Tunable and Switchable Control of Luminescence through Multiple Physical Stimulations in Aggregation-Based Monocomponent Systems

Abstract

This report describes how the luminescence of naphthalimide could be tuned by various physical stimuli, including heat, sonication, and grinding. Herein, instant and switchable control of color and fluorescent emissions has been achieved by the sonication-triggered gelation of an organic liquid with naphthalimide-based organogelators (N3-N7). Green emissive suspensions of the gelators in organic liquids are transformed into orange emissive gels upon brief irradiation with ultrasound with an emission wavelength red-shift of approximately 60 nm and fluorescence intensity quenching by a factor of 20, which can subsequently be reversed by heating. When sonication-triggered S-gels are evaporated to S-xerogels, the solid state xerogels (N3, N4, N6, N7) exhibit mechanochromism, the color of which changes from red to yellow and the emission color of which changes from orange to green with enhanced intensity by grinding. This mechanochromic property can be reversed through a regelation process. The mechanochromic character of the S-xerogel of N3 is thus applied to quantitatively sense the mechanical pressure range from 2 to 40 MPa through fluorescence changes, reflecting a new type of application for gelation assembly. The physical stimuli triggered fluorescence changes of these compounds strongly depend on the molecular structure and solvent. The results demonstrate that the different aggregation modes and long-range order arrangement of the molecules regulated by the stimulus may affect the internal charge transfer (ICT) process of the naphthalimide groups, resulting in the tunability of the photophysical properties of the gelators. This report provides a new strategy for tunable and switchable control of luminescence through nonchemical stimuli in aggregation-based monocomponent systems.

Steric‐Structure‐Dependent Gel Formation, Hierarchical Structures, Rheological Behavior, and Surface Wettability

“…These noncovalent interactions can provide highly organized molecular architectures that display reversible, instant, and visual changes in response to external stimuli, such as ultrasound, shearing stress, light, heating, magnetism, ions, pH, chiral compounds, enzymes, and gases. Typically, supramolecular gels are formed by heating a low‐molecular‐weight (LMW) gelator in an appropriate solvent at a specific concentration, then cooling . The transcription of intrinsic molecular features from the molecular level to complex supramolecular structures is realized in the sol‐to‐gel transition process.…”

“…Typically,s upramolecular gels are formed by heatingalow-molecular-weight (LMW) gelator in an appropriate solvent at as pecific concentration, then cooling. [26][27][28][29] The transcription of intrinsic molecular features from the molecularl evel to complex supramolecular structures is realized in the sol-to-gel transition process. However,n ot all self-assemblies of LMW molecules result in gelation.…”

Transient Catalytic Activity of a Triazole‐based Gelator Regulated by Molecular Gel Assembly/Disassembly

“…The dynamic self‐assembly behaviour of this catalytic system allows the consecutive addition of batches of reactants without the need of isolating the catalyst after each run, providing a greener, sustainable and less time‐consuming approach. This dynamic system resembles the dissipative systems previously reported, although in this case the gelator molecule is not subjected to any chemical transformation during the whole disassembly‐assembly process . One of the main novelties in this system is that the far‐from‐equilibrium behaviour of the gel Cu(I)‐ Et 2 NAzTzVal 12 is regulated by the model ‘click’ reaction.…”

“…Among the materials that can mimic the supramolecular organization of nature, molecular gels are metastable systems of great interest owing to their dynamic and reversible behaviour in response to a stimulus . Although several examples of these functional metastable dynamic systems that respond to physical or chemical stimulus can be found in literature, very few are able to achieve the status of a dissipative system …”

Highly Fluorescent Non‐Conventional Boron‐Difluoride‐Based π Organogel with Gelation‐Assisted Piezochromism

“…Since plasticity is very important for mechanochromism, the soft xerogel might have better sensitivity to pressure to make it an ideal ultrasensitivep ressure sensor, using fluorescenceasas ignal output. [11] Adigital powder compressing machine was used to measure the mechanochromic fluorescenceo fBOPIM-dPhA xerogel prepared by freeze-drying ( Figure 5). The initial xerogel showede missiona t5 88 nm, similart ot hat in ad ilute cyclohexane solution,a nd the fluorescent band clearly red-shifted upon pressure (33 nm red-shift at ap ressure of 0.99 MPa).…”