Dual-Functional, Visible-Light-Responsive Gemini Surfactants for Interfacial Catalysis of Knoevenagel Condensation in Emulsion Microreactors under Mild Conditions

Abstract

Fluorinated, visible-light-responsive surfactants incorporating azobenzene units, including Gemini-type architectures, were developed to address limitations in Knoevenagel reactions, such as harsh conditions and challenging product separation. The Gemini surfactant exhibited superior interfacial activity, high solubility, and rapid photoresponsiveness, enabling reversible emulsion switching under visible light. Acting simultaneously as an emulsifier and catalyst, it efficiently promoted Knoevenagel reactions under mild conditions, achieving >90% benzaldehyde conversion within 12 h. Mechanistic studies revealed surfactant-facilitated deprotonation, nucleophilic attack, and dehydration. Various benzaldehyde derivatives were successfully converted, and the emulsion maintained high reusability over five cycles. This system offers a light-controlled strategy for catalytic synthesis with facile product separation, promising substrate applicability, and excellent recyclability, highlighting its potential for practical applications in green and efficient chemical synthesis.