Electrochemistry and in situ fluorescence microscopy of octadecanol layers doped with a BODIPY-labeled phospholipid: Investigating an adsorbed heterogeneous layer

A heterogeneous floating multilayer created from a 99:1 mole mixture of 1-octadecanol and BODIPY-HPC was characterized by fluorescence microscopy. The monomer and the DIIDII dimer emission of the BODIPY moiety displayed a variety of structures including phase separated fluid-like regions (dimer-rich) and more rigid solid-like regions (monomer-rich). These layers were deposited onto a Au(1 1 1) electrode surface and characterized using capacitance measurements and in situ fluorescence microscopy. A direct comparison between the floating layer and the resulting deposited layer revealed an expansion of 1.3–2×1.3–2× with distortion in the fluorescent features due to the multilayer nature of the floating layer. A similar variety of structures or phases were observed to exist on the electrode which displayed different potential dependent changes in fluorescence. The monomer and dimer fluorescence intensity and their ratio were used to characterize the potential dependence of the various adsorbed phases. An example is presented that illustrates the influence of the solid substrate on the characteristics of the adsorbed layer. A region in the floating layer that appeared to be mixed in composition was transformed into a dimer-rich region that had potential dependent characteristics of both. This method is useful for probing the heterogeneity of organic layers adsorbed on electrode surfaces. The phase characteristics of the adsorbed organic layer can be probed using these types of dimer forming fluorescent probes and FRET methods but are complicated by the influence of the solid substrate and the photobleaching that occurs.