Bridgehead imine-substituted cyclopentadithiophene structural units, in combination with highly electronegative acceptors that exhibit progressively delocalized -systems, afford donor-acceptor (DA) conjugated polymers with broad absorption profiles that span technologically relevant wavelength () ranges from 0.7 < < 3.2 m. A joint theoretical and experimental study demonstrates that the presence of the cross-conjugated substituent at the donor bridgehead position results in the capability to fine-tune structural and electronic properties so as to achieve very narrow optical bandgaps (E-g(opt) < 0.5 eV). This strategy affords modular DA copolymers with broad- and long-wavelength light absorption in the infrared and materials with some of the narrowest bandgaps reported to date.