Dynamics of alkoxy-oligothiophene ground and excited states in nanochannels

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 auto-assembling host tris-o-phenylenedioxycyclotriphosphazene. The effect of the confinement on the structure and properties of the two dyes, in terms of conformational arrangements, dynamics, and photophys. 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 supramol. adducts from 4 K to room temp. Above 200 K surprisingly fast spinning rates of the dithiophene core were discovered, while the side chains showed 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 liqs. and a long triplet lifetime at unusually high temp. The nuclear magnetic properties of the guest dyes are also largely affected by the arom. 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 aliph. and arom. 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.