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Push-Pull Oligomers with 2,2-Dicyanovinyl Groups as Electron Acceptors
2007
Three conjugated oligomer series with terminal donor–acceptor substitution were studied: oligo(1,4-phenylenevinylene)s DAOPVs 4a–d (n = 1–4), oligo(1,4-phenyleneethynylene)s DAOPEs 6a–d (n = 1–4) and oligo(2,5-thienyleneethynylene)s DAOTEs 8a–e (n = 1–5). Dialkylamino or methoxy groups served as electron donors and 2,2-dicyanovinyl groups as strong electron acceptors. The push-pull effect polarizes the molecular chains – an effect which is documented by the splitting of the 13C chemical shifts of two carbon atoms of the double or triple bonds in the chain. For higher oligomers (n ≥ 3), the effect is mainly localized at the chain ends. The long-wavelength absorption results in a charge-trans…
Star-Shaped Compounds Having 1,3,5-Triazine Cores
2003
The 1,3,5-triazine derivatives 1−4 having styryl or higher oligo(phenylenevinylene) chains in the 2-, 4-, and 6-positions represent star-shaped push-pull compounds. Alkoxy or dimethylamino groups on the peripheral benzene rings, which act as electron donors, and the central 1,3,5-triazine ring, which acts as an electron acceptor, cause intramolecular charge transfer (ICT) to occur in the absorption S0⇄S1. Protonation of the 1,3,5-triazine core enhances the effect, as demonstrated by a bathochromic shift; a secondary protonation on the dimethylamino groups, however, leads to the breakdown of the ICT. Thus, the yellow compound 1d first becomes violet and then colorless upon the addition of tr…
Intramolecularly Coordinated Bis(crown ether)-Substituted Organotin Halides as Ditopic Salt Receptors
2013
The synthesis of the bis(crown ether)-substituted organostannanes X2Sn(CH2-[16]-crown-5)2 (3, X = I; 4, X = Br; 5, X = Cl; 6, X = F) and X2Sn(CH2-[13]-crown-4)2 (10, X = I; 11, X = Br; 12, X = F) is reported. The compounds have been characterized by 1H, 13C, 19F, and 119Sn NMR spectroscopy, elemental analyses, and electrospray ionization mass spectrometry (ESI-MS). Single-crystal X-ray diffraction analyses reveal a distorted-octahedral cis,cis,trans configuration of the tin atoms in compounds 4–6 and 10–12 as a result of intramolecular O→Sn coordination. The ability of the host molecules to form mono- and ditopic complexes with various halide salts in different solvents, including water, ha…
Mannich Reactions with Amino Alcohols
2000
The condensation of resorcarenes 1 with various amino alcohols and an excess of formaldehyde was studied. The tetrabenzoxazines 2a−e were found as the only products in the reaction with 6-aminohexan-1-ol, 4-aminobutan-1-ol, and 2-aminoethanol, while 3-aminopropan-1-ol forms the tetraoxazine 3 as the main product. In the case of aminoethanols substituted at the 2-position with alkyl groups, the tetraoxazolidines 4 are the preferred reaction products, while 1-methyl aminoethanol (1-amino-propan-2-ol) yields predominantly the tetrabenzoxazine 2f. The structures of all these compounds have been confirmed by NMR spectroscopy and additionally by single-crystal X-ray analysis in the case of 2a and…
Tri- and tetraurea piperazine cyclophanes: synthesis and complexation studies of preorganized and folded receptor molecules.
2010
A series of symmetrical tri- and tetrameric N-ethyl- and N-phenylurea-functionalized cyclophanes have been prepared in nearly quantitative yields (86-99 %) from the corresponding tri- and tetraamino-functionalized piperazine cyclophanes and ethyl or phenyl isocyanates. Their conformational and complexation properties have been studied by single-crystal X-ray diffraction, variable-temperature NMR spectroscopy, and ESI-MS analysis. The rigid 27-membered trimeric cyclophane skeleton assisted by a seam of intramolecular hydrogen bonds results in a preorganized ditopic recognition site with an all-syn conformation of the urea moieties that, complemented by a lipophilic cavity of the cyclophane, …
Effect of Protonated Organic Cations and Anion−π Interactions on the Magnetic Behavior of Hexabromorhenate(IV) Salts
2015
Two novel Re-IV compounds of formula (Hbpym)(2)[(ReBr6)-Br-IV]center dot 4H(2)O (1) and (H(4)biim)[(ReBr6)-Br-IV]center dot 4H(2)O (2) [Hbpym(+) = 2,2'-bipyrimidinium cation and H(4)biim(2+) = 2,2'-biimidazolium dication] have been prepared and magnetostructurally characterized. 1 and 2 exhibit distinct crystal packing, and the presence of weak intermolecular contacts, such as Re-Br...B-rRe (1 and 2), Re-Br center dot center dot center dot(H2O)center dot center dot center dot BrRe (1 and 2), and Re-Br center dot center dot center dot pi center dot center dot center dot Br-Re (2), lead to different magnetic behaviors. While 1 is antiferromagnetic, 2 is a ferromagnetic compound and indeed the…
Star-Shaped Push-Pull Compounds Having 1,3,5-Triazine Cores
2006
The 1,3,5-triazines 9–11 having OPV chains in the 2-, 4- and 6-position represent star-shaped compounds which exhibit strong push-pull effects. Their long-wavelength absorption S0 S1 is characterized by an intramolecular charge transfer (ICT) from the dialkylamino group as electron donor D via the conjugated chain to the 1,3,5-triazine core as electron acceptor A. Protonation of the dialkylamino group removes the donor capability, whereas protonation of the 1,3,5-triazine ring enhances the acceptor strength. Thus, the prevailing protonation site has a crucial influence on the push-pull effect and the ICT. The transition energies ΔE (S0 S1) pass through a minimum for the second generation 10…
Monolayers of Bolaform Amphiphiles: Influence of Alkyl Chain Length and Counterions
1994
We have prepared self-assembled monolayers of novel cationic bolaform amphiphiles on negatively charged substrates. Most of these amphiphiles form smooth, defect-free monolayers which can be used to reverse the substrate surface charge and thus allow subsequent adsorption of anionic molecules and construction of multilayers. Atomic force microscopy, surface force measurement, and surface plasmon spectroscopy were combined to probe the molecular orientation and ordering, mechanical properties, and surface electrical properties of the monolayers. In addition, the amphiphile aggregation behavior at an air-water interface was studied by surface tension measurement, and lyotropic phase behavior …
Thermodynamics of binary mixtures: Volumes, heat capacities, and dilution enthalpies for then-pentanol+2-methyl-2-butanol system
1983
The densities, heat capacities, and dilution enthalpies ofn-pentanol+2-methyl-2-butanol mixtures have been measured, in many cases as a function of temperature, over the complete mole fraction range. Excesses thermodynamic properties, apparent and partial molar heat capacities, volumes and expansibilities were derived. The concentration and temperature dependences of these functions are discussed in terms of the variations of the structure of the system caused by the participation of the two alcohol molecules (with quite different steric hindrance of the alkyl chain around the-OH group) in the dynamic intermolecular association process through hydrogen bonding.
Mukaiyama–Michael Reactions with trans-2,5-Diarylpyrrolidine Catalysts: Enantioselectivity Arises from Attractive Noncovalent Interactions, Not from …
2013
The scope of the enantioselective Mukaiyama-Michael reactions catalyzed by trans-2,5-diphenylpyrrolidine has been expanded to include both α- and β-substituted enals. However, the rationalization of the observed enantioselectivity is far from obvious since the catalyst is not very sterically hindered. DFT calculations were carried out to rationalize the observed stereoselectivities. Transition states of the C-C bond formation between iminium intermediates and silyloxyfurans were located and their relative energies were used to estimate the stereoselectivity data. We find excellent agreement between the predicted and observed stereoselectivities. The analysis of intermolecular forces reveals…