LAUSR

Abstract Two constitutional π-conjugated small molecular isomers M7a and M7b were prepared by regioselective Stille reactions. M7a and M7b have the same D1-A-D2-A-D1 structure configuration, where D1, A, and D2 are hexylthiophene, fluorobenzothiadiazole (FBT), and benzodithiophene (BDT), correspondingly. Nevertheless, they differ in the mode of fluoro substitution. Namely, F-substituents are located proximal and distal to the BDT central unit for M7a and M7b, respectively. M7a and M7b showed significant dissimilarities in their thermal, optical, electrochemical characteristics. Particularly, with the same device construction and under the identical test conditions, the organic solar cells based on M7a and M7b exhibited different photovoltaic performance. This study investigated the relationship between the substitution mode of fluorine atoms and the molecular properties, which will provide guidelines for future structural design regarding fine tuning of molecular properties and selection of regioisomeric π-conjugated small molecules.