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.
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