Photo‐activation of Tolane‐based Synthetic Ion Channel for Transmembrane Chloride Transport

Abstract

While natural channels respond to external stimuli to regulate ion concentration across cell membranes, creating a synthetic version remains challenging. Here, we present a photo‐responsive uncaging technique within an artificial ion channel system, which activates the ion transport process from a transport‐inactive o‐nitrobenzyl‐based caged system. From the comparative ion transport screening, 1b emerged as the most active transporter. Interestingly, its bis(o‐nitrobenzyl) derivative, i.e., protransporter 1b' was inefficient in transporting ions. Detailed transport studies indicated that compound 1b is an anion selective transporter with a prominent selectivity towards chloride ions by following the antiport mechanism. Compound 1b' did not form an ion channel, but after the o‐nitrobenzyl groups were photocleaved, it released 1b, forming a transmembrane ion channel. The channel exhibited an average diameter of 6.5 ± 0.2 Å and a permeability ratio of PCl‐⁄PK+ = 7.3 ± 1.5. The geometry‐optimization of protransporter 1b' indicated significant non‐planarity, corroborating its inefficient self‐assembly. In contrast, the crystal structure of 1b demonstrates strong self‐assembly via the formation of an intermolecular H‐bond. Geometry optimization studies revealed the plausible self‐assembled channel model and the interactions between the channel and chloride ion.