Motorized Macrocycle: A Photo-responsive Host with Switchable and Stereoselective Guest Recognition

Abstract

Designing photo-responsive host-guest systems can provide versatile supramolecular tools for constructing smart systems and materials. We designed photo-responsive macrocyclic hosts, modulated by light-driven molecular rotary motors enabling switchable chiral guest recognition. The intramolecular cyclization of the two arms of a first-generation molecular motor with flexible oligoethylene glycol chains of different lengths resulted in crown-ether-like macrocycles with intrinsic motor function. The octaethylene glycol linkage enables the successful unidirectional rotation of molecular motors, simultaneously allowing the 1:1 host-guest interaction with ammonium salt guests. The binding affinity and stereoselectivity of the motorized macrocycle can be reversibly modulated, owing to the multi-state light-driven switching of geometry and helicity of the molecular motors. This approach provides an attractive strategy to construct stimuli-responsive host-guest systems and dynamic materials.

Keywords: capture and release; host-guest interactions; motorized macrocycles; photo-responsiveness; stereoselectivity.

Figure 1

a) Representation of the structure of the novel motorized macrocycle. b) The rotation in an intramolecular confined space of motorized macrocycle 3. c) Reference compounds. d) Guest molecules.

Figure 2

a) UV/Vis absorption spectra of stable‐cis‐3 after the photoisomerization and THI processes (THF). b) Partial ¹H NMR spectra of stable‐cis‐3 (600 MHz, 203 K, CD₂Cl₂, 5 mM) during the photoisomerization and THI processes. c) UV/Vis absorption spectra of stable‐trans‐3 during the photoisomerization and THI processes (THF). d) Partial ¹H NMR spectra of stable‐trans‐3 (600 MHz, 203 K, CD₂Cl₂, 5 mM) during the photoisomerization and THI processes. For the proton assignment, see Figure 1 b. e) The energy minimized optimized geometries of motorized macrocycle 3.

Figure 3

a) Representation of the guest recognition. b) Partial ¹H NMR spectra of stable‐cis‐3 (5 mM, 400 MHz, 293 K, [D₆]acetone) upon the stepwise addition of G1 and c) Job's plot based on the proton shift of H_f in [D₆]acetone.

Figure 4

a) Representation of the guest capturing/releasing procedures of motorized macrocycle 3. b) UV/Vis absorption spectra of the host–guest system before/after photo‐ and thermal isomerization (THF): from [stable‐cis‐3 $\supset$ G1] to [stable‐trans‐3 and G1]. c) Partial ¹H NMR spectra during the isomerization processes of the host–guest system (600 MHz, 203 K, [D₆]acetone, 5 mM), starting from [stable‐cis‐3 $\supset$ G1]. d) UV/Vis absorption spectra of the host–guest system before/after photo‐ and thermal isomerization (THF): from [stable‐trans‐3 and G1] to [stable‐cis‐3 $\supset$ G1] and e) partial ¹H NMR spectra during the isomerization processes of the host–guest system (600 MHz, 203 K, [D₆]acetone, 5 mM), starting from [stable‐trans‐3 and G1].

Figure 5

a) Representation of stereoselective guest recognition. b) B3LYP/6‐31G++(d, p) optimized geometries of [(P, P)‐(R,R)‐cis‐3 $\supset$ G3(R)] (left), [(P, P)‐(R,R)‐cis‐3 $\supset$ G3(S)] (middle) and G3(R) (right). c) (i) CD (upper) and UV/Vis absorption (lower) spectra of (P, P)‐(R,R)‐cis‐3 (55 μM in CH₂Cl₂) before and after photoisomerization and THI: from (P, P)‐(R,R)‐cis‐3 to (P, P)‐(R,R)‐trans‐3, (ii) CD and UV/Vis absorption spectra of (P, P)‐(R,R)‐trans‐3 (75 μM in CH₂Cl₂) before and after photoisomerization and THI: from (P, P)‐(R,R)‐trans‐3 to (P, P)‐(R,R)‐cis‐3.