Exceptional Alignment in a Donor–Acceptor Conjugated Polymer via a Previously Unobserved Liquid Crystal Mesophase
[1];
[2];
[2];
[1]
- Department of Mechanical and Aerospace Engineering and Organic and Carbon Electronics Laboratories (ORaCEL) North Carolina State University Raleigh NC 27695 USA
- Department of Physics and ORaCEL North Carolina State University Raleigh NC 27695 USA
- Department of Chemistry University of North Carolina Chapel Hill NC 27599 USA
- Materials Science and Engineering Division National Institute of Standards and Technology Gaithersburg MD 20899 USA
- National Synchrotron Light Source II Brookhaven National Laboratory Upton NY 11973 USA
- Department of Electrical and Computer Engineering North Carolina State University Raleigh NC 27695 USA
Abstract Orienting polymer semiconductors is desirable to optimize device characteristics, provide insight into microstructure, and magnify subtle phase behavior. Here, a combination of uniaxial strain and subsequent heating of the donor–acceptor (DA) polymer PBnDT‐FTAZ is discovered to lead to exceptional optical dichroic ratios of up to 38 (and close to 50 near the polymer's absorption edge). This alignment is achieved due to the existence of a previously undetected thermotropic liquid crystal (LC) mesophase. The LC transition, not discernable through calorimetry, is uncovered through a combination of in situ UV–vis spectroscopy, X‐ray scattering, and dynamic mechanical analysis (DMA). Comparing PBnDT‐FTAZ to the non‐fluorinated PBnDT‐HTAZ and the homo polymer PBnDT, all of which show similar thermal transitions, reveals that exceptional alignment is only found in PBnDT‐FTAZ. This is attributed to the PBnDT‐FTAZ film having two distinct liquid crystal populations, and the polymer templating to a highly aligned, high‐clearing temperature population when heated. The DMA thermal relaxation behavior observed here is also seen in other DA conjugated polymers suggesting that such thermotropic LC mesophases may be common in these materials. These findings demonstrate a polymer semiconductor with remarkable alignment and uncover phase behavior with broad implications for process‐structure‐property relationships in polymer semiconductors.
- Sponsoring Organization:
- USDOE
- Grant/Contract Number:
- NONE; SC0012704; AC02-05CH11231
- OSTI ID:
- 2335518
- Alternate ID(s):
- OSTI ID: 2340733
- Journal Information:
- Advanced Functional Materials, Journal Name: Advanced Functional Materials Journal Issue: 30 Vol. 34; ISSN 1616-301X
- Publisher:
- Wiley Blackwell (John Wiley & Sons)Copyright Statement
- Country of Publication:
- Germany
- Language:
- English
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