Structure, spectra and internal rotation of bis(trimethylsilyl) acetylene: spectral analysis by scaling quantum-chemical force fields and two methods for calculating vibrational effects

Diffusion-Controlled Rotation of Triptycene in a Metal–Organic Framework (MOF) Sheds Light on the Viscosity of MOF-Confined Solvent

“…5 × 10 11 s –1 ), one would come to the conclusion that the temperature dependence of the rotational frequency does not reflect a static energy potential from permanent structural features in the crystal. , Knowing that gas phase rotation of the triptycene rotator about the two triple bond axle should be essentially free, hindrance must arise from interactions between triptycene and the solvent molecules in the crystal. Interestingly, spin–lattice relaxation studies carried out at ambient temperature in liquid CHCl 3 have shown that the correlation time for the rotation of triptycene about its 3-fold axis (50 ps) is about three times longer than the one for rotation about the perpendicular 2-fold axes (16 ps), while the difference between their moments of inertia is relatively small. − This suggests that solvent molecules fill the space between the three blades and slow down the rotation along the 3-fold axis, which is also suggested by the solid-state structural features shown in Figure B. Assuming that hydrodynamic theory can describe the behavior of a pinned molecular rotor in a strictly confined liquid, using a calculated molecular volume for triptycene of V mol = 2.3 × 10 –28 m 3 , and considering that it has a rotational correlation time of ca.…”

“…Interestingly, spin–lattice relaxation studies carried out at ambient temperature in liquid CHCl 3 have shown that the correlation time for the rotation of triptycene about its 3-fold axis (50 ps) is about three times longer than the one for rotation about the perpendicular 2-fold axes (16 ps), while the difference between their moments of inertia is relatively small. 46 − 48 This suggests that solvent molecules fill the space between the three blades and slow down the rotation along the 3-fold axis, which is also suggested by the solid-state structural features shown in Figure 3 B. Assuming that hydrodynamic theory can describe the behavior of a pinned molecular rotor in a strictly confined liquid, using a calculated molecular volume for triptycene of V mol = 2.3 × 10 –28 m 3 , and considering that it has a rotational correlation time of ca.…”

Artificial Molecular Rotors

“…Rotation about triple bonds, in particular acetylene linkages, yields intrinsic barriers that are calculated to be only a few hundred calories per mole. 107,108 Systems where metal atoms act as an axis can exhibit a wide range of barrier heights.…”

Systematic Studies on Photoluminescence of Oligo(arylene‐ethynylene)s: Tunability of Excited States and Derivatization as Luminescent Labeling Probes for Proteins

“…Previous reports have shown that rotation about the phenyl-acetylene single bond is essentially frictionless due to the cylindrical symmetry of the triple bond, which is able to maintain conjugation between the phenyl rings irrespective of the relative orientations of the aromatic planes. [27][28][29] This leads to the rapid equilibration and coexistence of the coplanar and twisted conformations in the ground state. Upon electronic excitation, on the other hand, changes in bond order along the C(phenyl)-CϵC fragment, from alternate single-triple bonds in the ground state (S 0 ) to a cumulene-type (C=C=C) bonding situation in the first singlet excited state (S 1 ), may afford larger energy differences between the coplanar and twisted conformations.…”