Communication: Modulation of the photopolymerization behavior of a diacetylene Langmuir-Blodgett film by means of a control azobenzene-containing monolayer is reported. It is shown that the color change resulting from the photopolymerization of the diacetylenic overlayer is affected by secondary changes depending on the isomerization state of the azobenzene surface beneath the overlayer. Extensions of the process may eventually be: useful as a new tool for the fabrication of displays and organic devices in optics and optoelectronics.