Investigating the Optical Properties of Thiophene Additions to s-Indacene Donors with Diketopyrrolopyrrole, Isoindigo, and Thienothiophene Acceptors

New donor–acceptor light harvesting polymers with either a 4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene or a 4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithienothiophene donor subunit and either a 2-(nonadecan-9-yl)-5-(2-octyldodecyl)-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, (E)-1,1′-bis(2-octyldodecyl)-[3,3′-biindolinylidene]-2,2′-dione, or 3-ethyl-1-(thieno[3,4-b]thiophen-2-yl)heptan-1-one acceptor were synthesized. In this study, the effects of donor conjugation length and donor-acceptor combination on the optical properties of the synthesized polymers were investigated using steady state, up-conversion, quantum chemical simulations and ultrafast and transient spectroscopic techniques. At high energies, it was observed that polymers with extended donor conjugation had significantly enhanced absorption, whereas those with stronger acceptors showed higher extinction coefficients at lower energies. Fluorescence up-convers...