Throwing in a Monkey Wrench to Test and Determine Geared Motion in the Dynamics of a Crystalline One-Dimensional (1D) Columnar Rotor Array

Abstract

Crystals of molecular rotor 1 with a central 1,4phenylene rotator linked to two molecules of the steroid mestranol were prepared with 1%, 5%, 20%, and up to 40% of the analogous 2, which contains a larger 2,3-difluorophenylene rotator and effectively acts as a monkey wrench that affects the rotation of the host. The packing motif of the desired P3 2 crystal form consists of 1D columns of nested rotors arranged in helical arrays with the central aromatic rotators disordered over two sites related by 85°rotation about their 1,4-axes. Rotational dynamics measured by quadrupolar echo 2 H NMR line shape analysis were analyzed in terms of a process model that involves degenerate 180°jumps in the fast exchange regime combined with a highly correlated and entropically demanding jump of 85°b etween the two dynamically disordered sites. While the enthalpic and entropic barriers for the 180°jump estimated from 2 H T 1 measurements were ΔH ⧧ = 2.7 ± 0.1 kcal mol −1 and ΔS ⧧ = −5.0 ± 0.5 cal mol −1 K −1 , respectively, the corresponding parameters for the slower 85°jumps, determined by line shape analysis, were ΔH ⧧ = 2.2 kcal mol −1 and ΔS ⧧ = −23 cal mol −1 K −1 . Increasing amounts of the larger molecular rotor 2 in the solid solution results in significant dynamic perturbations as the guest, acting as a monkey wrench, reaches values of one out of every five molecular rotors in the chain.

Rotation of a helical coordination polymer by mechanical grinding

“…4 Further bicycle-pedal or crankshaft motion is the most frequently observed in the solid state. [5][6][7][8][9][10][11][12][13][14] Rotation of helical 1D column of phenylene rotators by the influence of temperature has been studied by Garcia-Garibay et al 15 On the contrary, solid state reactions facilitated by grinding, which is popularly called ''mechanochemistry'', have been extensively explored. [16][17][18][19][20] Kaupp examined various molecular dynamic processes occurring in the solid state by mechanical forces.…”

“…Movements of the functional groups have been observed in CPs in the solid state. [15][16][17][18][19][20][21] Further, mechanical grinding has been known to promote pedal motion of crisscrossed olefin pairs, [8][9][10][11][12][13][14] movements of molecules, [29][30][31] and change in chemical composition. 32 Large molecular movement of ladders in the crystal lattice by mechanical grinding was reported to facilitate quantitative photodimerization.…”

Photogearing – A Concept for Translation of Precise Motions at the Nanoscale

“…(7) So far, mechanically controlled molecular systems have been developed ranging from more simple molecular breaks (46,47) to truly geared systems in which different molecular fragments or entities move in concert because of their tight intermeshing (see ref. (48)(49)(50)(51)(52)(53) for selected examples). More recent progress has allowed to switch gearing in an ON/OFF fashion.…”

Color‐ and Dimension‐Tunable Light‐Harvesting Organic Charge‐Transfer Alloys for Controllable Photon‐Transport Photonics

“…By contrast, alloys from organic materials are less studied. In particular, organic alloys are formed by replacing the molecules of one starting crystal with those of the other, giving new crystalline species whose structures and properties vary continuously over a wide composition range [1–15] . The compatible molecular structures, sizes, and physicochemical properties between two organic materials enable the random mixing in their crystalline mixtures.…”