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Circularly polarized luminescence dye using helically twisted oligophenylene units developed

Circularly polarized luminescence dye using helically twisted oligophenylene units developed

Dec 10, 2020Engineering

A group of researchers of Kitasato University, Kindai University, and Osaka University has prepared a dye that shows circularly polarized luminescence (CPL) by twisting [6]paraphenylene ([6]PP), or oligo(para-phenylene), anchoring a chiral binaphthyl scaffold.

Natural light can be divided into right-handed circularly polarized light and left-handed circularly polarized light; however, chiral luminescent materials emit left- or right-handed circularly polarized light and it is possible to design optical devices that do not need CPL filters. CPL materials enable high-performance 3D displays and CPL-active security inks for security devices.

3D displays are essential to get clear quality 3D imaging for endoscopic surgery and CPL-based 3D display panels provide clearer visions and make their structural design simpler. However, CPL is an excited-state chiroptical property associated with chiral molecules, so it was difficult to predict CPL and guidelines for designing CPL-active organic molecules were unknown.

In this study, the researchers synthesized molecules by anchoring oligophenylene, which is composed of benzene rings connected through single bonds, to a chiral binaphthyl scaffold.

Oligophenylene shows strong fluorescence. The dye synthesized in this study also exhibited strong green fluorescence in powder, polymethyl methacrylate (PMMA) film, and solution. The dye showed explicit CPL characteristics in its these states thanks to the helically twisted structure of PP units, contributing to increasing CPL.

This dye showed a high quantum yield* in PMMA, indicating the possibility that the dye can be applied to the development of organic EL devices which emit circular polarized light.

*The quantum yield, the ratio of the number of emitted photons to the number of absorbed photons per unit time, can be used as a direct measure on the efficiency of a material to convert absorbed light into emitted light.

This group’s discovery will promote the development of CP-OLED(circularly polarized organic light emitting diode)using a CPL dye, accelerating the development of 3D displays using CPL.

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The article, “Circularly Polarized Luminescence of a Stereogenic Curved Paraphenylene Anchoring a Chiral Binaphthyl in Solution and Solid State,” was published in Chemistry - A European Journal at DOI: https://doi.org/10.1002/chem.202004283.