An amphiphilic cytosine derivative containing an azobenzene chromophore was prepared in order to align azobenzene chromophores along single-strand DNA as a template. The trans-amphiphile was too coalescent to be spread as a monolayer at the air-water interface. On the other hand, the cis-amphiphile formed an expanded monolayer. After photoisomerization of the cis-monolayer with the visible light irradiation at the air-water inter-face, the regenerated trans-amphiphile can form a stable monolayer only on the guanosine subphase.