Multistimuli-Responsive Fluorescent Switches Based on Spirocyclic Meisenheimer Compounds: Smart Molecules for the Design of Optical Probes and Electrochromic Materials

Abstract

Fluorescent switches based on spirocyclic zwitterionic Meisenheimer (SZMC) complexes are stimuli-responsive organic molecules with application in a variety of areas. To expand their functionality, novel switching mechanisms are herein reported for these systems: (a) acid- and redox-triggered formation of an additional protonation state with distinct optical properties, and (b) solvent-induced fluorescence modulation. We demonstrate that these new features, which enable both multistimuli and multistate operation of SZMC switches, can be exploited in the preparation of smart organic materials: wide-range pH optical probes, electrochromic and electrofluorochromic films, and polymer-based fluorescent detectors of organic liquids.

Highly Reversible Electrofluorochromism from Electrochemically Decoupled but Electronically Coupled Molecular Dyads

“…Note that these materials have been used as the forms of multilayer or bulk‐heterojunction films, which attenuated the efficiencies of fluorescence modulation. Molecules exhibiting redox‐active fluorescence changes are advantageous for their efficiency and tunability (Figure b); however, not all fluorophores display electrofluorochromism . The limited observance of electrofluorochromism originates from the irreversibility of the process; redox‐responsive fluorophores usually undergo side reactions that involve destructive chemical step(s) following an electrochemical activation process …”

“…Molecules exhibiting redox-active fluorescence changes are advantageous for their efficiency and tunability ( Figure 1b); however, not all fluorophores display electrofluorochromism. [20][21][22][23][24][25][26]28,32,[44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] The limited observance of electrofluorochromism originates from the irreversibility of the process; redox-responsive fluorophores usually undergo side reactions that involve destructive chemical step(s) following an electrochemical activation process. [29] To achieve fatigue-resistant electrofluorochromism, redoxstable fluorophores must be created.…”

Janus Oligomers Demonstrating Full‐Spectrum Visible Light Reflection and Tunable Photoluminescence towards Dual‐Mode Dynamic Anti‐Counterfeiting

“…[ 6–11 ] They can be potentially applied in optoelectronic devices, photocatalysis, biomedical therapy, energy conversion, or anticounterfeiting. [ 12–19 ] The methodologies for combining different optical properties in a nanostructure or in a composite mainly include bulk physical mixing, host‐guest assembly, core‐shell synthetic chemistry, and epitaxial growth. The physical mixing is usually conducted by homogeneously mixing different optical materials to obtain optical composites.…”

Colorimetric sensing of acidic vapour through protonation of a Meisenheimer complex

“…The structure of these compounds is based on the Jackson–Meisenheimer intermediates of aromatic nucleophilic substitution reactions 39,40 . Scientists have applied them in various real‐life applications, including fluoride and cyanide sensors, moisture sensing, 41 as optical probes and electrochromic material, 42 in the preparation of nanostructures, 43 as fluorescent switches at the single molecule level, volatile organic compound sensors, 44 the removal of metal ions, fluoride and oil spills from water, and in stimuli‐responsive materials 35,37,45,46 . In general, the Meisenheimer complex contains a cyclohexadienyl anion system.…”

“…Very recently, Villabona et al investigated the protonation of another similar Meisenheimer complex 1b derived from picric acid and N,N‐diisopropylcarbodiimide (Figure 2). 42 The authors proposed the destruction of the spiro structure after the protonation and, consequently, a picramide derivative 3 was formed. Compound 3 cannot be deprotonated using bases weaker than guanidine, but in reality the opposite phenomenon was observed.…”