Dynamics of Alkoxy−Oligothiophene Ground and Excited States in Nanochannels

Abstract

Two oligothiophenes, 4,4'-dipentoxy-2,2'-dithiophene and 4,4"-dipentoxy-2,2':5',2":5",2' ''-tetrathiophene, have been included in the nanochannels of the autoassembling host TPP (tris-o-phenylenedioxycyclotriphosphazene). The effect of the confinement on the structure and properties of the two dyes, as conformational arrangements, dynamics, and photophysical behavior, was addressed by the combination of high spinning speed solid-state NMR and time-resolved EPR spectroscopy. We compared the conformations of the dyes in their ground and photoexcited triplet states and described in detail the dynamics of the supramolecular adducts from 4 K to room temperature. Above 200 K surprisingly fast spinning rates of the dithiophene core were discovered, while the side chains show far slower reorientation motion, being in bulky gauche-rich conformations. These lateral plugs keep the planar core as appended in the space like a nanoscale gyroscope, allowing a reorientation in the motion regime of liquids and a long triplet lifetime at unusually high temperature. The nuclear magnetic properties of the guest dyes are also largely affected by the aromatic rings of the neighboring host, imparting an impressive magnetic susceptibility effect (2 ppm proton shift). The high mobility is due to the formation of a nanocage in a channel where aliphatic and aromatic functions isolate the thiophene moieties. Instead, two conformers of the tetrathiophene twisted on the central bond are stabilized by interaction with the host. They interconvert fast enough to be averaged in the NMR time scale.

Microporous Molecular Materials from Dipeptides Containing Non‐proteinogenic Residues

“…Such high-field resonances are typical of n-alkane chain-end methyls, experiencing the effect of gauche conformations of the vicinal -CH2-CH2− bond (-gauche effect). [12] Since the trans-to-gauche conversion accounts for = -5 ppm in hydrocarbons, the observed CH3 chemical shifts of about 3 ppm upfield with respect to the expected trans conformation resonance, indicates that at least a 0.5 fraction of gauche conformation is explored, consistent with XRD data. Spin-lattice relaxation times from 0.3 to 1.7 s for Nva alkyl pendant group are close to the theoretical minimum value, indicating an efficient relaxation mechanism of about 10 8 Hz.…”

Time-Resolved Fluorescence Anisotropy of Bicyclo[1.1.1]pentane/Tolane-Based Molecular Rods Included in Tris(o-phenylenedioxy)cyclotriphosphazene (TPP)

“…The channels accept small molecules eagerly, 22 and detailed dynamic NMR and EPR studies of the motion of oligothiophenes included in TPP inclusion have been reported. 23 …”

Preparation and Characterization of New Inclusion Compounds Using Stable Nitroxide Radicals and an Organic 1-D Nanochannel as a Template

“…The molecular dynamics of guest molecules are mainly investigated using NMR, because the fast uni-axial rotation or the structural disorder of guest molecules makes the determination of the molecular structure or orientation in the nanochannels by single crystal X-ray diffraction difficult. This is even the case for TPP/benzene IC, in which the shape of guest molecules is simple and highly symmetric [16,17,18,19,20]. In addition, TPP is also a medium for gas storage because the strong affinity of the wall of the nanochannels makes it possible to include even gas molecules [21,22,23].…”