Enantiodifferentiation in the Photoisomerization of (<i>Z</i>,<i>Z</i>)-1,3-Cyclooctadiene in the Cavity of γ-Cyclodextrin–Curcubit[6]uril-Wheeled [4]Rotaxanes with an Encapsulated Photosensitizer

Yan, Zhiqiang; Huang, Qinfei; Liang, Wenting; Yu, Xingke; Zhou, Da‐Yang; Wu, Wanhua; Chruma, Jason J.; Yang, Cheng

doi:10.1021/acs.orglett.7b00057

Cited by 71 publications

(56 citation statements)

References 39 publications

(16 reference statements)

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“…The plots of ln(θ 0 /θ t ) against time gave straight lines, supporting the first-order kinetic model [25]. Increasing the temperature usually increases the reaction kinetics, and we have demonstrated that the temperature is critical for affecting the molecular recognition and stereoselectivity of supramolecular photochirogenesis [26][27][28][29][30][31][32][33]. To understand the temperature effect on the racemization of BP-f1, the CD ex versus time was recorded at different temperatures.…”

Section: Bp-f1supporting

confidence: 66%

Resolution and Racemization of a Planar-Chiral A1/A2-Disubstituted Pillar[5]arene

Xiao

Liang

et al. 2019

Symmetry

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Butoxycarbonyl (Boc)-protected pillar[4]arene[1]-diaminobenzene (BP) was synthesized by introducing the Boc protection onto the A1/A2 positions of BP. The oxygen-through-annulus rotation was partially inhibited because of the presence of the middle-sized Boc substituents. We succeeded in isolating the enantiopure R P (R P , R P , R P , R P , and R P )-and S P (S P , S P , S P , S P , and S P )-BP, and studied their circular dichroism (CD) spectral properties. As the Boc substituent is not large enough to completely prevent the flip of the benzene units, enantiopure BP-f1 underwent racemization in solution. It is found that the racemization kinetics is a function of the solvent and temperature employed. The chirality of the BP-f1 could be maintained in n-hexane and CH 2 Cl 2 for a long period at room temperature, whereas increasing the temperature or using solvents that cannot enter into the cavity of BP-f1 accelerated the racemization of BP-f1. The racemization kinetics and the thermodynamic parameters of racemization were studied in several different organic solvents. or bithienyl groups, have been chemically grafted onto one or more hydroquinone ether units, and the oxygen-through-annulus rotation was restrained or completely stopped [21,22]. It occurred to us that if introducing a group of suitable size, the oxygen-through-annulus could still be allowed, but the rotation velocity is slowed down. This will then provide a powerful tool to study the effect of the external factors, such as the temperature and solvent, on the rotational kinetics of pillar[5]arene. Herein, we report on the successful isolation of butoxycarbonyl (Boc)-protected pillar[4]arene-[1]diaminobenzene (BP) planar chiral enantiomers. Two middle-sized Boc-protected substituents on the A1/A2 positions significantly decelerated the flip of pillar[5]arene, to allow for the racemization of BP with an observable velocity. The thermodynamics and kinetics of the racemization were investigated under different solvent and temperature conditions, which may serve as a guideline in the isolation and control of the enantiomeric conformations of pillar[n]arenes by manipulating the external factors. Materials and MethodsAll of the compounds and reagents were obtained from commercial suppliers and were used as received. Chiral analytical HPLC was performed with a Chiralpak IA column (0.46 × 25 cm) by a Shimadzu LC Prominence 20 HPLC instrument (Shimadzu, Tokyo, Japan) equipped with a UV-VIS detector (conditions: injection volume: 20 µL of rac-BP (0.2 mM); mobile phase: hexane/dichloromethane, 70/30 (v/v); flow rate: 1.0 mL/min at 20 • C; retention time (t R ): 5.3 min for BP-f1, 5.7 min for BP-f2). Preparative column chromatography was carried out with a Chiralpak IA column (1.0 × 25 cm) by a recycling preparative HPLC LC9210NEXT instrument (JAI, Tokyo, Japan) equipped with a UV-VIS detector (conditions: injection volume: 3 mL of rac-BP (2 mM); mobile phase: hexane/dichloromethane, 70/30 (v/v); flow rate: 4.0 mL/min at 20 • C; retention time (t R ): 11.4 min ...

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Section: Bp-f1supporting

confidence: 66%

Resolution and Racemization of a Planar-Chiral A1/A2-Disubstituted Pillar[5]arene

Xiao

Liang

et al. 2019

Symmetry

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“…[9] We have demonstrated that CDsa re particularly suitable for conducting supramolecular photochemical reactions because these molecules are UV transparent. [10] g-CD-based A1 and A2 showedl argely improved solubility (> 5.0 mM)r elative to A3 (< 0.2 mM)i n aqueous solution of pH 9.0 by virtue of the excellent water sol- Figure 1. Schematic illustration of the TTA-UC process.…”

Section: Resultsmentioning

confidence: 99%

Supramolecular Assembly‐Improved Triplet–Triplet Annihilation Upconversion in Aqueous Solution

Liang

et al. 2018

Chemistry A European J

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Water-soluble 9,10-diphenylanthracene-modified γ-cyclodextrin derivatives A1 and A2, in which the γ-cyclodextrin unit serves as a molecular host for a binding sensitizer, and the 9,10-diphenylanthracene moiety plays a role as an emitter/annihilator, were synthesized to investigate the supramolecular triplet-triplet annihilation (TTA) upconversion in aqueous solution. Both A1 and A2 readily aggregate and form nanoscale assemblies in water as a combined result of host-guest complexation and π-π stacking among the 9,10-diphenylanthracenes. The aggregation behavior of the supramolecular emitters was fully characterized by using a diversity of methods, including dynamic light scattering (DLS), SEM, NMR, fluorescence, and circular dichroism studies. Fluorescence spectroscopic analysis reveals that the emitters have high fluorescence quantum yields in water (82 and 90 % for A1 and A2, respectively), thus demonstrating that aggregation does not quench the fluorescence. By using a coordinated ruthenium sensitizer, a high TTA upconversion quantum yield of up to 6.9 % was observed for this supramolecular TTA system, which is significantly higher than the value (<0.5 %) obtained with nonassembled emitters in organic solvent and in contrast to the fact that TTA upconversion emission in aqueous solution is usually low or negligible. We ascribe the strong TTA upconversion emission in the present supramolecular assembly system to an efficient TTA process, which is facilitated along the stacked emitters by triplet energy migration and improved triplet-triplet energy transfer through host-guest complexation.

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“…The CD and UV spectra were measured in a CH 2 Cl 2 solution of enantioenriched 8 derivatives (Figure 13c), which shows the CD signals of the mirror image, indicating that the compounds are of opposite bowl chirality. Recently, Yang and co-workers prepared azonia [6]helicene tethered with supramolecular host β-cyclodextrin, and used a chirality sensing probe for underivatized amino acids in water [89][90][91][92][93][94]. Indeed, tethered azonia [6]helicene acts as a conformationally robust chiral auxiliary to improve the chiral recognition ability of native cyclodextrins.…”

Section: Racemic (±)-21 Was Prepared By Aerobic Oxidation Of Racemic mentioning

confidence: 99%

Chiral Buckybowl Molecules

Kanagaraj

Lin

et al. 2017

Symmetry

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Buckybowls are polynuclear aromatic hydrocarbons that have a curved aromatic surface and are considered fragments of buckminsterfullerenes. The curved aromatic surface led to the loss of planar symmetry of the normal aromatic plane and may cause unique inherent chirality, so-called bowl chirality, which it is possible to thermally racemize through a bowl-to-bowl inversion process. In this short review, we summarize the studies concerning the special field of bowl chirality, focusing on recent practical aspects of attaining diastereo/enantioenriched chiral buckybowls through asymmetric synthesis, chiral optical resolution, selective chiral metal complexation, and chiral assembly formation.

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Enantiodifferentiation in the Photoisomerization of (Z,Z)-1,3-Cyclooctadiene in the Cavity of γ-Cyclodextrin–Curcubit[6]uril-Wheeled [4]Rotaxanes with an Encapsulated Photosensitizer

Cited by 71 publications

References 39 publications

Resolution and Racemization of a Planar-Chiral A1/A2-Disubstituted Pillar[5]arene

Resolution and Racemization of a Planar-Chiral A1/A2-Disubstituted Pillar[5]arene

Supramolecular Assembly‐Improved Triplet–Triplet Annihilation Upconversion in Aqueous Solution

Chiral Buckybowl Molecules

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