Tracking a photo-switchable surface-localised supramolecular interaction via refractive index

Abstract

As supramolecular chemistry evolves, from the design of interactions in the solution and the solid state to applications at surfaces, there is a need for the development of analytical techniques capable of directly interrogating surface-localised supramolecular interactions. We present a proof-of-concept integrated optical Bragg grating sensor, capable of evanescently detecting small changes in refractive index at infrared wavelengths within a microfluidic system. The high spectral fidelity of the Bragg gratings combined with precise thermal compensation enables direct monitoring of the surface throughout the experiment, enabling the sensor to probe changes in situ and in real-time during surface preparation and chemical modification, and then to follow the progress of a dynamic surface-localised supramolecular interaction. In this study the sensor is assessed through the investigation of a photoswitchable inclusion complex between an azobenzene-functionalised surface and cyclodextrin in aqueous solution. The ability to investigate supramolecular interactions directly in real-time upon a planar surface via refractive index offers a valuable new tool in the understanding of complex dynamic supramolecular systems.Scheme 1 The synthetic pathway for 4-phenylazophenoxyacetyl chloride, 4; (i) NaNO 2 , HCl, o5 1C, (ii) phenol, o5 1C, (iii) ethyl bromoacetate, K 2 CO 3 , NaI, acetone, (iv) NaOH, ethanol, and (v) thionyl chloride. Inset: Schematic and chemical structure of the macrocycle, a-cyclodextrin.

Photocontrol of pattern formation and hysteresis loops in polymer gels with host-guest interactions

“…The association and dissociation of the azobenzene moieties with the α-CD units, , where and are the association and dissociation rate constants, respectively, had been shown to occur significantly faster than the photoisomerization. 60 , 64 Specifically, the isomerization of the azobenzene had been demonstrated to be the rate-limiting reactive process and the complexation with the α-CD units had been shown not to affect the photostationary state of the azobenzene-functionalized surface. 64 Further, in the recent study of the photokinetics of the supramolecular Azo/CD complexes, the dissociation of the Azo compound from the complexes was considered to occur simultaneously with the isomerization kinetics.…”

“… 60 , 64 Specifically, the isomerization of the azobenzene had been demonstrated to be the rate-limiting reactive process and the complexation with the α-CD units had been shown not to affect the photostationary state of the azobenzene-functionalized surface. 64 Further, in the recent study of the photokinetics of the supramolecular Azo/CD complexes, the dissociation of the Azo compound from the complexes was considered to occur simultaneously with the isomerization kinetics. 60 Hence, we assume that the photoisomerization is the rate-limiting reaction process and that the complexation/decomplexation occurs simultaneously with the isomerization.…”

SiOx by magnetron sputtered revisited: Tailoring the photonic properties of multilayers

“…From the slope of this line, the sensitivity achieved using this measurement procedure can be estimated as 219.9 R(%) RIU -1 , which compares well with that reported for TiO 2 -SiO 2 optofluidic BMs operating in the visible, [47] or for electrochemically etched 3D porous self-supported silicon membranes. On the other hand, the use of these thin film BMs is advantageous because of their compatibility with NIR optical components currently utilized for the analysis of liquids or their manipulation [58][59][60][61] and very common in a large series of optical devices such as absorbing materials and night vision LCD monitors. [62] In comparison with typical porous silicon devices used for label free sensing of liquids and biomolecules, [1][2][3] gas sensors [52,53] or laser tunable [63] applications, a remarkable difference of the herein developed photonic structures is their thin film character and the fact that they can be prepared in one step on any kind of substrate, including polymers.…”