The conjugated backbone has been the focus of the most research, while the structure of the side chains has received less attention. Here, we focus on making new donor–acceptor–donor (D–A–D) type conjugated monomers by bearing a thieno[3,4-c]pyrrole-4,6-dione (TPD) with octyl chain at the imide nitrogen as the acceptor unit and 3,4-ethylenedioxythiophene (EDOT), and 3,3-didecyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine (ProDOT) as the donor units and their corresponding polymers. The optical and electrochemical properties of octyl substituted monomers and their corresponding polymers were compared with their ethylhexyl counterparts. Changing the alkyl side chain on the TPD unit from linear to branched has no effect on onset potential, optical band gap (Eg), perceived color, electrochromic contrast, or switching time. Nonetheless, donor strength has significant impact on the properties of monomers and their corresponding polymers. EDOT-bearing monomers and polymers have lower onset and oxidation potentials, Eg values than their ProDOT counterparts due to more electron donating ability of ethylenedioxy bridge in comparison to the propylenedioxy bridge. Octyl substituted monomers, P-Octyl and E-Octyl, demonstrated high sensitivity towards the Fe3+ ion, making them viable candidates for use in ion sensing, and their corresponding polymers, PE-Octyl and PP-Octyl, are both p- and n-dopable, which is a desirable property for conjugated polymers. Furthermore, PP-Octyl was found to be soluble in common solvents, and PP-Octyl in toluene can be oxidized with antimony pentachloride (SbCl5).