Steroidal Molecular Rotors with 1,4-Diethynylphenylene Rotators: Experimental and Theoretical Investigations Toward Seeking Efficient Properties

Abstract

Properly designed molecular rotors with sizable stators and a fast-moving rotator could provide efficient building blocks for amphidynamic crystals. Herein, we report the synthesis of steroidal compounds 1 , 2 , and 3 and their deuterated analogues 1D , 2D , and 3D envisioned to work as molecular rotors. The obtained compounds were characterized by attenuated total reflection-infrared, Raman, and circular dichroism (CD) spectroscopy measurements. The interpretation of spectra was supported by theoretical calculations using density functional theory methods. The analysis of the most characteristic bands confirmed different molecular dynamics of the rotors investigated. Angle-dependent polarized Raman spectra showed the crystallinity of some samples. Electronic CD (ECD) spectra of compounds 1–3 and their relevant deuterated analogues 1D–3D are identical. The increase of the band intensity with lowering the temperature shows that the equilibrium is shifted to the thermodynamically most stable conformer. ECD spectra simulated at the TDFFT level of theory for compound 3 were compared with experimental results. It was proved that conformer 3a , with a torsion angle of +50°, exhibits the best agreement with the experimental results. Simulated vibrational CD and IR spectra for conformer 3a and its deuterated analogue 3Da also display good agreement with experimental results. In light of our comprehensive investigations, we evidenced that steroidal compounds 1 , 2 , and 3 can work as molecular rotors.

Molecular Dynamics of Steroidal Rotors Probed by Theoretical, Spectroscopic and Dielectric Methods

“…The spectroscopic properties of rotors 3 – 5 were investigated using experimental and theoretical methods. Compounds 4 and 5 differ from previously investigated deuterated compounds [23,24] in that they have a rotating moiety composed of a dipolar fluorine‐substituted phenyl group. Compound 4 has one fluorine atom, while compound 5 has two, positioned on the same side of the aromatic ring.…”

“…We also considered two different conformations of the rotor molecule in terms of stator orientation, namely “A” and “B” (see Figure 2). We were unable to incorporate the rotational movement of the rotator in the rotor molecule in theoretical calculations, which is an unrealistic circumstance given that many articles demonstrate the rotational movement of the rotator [19–24,28] . It is evident that the rotation of the rotor should influence molecular dynamics, especially in the rotator and axles of rotation.…”

“…The change in the intensity ratio can be related to the rotator‘s symmetry, caused by replacing hydrogen with a fluorine atom(s) and/or the orientation of crystallites in the sample. The latter aspect was discussed in detail for other rotors in our previous papers [23,24] . Considering the lack of direct influence of fluorine substitution on triple CC bonds in the axle of rotation of the rotator, we can assume that the intensity of the Raman band assigned to triple CC bonds vibration can be treated as a reference band for the band attributed to C=C aromatic bonds vibration.…”

“…The topic was further investigated for compounds with steroidal stators created from two mestranol molecules, [21,22] with the focus of identifying different conformation and packing arrangements in solid state, depending on different rotator substitution, type of solvent, and crystallization temperature. In this paper, we concentrate on exploring molecular dynamics of molecular gyroscopes with 1,4‐diethynylphenylene based rotators and steroidal stators, extending our research into the topic of molecular rotors with deuterated rotators and steroidal stators [23,24] . Using vibrational spectroscopy, electronic circular dichroism (ECD), and impedance spectroscopy methods, we endeavour to show how different substitution with fluorine of the phenyl group of the rotator influences the molecular dynamics of the rotors investigated.…”

Base-Catalyzed, Solvent-Free Synthesis of Rigid V-Shaped Epoxydibenzo[b,f][1,5]diazocines

“…These two chiroptical spectroscopies are very sensitive to any stereochemical changes of the chiral system because they rely on electronic and vibrational transitions spanning the entire UV–vis–mid-IR spectral range. Thus, their complementary combinations provide a holistic view of the properties of any chiral molecules, enabling the conclusive assignment of their absolute configuration in solution and also deeper insight into dynamic stereochemistry …”