Helical systems for chiral organic light emitting diodes

Project Information

HEL4CHIROLED

Grant agreement ID: 859752

DOI

10.3030/859752

Project closed

EC signature date 9 August 2019

Start date 1 January 2020

End date 30 June 2024

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 4 108 852,94

EU contribution

€ 4 108 852,94

Coordinated by

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CNRS
France

Periodic Reporting for period 2 - HEL4CHIROLED (Helical systems for chiral organic light emitting diodes)

Reporting period: 2022-01-01 to 2024-06-30

Summary of the context and overall objectives of the project

Chirality is the property of left-handed and right-handed objects in the 3D space. In Nature, chirality is known to play a major role in biological systems such as in proteins and polysaccharides. In chemistry and materials science, chiral molecular and supramolecular architectures may also provide added value, related to their inherent 3D structure and their chirality-related electronic and optical properties.

The principal research goal of HEL4CHIROLED is the preparation of chiral Organic Light-Emitting Diodes (OLEDs) and other related opto-electronic devices based on new small helical molecules, helical π-conjugated oligomers and helical lanthanide complexes.

In this project, we explore new approaches to increase the performances of opto-electronic devices:

– Using the emission of circularly polarized light (CPL) to improve the performance of displays based OLEDs, and to allow additional functionalities in stereoscopic displays.

– Manipulating the spin of electrons by using a chiral molecule, to improve spin effects (Chiral Induced Spin Selectivity, CISS).

For these purposes, a great diversity of helical molecules, covalent and supramolecular polymers, together with chiral lanthanide complexes need to be prepared, thoroughly studied, and implemented into devices.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Within the project, helical molecular scaffolds and chiral lanthanide complexes have been constructed by incorporation of a diversity of chemical functionalities. Their chirality enabled improved absorption and emission of left-handed and right-handed circular light (circular dichroic - CD - response and circularly polarized luminescence - CPL), for wavelength domains ranging from blue to near-infrared.

Typical examples developed are enantiopure helicene-porphyrin and helicene-pyrene conjugates, cationic and organometallic helicenes. Compared to classical helicene derivatives, they exhibited very intense CD and CPL responses. Their structure-properties relationships have been examined in detail. This work opens a new field of helically chiral materials for optoelectronic applications.

Complexes with lanthanides (Ln), notably Ytterbium, Thulium and Erbium complexes were able to induce extraordinary chiroptical properties and give access to discrete energy domains within the NIR region, ranging from 900 to 1600 nm. Indeed, exceptionally high discrimination between left and right circularly polarized light, almost up to the theoretical maximum value, was observed in both absorption and emission for some complexes.

Several devices and imaging technologies have been developed :

- Some helical supramolecular polymeric systems revealed efficient chirality-induced spin polarization (CISS effect) as evidenced by magnetic conducting atomic force microscopy (mc-AFM) and magnetoresistance devices. These results clarify the understanding of the CISS effect being a result of chiral superstructures rather than chiral small molecules. These conclusions open new pathways for the construction of novel organic spintronic devices.

- Chiral OPVs and highly efficient CP-OLEDs have been developed from molecular or supramolecular polymeric systems.

- A biological imaging technique, consisting of a circularly polarized luminescence laser scanning confocal microscopy (CPL-LSCM) capable of simultaneous chiroptical contrast based live-cell imaging of endogenous and engineered CPL-active cellular probes, has been elaborated.

- Most of these results have been published in high-impact scientific journals and in national and international conferences.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

In the second period, the knowledge acquired and results obtained on circularly polarized luminescence (CPL) and chirality-induced spin selectivity (CISS effect) have been applied to the preparation of chiral Organic Light-Emitting Diodes (OLEDs), Organic Photovoltaics (OPVs), Spin-related devices and Chiral Imaging techniques.

- The generation of novel chiral/helical scaffolds, with improved chiroptical properties compared to the state-of-the-art, enabled us to incorporate them into optoelectronic devices. For example, circularly polarized OLEDs (CP-OLEDs) have been fabricated and highly improved efficiencies have been obtained.

- In OPVs, the impact of helical chirality onto charge transport properties has been explored and revealed improved efficiencies when 20% of chiral units were statistically incorporated within a covalent polymer.

- Helical supramolecular polymers displaying highly efficient spin-filtering have been used in magnetoresistant devices. This is another step toward the conception of spin-related OLED devices.

- Chiral lanthanide complexes appeared highly promising for two-photon CPL detection, NIR-CPL emitters in bioassays and NIR CP-OLEDs.

From a more general point of view, the HEL4CHIROLED project and the whole consortium has strongly contributed to the progress of knowledge about chiroptics and especially CPL activity, from its fundamental understanding to its diverse applications. The impact of the project on the whole scientific community is very significant.

Some societal impact can be potentially expected from the bioimaging techniques developed.

General results highlighted

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