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

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, 1 b emerged as the most active transporter. Interestingly, its bis(o-nitrobenzyl) derivative, i.e., protransporter 1 b' was inefficient in transporting ions. Detailed transport studies indicated that compound 1 b is an anion selective transporter with a prominent selectivity towards chloride ions by following the antiport mechanism. Compound 1 b' did not form an ion channel, but after the o-nitrobenzyl groups were photocleaved, it released 1 b, forming a transmembrane ion channel. The channel exhibited an average diameter of 6.5±0.2 Å and a permeability ratio of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>P</mml:mi> <mml:msup><mml:mrow><mml:mi>C</mml:mi> <mml:mi>l</mml:mi></mml:mrow> <mml:mo>-</mml:mo></mml:msup> </mml:msub> <mml:mo>/</mml:mo> <mml:msub><mml:mi>P</mml:mi> <mml:msup><mml:mrow><mml:mi>K</mml:mi></mml:mrow> <mml:mo>+</mml:mo></mml:msup> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>7</mml:mn> <mml:mo>.</mml:mo> <mml:mn>3</mml:mn> <mml:mo>±</mml:mo> <mml:mn>1</mml:mn> <mml:mo>.</mml:mo> <mml:mn>5</mml:mn></mml:mrow> <mml:annotation>${{P}_{{Cl}^{-}}/{P}_{{K}^{+}}=7.3\pm 1.5}$</mml:annotation> </mml:semantics> </mml:math> . The geometry-optimization of protransporter 1 b' indicated significant non-planarity, corroborating its inefficient self-assembly. In contrast, the crystal structure of 1 b 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.