Issue 25, 2021

Chiral polymer hosts for circularly polarized electroluminescence devices

Abstract

Polymer electroluminescence devices producing circularly polarized luminescence (CP PLEDs) have valuable photonic applications. The fabrication of a CP PLED requires a polymer host that provides the appropriate chiral environment around the emitting dopant. However, chemical strategies for the design of chiral polymer hosts remain underdeveloped. We have developed new polymer hosts for CP PLED applications. These polymers were prepared through a free-radical polymerization of 3-vinylcarbazole with a chiral N-alkyl unit. This chiral unit forces the carbazole repeat units to form mutually helical half-sandwich conformers with preferred (P)-helical sense along the polymer main chain. Electronic circular dichroism measurements demonstrate the occurrence of chirality transfer from chiral monomers to achiral monomers during chain growth. The (P)-helical-sense-enriched polymer interacts diastereoselectively with an enantiomeric pair of new phosphorescent (R)- and (S)-dopants. The magnitude of the Kuhn dissymmetry factor (gabs) for the (P)-helically-enriched polymer film doped with the (R)-dopant was found to be one order of magnitude higher than that of the film doped with the (S)-dopant. Photoluminescence dissymmetry factors (gPL) of the order of 10−3 were recorded for the doped films, but the magnitude of diastereomeric enhancement decreased to that of gabs. The chiral polymer host permits faster energy transfer to the phosphorescent dopants than the achiral polymer host. Our photophysical and morphological investigations indicate that the acceleration in the chiral polymer host is due to its longer Förster radius and improved compatibility with the dopants. Finally, multilayer CP PLEDs were fabricated and evaluated. Devices based on the chiral polymer host with the (R)- and (S)-dopants exhibit electroluminescence dissymmetry factors (gEL) of 1.09 × 10−4 and −1.02 × 10−4 at a wavelength of 540 nm, respectively. Although challenges remain in the development of polymer hosts for CP PLEDs, our research demonstrates that chiroptical performances can be amplified by using chiral polymer hosts.

Graphical abstract: Chiral polymer hosts for circularly polarized electroluminescence devices

Supplementary files

Article information

Article type
Edge Article
Submitted
15 apr 2021
Accepted
11 may 2021
First published
21 may 2021
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2021,12, 8668-8681

Chiral polymer hosts for circularly polarized electroluminescence devices

J. Hong, S. Kim, G. Park, Y. Lee, H. Kim, S. Kim, T. Lee, C. Kim and Y. You, Chem. Sci., 2021, 12, 8668 DOI: 10.1039/D1SC02095A

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