Supramolecular Photocatalysis by Utilizing the Host–Guest Charge‐Transfer Interaction: Visible‐Light‐Induced Generation of Triplet Anthracenes for [4+2] Cycloaddition Reactions

Abstract

Supramolecular photocatalysis via charge‐transfer excitation of a host–guest complex was developed by use of the macrocyclic boronic ester [2+2]BTH‐F containing highly electron‐deficient difluorobenzothiadiazole moieties. In the presence of a catalytic amount of [2+2]BTH‐F, the triplet excited state of anthracene was generated from the charge‐transfer excited state of anthracene@[2+2]BTH‐F by visible‐light irradiation, and cycloaddition of the excited anthracene with several dienes and alkenes proceeded in a [4+2] manner in high yields.

Manipulating Host‐Guest Charge Transfer of a Water‐Soluble Double‐Cavity Cyclophane for NIR‐II Photothermal Therapy

“…Similar to the CT paradigm of cocrystals, many cyclophane hosts, acting as either donors or acceptors, are capable of binding electronically complementary guest molecules to form colored host–guest CT complexes [27–35] . These host–guest cyclophane systems with high light‐absorption activity are ideal candidates as PTAs, which could be endowed with some unique advantages including i) molecular‐level well‐defined structure and uniform chemical composition favorable for more precise therapy, ii) high water solubility and good biocompatibility available for biological systems without additional surface modification, and iii) controllable light‐harvesting capacity by easily changing guest components.…”

Steering the Ultrafast Opening and Closure Dynamics of a Photochromic Coordination Cage by Guest Molecules

“…The confinement of molecules by pores, nanocontainers, micelles, or macromolecular structures has a multitude of applications, ranging from controlled transport and delivery of guest compounds to optimized environments for catalytic reactions inside the nanocage. As one of many versatile directions, the use of organic frameworks or self‐assembled coordination cages for this purpose has been advanced over the last decades, [1–11] with light‐induced exciton or charge‐transfer dynamics opening up new routes for synthesis involving host–guest systems [12–15] . A further functionality can be added if the cage can be switched by an external stimulus, for instance by light, allowing the controlled uptake or release of such guest molecules [16–21] .…”

Merging Charge Transfer into Metal–Organic Frameworks to Achieve High Reduction Potentials via Multiphoton Excitation

“…However, the intrinsic difficulty in matching the light absorption of photoexcitation between an electron-deficient dye and its radical anion limits the choice of photocatalyst for consecutive excitation. − Development of efficient heterogeneous manifolds to expand those applications in fine chemicals and pharmaceuticals remained unexplored areas for both catalytic strategies, with regard to the always poor conductivity of crystalline materials capable of accelerating chemical transformation after electrochemical generation of the radical anions. Charge-transfer interactions between the stacked aromatic donor and acceptor naturally reduced the energy barrier of electron transfer by partially sharing electrons at the ground states. − Irradiation of charge-transfer complexes would produce pairs of radical cations and anions quickly and prolong the lifetime of in situ formed radical anions, beneficial to the achievement of extreme reduction potentials via a consecutive photoexcitation. − Meanwhile, the absorption of aromatic donors and radical anions could be modified independently, , and we propose that merging the charge-transfer interaction into the consecutive PET activation manifold would be poised to confront the inherent requirements for expansion of multiphoton manifolds into a new strategic approach. − Taking advantage of the intrinsic crystalline nature of metal–organic frameworks for distributing high density organic dyes, − we envisioned that incorporating of electron-rich dyes into the ligand backbones would improve electron delocalization among the metal–organic frameworks, leading to the formation of efficient charge-transfer interaction with electron-deficient dyes. − Irradiation of the charge-transfer species initially achieved the stable charge-separated states that contained radical cations and radical anions. − Followed by the second excitation of the in situ formed radical anions, high reductive potential was achieved to expand the multiphoton manifolds both on dye scopes and reaction versions. − …”