Regioregular dithienosilole- and dithienogermole-based small molecules with symmetric distal/distal orientation of F atoms

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Dyes and Pigments, ISSN: 0143-7208, Vol: 155, Page: 7-13

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Han, Daehee; Lee, Jihoon; Lee, Sang Myeon; Seo, Jung Hwa; Park, Sung Heum; Yang, Changduk
Chemical Engineering
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This study describes the synthesis and characterization of a series of regioregular dithieno(3,2-b;2′,3′- d )-silole (DTSi)- and dithieno(3,2-b;2′,3′- d )-germole (DTGe)-based small molecules—7,7′-(4,4-bis(2-ethylhexyl)-4 H -silolo[3,2- b :4,5- b ′]dithiophene-2,6-diyl)bis(5-fluoro-4-(5′-hexyl-[2,2′-bithiophen]-5-yl)benzo[ c ][1,2,5]thiadiazole) (DTSi(BTFTh 2 ) 2 ), 7,7′-(4,4-bis(2-ethylhexyl)-4 H -germolo[3,2- b :4,5- b ′]dithiophene-2,6-diyl)bis(5-fluoro-4-(5′-hexyl-[2,2′-bithiophen]-5-yl)benzo[ c ][1,2,5]thiadiazole) (DTGe(BTFTh 2 ) 2 ), 7,7′-(4,4-bis(2-ethylhexyl)-4 H -silolo[3,2- b :4,5- b ′]dithiophene-2,6-diyl)bi-s(4-(benzofuran-2-yl)-5-fluorobenzo[ c ][1,2,5]thiadiazole) (DTSi(BTFBFu) 2 ), and 7,7′-(4,4-bis(2-ethylhexyl)-4 H -germolo[3,2- b :4,5- b ′]dithiophene-2,6-diyl)bis(4-(benzofuran-2-yl)-5-fluorobenzo[ c ][1,2,5]thiadiazole) (DTGe(BTFBFu) 2 ) (DTSi(BTFTh 2 ) 2, DTGe(BTFTh 2 ) 2, DTSi(BTFBFu) 2, and DTGe(BTFBFu) 2 in which two F atoms are in a symmetric distal/distal configuration relative to the central core units. The optical and electrochemical properties are strongly influenced owing to changes of the terminal units (BFu and Th 2 ) rather than by the tuning of the core units (DTSi and DTGe). In addition to a high fraction of the edge-on orientation in the neat films of all of the molecules, the presence of hexyl side chains in the Th 2 terminal units are found to play a critical role in forming high-quality films, leading to homogeneous and smooth surfaces in the films of Th 2 -containing molecules. When used as donor materials in small-molecule:fullerene solar cells, the best power-conversion efficiency of 3.26% was achieved with the DTSi(BTFTh 2 ) 2 -based system. Our study herein provides a relevant step toward understanding such isomorphic small molecules.