Simple Synthesis of Conjugated Polymers Enabled via Pyrrolo[3,2-b]pyrroles

Abstract

Accessing conjugated polymers suitable for applications ranging from organic photovoltaics to bioelectronics through simple synthetic protocols is desirable for the conjugated polymer community, as many polymer systems that meet device performance metrics require arduous synthetic protocols. To simplify and minimize monomer and polymer synthetic steps, a dibrominated dihydropyrrolopyrrole was synthesized in air using a single synthetic step and did not require column chromatography for purification. Subsequently, the first example of an electron-rich pyrrolopyrrole monomer being polymerized is accomplished via direct arylation polymerization using a dioxythiophene comonomer to access an alternating copolymer in a total of three synthetic steps. The resulting copolymer exhibits absorbance in the high-energy portion of the visible spectrum in solution and the solid state, a relatively low onset of oxidation (∼0.6 V vs Ag/AgCl), and yellow-to-black electrochromism. Finally, the synthetic complexity is calculated, and the pyrrolopyrrole-co-dioxythiophene polymer is less synthetically complex when compared to many conjugated polymers that find applicability in organic photovoltaics and electrochromism. These findings demonstrate the viability of incorporating dihydropyrrolopyrroles into the repeat unit structure of conjugated polymers via metal-catalyzed cross-coupling reactions and highlight their potential to offer a synthetically simple alternative to current state-of-the-art conjugated polymers.

Relating Design and Optoelectronic Properties of 1,4-Dihydropyrrolo[3,2-b]pyrroles Bearing Biphenyl Substituents

“…41 The similar energy gaps reported in Table 1 (E gaps ≈ 2.6−2.8 eV) for each DHPP may be attributed to the disrupted conjugation between the pyrrolopyrrole backbone and the π-extended substituents due to the large pyrrolopyrrole−benzene dihedral angle (∼35°) and the benzene− benzene dihedral angles (∼30°). 37,44,46,47 Ultimately, these results demonstrate how the choice of coupling partner enables control of the onset of oxidation through alterations in the electronic character without drastically manipulating the optical band gaps.…”

“…Here, we used Suzuki cross-coupling reactions to attain a structurally diverse family of π-extended DHPP chromophores. First, the halogenated starting material Br 2 DHPP was obtained via the Fe-catalyzed multicomponent reaction procedure adopted by our group and was used in Suzuki cross-coupling reactions (Scheme A) . The para -substituted chromophores, including methyl (DHPP 3 ), methoxy (DHPP 4 ), trifluoromethyl (DHPP 5 ), and cyano (DHPP 6 ) substituents, were synthesized in addition to chromophores with substituents at various positions around the benzene ring or alternative aromatics (DHPPs 7 – 12 , Scheme S2).…”

“…The calculated spectra support our observations that upon the removal of an electron, the optical transitions will shift to lower energies across the visible spectrum (Figure 4B). The transition to lower energies is in agreement with Figure 3, our previous results, 37 and observations reported by the Reynolds Group. 48−51 Overall, TDDFT provides confirmation that the trends seen within our experimental UV−vis absorbance spectra demonstrate a fundamental understanding of the structure−property relationships for this π-extended DHPP family.…”

“…The synthetic simplicity, structural tailorabilty, and expansive applicability of DHPPs motivated our group to synthesize and report the first example of a “synthetically simple” DHPP-containing copolymer . The resulting polymer was solution-processable and displayed yellow-to-black electrochromism with an applied electrochemical potential, which demonstrated that DHPP-based materials may be useful as multicolored electrochromes.…”

“…The synthetic simplicity, structural tailorabilty, and expansive applicability of DHPPs motivated our group to synthesize and report the first example of a "synthetically simple" DHPP-containing copolymer. 37 The resulting polymer was solution-processable and displayed yellow-to-black electrochromism with an applied electrochemical potential, which demonstrated that DHPP-based materials may be useful as multicolored electrochromes. However, for DHPPs to realize utility in electrochromic applications, it would be necessary to establish structure−property relationships that relate the choice of comonomers to optical, redox, and color properties of both neutral and oxidized species.…”