Designing a Length‐Modulated Azide Photocrosslinker to Improve the Stretchability of Semiconducting Polymers

Abstract

To impart high stretchability to semiconducting polymers, researchers have used a photocrosslinking approach based on the nitrene chemistry of an azide‐incorporated molecular additive. However, understanding of the molecular design of azide crosslinkers with respect to their effects on the electrical and mechanical properties of semiconducting polymer thin films is lacking. In this study, the effects of an azide photocrosslinker's molecular length and structure on the microstructural, electrical features, and stretchability of photocrosslinked conjugated polymer films is investigated. For a systematic comparison, a series of nitrene‐induced photocrosslinkers (n‐NIPSs) with different numbers of ethylene glycol repeating units (n = 1, 4, 8, 13) that bridge two tetrafluoro‐aryl azide end groups is synthesized. Two semicrystalline conjugated polymers and two nearly amorphous conjugated polymers are co‐processed with n‐NIPSs and crosslinked by brief exposure to UV light. It is found that, among the synthesized n‐NIPSs, the shortest one (1‐NIPS) is the most efficient in improving the stretchability of crosslinked indacenodithiophene‐benzothiadiazole films and that the improvement is achieved only with nearly amorphous polymers, not with semicrystalline conjugated polymers. On the basis of systematic studies, it is suggested that crosslinking density in amorphous regions is important in improving thin film stretchability.

Introduction of Metal Coordination Bonds into Conjugated Polymers to Increase Carrier Mobility and Stretchability

“…Additionally, molecular coupling between the donor and acceptor units results in a (0–0) peak at λ 0–0 = 680 nm in all absorption spectra. The absorption intensity of this peak is represented as I 0–0 (Figure d). , By comparing the normalized UV–vis absorption spectra, there is no shift of λ 0–1 or λ 0–0 . In addition, the relative absorption intensity ratio between 0 and 0 and 0–1 peaks ( I 0–0 / I 0–1 ) is a crucial parameter to evaluate the interchain aggregation of IDTBT chains (Figure e). , For the pristine film, I 0–0 / I 0–1 is 1.65.…”

“…The absorption intensity of this peak is represented as I 0−0 (Figure 6d). 30,54 By comparing the normalized UV−vis absorption spectra, there is no shift of λ 0−1 or λ 0−0 . In addition, the relative absorption intensity ratio between 0 and 0 and 0−1 peaks (I 0−0 /I 0−1 ) is a crucial parameter to evaluate the interchain aggregation of IDTBT chains (Figure 6e).…”

“…Nonetheless, the circular distribution of side chains allows for better chain flow, thereby enhancing the stretchability of the thin film. Additionally, researchers have proposed the use of nitrene-induced photocross-linkers as an alternative to interchain entanglements for improving the stretchability of IDTBT . By cross-linking the rigid conjugated backbones, irreversible chain sliding can be prevented, and elastic properties can be introduced to the material.…”

“…Additionally, researchers have proposed the use of nitrene-induced photocross-linkers as an alternative to interchain entanglements for improving the stretchability of IDTBT. 30 By cross-linking the rigid conjugated backbones, irreversible chain sliding can be prevented, and elastic properties can be introduced to the material. Furthermore, Bao et al developed an elastic semiconductor film with remarkable tensile properties by initiating in situ cross-linking of rubber-rubber and rubber-IDTBT.…”

Structural Insights into Conjugated Polymers for Stretchable Organic Transistors

“…We synthesized a cross-linking agent containing an azide functional group (n-NIPS), which can be cross-linked with hydrocarbons in the aliphatic side chain of conjugated polymers and improved the CoS of the IDTBT films from 35% to 100% through cross-linking. 115 The side chains of IDTBT formed a cross-linking network through n-NIPS to reduce chain slippage caused by stretching. As the number of repeating units of n-NIPS increased from 1 to 14, the hydrophilic interaction of n-NIPS became stronger.…”