Monolayers of Schiff bases derived from ethylene diamine and o-phenylene diamine with p-nitro cinnamaldehyde, (compounds 1 and 2) at air/water interface have been studied. Photolysis of 1 in chloroform solution undergoes cistrans isomerization on irradiation of white light while compound 2 does not undergo isomerization tinder photolytic conditions. The photolysis of 1 and 2 in Langmuir-Blodgett films (LB films) transferred to quartz plates form dimers. The change in product distribution is attributed to the influence of bridging group of the cinnamaldehyde moieties, molecular configuration and mobility of the compounds in solution:; solid state and the aggregation of molecules in monolayer assemblies. (C) 2002 Elsevier Science B.V. All rights reserved.