在极性溶剂THF溶液中施加外电场控制不同极性共轭聚合物聚芴的凝聚态结构【吉林大学】

2020-07-06

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Controlling condensed state structures of different polar conjugated polymer polyfluorenes (PFs) by applying an external electric field across a solution with polar solvent THF

Journal of Materials Chemistry C

Author

Bin Liu,a Hao Zhang,a Tengning Ma,a Lubing Bai,b Jinyi Lin,b and Dan Lu,a*

aState Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, 2699 Qianjin Avenue, Changchun, 130012, China 

bKey Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University (NanjingTech), 30 South Puzhu Road, Nanjing 211816, China

DOI

10.1039/d0tc00171f

Abstract

In this work, the control of condensed state structures of different polar conjugated polymer polyfluorenes (PFs) by applying an external electric field across a solution containing polar solvent tetrahydrofuran (THF), was investigated. We used photoluminescence (PL) spectroscopy, light scattering (LS), Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution-transmission electron microscopy (HR-TEM). An external electric field was applied across the optoelectronic conjugated polymer solutions for the first time. Interestingly, it was found that from dilute solutions (0.1 mg mL1) to concentrated solutions (5 mg mL1), the chain conformation of the weakest polar PFO changed the most dramatically and always transformed towards the more planar geometry, along with effective conjugated length increase. These findings subverted the conventional thought that weakly polar polymer chains cannot be easily affected by an external electric field, and only polar conjugated polymers can. Under this condition – applying an external electric field across solutions containing the polar solvent THF – the PFO b conformation content increased obviously in a concentrated 5 mg mL 1 solution, and by this simple physical method, the PFO chains oriented and self-assembled to directly form b-phase crystal films. Other b-phase crystal preparation methods are very difficult. Astoundingly, using this method, the long-wavelength green emission of PPFOH aggregation, which is an obstacle to the application of PFs, was also suppressed, and this has been a difficult issue for a long time. The mechanism of these changes were revealed; increasing the dielectric constant gap between the polymer chain and solvent molecules is key, rather than simply the polymer polarity. The above conclusions are also applicable to other conjugated polymer systems. This research is significant not only to enrich the understanding of the physical processes of conjugated polymer solution behaviours to enhance optoelectronic device performance, but also to control condensed state structures to achieve chain ordered packing as well as multi-color larger-area optoelectronic devices with high carrier mobility and efficiency.

Literature

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