Abstract
Molecular shuttles are typical molecular machines that could be applied in various fields. The motion modes of wheel components in rotaxanes could be strategically modulated by external stimuli, such as pH, ions, solvent, light, and so on. Light is particularly attractive because it is harmless and can be operated in a remote mode and usually no byproducts are formed. Over the past decade, many examples of light-driven molecular shuttles are emerging. Accordingly, this review summarizes the recent research progress of light-driven molecular shuttles. First, the light-driven mechanisms of molecular motions with different functional groups are discussed in detail, which show how to drive photoresponsive or non-photoresponsive molecular shuttles. Subsequently, the practical applications of molecular shuttles in different fields, such as optical information storage, catalysis for organic reactions, drug delivery, and so on, are demonstrated. Finally, the future development of light-driven molecular shuttle is briefly prospected.
Highlights
Mechanically interlocked molecules (MIMs) have received widespread attention for their well-defined and unique interlocked structures and appealing stimuli-responsive properties in various fields in artificial molecular machines and nanoscience (Erbas-Cakmak et al, 2015; Stoddart 2017; Sun et al, 2019; Dattler et al, 2020; Cai et al, 2021)
Several reversible photochemical reactions have been successful in constructing molecule shuttles, and one obvious feature of photochemical reactions is that they would release or require the addition of small molecular reagents to complete the whole reversible processes
The photoinduced electron transfers usually exist in donor-acceptor systems and need sacrifice reagents to assist supplementary
Summary
Mechanically interlocked molecules (MIMs) have received widespread attention for their well-defined and unique interlocked structures and appealing stimuli-responsive properties in various fields in artificial molecular machines and nanoscience (Erbas-Cakmak et al, 2015; Stoddart 2017; Sun et al, 2019; Dattler et al, 2020; Cai et al, 2021). Zhan et al (2016) employed the famous “blue box”, namely cyclobis (paraquat-p-phenylene) (CBPQT4+) macrocycle, as an acceptor host unit to construct an AB-based molecular shuttle (Figure 1C) They designed and synthesized two [2] rotaxanes 3a and 3b (Figure 1C), which were composed of an AB subunit and a 1,5-dioxynaphthalene (DNP, for 3a) subunit or a 3,3′-difluorobenzidine (DFBZ, for 3b) subunit as donor recognition stations, respectively. The trans-to-cis isomerizations of AB (λ = 365 nm) and NP-AB (λ = 420–430 nm) units correspond to lights of different characteristic wavelengths, and [3]rotaxane 4 is a unique orthogonal photoresponsive tristable molecular shuttle, which is of great importance for realizing complicated functionality and advanced applications. In contrast to the trans-cis isomerizations of N=N and C=C double bonds, both of which could be solely operated by light with different wavelengths, the cis−to−trans isomerization of the abovementioned C=N double bond needs an external addition of strong polar solvent to break hydrogen bonds, which might have an adverse effect on multiple cycle operations
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