Poly(ortho-phenylene ethynylene)s (PoPEs) have been synthesized via an in situ activation/coupling AB' polycondensation protocol. The resulting polymers have been characterized by several analytical methods and are shown to have no structural defects. Although the Sonogashira-Hagihara polycondensation reaction is less efficient than for the preparation of the corresponding meta- and para-linked polymers, presumably because of steric hindrance caused by the ortho substituents, the process can be accelerated by the use of microwave irradiation. Optical spectroscopy indicates solvent-dependent conformational changes between extended transoid and helical cisoid conformations, providing the first experimental evidence for solvophobically driven folding of the PoPE backbone. (c) 2006 Wiley Periodicals, Inc.