In situ scanning tunneling microscopy (STM) has been used to examine the spatial structures of mixed molecular adlayers of dithieno[2,3-b:3,2-d]thiophene diphenyl (C6H5-DTT-C6H5, 1), 2-pentafluorophenyl-6-phenyldithieno [2,3-b:3',2'-d]thiophene (C6F5-DTT-C6H5, 2), and 2,6-bis(pentafluorophenyl) dithieno[3,2-b;2',3'-d]thiophene (C6F5-DIT-C6F5, 3) codeposited on Au(1 1 1) from dosing solutions made of combinations of 1, 2, and 3. 1 and 3 were coadsorbed mainly in a mixed adlattice characterized as (3 root 13 x 3 root 13)R13.9 degrees - 1 + 3, and some minor striped structures due to 1. The phenyl and perfluorophenyl groups in 1 and 3 interacted so strongly that they arranged spatially in pairs. Three pairs of 1 and 3 formed a windmill pattern with their terminals converging to a distorted hexagon, which enabled formation of intermolecular hydrogen bonds between 1 and 3. By contrast, 2 and 3 were coadsorbed in segregated domains made of individual molecules. Electrostatic repulsion between C6F5 - groups in 2 and 3 appeared to exceed attraction between C6H5 and C6F5 groups, which drove segregation of 2 and 3. The relative strength of adsorption of these molecules on Au(1 1 1) was inferred from their coverages determined from STM results, which suggests a descending sequence of 1 > 3 > 2. Electrochemical potential controlled all spatial structures, as ordered structures were observed only between 0.2 and 0.7 V (vs. reversible hydrogen electrode). (C) 2014 Elsevier B.V. All rights reserved.