29 research outputs found

    Multiresponsive Photo‑, Solvato‑, Acido‑, and Ionochromic Schiff Base Probe

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    Nonclassical protomeric tautomerism in Schiff bases have the advantage of controlling and differentiating specific interactions in the −CN– linkage since its interactions are not governed by keto–enol tautomerism. Here, we report about the optical properties of a Schiff base probe (<b>P1</b>). X-ray structure analysis evidenced the existence of an intramolecular hydrogen bond which is responsible of a photochromic-fluorescent behavior. The properties of <b>P1</b> were investigated by UV–vis and fluorescence spectroscopy in solution and solid state. A positive solvatochromism resulting from specific interactions taking place in <b>P1</b> was studied by three different solvent scales, namely Lippert–Mataga, Kamlet–Taft, and Catalán, finding consistent results. Moreover, a strong acidochromic behavior was detected and the p<i>K</i><sub>a</sub> and p<i>K</i><sub>a</sub>* values were determined, finding a photobasic character. Further, an ionochromic behavior was stablished. <b>P1</b> exhibits a λ-ratiometric fluorescence response toward Sn­(IV) giving a luminescence color change from blue to green, displaying also a chromogenic response. Finally, theoretical calculations were conducted to analyze the probe mechanism in terms of natural transition orbitals (NTOs) and spatial extent of charge transfer excitations. The present contribution focused on the factors determining the ability of a single Schiff base probe to present photo-, solvato-, acido-, and ionochromism

    Photoinduced Isomerization of 23-Oxosapogenins: Conformational Analysis and Spectroscopic Characterization of 22-Isosapogenins

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    The first synthesis of 22-isospirostane derivatives is described. They were obtained by photochemical isomerization of 23-oxosapogenins. The structure of 23-oxo-22-isotigogenin acetate (<b>12</b>) was proved by a single crystal X-ray diffraction, while structures of 23-oxo-22-isodiosgenin acetate (<b>13</b>) and 23-oxo-22-isosarsasapogenin acetate (<b>14</b>) were elucidated by spectroscopic methods. 22-Isodiosgenin acetate (<b>17</b>) was obtained by NaBH<sub>4</sub> reduction of the 23-oxo derivative <b>13</b> followed by the two-step Barton–McCombie deoxygenation procedure. Conformational analysis of 22-iso compounds was carried out with CD and NMR, as well as DFT calculations

    Steroidal Wheel-and-Axle Host Type Molecules: Insights from Awkward Shape, Conformation, <i>Z</i>′ > 1 and Packing

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    The synthesis and crystal structure of three new molecular rotors derived from levonorgestrel and norethisterone are reported. The conformation, close contacts, and shape characteristics of these molecules exhibiting <i>Z</i>′ = 2 and the inclusion of solvent molecules were analyzed together with the crystal structures of parent molecules retrieved from the Cambridge Structural Database. For the set of estranes studied, we confirmed that whenever an alternative conformer cannot satisfy the crystallographic symmetry, a second molecule is incorporated in the asymmetric unit resulting in conformational isomorphism (<i>Z</i>′ > 1). The shape of these molecules could make them interesting as potential hosts

    Steroidal Wheel-and-Axle Host Type Molecules: Insights from Awkward Shape, Conformation, <i>Z</i>′ > 1 and Packing

    No full text
    The synthesis and crystal structure of three new molecular rotors derived from levonorgestrel and norethisterone are reported. The conformation, close contacts, and shape characteristics of these molecules exhibiting <i>Z</i>′ = 2 and the inclusion of solvent molecules were analyzed together with the crystal structures of parent molecules retrieved from the Cambridge Structural Database. For the set of estranes studied, we confirmed that whenever an alternative conformer cannot satisfy the crystallographic symmetry, a second molecule is incorporated in the asymmetric unit resulting in conformational isomorphism (<i>Z</i>′ > 1). The shape of these molecules could make them interesting as potential hosts

    Strong Dipolar Effects on an Octupolar Luminiscent Chromophore: Implications on their Linear and Nonlinear Optical Properties

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    Design parameters derived from structure–property relationships play a very important role in the development of efficient molecular-based functional materials with optical properties. Here, we report on the linear and nonlinear optical properties of a fluorene-derived dipolar system (<b>DS</b>) and its octupolar analogue (<b>OS</b>), in which donor and acceptor groups are connected by a phenylacetylene linkage, as a strategy to increase the number of delocalized electrons in the π-conjugated system. The optical nonlinear response was analyzed in detail by experimental and theoretical methods, showing that, in the octupolar system <b>OS</b>, the dipolar effects induced a strong two-photon absorption process whose magnitude is as large as 2210 GM at infrared wavelengths. Solvatochromism studies were implemented to obtain further insight on the charge transfer process. We found that the triple bond plays a fundamental role in the linear and nonlinear optical responses. The strong solvatochromism behavior in <b>DS</b> and <b>OS</b> was analyzed by using four empirical solvent scales, namely Lippert–Mataga, Kamlet–Taft, Catalán, and the recently proposed scale of Laurence et al., finding consistent results of strong solvent polarizability and viscosity dependence. Finally, the role of the acceptor groups was further studied by synthesizing the analogous compound <b>2DS</b>, having no acceptor group

    Macrocyclic Molecular Rotors with Bridged Steroidal Frameworks

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    In this work, we describe the synthesis and solid-state dynamics of isomeric molecular rotors <b>7</b><i><b>E</b></i> and <b>7</b><i><b>Z</b></i>, consisting of two androstane steroidal frameworks linked by the D rings by triple bonds at their C17 positions to a 1,4-phenylene rotator. They are also linked by the A rings by an alkenyl diester bridge to restrict the conformational flexibility of the molecules and reduce the number of potential crystalline arrays. The analysis of the resulting molecular structures and packing motifs offered insights of the internal dynamics that were later elucidated by means of line shape analyses of the spectral features obtained through variable-temperature solid-state <sup>13</sup>C NMR; such analysis revealed rotations in the solid state occurring at kilohertz frequency at room temperature

    Conformational Polymorphism and Isomorphism of Molecular Rotors with Fluoroaromatic Rotators and Mestranol Stators

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    We report the synthesis and characterization of four molecular rotors <b>2</b>, <b>3</b>, <b>4</b>, and <b>5</b> containing 2-fluoro-, 2,3-difluoro-, 2,5-difluoro-, and 2,3,5,6-tetrafluoro-substituted 1,4-phenylene rotators, respectively, that are axially linked through the triple bonds of rigid mestranol (3-methoxy-17α-ethynylestradiol) stators. Crystallization experiments using solvent mixtures of hexanes–ethyl acetate and acetonitrile–dichloromethane gave rise to polymorphic, pseudopolymorphic, and isomorphic crystals. Whereas two solids were obtained for compound <b>2</b>, four were indentified in the cases of compounds <b>3</b> and <b>4</b>, and three for compound <b>5</b>. The 13 solid forms were characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Two sets of isomorphous structures were obtained for solvated and solvent-free structures of compounds <b>3</b>–<b>5</b>. While polymorphic behavior of these compounds arises from their conformational freedom in solution, their isomorphism arises from the closely isosteric relation that exists between hydrogen and fluorine atoms

    Macrocyclic Molecular Rotors with Bridged Steroidal Frameworks

    No full text
    In this work, we describe the synthesis and solid-state dynamics of isomeric molecular rotors <b>7</b><i><b>E</b></i> and <b>7</b><i><b>Z</b></i>, consisting of two androstane steroidal frameworks linked by the D rings by triple bonds at their C17 positions to a 1,4-phenylene rotator. They are also linked by the A rings by an alkenyl diester bridge to restrict the conformational flexibility of the molecules and reduce the number of potential crystalline arrays. The analysis of the resulting molecular structures and packing motifs offered insights of the internal dynamics that were later elucidated by means of line shape analyses of the spectral features obtained through variable-temperature solid-state <sup>13</sup>C NMR; such analysis revealed rotations in the solid state occurring at kilohertz frequency at room temperature

    Conformational Polymorphism and Isomorphism of Molecular Rotors with Fluoroaromatic Rotators and Mestranol Stators

    No full text
    We report the synthesis and characterization of four molecular rotors <b>2</b>, <b>3</b>, <b>4</b>, and <b>5</b> containing 2-fluoro-, 2,3-difluoro-, 2,5-difluoro-, and 2,3,5,6-tetrafluoro-substituted 1,4-phenylene rotators, respectively, that are axially linked through the triple bonds of rigid mestranol (3-methoxy-17α-ethynylestradiol) stators. Crystallization experiments using solvent mixtures of hexanes–ethyl acetate and acetonitrile–dichloromethane gave rise to polymorphic, pseudopolymorphic, and isomorphic crystals. Whereas two solids were obtained for compound <b>2</b>, four were indentified in the cases of compounds <b>3</b> and <b>4</b>, and three for compound <b>5</b>. The 13 solid forms were characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Two sets of isomorphous structures were obtained for solvated and solvent-free structures of compounds <b>3</b>–<b>5</b>. While polymorphic behavior of these compounds arises from their conformational freedom in solution, their isomorphism arises from the closely isosteric relation that exists between hydrogen and fluorine atoms

    Conformational Polymorphism and Isomorphism of Molecular Rotors with Fluoroaromatic Rotators and Mestranol Stators

    No full text
    We report the synthesis and characterization of four molecular rotors <b>2</b>, <b>3</b>, <b>4</b>, and <b>5</b> containing 2-fluoro-, 2,3-difluoro-, 2,5-difluoro-, and 2,3,5,6-tetrafluoro-substituted 1,4-phenylene rotators, respectively, that are axially linked through the triple bonds of rigid mestranol (3-methoxy-17α-ethynylestradiol) stators. Crystallization experiments using solvent mixtures of hexanes–ethyl acetate and acetonitrile–dichloromethane gave rise to polymorphic, pseudopolymorphic, and isomorphic crystals. Whereas two solids were obtained for compound <b>2</b>, four were indentified in the cases of compounds <b>3</b> and <b>4</b>, and three for compound <b>5</b>. The 13 solid forms were characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Two sets of isomorphous structures were obtained for solvated and solvent-free structures of compounds <b>3</b>–<b>5</b>. While polymorphic behavior of these compounds arises from their conformational freedom in solution, their isomorphism arises from the closely isosteric relation that exists between hydrogen and fluorine atoms
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