## 3 Results and Discussion  
The synthesis of poly(((methylthionopyrrolo)furanyl)diketopyrrolopyrrol) **P(FDP-TP)** is shown in Scheme 1. Compounds 3,6-di(furan-2-yl)pyrrolol[3,4-c]pyrrole-1,4(2H,5H)-dione and 4-methyl-2,5-bis(trimethylstannyl)-4_H_-thieno[3,2-b]pyrrole (monomer **M2)** were synthesized according to a method reported in a literature [26]. Alkylation of 2,5-bis(2-decyltetradacyl)-3,6-di(furan-2-yl)pyrrolol[3,4-c]pyrrole-1,4(2H,5H)-dione carried out with 9-(bromomethyl)nonadecane followed by bromination using NBS in chloroform yielded the new monomer 3,6-bis(5-bromofuran-2-yl)-2,5-bis(2-decyltetradacyl)-2,5-dihydropypropyl[3,4-c]pyrrole-1,4-dione (**M1**). The detailed synthesis of monomer **M1** is included in the Supplementary Information (SI). Polymer synthesis was carried out with the Stille coupling polymerization reaction between **M1** and **M2** in anhydrous _o_-dichlorobenzene using Pd2(dba)3 catalyst and P(o-tolyl)3 ligand. After stirring at 130 \({}^{\circ}\)C for 36 h in a pressure flask under a nitrogen atmosphere, the polymerization reaction mixture was brought to room temperature and subsequently precipitated out in methanol. Successive Soxhlet extractions with methanol, acetone, and hexanes were performed for the crude solid before the final polymer product was collected into chloroform. The number average molecular weight (Mn) of the polymer **P(F)DP-TP** was 18.6 kDa with a PDI of 1.62, estimated from size exclusion chromatography using tetrahydrofuran solvent. The detailed procedure and characterization of synthesized polymer **P(F)DP-TP** are included in the SI (Figure S1-S5). The optical properties of the polymer in both solutions (CHCl3) and thin film were studied with UV-Vis spectroscopy. The UV-Vis absorption spectra obtained for **P(F)DP-TP** are shown in Figure 2a. In solution, two peaks were observed at 395 and 832 nm, attributed to \(\pi\)-\(\pi^{\text{n}}\) charge transfer and donor-acceptor charge transfer, respectively. In thin film, both peaks were red-shifted to 402 and 870 nm, indicating a favorable \(\pi\)-stacking between solid-state polymer chains, beneficial for charge carrier transport. The optical bandgap was 1.25 eV as calculated with the onset wavelength (1040 nm) of the polymer's solid-state absorbance spectrum. The experimental HOMO and LUMO energy levels of **P(FDPP-TP)** were determined using cyclic voltammetry (CV). The HOMO and LUMO energies were calculated using the onset potentials of oxidation and reduction peaks of the cyclic voltammogram. The equations E\({}_{HOMO}=-(\mathrm{E}_{\mathrm{ox}}+4.4)\) eV and E\({}_{LUMO}=-(\mathrm{E}_{\mathrm{red}}+4.4)\) eV were applied respectively to calculate HOMO and LUMO levels. The HOMO and LUMO energy levels were determined to be \(-4.64\) eV and \(-2.77\) eV, respectively. The HOMO energy level, close to the Au work function (\(-5.1\) eV), is expected to facilitate the hole injection from gold contacts in the p-type polymers [25,44]. The calculated electrochemical bandgap was 1.87 eV from CV measurements. The observed disparity in the optical and electrochemical bandgaps (0.62 eV) can be attributable to the material's exciton binding energy, which could vary between 0.4 and 1.0 eV [21,22,26]. Optoelectronic properties of **P(FDPP-TP)** were summarized in Table S1. Spartan 16 software at B3 LYP/6-3 IG* theory level was used to estimate the coplanarity of the backbone and torsional angles to calculate the theoretical electronic energy levels of the **P(FDPP-TP)** dimer replacing alkyl substituents with the methyl groups (Figure S6). The DPP unit had a slight twist between the DPP and the flanker unit furan, while the asymmetric thieno[3,2-b]pyrrole unit had two different angles on either side. The furan unit made a relatively low dihedral angle of 1.92\({}^{\circ}\) with the thiophene side of TP as expected, giving a better coplanarity to the polymer backbone, and the calculated torsional angle between the furan and pyrrole side of TP is 11.55\({}^{\circ}\).