Organic molecules for quantum detection

Figure 1 : Système expérimental pour les mesures à base de résonateur diélectrique fabriqué à Kharkiv, adapté à de très basses températures au LPS. © Les auteurs
Figure 1: Experimental system based on a dielectric resonator, adapted to very low temperatures at the LPS. © The authors
A Franco-British research team has developed a luminous organic molecule capable of revealing its quantum spin state by a simple change of colour, a result that opens up a new path towards simpler, more flexible and more affordable quantum sensors.

Quantum sensing is based on the manipulation of electron spin – a quantum property linked to magnetism – which is often difficult to read in conventional materials. Until now, technologies exploiting this property have required complex materials such as the NV centres in diamonds, which are difficult to produce on a large scale. In a recent work, researchers from a Franco-British collaboration have designed an organic molecule called a ‘diradical’, because it is composed of two radical units (capable of making chemical bonds, each carrying an unpaired electron) connected via a fluorene-based molecular bridge (see middle figure). Depending on the relative orientation of the two spins (singlet or triplet state), the molecule emits light of a different colour: orange for the triplet, near infrared for the singlet (see bottom figure). This phenomenon makes it possible to optically “read” the spin state, a major advance for quantum information technologies.

The present study was carried out in the following CNRS laboratory:

  • Laboratoire de Physique des Solides (LPS, CNRS/Université Paris-Saclay)

Thanks to close collaboration between chemists and physicists, the molecular design has been optimised so that the two states (singlet and triplet) are both stable, well differentiated in energy, and strongly luminescent. At the Laboratoire de Physique des Solides, the researchers adapted spectroscopy techniques based on highly sensitive dielectric resonators, developed in Kharkiv (IRE-NASU, Ukraine) to the very low temperature range (up to 200 mK), making it possible to follow the dynamics of the spin states (see figure above). They observed a significant optical contrast between different spin states, a very rarely observed molecular property.

Panneau supérieur : la structure moléculaire et les deux spins électroniques représentés dans l'état singulet antiparallèle | Panneau central : les fonctions d'onde de l'électron (rouge) et du trou (bleu) après transfert de charge dans l'état singulet de spin | Panneau inférieur : différentes couleurs de luminescence de l'état singulet (champ magnétique nul) et de l'état triplet (champ magnétique élevé).
Figure 2 : middle, top: The molecular structure and the two electron spins represented in the antiparallel singlet state. | middle, bottom: The wave functions of the electron (red) and the hole (blue) after charge transfer in the singlet spin state. | bottom curves: Different luminescence colours of the singlet state (red curve, zero magnetic field) and the triplet state (blue curve, magnetic field of 7 Teslas). @ The authors.

This discovery paves the way for a new class of quantum materials, namely organic molecules that are luminescent, easy to produce, chemically modulable and capable of interacting with weak magnetic signals or variations in temperature or environment. These properties are particularly promising for the development of portable quantum sensors that can be integrated on a chip. This research was supported by the European Research Council (ERC), and is part of a European strategy to explore new molecular supports for tomorrow’s quantum technologies. The results are published in the journal Nature Chemistry.

Références :

Bright triplet and bright charge-separated singlet excitons in organic diradicals enable optical read-out and writing of spin states, Rituparno Chowdhury, Petri Murto, Naitik A. Panjwani, Yan Sun, Pratyush Ghosh, Yorrick Boeije, Chiara Delpiano Cordeiro, Vadim Derkach, Seung-Je Woo, Oliver Millington, Daniel G. Congrave, Yao Fu, Tarig B. E. Mustafa, Miguel Monteverde, Jesús Cerdá, Giacomo Londi, Jan Behrends, Akshay Rao, David Beljonne, Alexei Chepelianskii, Hugo Bronstein, Richard H. Friend, Nature Chemistry 17, 1410–1417 – Publié le 29 juillet 2025.
DOI : doi.org/10.1038/s41557-025-01875-z
Archives ouvertes : arXiv

Contact

Alexei Chepelianskii, Chargé de recherche CNRS au Laboratoire de Physique des Solides (LPS) : chepelianskii@lps.u-psud.fr

Communication CNRS Physique : cnrs-physique.communication@cnrs.fr