A material possessing a very small energy gap between its singlet and triplet excited states, ΔE1−3, which allows efficient up-conversion of triplet excitons into a singlet state and leads to efficient thermally activated delayed fluorescence (TADF), is reported. The compound, 2-biphenyl-4,6-bis(12-phenylindolo[2,3-a] carbazole-11-yl)-1,3,5-triazine, breaks the restriction of a large energy gap, with a ΔE1−3 of just 0.11 eV, while maintaining a high fluorescent radiative decay rate (kr∼107). The intense TADF provides a pathway for highly efficient electroluminescence.
Electroluminescence based on TADF, that is, thermally activated delayed fluorescence, is demonstrated in Sn4+–porphyrin complexes. On excitation by a short electrical pulse, prompt and delayed electroluminescence components were clearly observed. The delayed component was composed of both TADF and phosphorescence (see figure), and the TADF component significantly increased with increasing temperature.
Amorphous nanoparticles of supramolecular coordination polymer networks are spontaneously self-assembled from nucleotides and lanthanide ions in water. They show intrinsic functions such as energy transfer from nucleobase to lanthanide ions and excellent performance as contrast enhancing agents for magnetic resonance imaging (MRI). Furthermore, adaptive inclusion properties are observed in the self-assembly process: functional materials such as fluorescent dyes, metal nanoparticles, and proteins are facilely encapsulated. Dyes in these nanoparticles fluoresce in high quantum yields with a single exponential decay, indicating that guest molecules are monomerically wrapped in the network. Gold nanoparticles and ferritin were also wrapped by the supramolecular shells. In addition, these nucleotide/lanthanide nanoparticles also serve as scaffolds for immobilizing enzymes. The adaptive nature of present supramolecular nanoparticles provides a versatile platform that can be utilized in a variety of applications ranging from material to biomedical sciences. As examples, biocompatibility and liver-directing characteristics in in vivo tissue localization experiments are demonstrated.
Small molecule organic light-emitting diodes (SM-OLEDs) are efficient large area light sources facing their market entry. However, a low light outcoupling efficiency of typically 20% still strongly limits device performance. Here, we highlight the potential of employing dye-doped emission layers with emitting molecules having horizontally oriented transition dipole moments. The effect of molecular orientation is explained by studying optical simulations that distinguish between horizontal and vertical dipole orientation. In addition, an experimental method that enables straightforward determination of dipole orientation in guest-host systems is presented and used for the analysis of two materials that are very similar except for their orientation. By measuring the external electroluminescence quantum efficiency of SM-OLEDs based on these materials, evidence is found that a mainly horizontal dipole orientation enhances light outcoupling by around 45%. Furthermore, the effect of orientation in SM-OLEDs offers many additional benefits concerning stack design and has fundamental implications for material choice.
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