Other Definitions
azobenzene (dict)
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AzobenzeneAzobenzene is a chemical compound composed of two phenyl rings and one N-N double bond, the former of which are bridged by the latter. One of its most intriguing properties is photoisomerization behavior between two isomers, the trans- and cis- configurations. The two isomers can be switched with particular wavelengths of light: ultraviolet light, which corresponds to the energy gap of the π-π* (S2 state) transition, for trans-to-cis conversion, and blue light, which is equivalent to that of the n-π* (S1 state) transition, for cis-to-trans isomerization. Since the cis- isomer has a distorted configuration and is thus thermally unstable, thermal cis-to-trans isomerization can also occur. As the mechanism of the photoisomerization behavior, it has been suggested that the rotation of the N-N double bond affords the trans-to-cis conversion via the S2 state (rotational mechanism) and that the inversion of the phenyl ring gives rise to the cis-to-trans conversion. It is still under discussion which excited state plays a direct role in the series of the photoisomerization behavior. However, the latest research on femtosecond transition spectroscopy has suggested that the S2 state undergoes internal conversion to the S1 state, and then the trans-to-cis isomerization proceeds.
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