Synthesis, isomerization and functions of cyclophanes containing azobenzene units in the main frame

The photochromic reaction of azobenzenes has been applied to many soft materials whose functions can be controlled by the action of light. In order to accomplish a selective photochromic reaction, a new strategy utilizing a macrocyclic structure in which photochromic units are inserted into the main frame of the ring is proposed. The isomerization rate of azobenzene units from a cis form to a trans form is affected by the ring strain, the extent of which depends on the length of the spacers and the positions connecting azobenzene chromophores. This effect was applied to realize the bistability and light-intensity dependence in the photochromic systems. The concept shown here can be used for the photoresponsive molecular machines or the molecular memory.