A series of sensitive and visible fluorescence-turn-on probes for CMC of ionic surfactants: Design, synthesis, structure influence on CMC and sensitivity, and fast detection via a plate reader and a UV light

We recently developed a unique and sensitive fluorescence-turn-on probe (THP-1, a C-6 unsubstituted tetrahydropyrimide) for critical micelle concentration (CMC) of ionic surfactants based on its unusual properties: no emission in micelles but strong aggregation-induced emission (AIE) in solution. Herein other fifteen THPs (THP-2–16) were designed and synthesized to investigate into structure influence on the CMC values of ionic surfactants (anionic SDS, cationic CTAB and zwitterionic CHAPS) and their fluorescent sensitivities. All these THPs show the unusual properties in these surfactant solutions as THP-1 and can be used as fluorescence-turn-on probes. The determined CMC values are in the range reported. It was found that 4-CF3 is a crucial functional group for increase of sensitivities of THP probes. Compared with THP-1, the concentration detecting CMC decreased by 10.8 times but fluorescence intensity increased 2.8 times. It worth mentioning that the changes in the fluorescent intensity of THPs about CMC of SDS and CTAB are so sensitive that the CMC values of SDS and CTAB can be detected using a simple UV light. In addition, we investigated into the practical applications of THPs in semi-micro and high throughput CMC determination. Since AIE fluorophores and surfactants have wide applications, it is expected these highly sensitive fluorescence-turn-on probes for CMC based on unusual no emission in surfactant micelles but strong AIE in surfactant solutions can be used in wide practical application areas.

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