The thermochromic and solvatochromic properties of a series of phenylene-ba
sed conjugated polymers have been investigated experimentally and theoretic
ally. Poly(1,4-(2,5-dioctyloxyphenylene)2,5-thiophene), poly(1,4-(2, 5-dioc
tylphenylene)-2,5-furan), and poly(1,4-(2,5-didodecyloxyphenylene)-2,5-(3,4
-diethylenedioxythiophene)) have revealed interesting chromic effects which
, on the basis of calculations on dimer model compounds, seem to be related
to a rather flexible backbone with an energy barrier against planarity <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 conjugated polymer can
maintain a highly conjugated (coplanar or nearly coplanar) conformation, e
ven at high temperatures or in dilute solutions. Finally, as observed with
poly(1,4-(2,5-dioctylphenylene)-2,5-thiophene) if the steric interactions a
re too strong, no coplanar conformation can be adopted upon cooling or aggr
egation.