Synthesis and characterization of dissymmetric molecular rotors based on 1,4-diethynylphenylene rotators and steroidal/trityl type stators

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Two, acyclic (1) and cyclic (2), steroidal molecular rotors containing 1,4-diethynyl-2,3-difluoro-phenylene units as rotators were investigated by means of single crystal X-ray diffraction, high resolution solid state NMR spectroscopy, and computer methods. The aim of this study was to understand and search for a correlation between the size of difluoro-phenylene units and free space in the crystal lattice required for molecular reorientation as well as the topology and time scale of dynamic processes. As a primary tool for analysis of molecular motions in the solid state, 1H–13C PISEMA, a technique which allows following the dynamics in the range of 10–3–10–6 s, was employed. The PISEMA data defining the 1H–13C dipolar couplings, whose values are sensitive to local motion, were confronted with 13C CSA parameters. Our studies revealed that replacing hydrogen by fluorine in acyclic rotors has significant consequences for dynamic processes. In the case of hydrogen-substituted species, free rotation around the 1–4 axis of the benzene ring was proven. For fluorine derivatives 1, only small amplitude wobbling of aromatic residues was observed. The only large amplitude reorientation, a so-called π-jump around the 1–4 axis, was observed during the phase transition related with solvent migration from the crystal lattice. For cyclic rotors (2) two crystallographic forms 2A (triclinic, P1 space group) and 2B (monoclinic, P21 space group) are established. The form 2B containing a heptane molecule in the crystal lattice undergoes a thermal transition with large amplitude motion of building units of the steroidal frame. The high dynamics of the fluorinated rotator for 2A is proven.

Section: Introductionmentioning

confidence: 99%

Influence of Hydrogen/Fluorine Substitution on Structure, Thermal Phase Transitions, and Internal Molecular Motion of Aromatic Residues in the Crystal Lattice of Steroidal Rotors

Pawlak

Czajkowska-Szczykowska

Jastrzębska

et al. 2020

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“…During the past decade, our group has focused on the design and development of molecular rotors based on steroidal stators with acyclic, 21−27 macrocyclic, 28−31 and hybrid scaffolds 32 (Figure 1). A large variety of molecular architectures can be constructed through alkyne bridging at the A, C, or D ring of the steroidal skeleton and by introducing different substituted phenylene rotators.…”

Section: Introductionmentioning

confidence: 99%

“…Typically, stators are bulky molecular fragments covalently or supramolecularly linked to an alkynyl bridged phenylene (∼5 Å), diaza- or bicyclo[2.2.2]octane (∼6 Å) and trypticene (∼11 Å) rotator. − Depending on the rotator size and the organization in the crystal structure, these amphidynamic systems display a wide range of rotational frequencies (10 –6 to 10 –12 s –1 ), even at room temperature. During the past decade, our group has focused on the design and development of molecular rotors based on steroidal stators with acyclic, − macrocyclic, − and hybrid scaffolds (Figure ).…”

Section: Introductionmentioning

confidence: 99%

Asymmetric Molecular Rotors Based on Steroidal Fragments. Organic Building Blocks Displaying Versatile Supramolecular Steroid-Stacking Interactions

Ochoa

Arcos‐Ramos

Ramirez-Montes

et al. 2019

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The synthesis, characterization, and crystal structure analysis of five new steroidal molecular rotors constructed from two different building blocks, viz., mestranol, ethynylestradiol, levonorgestrel, ethisterone, norethisterone, and 17α-ethynyl-5α-androstane-3β-17β-diacetate, are reported. The different steroidal frameworks were examined in order to correlate intermolecular interactions displayed by their functional groups with defined supramolecular arrangements. The reaction cavity concept was explored as an aid to rationalize the potential dynamic behavior of these systems; however, reorganization of the lattice during the plausible phenylene flips precluded a straightforward interpretation. Asymmetric molecular rotors displayed stacked steroidal fragments that are structurally related to the steroid α•••π stacking observed in previously reported systems. Additionally, these systems could be useful to explore cooperativity between supramolecular interactions involving small solvent molecules.

“…Molecular rotors, which exhibit rotation in part of the molecule, have been widely investigated. Because molecular motion may affect the chemical properties of the molecules, controlling molecular motion inside molecular aggregates, e.g., single crystals, could be a guiding principle in developing novel molecule-based materials. − There have been many reports regarding the synthesis and characterization of molecular rotors, and the relationship between dynamics and properties have been investigated. − In particular, molecular rotors with a dipole moment in the rotor have received much attention. Crystalline three-dimensional arrays of dipolar molecular rotors have recently been studied and characterized. ,,,− Investigation of the arrays of dipolar rotors remains significant to understanding the dielectric properties of these materials.…”

Section: Introductionmentioning

confidence: 99%

Molecular Gyrotops with a Five-Membered Heteroaromatic Ring: Synthesis, Temperature-Dependent Orientation of Dipolar Rotors inside the Crystal, and its Birefringence Change

Masuda

Arase

Inagaki

et al. 2016

Three-dimensional arrays of dipolar rotors were constructed as single crystals of molecular gyrotops, which are macrocage molecules with a bridged dipolar rotor. In this study, we synthesized novel molecular gyrotops with a five-membered heteroring, i.e., furan-diyl (1), thiophene-diyl (2), and selenophene-diyl (3), and investigated the temperature-dependent orientation and rotation of the dipolar rotors inside the crystal. Unfortunately, furan derivative 1 did not crystallize; however, crystal structures of the other molecular gyrotops, i.e., 2 and 3, showed three-dimensional arrays of dipolar rotors. Thermal order−disorder transitions of the dipolar rotor orientation inside the crystal were observed in 2 and 3 with the transition temperature in selenophene derivative 3 being lower than that of thiophene derivative 2. This may be ascribed to subtle differences in the molecular structure, e.g., the intersection angle between two Si−C(aryl) bonds corresponding to the rotation axis. In accordance with the thermal change of the crystal structure, temperature-dependent optical properties of a single crystal were observed by analysis of birefringence of the crystal.