Color transitions in monolayers of a polymerizable single-chain diacetylenic lipid

We report on the polymerization kinetics of floating and supported monolayers of the lipid ethyl morpholine pentacosadiynoic amide. The in situ absorption measurements on a floating monolayer at the air/water interface enabled us to study the reaction kinetics of the diacetylenic UV-triggered photopolymerization. The rate constants for a first-order consecutive reaction M → B → R (monomer to blue polymer to red polymer) were determined. The mechanical action of the atomic force microscope (AFM) tip had an immense impact on the scanned regions of the deposited film, changing locally the properties of the monolayer toward the red, fluorescing moiety. Distinct levels of fluorescence were observed which were contributed to distinct levels of interaction of the AFM tip with the monolayer. The results suggest that the spectral shift arises from a slight rearrangement in the packing of the side chains in the polymeric backbone.