The significant variation in photoluminescence emission of poly(diphenylacetylene) derivatives according to the substitution position is due to the differences in the intramolecular pi-stack structure and chain conformation.
A combined
experimental and mechanistic study of the chemoselective
hydroboration of carbonyls by the paramagnetic bis-amido Mn[SMeNSMe]2 complex (1) is
described. The catalyst allows for room-temperature hydroboration
of carbonyls at low catalyst loadings (0.1 mol %) and reaction times
(<30 min). A series of mechanistic studies highlight the significance
of bifunctional amido bis(thioether) ligand L to the
success of the reaction, insight otherwise difficult to attain in
paramagnetic systems. Kinetic studies using variable time normalization
analysis revealed no unusual reaction kinetics, indicating the absence
of side reactions. A borylated analogue of L was observed
and characterized via mass spectrometry. Density functional theory
(DFT) calculations showed that thioether hemilability of L is crucial during catalysis for providing the active coordinating
site. Also, the frequently proposed Mn–H intermediate was found
not to be the active species responsible for catalysis. Instead, an
inner-sphere reaction pathway with carbonyl coordination to the metal
center and amido-promoted B–H reactivity is proposed to be
operative.
Copper-catalyzed
[5 + 1] cycloadditions of N-aromatic zwitterions
have been accomplished by chelation-assisted 1,2-dearomative addition
of electron-deficient terminal alkynes. The unique modular skeleton
of pyrazino[1,2-a]quinoline could be obtained from
the regio- and stereoselective cascade annulation process, which was
supported by computational studies. Further, an asymmetric variant
of the developed strategy has been successfully extended for enabling
access to optically enriched six-member cyclic systems.
Swollen up: Poly(diphenylacetylene) derivatives with different alkyl groups show intramolecular excimer emission that arises from the phenyl–phenyl stack structure in the side chains. The excimer emission is intrinsically correlated with lamellar layer distance. Film‐swelling experiments verify that the excimer emission can be modulated by changing the lamella layer distance (see picture).
Aufgequollen: Aufgrund der Stapelung von Phenylgruppen in den Seitenketten zeigen Poly(diphenylacetylen)‐Derivate mit unterschiedlich langen Alkylgruppen eine intramolekulare Excimer‐Emission, die intrinsisch mit dem Schichtenabstand in Filmen zusammenhängt. In Quellexperimenten konnte die Excimer‐Emission durch Veränderung dieses Abstands variiert werden (siehe Bild).
Finely structured diphenylacetylene polymer nanofibers were successfully prepared by a freeze drying method. SEM revealed that the morphology and structure of the fibers were significantly dependent on the concentration of the polymer solution, the ‘frozen in’ quenching temperature and the chemical structure of the polymer derivatives. Polarized fluorescence spectroscopy revealed that the polymer chains within the nanofiber were uniaxially oriented and highly elongated. The polymer nanofiber was remarkably sensitive to explosive nitroaromatic compounds when compared to the corresponding thin films. The fluorescence of polymer nanofiber obtained from 0.003 wt.‐% cryogenic benzene solution rapidly decreased to 50% of its initial value in ≈35 s by exposing to 2,4‐dinitrotoluene.
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