Efficient Optoelectronic Sensing of HCl Vapor and Effective Iodine Capture/Storage by Hybrid Porous Organic Polymers Incorporating Triptycene and Phosphazene Motifs

A set of two unique hybrid POPs (HPOP-1 and HPOP-2) bearing triptycene and phosphazene units has been developed for their use as strategic materials capable of sensing HCl acid vapor and capturing/storing iodine. The materials were synthesized via the well-known Schiff base reaction, leading to the inclusion of ample imine linkages in the resultant HPOPs that were characterized thoroughly using various techniques. High thermal stability of HPOPs was evident from the TGA plots. The protonation of phosphazene and imine moieties in HPOPs, upon exposure to corrosive HCl vapors, acts like a chemical trigger that could be perceived not only by a "turn-on" fluorescence response but also by a color change visible to the unaided (naked) eye. The optical and electronic response of the HPOPs in the presence of HCl vapors is fully reversible using NH3 vapors as a chemical switch. These HPOPs were also found to be suitable for trapping iodine vapors and iodine species present in water or hexane solutions. This additional utility of HPOPs arises due to the presence of ample N, O, and P heteroatoms and imine linkages in the polymeric network. HPOPs can trap up to 4.90 g g–1 of iodine at 75 °C. The iodine removal efficiency at ambient temperature (25 °C) under dry as well as humid conditions is also quite promising, and performances are better than that of previously reported porous materials under similar experimental conditions. HPOPs can also efficiently remove iodine dissolved in water and hexane. All of these results indicate that HPOP-1 and HPOP-2 are potential materials for versatile environmental applications.