A detailed investigation is presented of the redox states of three oligothiophenes (nT) with 6, 9, and 12 thiophene units. While open-shell radical cations (polarons) and closed-shell dications (bipolarons) are usually invoked as the primary redox species in these systems, we have obtained evidence that the dication of the longest oligothiophene (12T) has an electronic structure with two individual polarons. The redox states of 6T, 9T, and 12T have been fully characterized using UV/visible/near-IR and ESR spectroscopy in combination with electrospray mass spectrometry. For 6T and 9T, singleelectron oxidation in dichloromethane produces the corresponding radical cations, which form spinless p dimers at lower temperatures. A second oxidation step forms dications which possess a bipolaronic electronic structure. However, the redox behavior of the longest oligothiophene, 12T, is entirely different. Radical cations of 12T disproportionate into neutral oligomers and dications, except at the lowest oxidation levels. The spectral data for doubly oxidized 12T are incompatible with those expected for a bipolaronic structure but are consistent with the formation of two individual polarons on a single chain; this interpretation is also supported by the results from correlated quantum chemical calculations.

Ein Plätzchen zum Kuppeln: Proteine wie das gelb fluoreszierende Protein (YFP), die ein N‐terminales FGG‐Motiv tragen, dimerisieren unter Mitwirkung von supramolekularen Wechselwirkungen innerhalb des Cucurbit[8]uril‐Rings (siehe Schema). Die durch FRET und Größenausschlusschromatographie beobachtbare Dimerisierung lässt sich durch Zugabe von Methylviologen umkehren, das als bioorthogonaler Ligand die FGG‐Motive aus dem Cucurbit[8]uril‐Wirt verdrängt.

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Electrospray mass spectrometry (ESI‐MS) is used to analyze in detail the structure of the first five generations of the poly(propylene imine) dendrimers with 4–64 end groups. Although the reaction sequence to prepare these dendrimers is highly optimized, an accumulation of statistical defects is observed at higher generations. A simple statistical simulation allows the assignment of all peaks in the deconvoluted spectrum and the determination of yields for each side reaction in the formation of each generation. The fifth generation of the poly(propylene imine) dendrimer containing amine end groups, which is formed after 248 consecutive reaction steps, possesses a dendritic purity of approx. 20%, which corresponds to a polydispersity of approximately 1.002. The defects in the divergent growth patterns of dendrimers are compared to those observed in the Merrifield synthesis of polypeptides.

Thiophenebisboronic derivatives (acids and esters) have been successfully utilized for the first time in palladium-catalyzed Suzuki polycondensations to prepare well-defined alternating thiophenephenylene copolymers. 2,5-Thiophenebis(boronic acid) and its corresponding 1,3-propanediol and pinacol diesters have been synthesized and polymerized with 2,5-dialkoxy-1,4-diiodobenzenes in the presence of Pd(OAc) 2 or Pd(PPh3)4 catalysts. SEC analysis showed that the polymers have moderate molecular weight with a polydispersity of 1.2 to 2.4. The role of the boronic derivatives and the catalyst on the yield and molecular weight of the resulting polymers have been investigated in detail. MALDI-TOF mass spectrometry has been used to elucidate the limiting steps in the polymerization and to assess the end groups. The results suggest that hydrolytic deboronation limits the formation of high molecular weight polymers. The polymers prepared using Pd(OAc) 2 possess various end groups and contain macrocycles, whereas Pd(PPh3)4 produces much cleaner polymers. However, the use of Pd(PPh3)4 introduces phenyl end groups via aryl-aryl exchange between the catalytic palladium intermediate and the triphenylphosphine ligand. We found that this aryl-aryl exchange can be suppressed by the introduction of side chain branching in the 2,5-dialkoxy-1,4-diiodobenzene, and as result defect-free, perfectly alternating, chains with mainly thiophene end groups have been obtained in monomodal molecular weight distribution.