Photophysical processes of tetraphenylporphyrin (TPP) units incorporated into a polymer monolayer have been studied by fluorescence spectroscopy with emphasis on energy migration and aggregate formation of TPPs in the two-dimensional sheet. Although UV-VIS absorption spectra showed few of TPP aggregates, the fluorescence was largely quenched in the high-TPP samples due to efficient energy migration and following energy transfer to the aggregates. With the aid of computer simulation, time-resolving decay analysis revealed the large diffusion coefficient of excitation energy and a low concentration of aggregate, suggesting that the TPP moieties were placed in the plane not with a random distribution, but with an ordered arrangement, probably due to some mutual repulsive forces which prevented overlap of the TPP units at the air-water interface. These results suggest that the polymer monolayer containing TPP units can be utilized as a component of molecular assemblies for designing efficient energy harvesting systems. (c) 2005 Elsevier B.V. All rights reserved.