Keywords:isomerization, transient absorption, azobenzene derivatives
Photochemical reaction has many pathways, and the knowledge of the reaction path network is important to understand the photoreaction. However, for the molecules that have several stable configurations known as isomers, conventional pump-probe technique is unsuitable to observe each isomerization reaction selectively and determine their pathways and reaction rates. In this work, we have developed an experimental system for millisecond time-resolved measurements based on ON/OFF switching of two color excitation laser to observe the temporal change of photostationary state. The developed system was applied to the measurements on isomerization process of SR7B (oil violet) which is a kind of azobenzene derivatives and has several stable configurations as isomer. We succeeded to observe temporal change of absorption spectra in the order of milliseconds and determine reaction pathways and each reaction rate of thermal isomerization.