Pillar[n]arenes (n = 5-10), composed of hydroquinone units linked by methylene bridges at para positions, are rigid and easily soluble in organic solvents as well as conveniently functionalizable with various substituents at the hydroquinone unit. Both cations and neutral molecules can be incorporated into their cavities.2 These attributes make pillararenes attractive macrocyclic hosts in supramolecular chemistry.Monofunctionalized pillararenes have been shown to have very interesting self-assembly behaviour, including the formation of rotaxanes (or pseudorotaxanes),[c2] daisy chains and supramolecular polymers. The control of the self-assembly behaviour of monofunctionalized pillararenes by external stimuli is promising for use in smart functional materials, but it remains rarely explored. Among diverse external stimuli (chemical, electrostatic and electromagnetic), light is unique in allowing a remote control of assembly behaviour with potentially excellent temporaspatial resolution and without adding any chemical agents to the system.

Scientists of TIPC, CAS report a photoresponsive monofunctionalized pillar arene based on stiff stilbene (1,1-biindane, Scheme 1). The configuration of Z-1 is favourable for forming selfcomplexing pseudorotaxanes or daisy chains, while E-1 forms supramolecular polymers. Furthermore, the degree of 35 polymerization of E-1 can be controlled by pH, by protonation of the imidazole guest.

Chem. Commun.,2014

Chemical structures of Z-1, E-1, E-2

The illustrations of the supramolecular assemblies of Z-1

The illustrations of the supramolecular assemblies of E-1, E-2

The structure of Z-5 reported in reference and the illustrations of the photoisomerization processes of Z-1