Polarized electronic energy transfer in Langmuir-Blodgett films

Aggregation of cyanine dyes within Langmuir-Blodgett (LB) films is exploited to form heterodimers within mixed dye monolayers. The geometrical constraints imposed on the amphiphilic dye molecules within an LB monolayer are utilized to facilitate polarized energy transfer, Time-correlated single-photon counting is used to measure the residual polarization of electronic energy transfer from donor oxacyanine molecules to acceptor oxacarbocyanine molecules. The residual polarization decay profiles are fit to a biexponential and are contrasted for two types of LB matrixes. In a neutral tripalmitin LB matrix, the residual polarization of this mixed cyanine dye system is as high as 0.13 and decays with decay times of 170 ps and 2.8 ns to 0.03. In an ionic fatty acid LB matrix the residual polarization reaches 0.11 and decays to 0.06 with decay times of 620 ps and 5.3 ns. The concentration depolarization of these residual polarizations suggests that heterodimers are randomly distributed throughout the LB monolayer.