Light-Modulated Self-Blockage of a Urea Binding Site in a Stiff-Stilbene Based Anion Receptor

Abstract

Anion binding to a receptor based on stiff-stilbene, which is equipped with a urea hydrogen bond donating group and a phosphate or phosphinate hydrogen bond accepting group, can be controlled by light. In one photoaddressable state (E isomer) the urea binding site is available for binding, while in the other (Z isomer) it is blocked because of an intramolecular interaction with its hydrogen bond accepting motif. This intramolecular interaction is supported by DFT calculations and ¹ H NMR titrations reveal a significantly lower anion binding strength for the state in which anion binding is blocked. Furthermore, the molecular switching process has been studied in detail by UV/Vis and NMR spectroscopy. The presented approach opens up new opportunities toward the development of photoresponsive anion receptors.

Keywords: anion binding; molecular recognition; molecular switches; photochromism; stiff-stilbene.

Scheme 1

Photocontrolled anion binding and release by blockage of the urea binding site through intramolecular hydrogen bonding.

Figure 1

DFT optimized structures [B3LYP/6‐31G++(d,p)] of (Z)‐1 (left) and (Z)‐2 (right).

Scheme 2

Synthesis of receptors (E)‐1 and (E)‐2.

Figure 2

UV/Vis spectral changes starting from (E)‐1 (A) and (E)‐2 (B) upon 340 nm irradiation followed by 385 nm irradiation (c=2×10⁻⁵ M in degassed DMSO). The insets show 340/385 nm irradiation cycles.

Figure 3

NMR spectral changes upon consecutive irradiation of solutions of (E)‐1 (A) and (E)‐2 (B) in degassed DMSO‐d ₆ with 340 nm and 385 nm light.