Tuning molecular emission of organic emitters from fluorescence to phosphorescence through push-pull electronic effects

Abstract

Organic emitters with persistent phosphorescence have shown potential application in optoelectronic devices. However, rational design and phosphorescence tuning are still challenging. Here, a series of metal-free luminophores without heavy atoms and carbonyl groups from commercial/lab-synthesized carbazole and benzene were synthesized to realize tunable molecular emission from fluorescence to phosphorescence by simply substituent variation. All the molecules emit blue fluorescence in both solution and solid state. Upon removal of excitation source, the fluorinated luminophores show obvious phosphorescence. The labsynthesized carbazole based molecules exhibit a huge lifetime difference to the commercially purchased ones due to the existence of isomer in the latter samples. The small energy gap between singlet and triplet state and low reorganization energy help enhance intersystem crossing to contribute to a more competitive radiative process from triplet to ground state. Blue and white organic light-emitting devices are fabricated by using fluorinated luminophore as emitting layer.

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

“…The study of acceptor effects on multi-carbazole functional properties such as TADF and room temperature phosphorescence is a topic of recent interest. 23,39 We show that 4CzPyz does not exhibit the large emission shifts between high polarity solution and solid-state that 4CzCNPy and 4CzTPN are subject to, establishing 4CzPyz as the most colour stable of the three emitters. Alongside 4CzPyz we also present 2Cz2CNPyz and 3CzCNPyz; related cyanopyrazine systems that also show resistance towards dimer formation.…”

Conformational Dependence of Triplet Energies in Rotationally Hindered N‐ and S‐Heterocyclic Dimers: New Design and Measurement Rules for High Triplet Energy OLED Host Materials

“…Uniquely in this series, green room temperature phosphorescence (RTP) lasting over 5 seconds was also observed for 22Cz in Zeonex film. 1 H ‐Benzo[ f ]indole is a significant contaminant in commercial‐grade carbazole which was recently confirmed as the cause of yellow/orange RTP in various carbazole derivatives [57, 58] . As the synthetic route for 22Cz does not employ commercial sources of carbazole, instead relying upon P(OEt) 3 mediated cyclisation of intermediate 4 , this allows us to disregard the possibility that the RTP arises from residual 1 H ‐benzo[ f ]indole or similar isomeric impurity.…”

Simple Vanilla Derivatives for Long-Lived Room-Temperature Polymer Phosphorescence as Invisible Security Inks

“…Video S4 (.avi format): emission of M1-0.3 mg-doped PVA ink hand-drawn on paper V when the UV light is on and off. See References [ 48 – 50 ].…”