Polarized blue photoluminescence of mesoscopically ordered electrospun non-conjugated polyacrylonitrile nanofibers

• Published in: Materials horizons Vol. 7; no. 6; pp. 165 - 1612
• Main Authors: Liao, Xiaojian, Kahle, Frank-Julian, Liu, Bin, Bässler, Heinz, Zhang, Xinghong, Köhler, Anna, Greiner, Andreas
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 08.06.2020
• Subjects: Anisotropy; Coherent scattering; Electrospinning; Fluorescence; Luminescence; Nanofibers; Oligomers; Optoelectronic devices; Organic light emitting diodes; Phosphorescence; Photoluminescence; Polarized light; Polyacrylonitrile; Room temperature; Small angle X ray scattering; Tensile strength; Upconversion
• ISSN: 2051-6347; 2051-6355
• DOI: 10.1039/d0mh00002g

Conjugated polymers and oligomers that emit polarized light are used as active materials in various optoelectronic device applications, notably organic light-emitting diodes (OLEDs). Here, we demonstrate the fabrication of electrospun polarized light-emitting fibers from a non-conjugated polymer that can be aligned by a simple heat-stretching process. Upon excitation at 340 nm, ribbons made from the nanofibers show polarized deep blue luminescence with an anisotropy of 0.37 and a quantum yield of about 31%. Furthermore, they exhibit room temperature green phosphorescence with a lifetime of about 200 ms as well as a delayed deep blue fluorescence resulting from triplet-triplet annihilation (non-coherent photon upconversion) (TTA). Wide and small angle X-ray scattering experiments show that the stretched electrospun fibers are highly aligned with nearly perfect uniaxial orientation within the fabricated ribbons. This results in a mechanically robust and flexible material, with a high specific tensile strength (534 ± 28) MPa cm 3 g −1 and toughness (79 ± 7) J g −1 . The combination of efficient polarized deep blue luminescence, room temperature phosphorescence, TTA, mechanical robustness and flexibility of these fibers opens up new avenues for applications of non-conjugated polymers. Electrospun fibres from the non-conjugated polymer polyacrylonitrile are aligned by heat-stretching. These aligned fibers emit polarized blue fluorescence and green phosphorescence.