Designing Squaraine Dyes with Bright Deep‐Red Aggregation‐Induced Emission for Specific and Ratiometric Fluorescent Detection of Hypochlorite

Abstract

Development of ratiometric fluorescent hypochlorite probes with strong long wavelength fluorescence in aqueous medium, high resistance to photobleaching, high sensitivity and selectivity, and low biological toxicity remains a challenge. In this work, a molecular design strategy is proposed that can transform the traditional squaraine dyes (SQs) with aggregationcaused quenching character into aggregation-induced emission (AIE)-active luminogens by functionalizing the end-groups with tetraphenylethylene units and further introducing hydrophilic sulfonate group as the side chains. The resulting TPE-SQ5 not only emits strong deep-red fluorescence with a high quantum yield of 11.0% and high photostability, but more encouragingly can serve as a ratiometric fluorescent hypochlorite probe with high selectivity and sensitivity (detection limit: 5.6 nm), which indeed is the first report for SQs. The detailed sensing mechanism study demonstrates that the oxindole product with sulfonate substitution is responsible for the ratiometric fluorescent response. Furthermore, TPE-SQ5 nanoparticles with high biocompatibility and low cytotoxicity are successfully used for ratiometrically imaging exogenous and endogenous hypochlorite in living cells.

Deep‐Red Emissive Squaraine‐AIEgen in Elastomer Enabling High Contrast and Fast Thermoresponse for Anti‐Counterfeiting and Temperature Sensing**

“…SQs are a type of zwitterionic cyanine dyes with numerous advantages including strong absorption and emission in visible to NIR regions, high photostability, and simple functionalization routes, which enables them to be implemented in photovoltaic devices, biosensors, and metal ion detectors [22] . In general, SQs suffer from strong ACQ effect, however we previously demonstrated SQs can be AIE‐active by simply using TPE‐functionalized diarylamine subunit as the end group [7b,11b] . Unfortunately, the resulting deep‐red AIE‐active SQs (e. g. TPE‐SQ3‐5, Chart S1) show poor thermoresponsive performance (Figure 1a).…”

“…Due to the introduction of TPE building block and asymmetric structure design, TPE‐SQ12 shows attractive AIE characteristic [7b,11b] . We first conducted photoluminescence (PL) experiment in THF/water mixture by changing water fraction ( f w ).…”

Reactive Species-Activatable AIEgens for Biomedical Applications

“…For O 2 •− detection, the diphenyl phosphinyl group can be introduced into an organic compound, in which the fluorescence is strongly quenched at first, and obvious turn-on fluorescent signal is realized in the presence of O 2 •− [ 99 , 100 ]. The oxidative properties of ClO − can be utilized to destroy C=C or C=N bonds rapidly, therefor, the conjugation of fluorescence quencher through C=C or C=N bonds has turned out to be an efficient strategy to construct ClO − probes [ 101 , 102 ]. Some arylboronate groups, diphenylphosphinate groups, and nitrophenyloxoacetamide moieties have been employed as the response substitutes for ONOO − detection [ 103 , 104 , 105 ].…”

A highly selective A–π–A “turn-on” fluorescent probe for hypochlorite in tap water

“…Hypochlorous acid (HOCl), one of the representatives of reactive oxygen species (ROS) as redox regulators, is the core bactericidal substance in the biological immune system. 1,2 HOCl is generated from the reaction of H 2 O 2 and Cl − catalyzed by myeloperoxidase (MPO) in the life activities of organisms. 3–8 Excessive intracellular ClO − as oxidative stressors may cause tissue damage in the human body and even harm human organs.…”