Controllable FRET Behaviors of Supramolecular Host–Guest Systems as Ratiometric Aluminum Ion Sensors Manipulated by Tetraphenylethylene-Functionalized Macrocyclic Host Donor and Multistimuli-Responsive Fluorescein-Based Guest Acceptor

Abstract

The novel multistimuli-responsive monofluorophoric supramolecular polymer Poly­(TPE-DBC)/FL-DBA and pseudo[3]­rotaxane TPE-DBC/FL-DBA consisted of the closed form of nonemissive fluorescein guest FL-DBA along with TPE-based main-chain macrocyclic polymer Poly­(TPE-DBC) and TPE-functionalized macrocycle TPE-DBC hosts, respectively. By the combination of various external stimuli, these fluorescent supramolecular host–guest systems could reveal interesting photoluminescence (PL) properties in DMF/H2O (1:1, v/v) solutions, including bifluorophoric host–guest systems after the complexation of Al3+ ion, i.e., TPE-DBC/FL-DBA-Al 3+ and Poly­(TPE-DBC)/FL-DBA-Al 3+ with their corresponding open form of fluorescein guest FL-DBA-Al 3+ . Importantly, the Förster resonance energy transfer (FRET) processes occurred in both bifluorophoric host–guest systems between blue-emissive TPE donors (λem = 470 nm) and green-emissive fluorescein acceptors (λem = 527 nm) after aluminum detection, which were further verified by time-resolved photoluminescence (TRPL) measurements to acquire their FRET efficiencies of 40.4 and 31.1%, respectively. Both supramolecular host–guest systems exhibited stronger green fluorescein emissions as well as appealing ratiometric PL behaviors within the desirable donor–acceptor distances of FRET processes in comparison with their detached analogous mixtures. Regarding the pH effects, the optimum green fluorescein emissions with effective FRET processes of all compounds and host–guest systems were sustained in the range pH = 7–10. Interestingly, both host–guest systems TPE-DBC/FL-DBA and Poly­(TPE-DBC)/FL-DBA possessed high sensitivities and selectivities toward aluminum ion to display their strong green emissions via FRET-ON behaviors due to the chelation-induced ring opening of spirolactam moieties to become green-emissive guest acceptor FL-DBA-Al 3+ , which offered excellent limit of detection (LOD) values of 50.61 and 38.59 nM, respectively, to be further applied for the fabrication of facile test strips toward aluminum detection. Accordingly, the inventive ratiometric PL and FRET sensor approaches of supramolecular host–guest systems toward aluminum ion with prominent sensitivities and selectivities were well-established in this study.

Controllable Aggregation-Induced Emission and Förster Resonance Energy Transfer Behaviors of Bistable [c2] Daisy Chain Rotaxanes for White-Light Emission and Temperature-Sensing Applications

“…Interestingly, in 2001, Tang et al reported the opposite photophysical properties, i.e., aggregation-induced emission (AIE) behaviors, in which luminogens that show weak fluorescent at low concentrations become strong emissions in aggregation states, owing to the restrictions of intramolecular rotations . Since then, AIE luminogens (AIEgens) have obtained in-depth attention and shown wide applications in light emissions, chemosensors, biosensors, and so on. − Förster resonance energy transfer (FRET) processes are well-known photophysical properties that perform the energy transfer between donor and acceptor moieties by means of nonradiative dipole–dipole couplings . Taking advantage of FRET techniques, chemists have explored different combinations of donors and acceptors in various platforms, such as small molecules, dendrimers, organo gels, polymers, biomaterials, metal–organic framework motifs, and supramolecules. − In fact, AIE properties can be incorporated with FRET processes to serve as simple and effective approaches for the development of tunable and multiple fluorescent materials .…”

Portable Smartphone Platform Based on Aggregation-Induced Enhanced Emission Carbon Dots for Ratiometric Quantitative Sensing of Fluoride Ions

“…The XPS-deconvoluted spectrum of Al 2p showed that its characteristic peaks at 72.65 and 73.47 eV are attributed to the Al–O bond (Figure D), which was consistent with the fact that AA-CDs were rich in active functional groups such as hydroxyl groups in Figure C, indicating that OH – /COO – in AA-CDs interacted with Al 3+ to induce cross-linking and aggregation of AA-CDs. Based on the above findings, we inferred that Al 3+ formed Al–O bonds after combining with AA-CDs, which limited the vibration and rotation of active functional groups in AA-CDs, and the formation of aggregated states also reduced the interaction between AA-CDs and solvents, thereby reducing the probability of nonradiative transitions, resulting in enhanced fluorescence and lifetime of AA-CDs, and this phenomenon was attributed to Al 3+ -induced fluorescence AIE enhancement properties. ,− Furthermore, the fluorescence intensity of AA-CDs was positively correlated with the concentration of Al 3+ (Figure E), and the change trend of the fluorescence intensity and the B/R ratio was nearly identical, demonstrating that the B/R ratio can replace fluorescence as a signal reading method for quantitative detection (Figure F). However, the variation range of a single fluorescence color is narrow and the poor visual resolution hinders its practical application.…”

Tunable Nano‐Bending Structures of Loosened/Tightened Lassos with Bi‐Stable Vibration‐Induced Emissions for Multi‐Manipulations of White‐Light Emissions and Sensor Applications

“…[30][31][32][33][34][35][36] Recently, a series of multi-color fluorescent materials based on supramolecular architectures of pseudo-rotaxanes, [2]rotaxanes, [1]rotaxanes, and [c2] daisy rotaxanes were developed to provide stable and tunable optical properties for different applications of sensing, bioimaging, photo-patterning, logic-gating, and white-light-emitting. [37][38][39][40][41][42][43][44] Among tunable optical applications, only limited novel MIMs have been explored for the applications of white-light-emitting materials. [8,43,44] For example, the successful construction of a dual-component fluorescent molecular system within a [2]rotaxane by Qu et al enabled the reversible tuning of emission colors, including white-light emission through external acid/base stimuli.…”