Managing Local Order in Conjugated Polymer Blends via Polarity Contrast

Matthew J Dyson,Ruipeng Li,Paul N Stavrinou,Paul D Topham,Guillaume Wantz,Harikrishna Erothu,Eirini Lariou,Olivier J Dautel,Jaime Martin,Sophia C Hayes,Natalie Stingelin

doi:10.1021/acs.chemmater.8b05259

Abstract

The optoelectronic landscape of conjugated polymers is intimately related to their molecular arrangement and packing, with minute changes in local order, such as chain conformation and torsional backbone order/disorder, frequently having a substantial effect on macroscopic properties. While many of these local features can be manipulated via chemical design, the synthesis of a series of compounds is often required to elucidate correlations between chemical structure and macromolecular ordering. Here, we show that blending semiconducting polymers with insulating commodity plastics enables controlled manipulation of the semiconductor backbone planarity. The key is to create a polarity difference between the semiconductor backbone and its side chains, while matching the polarity of the side chains and the additive. We demonstrate the applicability of this approach through judicious comparison of regioregular poly(3-hexylthiophene) (P3HT) with two of its more polar derivatives, namely the diblock copolymer poly(3-hexylthiophene)-block-poly(ethylene oxide) (P3HT-b-PEO) and the graft polymer poly[3-but(ethylene oxide)thiophene] (P3BEOT), as well as their blends with poly(ethylene oxide) (PEO). Proximity between polar side chains and a similarly polar additive reduces steric hindrance between individual chain segments by essentially ‘expelling’ the side chains away from the semiconducting backbones. This process, which has been shown to be facilitated via exposure to polar environments such as humid air/water vapor, facilitates backbone realignment to-wards specific chain arrangements and, in particular, planar backbone configurations.

Highlights

Chemistry of Materials Article molecular arrangement and packing, including torsional back- bone order/disorder, lamellar stacking, and π-stacking. This can affect often strongly contingent elegant pathway to expand the functionality of the semiconductor, perhaps best exemplified by blends of prototypical poly(3-hexyl thiophene) (P3HT) with bulk insulating plastics such as poly(ethylene oxide) (PEO) that can be manipulated to display drastically different absorption behavior compared to the neat semiconductor
We begin our discussion with the linear absorption and photoluminescence (PL) spectra of thin films of the three neat polymers: P3HT, P3HT51-b-PEO13 (Mw = 9.1 kg mol−1), and poly[3-but(ethylene oxide)thiophene] (P3BEOT) (Mw = 23 kg mol−1, Đ = 1.4, regioregularity 85%+) (Figure 1b,c; films wirebar coated in air from CHCl3 solution with 10 mg mL−1 total polymer content)
The 0−0/0−1 vibronic peak ratios in both absorption and emission, which are widely used sensitive indicators of the balance between intra- and interchain coupling,[26,28−31] are essentially identical for P3HT and P3HTb-PEO. This is attributed to the P3HT segments in the block copolymer microphase separating from the PEO segments,[32−35] leaving the former virtually unaffected by the latter and, keeping the typical characteristics of P3HT

Summary

■ INTRODUCTION

In functional polymers, such as semiconducting plastics, chemical substitution with side chains is a frequently used strategy to manipulate and control the local macro-. Molecular arrangement and packing, including torsional back- bone order/disorder, lamellar stacking, and π-stacking This can affect often strongly contingent elegant pathway to expand the functionality of the semiconductor, perhaps best exemplified by blends of prototypical poly(3-hexyl thiophene) (P3HT) with bulk insulating plastics such as poly(ethylene oxide) (PEO) that can be manipulated to display drastically different absorption behavior compared to the neat semiconductor. Alternative approaches to control structural (and other) features of polymer semiconductors have been (P3HT-b-PEO), and the graft polymer poly[3-but(ethylene oxide)thiophene] (P3BEOT; for chemical structures see Figure 1b,c insets) and their blends with PEO These judicious combinations of chemical structures and functionalities enable us to explore if blends can be designed from the outset such that as a commodity plastic. Utilizing the sensitivity of the optical properties of polythiophenes and their derivatives to backbone conformation[26,27] thereby allows their local microstructure to be probed with a high degree of insight, providing a platform for future materials selection and processing criteria

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ REFERENCES