The emission of circularly-polarized (CP) light is central to many applications, including data storage, quantum computation, biosensing, environmental monitoring and display technologies. For display technology, controlling the dissymmetry of CP light in devices could generate superior efficiencies and brightness, whilst simplifying the device architecture as polarizers would no longer be required. CP light is usually assumed to require the use of chiral molecules. However, an emerging approach is to blend achiral polymers and chiral small molecule additives, which has been shown to induce CP electroluminescence.<br/><br/>Recent discussions have proposed two mechanisms responsible for the emission of CP light in circularly polarized organic light emitting diodes (CP-OLEDs). The first is the intrinsic emission from the CP chromophore. The second is the extrinsic CP emission arising from the interaction between domains of chromophores within the active layer of a device. However, the contribution of each component and the molecular factors controlling them is still rather surprisingly unknown.<br/><br/>In this work, we implement a computational study to establish the origin of CP light. Insight into the intrinsic properties of the CP light emitters is first understood using small chiral chromophores. Subsequently, the understanding is developed to larger polymers, namely poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), which achieve CP light by adopting a helical structure when blended with an enantiopure chiral small molecule additive. We demonstrate that the size of the dissymmetry in the CP light can be understood by considering the fundamental aspects of light-matter interactions and the interactions between the electric and magnetic dipole moments. The involvement of the latter places an upper limit on the intrinsic CP light that can be achieved. For the polymers, we investigate how the luminescence is influenced by the inter-unit torsion of the polymer backbone, as well as the impact of repeat units.

On the origin of circularly-polarized luminescence from achiral polymers

2019 Fall National Meeting

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