Investigation of Random Copolymer Analogues of a Semi-Random Conjugated Polymer Incorporating Thieno[3,4-b]pyrazine

Abstract

Semi-random conjugated polymers based on 3-hexylthiophene have been extensively investigated within the past several years as an effective route to broadening absorption without losing desirable properties of poly­(3-hexyl­thiophene) (P3HT). Here, we closely investigate the structural, optical, and electronic differences found in randomized analogues of poly­(3-hexylthiophene–thiophene–2,3-dimethylthieno­[3,4-b]­pyrazine) (P3HTT-TP) semi-random polymers. Proton nuclear Overhauser effect spectroscopy is used to identify linkages within the conjugated backbone, and UV–vis, cyclic voltammetry, and grazing incidence X-ray diffraction are used to determine the influence of the subtle differences in monomer connectivities. Semi-random P3HTT-TP was found to have a stronger intramolecular charge transfer absorption band and higher thermal transitions compared to its randomized analogue. Additionally, the function of the thiophene unit in the semi-random polymers is observed and demonstrated to have key electronic effects as well as maintaining a higher HOMO level, aside from providing needed stoichiometric balance to the acceptor monomer. This work demonstrates the utility of the semi-random polymer approach as a robust tool for incorporating small amount of electron-poor monomers for the purpose of improving the absorption breadth of P3HT-based polymers.

Exploring the influence of acceptor content on semi‐random conjugated polymers

“…A resulting decrease in the polymer absorption in the visible region of the solar spectrum can hinder the desired increase in the J SC , and ultimately the efficiency. In order to improve the photovoltaic properties, several polymer backbones have been studied as alternatives to the perfectly alternating D/A approach such as random, and block copolymers . Further modifications of the polymer backbone include graft copolymers .…”

Design of Random and Semi‐Random Conjugated Polymers for Organic Solar Cells

“…The distinction between random, semi‐random, and semi‐alternating polymers in literature has been inconsistent. Recent studies to differentiate random, semi‐alternating, and alternating polymers have illuminated the general disagreement about how to classify polymers that exist between truly random and perfectly alternating regimes . Namely, semi‐alternating polymers are most often generalized as random and have been incorrectly categorized as semi‐random.…”

“…Recently, we investigated differences between random and semi‐random donor‐acceptor polymers by preparing a family of polymers based on 3‐hexylthiophene, thiophene, and 2,3‐dimethylthieno[3,4‐ b ]pyrazine ( Scheme ) . This careful structural study revealed that semi‐random poly(3‐hexylthiophene‐thiophene‐ co ‐2,3‐dimethylthieno[3,4‐ b ]pyrazine) ( sr ‐P3HTT‐TP) exhibited higher absorptivity in the intramolecular charge transfer (ICT) bands compared to random analogs ( r ‐P3HTT‐TP and r ‐P3HT‐TP).…”

“…Random copolymerization is typically achieved by Stille polycondensation using AB functionalized monomers. While alkyl thiophenes are prepared through a standard lithiation and subsequent stannylation procedure, other polar functional groups are obtained through an organo‐magnesium intermediate ( Scheme ) . Specifically, the commercially available Knöchel‐Hauser base (2,2,6,6‐tetramethylpiperdinylmagesium chloride lithium chloride complex, TMPMgCl•LiCl) is utilized for selective formation of the required organo‐magensium intermediates, facilitating the synthesis of previously unreported monomers 1 – 5 (Scheme ).…”

“…Preparation of monomers 1 , 2 , 3 , and 4, 5 using Knöchel‐Hauser base to form organo‐magnesium intermediates, followed by subsequent stannylation.…”