Migration and transfer of excitation energy in homogeneously dispersed porphyrin monolayers prepared from amphiphilic copolymers

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.