complexes.

Chemical modification of phenothiazine-benzophenone derivatives tunes the emission behavior from triplet states by selecting the geometry of the intramolecular charge transfer (ICT) state.Afundamental principle of planar ICT (PICT) and twisted ICT (TICT) is demonstrated to obtain selectively either room temperature phosphorescence (RTP) or thermally activated delayed fluorescence (TADF), respectively.T imeresolved spectroscopya nd time-dependent density functional theory (TD-DFT) investigations on polymorphic single crystals demonstrate the roles of PICT and TICT states in the underlying photophysics.This has resulted in aRTP molecule OPM,w here the triplet states contribute with 89 %o ft he luminescence,a nd an isomeric TADF molecule OMP,w here the triplet states contribute with 95 %ofthe luminescence.

A novel dinuclear platinum(II) complex featuring a ditopic, bis-tetradentate ligand has been prepared. The ligand offers each metal ion a planar O^N^C^N coordination environment, with the two metal ions bound...

A novel acridone derivative is presented showing TADF and narrow blue electroluminescence.