Convenient construction of unique bis-[1]rotaxanes based on azobenzene-bridged dipillar[5]arenes

Abstract

A series of azobenzene-bridged dipillar [5]arenes were conveniently synthesized by coupling reaction of aminoalkyl-functionalized pillar [5]arenes with azobenzene-4,4'-dioxyacetic acid or azobenzene-4,4'-dioxybutanoic acid in dry chloroform under the combinatorial catalysis of HOBt/EDCl. 1 H NMR, 2D NOESY spectra and single crystal structure clearly indicated that the unique bis-[1]rotaxanes could be formed by threading two diaminoalkylene units into the two cavities of pillar [5] arenes depending on the length of the diaminoalkylene chains. Under light irradiation at 365 nm, the trans-azobenzene unit transferred to cis-configuration, while the basic bis-[1]rotaxane structure was kept unchanged.

Noncovalently bound and mechanically interlocked systems using pillar[n]arenes

“…On the basis of similar methods, several [1]rotaxane-type SCMs were produced (P54-P60, P62). [148][149][150][151][152][153][154] The alkyl chain length was again of great importance for the threaded structures. When the alkyl segments did not possess sufficient length (P54), only one of the two pillar [5]arenes adopted the self-inclusion form.…”

“…One of these compounds was confirmed by single-crystal X-ray analysis (P54 6 ). 148 Various units have been introduced at the centre of the linker units to date, including azobenzene (P56), 149 the imine of salicylaldehyde (P57), 150 thiourea (P58, P59), 151,152 imidazole (P62), 153 and another pillar [5]arene segment (P60). 154 Pillar[n]arene-based [1]rotaxane-type SCMs usually exist as a pair of enantiomers that interconvert via free states if they are accessible through dethreading or ring flipping.…”

“…One of these compounds was confirmed by single-crystal X-ray analysis ( P54 6 ). 148 Various units have been introduced at the centre of the linker units to date, including azobenzene ( P56 ), 149 the imine of salicylaldehyde ( P57 ), 150 thiourea ( P58 , P 59 ), 151,152 imidazole ( P62 ), 153 and another pillar[5]arene segment ( P60 ). 154…”