Single Molecule Spectroscopy Studies on the Fluorescent Properties of PCDTBT

Conjugated polymers are a class of materials which acquired an increasing scientific interest in recent decades, due to their distinct photophysical properties. A consequence of their unique chemical structure, characterised by a system of delocalised pi electrons, their properties makes them suitable for optoelectronic applications. In this project we studied the optical properties in single molecule domain of a polycarbazole type conjugated polymer, poly[N-9’-heptadecanyl-2,7-carbazole-alt-5,5-(4’,7’- di-2-thienyl-2’,1’, 3’- benzothiadiazole)], commonly known as PCDTBT by means of single molecule spectroscopy and fluorescence blinking.

Photoluminescence spectroscopy, characterised by multiple chromophore fluorescence emission, and lifetime imaging of PCDTBT single molecules suggest an emission mechanism based on intrachain energy transfer. We then use photo blinking measurements to reveal the mechanism responsible for the intermittent fluorescence emission as well as the origin of the material’s emission. Three fluorescent states were observed, which is an indication of intramolecular aggregates that allow direct energy transfer between various chemical groups composing the polymer backbone. A statistical analysis of the measured fluorescence time traces shows that a tunnelling mechanism is present in the sample which is likely responsible for the intermittent fluorescence emission.