Azopyrazole-Based Photoswitchable Anion Receptor for Dihydrogen Phosphate Transport.

Small-molecule anion carriers are potential reagents used in the treatment of diseases caused by dysregulated anion transport. Photoswitchable anion receptors, which can be reversibly switched between isomers by light and thereby cause reversible changes in anion binding affinity, have been receiving enormous interest. Here, based on the well-known photoswitch 1-N-methyl-3-phenylazopyrazole (3pzH), we designed a novel tetramethylamide-3pzH (3pzH_TA) photoswitchable receptor that achieves highly efficient and durable anion transportation. It enables high photoisomerization ratios of E → Z (>98%) and Z → E (97%) with a thermal half-life two times longer than that of 3pzH. We further demonstrated the high sensitivity of 3pzH_TA toward H2PO4- anion and revealed the key role of hydrogen bonds between H2PO4- and Z isomer in the strength of anion binding. Our findings open up a new strategy for the rational design and understanding of new types of photoswitchable anion receptors.