Photoswitchable dithienylethene groups, added to both alpha-ends of a sexithiophene molecular wire, switch reversibly between their open and closed forms upon irradiation. The open form has an excited state lifetime of 500 ps and is highly fluorescent, as is typical for oligothiophenes. In contrast the closed form is non-fluorescent and the excited state lifetime is a shorter by a factor of 100, reminiscent of a dithienylethene. In this system, we control the fundamental character of a molecular system through optical switching; toggling between a sexithiophene molecular wire and a dithienylethene reversibly. (C) 2009 Published by Elsevier B.V.