Structurally Locked Xanthene Dye-Stitched Nanoporous Organic Polymers for Efficient Photooxidative Reactions

Xanthene-based dyes, namely, fluorescein, eosin yellow, and erythrosine blue, have been successfully integrated within porous organic polymers such as F-POP, EY-POP, and EB-POP, respectively, via nucleophilic substitution reactions with 1,3,5-tri(bromomethyl)benzene. As an advantage, this strategy locks the dye structures in their “open” conjugated quinoid form in the resulting POPs that are crucial for their interesting photoactivity which enabled them for various photocatalytic reactions in both acidic and basic media. These polymers possess excellent thermal endurance up to 230 °C (for F-POP and EB-POP ) and were insoluble in most of the common organic solvents. Due to a higher absorption edge in the visible region, EB-POP exhibited a narrow band gap (1.99 eV), which was crucial for its enhanced photocatalytic activity. The resultant polymers exhibited substantial porosity ( S BET = 13–85 m 2 /g) and demonstrated high activity in heterogeneous photocatalysis toward the superoxide anion radical-mediated oxidative hydroxylation of phenylboronic acids to phenols for a variety of substrates at room temperature with good to excellent isolated yields (78% for EB-POP ). Additionally, EB-POP showed strong recycling capabilities with good photoactivity retention over five cycles without a significant loss in yield (70%). Furthermore, these metal-free photocatalysts also exhibited efficient photocatalytic activity in producing crucial biologically active 1,3-oxathiolane-2-thiones from styrene with 75% yield for EB-POP . These data showed that our dye-containing nanoporous organic polymers were thermally stable, possessed stronger visible-light absorption capacity, and were recyclable at least five times without significant loss in photocatalytic activity.