Study on Intrinsic Stretchability of Diketopyrrolopyrrole-Based π-Conjugated Copolymers with Poly(acryl amide) Side Chains for Organic Field-Effect Transistors

Abstract

The development of a π-conjugated polymer with hydrogen-bonding moieties has aroused great attention because of the improved molecular stacking and the hydrogen-bonding network. In this study, PDPPTVT (diketopyrrolopyrrole-thiophenevinylenethiophene) and PDPPSe (diketopyrrolopyrrole-selenophene) alkylated with a carbosilane (SiC8) side chain and poly­(acryl amide) (PAM)-incorporated alkyl side chain were prepared, and their structure–performance and structure–stretchability correlation were evaluated. By incorporating the DPPTVT backbone and 0, 5, 10, or 20% PAM-incorporated alkyl side chain, the μh value could reach 2.0, 0.97, 0.74, and 0.42 cm2 V–1 s–1, respectively (P1 to P4). The polymer with the PDPPSe backbone and 5% PAM-incorporated alkyl side-chain (P5) exhibited the maximum μh value of 0.96 cm2 V–1 s–1. By extending the PAM moiety from the backbone with alkyl spacers, the solid-state packing and edge-on orientation can be properly maintained. Surprisingly, the PAM-incorporated alkyl side-chain can provide a hydrogen-bonding network serving as sacrificial bonding to mechanical deformation. Therefore, the relevant changes in the crystallographic parameters including the crystalline size and the in-plane π–π stacking distance with a 100% external strain were less than 4 and 0.8%, respectively, from P1 to P3. Therefore, P3 achieved an excellent stretchability while maintaining its molecular orientation and charge-transporting performance. Even with 100% external strain, P3 still provided an orthogonal μh over 0.1 cm2 V–1 s–1. Moreover, by substituting the TVT moiety with the Se moiety, the ductility of the backbone can be further increased when the elastic modulus decreases from 0.80 to 0.36 GPa for P2 to P5. The achieved high μh retention is over 20% after 500 stretching–releasing cycles with a 60% external strain perpendicular to the channel direction for the polymer composed of PDPPSe and 5% PAM content. The results manifest that our newly designed DPP with the PAM-incorporated alkyl side chain provides a promising approach to promote the intrinsic stretchability of the π-conjugated polymers.

Investigation of the Mobility–Stretchability Properties of Naphthalenediimide-Based Conjugated Random Terpolymers with a Functionalized Conjugation Break Spacer

“…Characterizations of thermal, optical, and electrochemical properties including thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), UV−vis absorption, and cyclic voltammetry (CV) were conducted according to our previous publications and are briefly introduced in the Supporting Information. 15 Polarized UV−vis absorption spectrum was obtained by equipping a rotational polarizer on the spectrophotometer, and the dichroic ratio (R) of the transferred and stretched films was accordingly calculated based on the equation R = A ∥ /A ⊥ , where A ∥ and A ⊥ are the absorption intensities of the polarized incident light parallel and perpendicular to the stretching direction, respectively. Grazing incidence X-ray diffraction (GIXD) analyses of polymer films were carried out on beamline 13A1 in National Synchrotron Radiation Research Center (NSRRC), Taiwan, with an X-ray wavelength of 1.022 Å and an incident angle at 0.12°.…”

“…Diverse structural modifications have been proposed to improve the mobility–stretchability properties of conjugated polymers, and they are mainly classified into two main types: side-chain engineering and backbone engineering. The introduction of side-chain bulkiness, geometric mismatch, and hydrogen bonds , has been shown to improve the stretchability of the polymer while retaining certain backbone crystallinity for efficient intrachain/interchain charge transport. However, side-chain modification on a rigid and brittle backbone might impede effective interchain hopping between polymer chains, which might underutilize backbone conjugation in some cases.…”

Incorporation of hydrogen‐bonding units into polymeric semiconductors toward boosting charge mobility, intrinsic stretchability, and self‐healing ability

“…As a result, the polymers can maintain good charge transport properties at high deformation. Scheme 1 shows chemical structures of representative stretchable conjugated polymers ( P35 – P69 ), 41,45,46,78,78,79 which contain H‐bonding units such as ester, amide and urea.…”

“…Moreover, the device performance showed no noticeable decrease on human skin after folding, twisting and stretching with the movement of human body. This strategy was also successfully applied to other semiconducting polymers to enhance the flexibility and stretchability of the semiconducting thin films 39,41,78,79 …”

“…As for side chain engineering, the structures of side alkyl chains with regard to the branching site and the lengths of side chains have been usually finely tailored 9,34–37 . Meanwhile, incorporation of H‐bonding units into conjugated polymers is an effective means to regulate the crystalline behaviors and mechanical properties 38–47 …”