Probing phase segregation in porphyrin-polymer blends with multidimensional IR spectroscopy

Multidimensional IR spectroscopy is used to study blends of the regioregular semiconducting polymer, poly(3-hexylthiophene) with ruthenium porphyrins in solid state thin films. A ruthenium-bound carbon monoxide ligand is a sensitive reporter of the local electrostatic environment and indicates that the porphyrins localize into phase-segregated domains upon annealing in solvent vapor. The FTIR spectrum of this ligand reports on the state of aggregation, which we then correlate with transmission electron microscopy images of these films before and after annealing. We then use 2D-IR spectroscopy, an ultrafast IR technique, to measure the fast structural dynamics that are present in the vicinity of the CO ligand when it is homogeneously blended in the polymer film and phase segregated into purely porphyrinic domains.