Organic thin film transistors (OTFTs) of a series of twenty dipolar donor-acceptor-substituted polymethine dyes (D-A dyes, dipole moments from 3-15 D) are investigated. The employed merocyanine dyes contain a dime-thine bridge that is substituted with 1-alkyl-3,3-dimethylindolin-2-ylidene ("Fischer base"), 3-alkyl-2,3-dihydrobenzothiazol-2-ylidene or 1,3-benzodithiole-2-ylidene, respectively, as electron-donating unit and various acceptor heterocycles. These studies show that thin films formed by these D-A dyes upon deposition in high vacuum are all composed of antiparallel pi-stacked dimers. However, they are either amorphous, discontinuous or highly crystalline due to the interplay between molecule-substrate and dimer-dimer interactions. With the help of single crystal X-ray analysis, out-of-plane X-ray studies (XRD), selected area electron diffraction (SAED), and atomic force microscopy (AFM), a correlation between the molecular structure, film ordering, and hole charge transport ability can be established. The mobility values are compared to Bassler's disorder charge transport theory and a film growth mechanism is proposed based on DFT calculations and single crystal structures. The results show that with carefully adjusted bulky substituents and high dipolarity an intimate centrosymmetric packing with a slipped, but tight pi-stacking arrangement could be realized. This provides two-dimensional percolation pathways for holes and ultimately results in charge carrier mobilities up to 0.18 cm(2) V-1 s(-1).