Photoisomerisation azobenzene unit

Photoisomerisations of azobenzene units have been found to proceed particularly clearly and to be well suited for experimental studies. The thermodynamically more stable E-isomer can be transformed photophysically into the Z-form, which can return to the E-form on photoexcitation or thermal treatment (Fig. 5.20). 

A light-controlled dendritic box was investigated in analogous fourth-generation POPAM dendrimers whose periphery alternately bore azobenzene and naphthyl moieties. Measurements of photoisomerisation at a wavelength of 365 nm in dichloromethane showed that not all azobenzene units in the E form are transformed into the Z form, but that, for example, four units remain in the E form and some 28 units isomerise to the Z form. At pH 7, six eosin molecules per host molecule were taken up by this mixture of isomers. On the other hand, the dendrimer having all azobenzene groups in the E form takes... 

Cis-trans photoisomerisation in organic molecules is a well-studied process. Photoisomerisation of alkenes and azobenzenes forms a basis for applications ranging from information storage to molecular motors [3]. Usually, due to absorption properties of the organic compounds, UV light is required to initiate photoisomerisation. Attachment of the photoisomerisable units to transition metals opens up a route to use low energy, non-destructive visible light to initiate isomerisation via CT states. 

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