The structure and orientation of pyranine-adsorbed octadecylamine (ODA) LB films were investigated by several spectroscopic methods (UV-vis and fluorescence) and X-ray diffraction. Depending on preparation manners ( deposition of a mixed monolayer of ODA and pyranine at the air/water interface or immersion of ODA LB films into a pyranine solution), pyranine-adsorbed films, respectively, exhibit unique structures and photo-excited relaxation processes. The excited state proton transfer (ESPT) in the pyranine-adsorbed ODA LB films was investigated by measurement of fluorescence lifetimes. From the results, the effect of pi-pi stacking interaction upon the ESPT in the LB films is considered to be similar to the one of the electron-withdrawing substitute in the bulk solution. (c) 2008 Elsevier B. V. All rights reserved.