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19 pages, 5385 KiB

Open AccessArticle

Synthesis and Characterization of a Two-Station Two-Gate Calix[6]arene-Based [2]Catenane

by Margherita Bazzoni, Francesco Rispoli, Sara Venturelli, Gianpiero Cera and Andrea Secchi

Molecules 2025, 30(3), 732; https://doi.org/10.3390/molecules30030732 - 6 Feb 2025

Viewed by 816

The design, construction, and operation of devices and machines at the molecular scale using the bottom-up approach captivates a lot of interest in nanoscience. Particularly intriguing are interlocked molecular architectures, which are ideal candidates for these aims. [n]Pseudorotaxanes, [n]rotaxanes, and [n]catenanes serve as versatile prototypes for constructing molecular machines because they can be engineered to execute a diverse range of functions, including mechanical-like movements in response to chemical, photochemical, or electrochemical stimuli. The study explores the synthesis and characterization of a two-station two-gate calix[6]arene-based [2]catenane. Building on prior work with calix[6]arene-based Mechanically Interlocked Molecules (MIMs), this research integrates two functional gates—an azobenzene unit and a stilbene unit —into a two-station “track” ring. The synthesis employed threading and capping strategies to prepare the precursor [2]rotaxane isomers 12(azo-up) and 12(azo-down). Challenges in the deprotection of TBS groups led to the adoption of a supramolecular-assisted approach for the direct synthesis of the desired pseudorotaxane. The final catenation reaction, using a trans-stilbene-based bisacyl chloride as the “clipping unit”, afforded the [2]catenane C3(azo-down) in 25% yield after purification. Mass spectrometry and NMR spectroscopy confirmed the successful synthesis and orientation of C3(azo-down). Full article

(This article belongs to the Section Organic Chemistry)

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17 pages, 1592 KiB

Open AccessArticle

Pseudo-Stilbene- and Azobenzene-Type Systems for Optical Frequency Conversion: Estimating the First-Order Molecular Hyperpolarizability

by Raiane S. Araújo, José J. Rodrigues, Márcio A. R. C. Alencar, Jamal Rafique, Sumbal Saba and Luis M. G. Abegão

Photonics 2024, 11(3), 283; https://doi.org/10.3390/photonics11030283 - 21 Mar 2024

Cited by 2 | Viewed by 2017

Abstract

This study investigates the potential of a set of pseudo-stilbene and azobenzene molecular structures to become optical frequency converters for optical communications based on a detailed exploration of the first-order molecular hyperpolarizability (

β_{H R S}

), which is the microscopic counterpart [...] Read more.

β_{H R S}

), which is the microscopic counterpart of second harmonic generation (SHG).

β_{H R S}

values were obtained via quantum chemical calculations using the Gaussian 16 software package in solvent and gas-phase media at different wavelengths, i.e., 1064 nm, 1310 nm, and 1510 nm. The latter two wavelengths are of particular interest for optical communications. Our study focused on discerning how the molecular structure influences the

β_{H R S}

response, explicitly highlighting the influence of the azomethine group (CH=N). The results revealed that the molecular planarity, affected by this group, plays a crucial role in modulating the optical properties. The highest

β_{H R S}

value in a solvent medium using the CAM-B3LYP/6-311+G(2d,p) level of theory achieved in this work was around

1400 \times 10^{- 30} {cm}^{4} {startvolt}^{- 1}

, four orders of magnitude higher than KDP (0.2

\times 10^{- 30} {cm}^{4} {startvolt}^{- 1}

), which is a reference in SHG experiments at 1064 nm. The highest calculated

β_{H R S}

value at the same level of theory and solvent at 1310 nm and 1550 nm was

631 \times 10^{- 30} {cm}^{4} {startvolt}^{- 1}

and

4 56 \times 10^{- 30} {cm}^{4} {startvolt}^{- 1}

, respectively. All these values belong to molecular structures with azo-coupling with donor (4-NMe₂) and acceptor (4′-NO₂) peripheral groups, designated as AB-3. Full article

(This article belongs to the Special Issue Nonlinear Optics and Hyperspectral Polarization Imaging)

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13 pages, 3623 KiB

Open AccessFeature PaperReview

Aza- and Azo-Stilbenes: Bio-Isosteric Analogs of Resveratrol

by Gérard Lizard, Norbert Latruffe and Dominique Vervandier-Fasseur

Molecules 2020, 25(3), 605; https://doi.org/10.3390/molecules25030605 - 30 Jan 2020

Cited by 28 | Viewed by 4947

Abstract

Several series of natural polyphenols are described for their biological and therapeutic potential. Natural stilbenoid polyphenols, such as trans-resveratrol, pterostilbene and piceatannol are well-known for their numerous biological activities. However, their moderate bio-availabilities, especially for trans-resveratrol, prompted numerous research groups to investigate innovative and relevant synthetic resveratrol derivatives. This review is focused on isosteric resveratrol analogs aza-stilbenes and azo-stilbenes in which the C=C bond between both aromatic rings was replaced with C=N or N=N bonds, respectively. In each series, synthetic ways will be displayed, and structural sights will be highlighted and compared with those of resveratrol. The biological activities of some of these molecules will be presented as well as their potential therapeutic applications. In some cases, structure-activity relationships will be discussed. Full article

(This article belongs to the Special Issue From Natural Polyphenols to Synthetic Bioactive Analogues)

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