anionic form under the alkylation conditions. This same trend was observed for the alkylation of pyrido [2,3,4,5-lmn ]phenanthridine under basic conditions. [ 24 ] Owing to the different functional groups, M1 and M2 can be easily separated on a chromatographic column or purifi ed by recrystallization. To obtain low band gap and processable materials, these monomers were copolymerized with 2,5-bis(2-octyldodecyl)-3,6-di(thien-2-yl)pyrrolo [3,4-c ]pyrrole-1,4-dione ( M3 ) (see the Supporting Information). [ 25 ] The polymerization reactions are also described in Scheme 1 . Two alternating copolymers ( P1 and P2 ) and one random terpolymer ( P3 ) were synthesized via simple direct (hetero)arylation polymerization (DHAP) (see the Supporting Information), a "greener" method which has rapidly developed in recent years. [26][27][28] The advantages of DHAP are manifold, and include a reduction in the number of reaction steps and the elimination of toxic organometallic by-products. The polymerization conditions utilized here are based on a recent report which has shown a high selectivity between aryl-bromide and non-substituted thiophene units. [ 29 ] Suzuki cross-coupling polymerization reactions were also performed for comparison purposes (see the Supporting Information). All polymers are soluble in common chlorinated solvents, such as chloroform (CF) and o -dichlorobenzene (ODCB), as well as chlorine-free solvents such as o -xylene. Interestingly, it has been noted that P2 ( M n = 60 kDa, PDI = 4.0) always afforded higher molecular weights than P1 ( M n = 43 kDa, PDI = 4.0). This could be explained by the greater solubility of P2 . Finally, a terpolymer P3 was obtained by copolymerizing the resulting 35:65 mixture of M1 and M2 with one equivalent of M3 . With a high ratio (65%) of monomer M2 into the structure of the random terpolymer P3 , this polymer ( M n = 57 kDa, PDI = 2.9) displays a good solubility in common solvents. The electrochemical properties of the polymers were investigated by cyclic voltammetry (CV) and are reported in Figure 1 b and Table S1 (Supporting Information). The occupied and unoccupied molecular orbital (HOMO/ LUMO) levels of P1 , P2 , and P3 are −5.48/−3.93, −5.46/−3.95, and −5.43/−3.92 eV, respectively, which indicate good stability in air and similar electronic properties between polymers. As reported in Figure 1 , the pristine green polymers ( P1 , P2 , and P3 ) exhibit broad UV-vis absorption spectra with an optical band gap ( E g opt ) of 1.64-1.65 eV, which is in agreement with the measured electrochemical band gap ( E g elect = 1.51-1.55 eV). Thermogravimetric analyses revealed that all polymers are stable up to 400 °C ( Figure S11, Supporting Information). Also, differential scanning calorimetry (DSC) measurements indicate that all these non-symmetric polymers are amorphous, as no glass transition temperature is observed between 25 and 250 °C. The DSC results are corroborated by X-ray diffraction (XRD) measurements (see the Supporting Information).Organic solar cells (OSC) have attrac...
