Development of an improved synthetic route to triply linked di(perylene bisimides) with varied substituents and their performance as non-fullerene acceptors in polymer photovoltaics

A series of triply-linked perylene bisimide dimers (diPBIs) with varied solubilizing groups (short-chain aliphatic, long-chain aliphatic, and aryl) were synthesized to determine the structure-property relationships that govern their performance as non-fullerene acceptors in conventional polymer photovoltaic devices. In the synthesis of the intermediates, a new solvent and ligand system for dehalogenation of 1,6,7,12-tetrabromo-perylene bisimides to 1,12 dibromo-perylene bisimides was developed in order to access PBI systems that are not available via procedures previously reported. The new dimethylacetamide/2-picolinic acid system expands the available R-groups for inclusion on perylene bisimides that render them insoluble in the conventional DMSO/L-proline system, while providing milder conditions and higher yields. A cosolvent system of DMSO/diphenyl sulfoxide was utilized to couple the brominated perylene bisimides, allowing for direct coupling of aliphatic-substituted perylene bisimides. The resulting diPBIs showed only very small differences in optoelectronic properties, but aliphatic-substituted diPBIs provided better performance due to their better solubility and ability to form co-continuous films with the donor polymer PTB7.