A novel -: Poly[2,6-(4-dialkylmethylenecyclopentadithiophene)] with "in-plane" alkyl substituents

The synthesis of cyclopentadithiophene-based (4H-cyclopenta[2,1-b:3,4-b'] dithiophene (CPDT)-type polymers and monomers bearing the alkyl side chains in-plane through an olefenic dialkyl-methylene group in 4-position is discussed. The resulting polymers were expected to show strong solid state interaction of the polymer chains by π-stacking that benefited both from the symmetrical structure and the planar geometry of the repeat unit. comparison of the ultraviolet (UV) absorption spectra of poly(cyclopentadithiophene)s with either in-plane or out-of-the plane alkyl chains revealed a strong preference for intermolecular π-stacking for the polymers composed of planarized building blocks. An important design rule was defined for the semiconducting polymers with optimized solid state π-stacking. It can be concluded that the in-plane alkyl chains are superior over an out-of-plane arrangement of the solubilizing subsistent.