Spectroscopic studies of different poly3hexylthiophene chain environments in a polyfluorene matrix

Optical properties of blends made of poly(9,9-dioctyl-fluorene-2,7-diyl) (PFO) and poly(3-hexylthiophene-2,5-diyl) (P3HT) were investigated and compared to those of poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) by steady state optical spectroscopy. In addition to the individual emissions of PFO and P3HT chromophores, the blends composed by these two polymers show a new peak emission around 590 nm. The new peak is attributed to well dissolved, “isolated”, P3HT chains dispersed into the PFO matrix. It was observed that the well dissolved P3HT chains are activated by Förster energy transfer, where PFO and P3HT molecules act as a donor and an acceptor, respectively. Further, emission from ordered aggregates of P3HT is clearly observed and the interplay between aggregate and isolate P3HT chains was studied. In contrast to the PFO:P3HT blends, the emission spectra from F8T2 co-polymer show clear interaction in the ground state between the dioctylfluorene and bithiophene monomer-units, giving rise to a wholly new chromophore conformation on the backbone.