Polymerization of a boronate-functionalized fluorophore by double transesterification: applications to fluorescence detection of hydrogen peroxide vapor

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Abstract
The double transesterification polymerization of 3′,6′-bis(pinacolatoboron)fluoran and pentaerythritol is reported. A model dimeric compound was synthesized to demonstrate the effectiveness of bis-diols to undergo a double transesterification, which is driven by formation of the energetically favored six-membered di-ester ring from a monomer containing a five-membered di-ester ring. This synthetic procedure provides a new route to boronate based polymers, avoiding unstable boronic acid monomers. Formation of poly-3′,6′-bis(1,3,2-dioxaborinane)fluoran, with a molecular weight of 10 000, is complete after 48 h at 50 °C. The thermodynamic stability of the six-membered boronic ester rings present in the polymer backbone also improves the stability of the polymer and its resistance to oxidation under ambient and UV light conditions. A surface detection method for the analysis of H2O2 vapor by a fluorescence turn-on response was explored. The fluorescent response results from oxidative deprotection of the boronate functionalities forming green luminescent fluorescein. Detection limits as low as 3 ppb were observed for H2O2 over an 8 h period. Detection of H2O2 in liquids can also be carried out through spot tests at concentrations as low as 1 ppm after 5 min. This new vapor-phase sensor for H2O2 provides a robust, low-cost alternative to current technology for potential applications as a self-integrating sensor for the detection of H2O2 as well as the direct monitoring of H2O2 levels in areas such as cargo shipments, chemical facilities, and pulp bleaching.