3 research outputs found
Design, Synthesis, and Isomerization Studies of Light-Driven Molecular Motors for Single Molecular Imaging
The
design of a multicomponent system that aims at the direct visualization
of a synthetic rotary motor at the single molecule level on surfaces
is presented. The synthesis of two functional motors enabling photochemical
rotation and fluorescent detection is described. The light-driven
molecular motor is found to operate in the presence of a fluorescent
tag if a rigid long rod (32 Ć
) is installed between both photoactive
moieties. The photochemical isomerization and subsequent thermal helix
inversion steps are confirmed by <sup>1</sup>H NMR and UVāvis
absorption spectroscopies. In addition, the tetra-acid functioned
motor can be successfully grafted onto amine-coated quartz and it
is shown that the light responsive rotary motion on surfaces is preserved
Dynamic Cross-Linking of Polyethylene via Sextuple Hydrogen Bonding Array
Multiple hydrogen bonding motifs are promising tools for polymer functionalization to obtain adaptable networks combining advantages of permanently cross-linked systems with processability of thermoplastics. Here we describe the use of a new multiple hydrogen bonding motif to impart increased tensile strength, stiffness, barrier properties, and a plateau modulus after melting to functional polyolefins, while retaining adaptability of the polymer network. The cross-linked nature of these polymers was elucidated by thermal and mechanical analysis, revealing a raised glass transition and rheology similar to permanently cross-linked polymer matrices. The apolar polymer matrix was found to stabilize the new hydrogen bonding motif at elevated temperatures. The resulting polymer showed thermal resistance superior to ureidopyrimidone (UPy) motif functionalized materials, the most commonly employed synthetic multiple hydrogen bonding motif to date
Restricted Guest Tumbling in Phosphorylated Self-Assembled Capsules
International audienceABii diphosphonatocavitands self-assemble in chloroform solution to form dimeric molecular capsules. The molecular capsules can incarcerate an N-methylpyridinium or N-methylpicolinium guest. We have demonstrated that the supramolecular assembly acts as a molecular rotor as a result of the restricted motion of the guest inside the molecular cavity. In the solid state, X-ray diffraction analysis of the free host showed that two cavitands interact through strong hydrogen bonds to give the supramolecular self-assembled capsule. The solid-state structure of the N-methylpicolinium complex is comparable to that of the free host and indicates that the guest is not a prerequisite for the formation of the capsule. DOSY NMR studies provided a definitive argument for the formation of the free and complexed supramolecular capsule in CDCl3 solution. In solution, the tumbling of the N-methylpyridinium and N-methylpicolinium guests about the equatorial axes of the host can be frozen and differs by the respective energy barriers, with the larger picolinium substrate having a larger value (ĪGā§§ = 69.7 kJ molā1) than the shorter pyridinium guest (ĪGā§§ = 44.8 kJ molā1). This behavior corresponds to the restricted rotation of a rotator in a supramolecular rotor