Impact of alkoxy side chains on morphology and excitonic coupling in PPE-PPV copolymer thin films

We investigate the role of the alkoxy side chains, of a series of five poly (p-phenyleneethylene)-alt-poly (p-phenylene-vinylene)s (PPE-PPVs) polymers as thin films, on the photophysics properties and the type of electronic coupling. By steady-state and time-resolved photoluminescence (PL) spectroscopy, we identify the different emissive species in all PPE-PPVs thin films. We show that the polymers with symmetrical and partial dissymmetrical side chains present emission from unaggregated and aggregated chain segments, while the polymer with total dissymmetrical side chains presents emission from aggregated chain segments. Excimer emission is also observed in the polymer with symmetrical long alkoxy side chains grafted on the PPE section. Here, we identify the types of electronic coupling in these different emissive species. Implementing Franck-Condon (FC) analysis, we analyze the PL spectra and we show that there is a Förster energy transfer between unaggregated and aggregated chain segments. We show that the polymer with symmetrical long alkoxy side chains grafted on the PPE section is characterized by a high energy transfer from unaggregated chain segments to aggregated chain segments.