Communication: The chromic properties of conjugated polymers, i.e., the shift in their optical spectra with various parameters, make them of interest for sensors. In order to test the prediction that poly(3,3'-di(alkylthio)-2,2'-bithiophene)s should exhibit thermochromic features and to verify the simple theoretical model behind this prediction, the synthesis of the butyl member of the series and the characterization of its thermochromic properties are reported. It is concluded that the rational design of novel chromic conjugated molecules is possible.