Excitation energy transfer in Langmuir–Blodgett films of 5-(4- N-octadecylpyridyl)-10,15,20-tri- p-tolylporphyrin on gold-evaporated glass substrates studied by time-resolved fluorescence spectroscopy

Abstract

The fluorescence decays in mono- and multilayer Langmuir–Blodgett (LB) films of 5-(4- N-octadecylpyridyl)-10,15,20-tri- p-tolylporphyrin (porphyrin 338a) deposited on gold-evaporated glass substrates were measured to explore various channels for excitation energy transfer processes. The decays in the 1-layer LB films of porphyrin 338a separated from gold surface by LB film of arachidic acid were also measured as a function of the thickness of the spacer, i.e. thickness of the LB films of arachidic acid. Consistent with our previous steady-state fluorescence study, the expectation values of the lifetime obtained by fitting the decay curves with two exponential functions for the LB films indicate that at the short separation distance, the energy transfer from the porphyrin molecules to the gold surface overshadows other processes, including intra- and interlayer energy transfers. The deviation of energy transfer rate from Chance et al. (CPS) prediction of inverse distance cubed in our case may be interpreted by assuming the presence of additional excitation energy decay pathways in the LB films of porphyrin 338a on the gold-evaporated glass substrates.