Insight into functionalized-macrocycles-guided supramolecular photocatalysis

Abstract

Due to the unique characteristics of macrocycles (e.g., the ease of modification, hydrophobic cavities, and specific guest recognition), they can provide a suitable environment to realize photocatalysis via noncovalent interactions with different substrates. In this minireview, we emphasized the photochemical transformation and catalytic reactivity of different guests based on the binding with various macrocyclic hosts as well as on the role of macrocyclic-hosts-assisted hybrid materials in energy transfer. To keep the clarity of this review, the macrocycles are categorized into the most commonly used supramolecular hosts, including crown ethers, cyclodextrins, cucurbiturils, calixarenes, and pillararenes. This minireview not only summarizes the role that macrocycles play in photocatalytic reactions but also clarifies the photocatalytic mechanisms. Finally, the future research efforts and new pathways to apply macrocycles and supramolecular hybrid materials in photocatalysis are also discussed.

Keywords: host–guest chemistry; macrocycles; noncovalent interactions; supramolecular photocatalysis.

Figure 1

Chemical structures of representative macrocycles.

Figure 2

Ba²⁺-induced intermolecular [2 + 2]-photocycloaddition of crown ether-functionalized substrates 1 and 2 to form cycloadduct 3. Republished with permission of The Royal Society of Chemistry from [18] (“Supramolecular photochemical synthesis of an unsymmetrical cyclobutane” by O. Fedorova et al., Photochem. Photobiol. Sci. vol. 6, issue 10, © 2007); permission conveyed through Copyright Clearing Center, Inc.

Figure 3

Energy transfer system constructed of a BODIPY–zinc porphyrin–crown ether triad assembly bound to a fulleropyrrolidine. Adapted with permission from [19], Copyright 2009 American Chemical Society.

Figure 4

The sensitizer 5 was prepared by a flavin–zinc(II)–cyclen complex for the photooxidation of benzyl alcohol. Figure 4 reproduced from [20]. Copyright © 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim. Used with permission from R. Cibulka et al., Catalytic Photooxidation of 4‐Methoxybenzyl Alcohol with a Flavin–Zinc(II)‐Cyclen Complex, Chemistry – A European Journal, John Wiley and Sons.

Figure 5

Enantiodifferentiating Z–E photoisomerization of cyclooctene sensitized by a chiral sensitizer as the host. Adapted with permission from [24], Copyright 2000 American Chemical Society.

Figure 6

Structures of the modified CDs as chiral sensitizing hosts. Adapted with permission from [24], Copyright 2000 American Chemical Society.

Figure 7

Supramolecular 1:1 and 2:2 complexations of AC with the cationic β-CD derivatives 16–21 and subsequent photocyclodimerization to give the classical 9,10:9',10'-cyclodimers 10–13 and the nonclassical 5,8:9',10'-cyclodimers 14 and 15. Adapted with permission from [25], Copyright 2018 American Chemical Society.

Figure 8

Construction of the TiO₂–AuNCs@β-CD photocatalyst. Republished with permission of The Royal Society of Chemistry from [28] (“Cyclodextrin–gold nanocluster decorated TiO₂ enhances photocatalytic decomposition of organic pollutants” by H. Zhu et al., J. Mater. Chem. A vol. 6, © 2017); permission conveyed through Copyright Clearing Center, Inc.

Figure 9

Visible-light-driven conversion of benzyl alcohol to H₂ and a vicinal diol or to H₂ and benzaldehyde by CdS–CD. This figure has been published in CCS Chemistry [2020]; [β-Cyclodextrin Decorated CdS Nanocrystals Boosting the Photocatalytic Conversion of Alcohols] is available online at [DOI; https://www.chinesechemsoc.org/doi/10.31635/ccschem.020.201900093].

Figure 10

(a) Structures of CDs, (b) CoPyS, and (c) EY. Republished with permission of The Royal Society of Chemistry from [30] (“Host–guest chemistry between cyclodextrin and a hydrogen evolution catalyst cobaloxime” by M. Kato et al., New J. Chem. vol. 43, © 2019); permission conveyed through Copyright Clearing Center, Inc.

Figure 11

Conversion of CO₂ to CO by ReP/HO-TPA–TiO₂. Republished with permission of The Royal Society of Chemistry from [36] (“A porous hybrid material based on calixarene dye and TiO₂ demonstrating high and stable photocatalytic performance” by Y. Chen et al., J. Mater. Chem. A vol. 7, © 2019); permission conveyed through Copyright Clearing Center, Inc.

Figure 12

Thiacalix[4]arene-protected TiO₂ clusters for H₂ evolution. Reprinted with permission from [37], Copyright 2020 American Chemical Society.

Figure 13

4-Methoxycalix[7]arene film-based TiO₂ photocatalytic system. Reprinted from [38], Materials Today Chemistry, vol. 1–2, by R. Zhou, M. P. Srinivasan “Fabrication of anti-poisoning core-shell TiO₂ photocatalytic system through a 4-methoxycalix[7]arene film’’ pages 1–6, Copyright (2016), with permission from Elsevier.

Figure 14

(a) Photodimerization of 6-methylcoumarin (22). (b) Catalytic cycle for the photodimerization of 22, mediated by CB[8]. Republished with permission of The Royal Society of Chemistry from [47] (“Supramolecular photocatalysis by confinement—photodimerization of coumarins within cucurbit[8]urils” by B. C. Pemberton et al., Chem. Commun. vol. 46, © 2010); permission conveyed through Copyright Clearing Center, Inc.

Figure 15

Formation of a supramolecular PDI–CB[7] complex and structures of monomers and the chain transfer agent. Republished with permission of The Royal Society of Chemistry from [48] (“Visible light induced aqueous RAFT polymerization using a supramolecular perylene diimide/cucurbit[7]uril complex” by Y. Yang et al., Polym. Chem. vol. 10, © 2019); permission conveyed through Copyright Clearing Center, Inc.

Figure 16

Ternary self-assembled system for photocatalytic H₂ evolution (a) and structure of 27 (b). Figure 16 reproduced from [49]. © 2019 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim. Used with permission from D. Song et al., Orthogonal Supramolecular Assembly Triggered by Inclusion and Exclusion Interactions with Cucurbit[7]uril for Photocatalytic H₂ Evolution, ChemSusChem, John Wiley and Sons.

Figure 17

Structures of COP-1, CMP-1, and their substrate S-1 and S-2.

Figure 18

Supramolecular self-assembly of the light-harvesting system formed by WP5, β-CAR, and Chl-b. Reproduced from [56] (© 2016 Guowang Diao et al., distributed under the terms of the Creative Commons Attribution 4.0 International License, https://creativecommons.org/licenses/by/4.0).

Figure 19

Photocyclodimerization of AC based on WP5 and WP6.