Conjugated polymers offer the opportunity for the solution-based fabrication of low-cost optoelectronic devices. There is considerable interest in understanding structure-function-property relationships and expanding the scope of these materials to achieve complementary functionality in the near-infrared. Here,we explore donor-acceptor (DA) copolymers employing bridgehead imine substituted 4H-cyclopenta[2,1-b:3,4-b']dithiophene (CPDT) donors appended with increasingly bulky substituents. This affords the capability to influence the degree of intermolecular coupling in the solid-state and ascertain the effect on the optoelectronic properties. Grazing incidence wide-angle x-ray scattering (GIWAXS) shows that systematic increases in steric bulk increase both p-p stacking, from 3.6 � to 4.2 �, and spacing in a semi-crystalline face-on morphology until an amorphous packing is reached. This correlates with a progressive blue shift in the absorption maxima, increase in the onset of oxidation, and widening of electrochemical bandgap. Furthermore, we demonstrate that cross-conjugated structural motifs in combination with highly electronegative acceptors with progressively delocalized p-systems affords DA copolymers with broad absorption profiles that span technologically relevant wavelength (?) ranges from 0.7 < ? < 3.2 �m.The presence of the cross-conjugated substituent at the donor bridgehead position results in the capability to fine-tune structural and electronic properties and overcome conjugation saturation behavior to achieve very narrow optical bands (Egopt< 0.5 eV). This strategy affords modular DA copolymers with absorption in the infrared, and solution processable materials with the narrowest band gaps reported to date.

Elucidation of features relevant to structural control and band gap narrowing in donor acceptor copolymers using bridgehead imine substituted cyclopentadithiophene derivatives

248th National Meeting (2014)

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