Arrays of Molecular Rotors with Triptycene Stoppers: Surface Inclusion in Hexagonal Tris(o-phenylenedioxy)cyclotriphosphazene

Abstract

A new generation of rod-shaped dipolar molecular rotors designed for controlled insertion into channel arrays in the surface of hexagonal tris(o-phenylenedioxy)cyclotriphosphazene (TPP) has been designed and synthesized. Triptycene is used as a stopper intended to prevent complete insertion, forcing the formation of a surface inclusion. Two widely separated (13)C NMR markers are present in the shaft for monitoring the degree of insertion. The structure of the two-dimensional rotor arrays contained in these surface inclusions was examined by solid-state NMR and X-ray powder diffraction. The NMR markers and the triptycene stopper functioned as designed, but half of the guest molecules were not inserted as deeply into the TPP channels as the other half. As a result, the dipolar rotators were distributed equally in two planes parallel to the crystal surface instead of being located in a single plane as would be required for ferroelectricity. Dielectric spectroscopy revealed rotational barriers of ∼4 kcal/mol but no ferroelectric behavior.

Gearing motion in cogwheel pairs of molecular rotors: weak-coupling limit

“…The molecular rod 1 was synthesized as reported earlier. 9 Plate-like colourless crystals were obtained by slow cooling of an ethyl acetate solution and their structure was determined by X-ray diffraction at 293 K and 120 K. ‡ § As exemplified in Fig. 1, a striking feature distinguishes the patterns of self-assembly, and thus the topologies, of crystalline arrays of 1 and 2.…”

“…Understanding the mechanism of motion in crystalline arrays of molecular rotors with complex dynamics 1 is a key step that will foster the development of molecular machines capable of performing useful work. [2][3][4][5][6][7][8] The present investigation of the topology and dynamics of solid state assemblies of the rodlike molecule bisIJ3-(pyrid-4-ylethynyl)bicycloij1.1.1]pent-1-yl)buta-1,3-diyne (1) that contains two 1,3-bisIJethynyl)bicyclo-ij1.1.1]pentane (BCP) rotators linked by a diyne fragment (Chart 1), 9 was prompted (i) by our recent report 10 of a correlated gearing motion in cogwheel pairs of a similar rod (2) with 1,4-bisIJethynyl)bicycloij2.2.2]octane (BCO) rotators 8 instead; and (ii) the demonstration that, in keeping with the one-dimensional topology of 2, a 4 Å shift of the rotor axles with respect to each other in the thermodynamic polymorph of 2 effectively suppresses the gearing motion. 11 Another, yet different, example of correlated rotational motion in a pair is reported here for 1.…”

Triple and Quadruple Triptycene Gears in Rigid Macrocyclic Frameworks

“…Unit U2 was prepared by the complete desilylation of 18 or 9,10‐bis[(trimethylsilyl)ethynyl]triptycene by using a known method. [9b], …”

“…For 9‐(phenylethynyl)triptycene derivatives, the rotational barrier about the acetylene axis is known to be very low or almost zero. [15d], Hence, the calculated rotational barrier of B′ results from interactions between the Tp units. Because the four Tp units concurrently rotate in the same direction while keeping any contacts and conformational changes from B′ ‐M1 or B′ ‐M2 to B′ ‐TS small, the overall energy change becomes very small during the rotation.…”

Molecular Rods: Facile Desymmetrization of 1,4‐Diethynylbicyclo[2.2.2]octane

“…They are also essential motifs in systems designed for studying various physical phenomena such as singlet energy or electron, transfer. Efforts to construct regular two‐dimensional and three‐dimensional arrays of rotors frequently rely on the use of bridgehead substituted bicyclo[1.1.1]pentanes (BCP),, , , bicyclo[2.2.2]octanes (BCO),, and triptycenes as key building blocks. A few of the BCO‐based systems already showed ultra‐fast rotation, in the solid state and interesting phenomena such as correlated motion in pairs of neighboring rotators, as well as second harmonic generation responses due to local space‐inversion symmetry breaking in centrosymmetric crystals , …”