A Smart Cyclic Azobenzene as Pendant Groups on Polymer Chains: Topological Effect of the Cyclization on Thermal and Photoresponsive Properties of the Azobenzene and the Polymer

摘要

Over the past two decades, azobenzene compounds have developed to become one of the most powerful classes of photochromic materials, owing to a number of important discoveries and applications, such as optical-data storage, liquid-crystal displays, optical switching, and photoinduced surface-relief gratings (SRGs), that have been made in this field. The reversible transformation between the E and Z forms of an azobenzene can be induced by irradiation with UV light and reversed upon heating or irradiation with visible light. Typically, the Z isomer of an azobenzene is less stable than the E isomer. However, the Z isomers can be "locked" when azobenzene chromophores are placed under conformational strain. For example, the Z isomers can be stabilized by incorporating azobenzene into cyclic molecular systems. Tamaoki and co-workers synthesized a cyclic azobenzene dimer and showed that the ring strain increased the activation energy and activation entropy for the thermal Z-to-E isomerization of the azobenzene moiety.