Fluorescence studies of Langmuir-Blodgett films of chlorophyll a mixed with phytol

The fluorescence properties of chlorophyll a mixed with phytol (in a 1:100 molar ratio) were studied in Langmuir-Blodgett films. Fluorescence excitation and fluorescence emission spectra of the chlorophyll a-phytol system in Langmuir-Blodgett films, prepared from an argon-saturated subphase, have maxima at 444 nm and 684 nm respectively. Two lifetime components describe the state of chlorophyll a in Langmuir-Blodgett films: τ₁ = 5.18 ns (33%) and τ₂ = 1.83 ns (67%); these are assigned to single molecules of chlorophyll a and to hydrated dimers or oligomers of chlorophyll a respectively. For films prepared from an oxygen-saturated subphase, the maxima of the fluorescence excitation and fluorescence emission spectra of the chlorophyll a-phytol system are shifted to 423 nm and 678 nm respectively. The lifetime components in the time-resolved fluorescence decay curve of the film are τ₁ = 3.81 ns (54%) and τ₂ = 1.56 ns (46%). The observed changes in the fluorescence parameters of the chlorophyll a-phytol Langmuir-Blodgett films are discussed in view of the chemical effect of molecular oxygen on the mixed chlorophyll a-phytol monolayer at the air-water interface.