Molecular design of chromic functionalized conjugated polymers

The thermochromic and solvatochromic properties of a series of polyphenylen es and polyfluorenes have been investigated experimentally and theoreticall y. For instance, poly[1,4-(2,5-dioctyloxyphenylene)-2,5-thiopene], poly[1,4 -(2,5-dioctylphenylenef-2,5-furan] have revealed interesting chromic effect s which, on the basis of calculations on dimer model compounds, seem to be related to a rather flexible backbone with an energy barrier against planar ity of < 1.3 kcal/mol. However, in the absence of sterically demanding side chains (e.g. poly[1,4-(2,5-dioctyloxyphenylene)-2,5-furan) ], the conjugat ed polymer can maintain a highly conjugated (co-planar or nearly co-planar) conformation, even at high temperatures or in dilute solutions. Also, as o bserved with poly[1,4-(2,5-dioctylphenylene)-2,5-thiophene], if the steric interactions are too strong, no co-planar conformation can be adopted upon cooling or aggregation. Finally, a comparative table shows the minimum ener gy angle and energy barrier against planarity of various repeat units which could help in the rational design of chromic polymers.