AbstractSummary: Two polythiophenes, containing either one (PTT) or two (PBTT) 2,5,8‐trioxanonyl side chains per repeating unit, were synthesized with the objective of developing hybrid inorganic/organic semiconductor systems. From absorption and fluorescence spectroscopy and cyclic voltammetry it appears that introduction of a second 2,5,8‐trioxanonyl side chain on a repeating unit leads to a very short conjugation length. Atomic Force Microscopy (AFM) performed on composites of the two polythiophenes and a ZnSe single crystal reveals excellent wetting of the crystal by the polymers, leading to the formation of thin films. For the PTT/ZnSe composite, good contact between the constituents is substantiated by a red‐shift of the PTT absorption relative to that of PTT on quartz. Fluorescence measurements indicate the occurrence of energy transfer from ZnSe to PTT, which might imply that there is electronic contact between ZnSe and PTT. Because of its highly distorted backbone, neither a significant red‐shift compared with a film on quartz nor excitation energy transfer was found for the thin film of PBTT deposited on ZnSe. Nevertheless, it is shown that the presence of polar 2,5,8‐trioxanonyl side chains guarantees strong binding of polythiophenes to the ZnSe surface.AFM contact mode topographical image of a PBTT film cast onto a ZnSe single crystal.magnified imageAFM contact mode topographical image of a PBTT film cast onto a ZnSe single crystal.