Influence of Coupling - Regioregular PAT

The properties of PAT correlate with the degree of regioregularity and the type of coupling between substituted thiophene rings. 

Polymers with the largest percentage of HT-HT coupling exhibit 

The shift to lower energy of the absorption maximum of HT-HT coupled PATs is up to 14 nm in solution, 46 nm in the solid state, and other intensive lower energy peaks with shifts of up to 129 nm (609 nm) from the normal PATs [95]. A blue shift of the absorption maximum with increasing coplanar block length is observed in copolymers of thiophene and HH coupled 3-octylthiophene, which interrupts the coplanarity of the polymer backbone [504]. In PHT and in copolymers of thiophene/HH coupled 3-octylthiophene it was found that, with increasing HT-HT coupling content, 

The repulsive forces due to the steric hindrance in HH coupling are partially relieved in the excited state. 

The quantum yields of fluorescence from PHT solutions increase [100] owing to a larger conjugation length, higher rigidity, and consequently a decrease in non-radiative, torsional mode shunt processes (intramolecular decay manifolds) [100]. 

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