Submolecular observation of photosensitive macrocycles and their isomerization effects on host-guest network.

The macrocyclic compounds consisting of photosensitive units as parts of the frame have been extensively studied to mimic photoregulated functions in nature. In this paper, controlled assembly of well-ordered arrays of photosensitive macrocyclic rectangles is demonstrated by using a host-guest molecular template. 4NN-Macrocycle molecules are observed to photoisomerize from trans-trans-trans-trans (t,t,t,t) to a range of isomers including trans-trans-trans-cis (t,t,t,c) and trans-cis-trans-cis (t,c,t,c) isomers after irradiation of UV light. The photoisomers are also observed to affect the guest-host network characteristic appreciably. In the STM observations we can distinguish three (t,t,t,t) conformational isomers, three (t,t,t,c) conformational isomers, and one (t,c,t,c) isomer, which self-assemble into different adlayers with TCDB on a HOPG surface. This study provides a facile approach to study the photoisomerization processes of the azobenzene groups and the conformational photoisomers.