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Organisationseinheit der BAM
In this proof-of-concept study, we show that polyfluorinated trityl radicals with the, to this date, highest fluorination grade can be accessed in quantitative yields in a straightforward manner starting from the perfluorinated trityl cation. The trityl skeleton is functionalized with trimethylsilyl halides to yield perhalofluoro trityl cations, which are subsequently reduced using commercial zinc powder. In this way, we prepare three perhalofluoro trityl radicals and analyze the impact of the fluorine ligands on their electro-optical properties, revealing some interesting trends. In comparison to literature-known polychlorinated trityl radicals, the new polyfluorinated derivatives exhibit substantially higher fluorescence quantum yields, longer luminescence lifetimes, and an expanded emission range that extends into the yellow spectral region. They further display enhanced photostability under light irradiation. In radical-stained polystyrene nanoparticles, an additional broad emission band in the red−NIR wavelength region is observed, which is attributed to excimer formation. Finally, the stability of the new radicals is investigated under ambient conditions, showing the slow conversion with atmospheric oxygen yielding the respective peroxides, which are characterized by single-crystal X-ray diffraction. All in all, our study extends the present scope of luminescent trityl radicals, as the functionalization of the perfluorinated cationic precursor unlocks the path toward a vast variety of polyfluorinated trityl radicals.
We report the synthesis of a fluorescent polycyclic aromatic hydrocarbon dye with a “symmetry-broken” core, derived from the related hexa-peri-benzocoronene (HBC) core with fluoranthene subunit. The fluorophore is composed of a pure Carbon skeleton without heteroatoms and exhibits remarkable photo luminescence properties with a photoluminescence Quantum yield (PLQY) of up to 67% in toluene, exceeding that of theparent HBC by a factor of 30. The single crystal X-ray structure reveals the distorted polycyclic aromatic hydrocarbon structure, which is responsible for the optoelectronic properties, as supported by density functional theory calculations. We show that the new fluorescent dye can be readily used for the fabrication of organic light-emitting diodes (OLED) without extensive optimization, whereby solubility in a variety of solvents and successful film formation are decisive.
Photoinstability of Aryl‐Functionalized Perylene Bisimides at Bay Positions in Ambient Environment
(2026)
Dye molecules are widely used as active layers in optoelectronic devices, making their photostability crucial for long‐term device performance. In this study, we investigated the photostability of a typical class of dye molecules, aryl‐functionalized perylene bisimides (PBIs) at the bay position and observed significant color changes in their solutions upon exposure to visible light under ambient conditions within hours. UV–vis absorption spectra revealed a blueshift accompanied by changes in peak intensities. This spectral shift was more prominent for aryl‐functionalized PBI dyes with electron‐withdrawing bay substituents than with electron‐donating ones. Although the observed spectral shift resembled aggregation behavior, it is temperature‐independent, effectively ruling out aggregation as the underlying cause. Interestingly, the effect was more pronounced in diluted dye solutions, while concentrated dye solutions remained photostable. Mass spectrometric analysis indicated the formation of dehydrogenated species upon light exposure in solution, supporting the hypothesis of a photoinduced reaction. The isolated dehydrogenated products exhibited identical spectral features to those of the light‐exposed diluted solutions, confirming that spontaneous dehydrogenation under ambient light is responsible for the reduced photostability of aryl‐functionalized PBIs at the bay position in solution.
Hexacyanotrimethylenecyclopropane (CN6CP) is an exceptionally strong organic electron acceptor in its neutral form, and widely applied for molecular doping to induce charge transfer processes and enable electrochemical systems. Yet, its fundamental molecular properties have remained largely unknown. Here, we show the first comprehensive structure‐analytical characterization of CN6CP, enabled by an improved, low‐temperature synthesis and the first solid‐state structure of the neutral compound. The resulting procedure affords isolable, crystalline CN6CP that is stable for weeks at –30°C and can be recrystallised. Across all redox states, combined IR/Raman, UV–Vis and NMR measurements, together with NICS calculations, reveal an oxidation‐state‐dependent redistribution of electron density. These data show that CN6CP possesses a σ‐aromatic cyclopropane core with tunable π‐delocalisation, which is enhanced upon reduction while the additional charge is predominantly localised on the exocyclic acceptor framework. Cyclic voltammetry experiments unveil two reversible one‐electron processes and an exceptionally low LUMO energy of –5.85 eV, which is the lowest reported for small organic molecules being significantly lower than those of benchmark acceptors such as F4TCNQ or F6TCNNQ. All together, these findings establish CN6CP as a structurally unique, extremely strong electron acceptor and provide the molecular basis underlying its performance in organic electronics and redox‐active materials.
