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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. On the other hand, the construction of 2D hydrogen-bonded porous networks, which can accommodate guest molecules, has been the subject of intense investigations due to potential applications in the fabrication of molecular scale devices.
 
With the financial support of National Natural Science Foundation of China, the Ministry of Science and Technology of China, and the Chinese Academy of Sciences, the researchers at National Center for Nanoscience and Technology found that controlled assembly of well-ordered arrays of photosensitive macrocyclic rectangles is demonstrated by using a host-guest molecular template. The photosensitive macrocycles are immobilized in the TCDB network. STM images reveal the details of the well-ordered adlayers. The stoichiometry of TCDB/4NN-Macrocycle affects the structure of TCDB/4NNMacrocycle. 4NN-Macrocycle molecules are observed to photoisomerize from (t,t,t,t) to (t,t,t,c) and (t,c,t,c) photoisomers after irradiation with UV light. The direct observation about photoisomerization of macrocycles on HOPG at the single molecular level is obtained. Additionally three kinds of (t,t,t,c) or (t,t,t,t) conformational photoisomers at the same time on surface can be distinguished. This method provides a facile approach to study the photoisomerizations of the macrocycles containing azobenzene groups. It could be beneficial for the fabrication of the nanostructure and the development of photosensitive nanodevices. The results were published in Journal of the American Chemical Society (2009, Vol. 131, p. 6174-6180).

Figure High-resolution STM image of a self-assembly monolayer of irradiated TCDB/4NN-Macrocycle  adlayers on HOPG surface (left) and molecular models of the conformation of photoisomers in the photoisomerization (right).

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