Solid Multiresponsive Materials Based on Nitrospiropyran-Doped Ionogels.

Sara Santiago,Xavier Muñoz-Berbel,Pablo Giménez-Gómez,Gonzalo Guirado,Jordi Hernando

doi:10.1021/acsami.1c04159

Abstract

The application of molecular switches for the fabrication of multistimuli-responsive chromic materials and devices still remains a challenge because of the restrictions imposed by the supporting solid matrices where these compounds must be incorporated: they often critically affect the chromic response as well as limit the type and nature of external stimuli that can be applied. In this work, we propose the use of ionogels to overcome these constraints, as they provide a soft, fluidic, transparent, thermally stable, and ionic-conductive environment where molecular switches preserve their solution-like properties and can be exposed to a number of different stimuli. By exploiting this strategy, we herein pioneer the preparation of nitrospiropyran-based materials using a single solid platform that exhibit optimal photo-, halo-, thermo-, and electrochromic switching behaviors.

Highlights

Despite their broad functionality and versatility, the application of spiropyrans to the fabrication of truly smart materials and devices suffers from a major bottleneck: the influence of the surrounding matrix when these compounds are transferred from solution to a solid state, which often dramatically alters their switching performance.[34−37] Two main factors account for this behavior: (a) the large geometrical changes needed to interconvert between the spirocyclic and open states of spiropyrans, which are hindered in rigid environments; and (b) the strong interaction that takes place with the surrounding solid matrix, which may vary the relative energy of their different states
Based on our previous experience on the preparation of ionogels loaded with molecular switches,[55] IG membranes were prepared by blending a fluorinated polymer (poly(vinylidene fluoride-co-hexafluoropropylene), P(VDF-co
We have demonstrated the potential of ionogels to be used as platforms for the preparation of smart materials based on multistimuli-responsive molecular switches

Summary

Introduction

Smart functional solid materials that exhibit multistimuliresponsive behavior are of crucial importance for the construction of novel dynamic systems and devices.[1−5] A major toolbox toward this goal are molecular switches.[6−11] Among them, spiropyrans are frequently preferred due to their capacity to reversibly interconvert between states with strikingly different properties (e.g., color and polarity) upon application of a broad range of stimuli.[12−15] On the one hand, spiropyran switches are well known to photoisomerize between their colorless spirocyclic (SP) and colored merocyanine isomers (MC).[15−17] On the other hand, they have been found to respond to other external stimuli[18−20] such as pH,[21−23] metal ions,[24−27] solvent polarity,[28−30] and redox potentials.[31−33] In some cases, this allows the formation of other states apart from SP and MC (e.g., the protonated merocyanine state MCH+, the spiropyran dimer SP−SP) that modify the photochromic response of the system,[21,23,25−27,30] which further enriches the stimulussensitive activity of spiropyran switches.Despite their broad functionality and versatility, the application of spiropyrans (and other switches) to the fabrication of truly smart materials and devices suffers from a major bottleneck: the influence of the surrounding matrix when these compounds are transferred from solution to a solid state (the so-called matrix effect), which often dramatically alters their switching performance.[34−37] Two main factors account for this behavior: (a) the large geometrical changes needed to interconvert between the spirocyclic and open states of spiropyrans, which are hindered in rigid environments; and (b) the strong interaction that takes place with the surrounding solid matrix, which may vary the relative energy of their different states. This is the case of nanoporous solids (e.g., metal−organic[39,40] and covalent organic[41] frameworks) and soft polymeric matrices (e.g., lowTg polymeric domains,[36,42,43] polymer gels[44−46]).

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Conclusion