A series of step-ladder copolymers based on thiophene-phenylene-thiophene SL1-SL3 and thiophene-naphthylene-thiophene SL4 repeat units with varying lengths of the oligothiophene segment has been designed and synthesized via a microwave-assisted Stille-type cross-coupling reaction followed by a polymer-analogous cyclization reaction. The optical properties of the step-ladder copolymers have been investigated in detail, in particular at low temperature and in the solid-state. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7342-7353, 2008