Photochemical Degradation of Various Bridge-Substituted Fluorene-Based Materials

Chromium(III)-Catalyzed Desymmetrization of meso-Epoxides via Remote Stereocontrol: Synthesis of Chiral Fluorenes Bearing All-Carbon Quaternary Stereocenters

An asymmetric desymmetrization of fluorene-derived meso-epoxides is disclosed for the construction of chiral fluorenes bearing an all-carbon quaternary stereocenter at C9. This desymmetrization is catalyzed by a chiral (salen)CrIII complex via remote stereocontrol, producing diverse chiral fluorenes with excellent yields and stereoselectivity. The practicality of this protocol was demonstrated through the transformation of the obtained products to some intriguing enantioenriched polymerizable monomers.

Thermal Degradation of Photoluminescence Poly(9,9-dioctylfluorene) Solvent-Tuned Aggregate Films

The progression of the green emission spectrum during the decomposition of polyfluorenes (PFs) has impeded the development and commercialization of the materials. Herein, we constructed a solvent-tuned aggregated PFO film with the aim of retarding the material’s thermal degradation behavior which causes a significant decline in optical properties as a result of phase transformation. The tuning of the aggregate amount and distribution was executed by applying a poor alcohol-based solvent in chloroform. It emerges that at a lower boiling point methanol evaporates quickly, limiting the aggregate propagation in the film which gives rise to a more transparent film. Furthermore, because of the modulated β-phase conformation, the absorption spectra of PFO films were red-shifted and broadened. The increase in methanol percentage also led to a rise in β-phase percentage. As for the thermal degradation reactions, both pristine and aggregated PFO films exhibited apparent changes in the UV-Vis spectra and PL spectra. In addition, a 97:3 (chloroform:methanol) aggregated PFO film showed a more defined emission spectrum, which demonstrates that the existence of β-phase is able to suppress the unwanted green emission.

Organic Laser Molecule with High Mobility, High Photoluminescence Quantum Yield, and Deep-Blue Lasing Characteristics

Here, we design and synthesize an organic laser molecule, 2,7-diphenyl-9H-fluorene (LD-1), which has state-of-the-art integrated optoelectronic properties with a high mobility of 0.25 cm² V^-1 s^-1, a high photoluminescence quantum yield of 60.3%, and superior deep-blue laser characteristics (low threshold of P_th = 71 μJ cm^-2 and P_th = 53 μJ cm^-2 and high quality factor (Q) of ∼3100 and ∼2700 at emission peaks of 390 and 410 nm, respectively). Organic light-emitting transistors based on LD-1 are for the first time demonstrated with obvious electroluminescent emission and gate tunable features. This work opens the door for a new class of organic semiconductor laser molecules and is critical for deep-blue optical and laser applications.

Organic Glasses of High Glass Transition Temperatures Due To Substitution with Nitrile Groups

The glass transition temperature (T_g) of a molecular glass depends on its molar mass. However, the nature of intermolecular interactions also plays a major role in both the glass transition temperature and its glass-forming ability. In this context, we report on novel molecular glasses containing nitrile groups and investigate the influence of this highly polar group on T_g and the glass-forming ability. As reference compounds, we studied the thermal properties of synthesized molecular glasses with C-C-bonded phenyl rings. The molar mass of the studied compounds ranges from 341 to 568 g/mol. Despite their relatively low molar mass, glass transition temperatures from 347 K (74 °C) to 471 K (198 °C) were observed. Most of the compounds possess high T_g/T_mratios between 0.7 and 0.8. By introducing highly interacting nitrile groups, the dependence of the molar mass on T_g could be increased by a factor of 2-3.

Crystal structure and mesogenic behaviour of a new fluorene derivative: 9,9-dimethyl-2,7-bis(4-pentylphenyl)-9H-fluorene

The title compound, C₃₇H₄₂, is a new mesogenic compound containing the fluorene moiety. It exhibits enantiotropic nematic liquid crystalline behaviour with melting at 125 °C and isotropization at 175 °C. The crystallographically independent unit contains two molecules oriented face-to-edge with respect to each other. The two molecules have nearly the same conformation of the bis-phenyl fluorene moiety. The molecular packing in the crystal phase is nematic-like.

Solid-state Suzuki-Miyaura cross-coupling reactions: olefin-accelerated C-C coupling using mechanochemistry

The Suzuki-Miyaura cross-coupling reaction is one of the most reliable methods for the construction of carbon-carbon bonds in solution. However, examples for the corresponding solid-state cross-coupling reactions remain scarce. Herein, we report the first broadly applicable mechanochemical protocol for a solid-state palladium-catalyzed organoboron cross-coupling reaction using an olefin additive. Compared to previous studies, the newly developed protocol shows a substantially broadened substrate scope. Our mechanistic data suggest that olefin additives might act as dispersants for the palladium-based catalyst to suppress higher aggregation of the nanoparticles, and also as stabilizer for the active monomeric Pd(0) species, thus facilitating these challenging solid-state C-C bond forming cross-coupling reactions.

Tuning the π-bridge of quadrupolar triarylborane chromophores for one- and two-photon excited fluorescence imaging of lysosomes in live cells

A series of tetracationic quadrupolar chromophores containing three-coordinate boron π-acceptors linked by different π-bridges, namely 4,4'-biphenyl, 2,7-pyrene, 2,7-fluorene, 3,6-carbazole and 5,5'-di(thien-2-yl)-3,6-diketopyrrolopyrrole, were synthesized. While their neutral precursors 1-5 displayed highly solvatochromic fluorescence, the water-soluble tetracationic target molecules 1M-5M, did not, but their emission colour could be tuned from blue to pink by changing the π-bridge. Compound 5M, containing the diketopyrrolopyrrole bridge, exhibits the most red-shifted absorption and emission maxima and the largest two-photon absorption cross-section (4560 GM at 740 nm in MeCN). Confocal laser scanning fluorescence microscopy studies in live cells confirm localization of the dye at the lysosome. Moreover, the low cytotoxicity, and high photostability of 5M combined with two-photon excited fluorescence imaging studies demonstrate its excellent potential for lysosomal imaging in live cells.