Thermally Controlled Exciplex Fluorescence in a Dynamic Homo[2]catenane

Abstract

Motion-induced change in emission (MICE) is a phenomenon that can be employed to develop various types of probes, including temperature and viscosity sensors. Although MICE, arising from the conformational motion in particular compounds, has been studied extensively, this phenomenon has not been investigated in depth in mechanically interlocked molecules (MIMs) undergoing coconformational changes. Herein, we report the investigation of a thermoresponsive dynamic homo[2]catenane incorporating pyrene units and displaying relative circumrotational motions of its cyclophanes as evidenced by variable-temperature 1 H NMR spectroscopy and supported by its visualization through molecular dynamics simulations and quantum mechanics calculations. The relative coconformational motions induce a significant change in the fluorescence emission of the homo[2]catenane upon changes in temperature compared with its component cyclophanes. This variation in the exciplex emission of the homo[2]catenane is reversible as demonstrated by four complete cooling and heating cycles. This research opens up possibilities of using the coconformational changes in MIMs-based chromophores for probing fluctuations in temperature which could lead to applications in biomedicine or materials science.

Casting light on molecular motions: controlling optical signal outputs of mechanically interlocked molecules

“…Scientists always learn from nature and never stop exploring the possibility to create functional artificial systems. 47–66…”

“…8, [2]rotaxane unit 7 with a weakly interacting fluorophore/quencher pair was designed and integrated into a polyurethane elastomer. The 1,5-dinaphtho [38]crown-10 macrocycle was modified to include a 4,7-bis(phenylethynyl)-2,1,3-benzothiadiazole (BTH) unit whose emission could be quenched by the electron-poor 1,4,5,8-naphthalenetetracarboxylic diimide (NpI) motif. In the idle state, the macrocycle host preferably located in the NpI station, with the fluorescence quenched.…”

The Green Box: Selenoviologen-Based Tetracationic Cyclophane for Electrochromism, Host–Guest Interactions, and Visible-Light Photocatalysis

“…Cationic cyclophane as novel macrocyclic hosts has been widely used in host–guest chemistry, − mechanically interlocked molecules, − luminescent materials, − drug delivery, − molecular catalysis, − and other fields due to their advantages of the rigid cavity, excellent electron-deficient, good redox properties, and so on. − Especially, cyclobis­(paraquant- p -phenylene), also known as the blue box ( 1 ), was developed by Stoddart and co-workers, which exhibited excellent applications in supramolecular architectures, host–guest complexes, catalysis, and mechanically interlocked molecules during the past 35 years. − Inspired by this, some novel box-like derivatives have been reported . For example, Stoddart and co-workers designed and synthesized the tetrazine box, a structurally transformative tetrazine-containing tetracationic cyclophane, existing in three different reversible redox states which can be manipulated and visited by delicately controlled redox chemistry .…”

The use of molecular electronic structure methods to investigate mechanically interlocked molecules

“…The analysis of MIMs by molecular mechanics (MMs) calculations 24–26 or molecular dynamics (MDs) simulations, 27–32 sometimes coupled or supported by density functional theory (DFT) methods, has led to important advances in the field of mechanomolecules. However, since 2008, researchers have demonstrated concerns about the accuracy of MMs and MD calculations in relation to the geometries of superstructures, and the relative binding energies.…”

“…The association constant between the protonated rotaxane and the anions shows the following trend: Cl À 4 Br À 4 MsO À 4 HSO 4 À 4 TsO À 4 I À , which reflects the ability of the anions to form hydrogen bonds. The analysis of MIMs by molecular mechanics (MMs) calculations [24][25][26] or molecular dynamics (MDs) simulations, [27][28][29][30][31][32] sometimes coupled or supported by density functional theory (DFT) methods, has led to important advances in the field of mechanomolecules. However, since 2008, researchers have demonstrated concerns about the accuracy of MMs and MD calculations in relation to the geometries of superstructures, and the relative binding energies.…”