Light harvesting and energy transfer in two oligomer-dye assemblies has been investigated. In both cases the oligomer was a poly(terphenylenecyanovinylene) derivative while two different dyes was used, a porphyrin and an ionic dye. It is well known that the efficiency of solar cells consisting of a single homopolymer is limited. To increase overall efficiency different strategies have been used. One possible strategy aims at covalently linking different domains. With careful design, this type of assemblies is envisaged to show improved charge separation and charge transport properties. We have shown how photophysical measurements can be used to determine what happens to an exciton formed on any of the domains. From fluorescence and absorption measurements on the assemblies, along with model compounds, it was possible to quantify the number of excitons that are emitted (fluorescence), transferred between domains or lost in internal transfer processes. Both steady state and lifetime measurements were performed in solution and on solid films. The effect of acid was investigated in the cases of the oligomer-porphyrin assembly. We found that in solution the effect of acid was an increase in the time of energy transfer, probably due to acid induced structural change of the porphyrin moiety. It was possible to make LB-films of the ionic dye-assembly, which made it possible to investigate a monolayer of the assembly.
Porphyrins have attracted a lot of interest as potential light harvesting dyes in polymer solar cells due to a broad absorption range, wherein the porphyrin serves as a synthetic surrogate for chlorophyll. Asymmetric porphyrins are essential building blocks in one of our polymer solar cell projects. Synthesizing these asymmetric porphyrins on large scale, in good yield, with few scrambling byproducts and without the necessity for chromatographic workup proved to be a challenge. Here we present different approaches to the synthesis of asymmetric trans-A2B2-porphyrins and trans-AB2C-porphyrins on a large scale and detail problems associated with the synthetic work. The products were characterized using SEC, MALDI-TOF, UV-vis and NMR.