Single-Molecule Spectroscopy: Novel methods and their application to the analysis of polyfluorene conjugated polymers

This thesis is dedicated to the study of fluorescent conjugated polymers made of fluorene labelled with rylene moieties. Those polymers are important candidates for use in Organic Light Emitting Devices (OLEDs). The dyes present in the polymers were studied at the single-molecule level. The first part of the work is devoted to the construction and validation of an epi-fluorescent confocal/widefield/Total Internal Reflection microscope. The ensemble properties of the samples are first measured in solution. The combination of steady-state and time-resolved spectroscopies allows us to unravel the photophysics of the conjugated polyfluorene polymer containing perylenediimides in its backbone. Energy transfer is found to occur between the polyfluorene and the perylenediimide units. Beside energy transfer, a photoinduced electron transfer is also supposed to take place. Widefield microscopy is used to measure the end-to-end distance in single polymer chains. From those measurements the polymer is shown to present a quasi linear shape inside its host matrix. From the simulation of the end-to-end distance distribution, a conjugation length of 4-6 fluorene units is found. The introduction of a new subtraction method associated with defocused imaging allows us to study a more complicated polymer containing more perylenediimide units. The location and the 3D orientation of the incorporated dyes were measured at the same time by this new technique named SPIDER. Finally, the sequential two-color measurements allow us to get useful informations concerning the energy transfer occurring between polyfluorene backbone and perylenediimide units at the single molecule level.