Three stereoisomers (EE, EZ, and ZZ) of 1,4-diethoxy-2,5-bis[2-(thien-2-yl)ethenyl]benzene were synthesized and characterized. It is shown that the electrochemical and optical properties depend on the configuration of the molecules. It is also shown that both electrochemical polymerization and photoactivation of the EZ and ZZ isomers cause transformation of the molecules to the most stable EE configuration. (C) 2004 The Electrochemical Society.