Coupled Molecular Crowding and Spatial Confinement Enable Reversible Sensing of Dissolved Chlorine Dioxide

Reversible fluorescence sensing of chlorine dioxide (ClO2) is challenging because its strong oxidizing character commonly drives irreversible probe conversion. Here, we show that a porous polymer microenvironment can activate reversible ClO2 sensing in a luminogen that is essentially unresponsive in homogeneous solution. A tripodal o-carborane luminogen, Ph-3Na, was designed to combine molecular crowding with efficient charge-transfer and aggregation-induced emission, affording a 577-fold aggregation-induced fluorescence enhancement and an aggregate-state quantum yield of 47.6%. Immobilization of Ph-3Na within cross-linked porous polystyrene generated a bright sensing material that undergoes pronounced fluorescence attenuation upon exposure to dissolved ClO2 without detectable bulk analyte consumption. Time-resolved fluorescence measurements reveal a shortened excited-state lifetime upon ClO2 exposure, supporting a dynamic-quenching contribution, while calculated frontier-orbital alignment is consistent with a possible photoinduced electron transfer (PET) pathway. The material responds within 45 s over 0.31-20 mg L-1 and retains reversible switching over 150 cycles. Integration into a flow-through device further enables quantitative ClO2 monitoring in environmental and food-disinfection samples. These results establish spatial confinement as a means to promote analyte access and activate reversible PET-based fluorescence sensing beyond conventional molecular probe design.