Recently developed graphene quantum dots (G-QDs), presenting exceptional dispersion stability, a precisely controlled number of conjugated carbon rings and a photoluminescence quantum yield of almost unity, allow scrutinization of their intrinsic photophysics and potential quantum-confined effects related to their excited-state dynamics. Here we use transient absorption with 30-40 fs resolution to probe electronic relaxation in rectangular G-QDs composed of exactly 96, 114 and 132 carbon atoms. Through the growth of excited-state emission signals over the ground-state bleaching ones, the dynamics of relaxation are unveiled. The relaxation time ranges between 130 and 180 fs, which leads to a maximum global energy-loss rate of 5 eV ps-1. Energy-selective excitation measurements show that this ultrafast relaxation rate is limited by vibrational relaxation rather than the internal conversion process. This reveals the proximity between the excited-state energy surfaces and the key role of high-frequency vibrational modes in driving these ultrafast relaxation dynamics.

The low temperature magnetoresistance of graphene functionalized by an array of magnetic Terbium Phthalocyanines molecules is found to exhibit a magnetic field-dependent 1/f noise, along with universal conductance fluctuations (UCFs) typical of a mesoscopic phase-coherent sample. A thorough analysis of the magnetic field, temperature and chemical potential dependence of this 1/f noise and UCFs reveals that long range, 2D Ising spin-glass like, magnetic correlations are induced in graphene through exchange interactions between the magnetic molecules and charge carriers in graphene. These experiments show that graphene functionalized with organic molecules constitutes a versatile platform for the investigation of magnetic phase transitions in two dimensions.

This study explores the organization of graphene quantum dots on the surface of monocrystalline halide perovskite. We show that graphene quantum dots tend to aggregate on the surface of perovskite, unlike in solution or on other substrates, even at a very low concentration of the initial solution that should yield single-molecule samples. Spectral analysis on small clusters shows a back-and-forth dynamical transition between an uncoupled, monomer-like state and an excimer state. Following this "dance" between states,a drastic one-way increase in fluorescence intensity, combined with a shortening of the excited state lifetime, has been observed on some clusters. This behavior is related to the emission of a collective state that may be a consequence of the dynamical organization of graphene quantum dots under illumination on the surface of the perovskite.

A significant challenge in the field of organic light-emitting diodes (OLEDs) technology is the development of stable, cost-effective, and sustainable emitters. Current emitters are frequently based on rare metals and heteroatom-based chromophores. Carbon-based nanomaterials, such as carbon dots (CDs) or nanographenes (NGs), offer a promising alternative due to their high photoluminescence quantum yields, the abundance of carbon materials, and the versatility of their syntheses. In this work, we fabricated green-light-emitting electroluminescent devices containing C 60 - t Bu 8 nanographene acting as the emitter. This nanographene contains 60 sp 2 carbon atoms and tert-butyl solubilizing group on the periphery; it was synthesized via the bottom-up approach. The C 60 - t Bu 8 was fully characterized, and it was incorporated into the emissive layer of a benchmark OLED stack (ITO/PEDOT:PSS/NG-containing active layer/BCP/TmPyPB/LiF/Al). The OLED devices containing the C 60 - t Bu 8 exhibited current and power efficiencies (CE and PE) of 2.27 cdA-1, 0.28 lmW-1 and luminance of 164 cdm-2. The performance remains modest in comparison to state-of-the-art OLEDs, but it outperforms previous attempts to utilize nanographenes as active materials for fluorescent OLEDs. Following the initial results, we also tested two other NGs (C 78 - t Bu 6 and C 96 - t Bu 8 ), which contain 78 and 96 sp 2 carbon atoms as fluorescent emitters in OLEDs. The objective was to fine-tune the electroluminescence to yellow-orange and red light.

In the context of the development of new quantum emitters, nanographenes have great assets. Indeed, their synthesis by bottom-up chemistry allows a total control on their structure, which opens the way to wide customization of their optical, and spin properties [1–3]. In particular, we have shown that nanographenes are efficient single photon emitters at room temperature with tunable energy [4-7]. The next step would be to reach the emission of indistiguishable photons at low temperature. In this talk, I will report on a study of the photophysics of nanographenes embedded in original molecular crystals. I will describe the synthesis and characterization of these original molecular crystals and the protocol to embed the GQDs. Finally, I will show photoluminescence studies of GQDs down to the single nanographene both at room and low temperature [8]. [1] M. G. Debije, J. Am. Chem. Soc. 126, 4641 (2004) [2] X. Yan, X. Cui, and L.-s. Li, J. Am. Chem. Soc. 132, 5944 (2010) [3] A. Konishi et al, J. Am. Chem. Soc. 132, 11021 (2010) [4] S. Zhao et al, Nature Communications, 9, 3470 (2018) [5] T. Liu et al, Nanoscale, 14, 3826 – 3833 (2022) [6] T. Liu et al, Journal of Chemical Physics 156, 104302 (2022) [7] D. Medina-Lopez et al, Nature Communications 14, 4728 (2023) [8] Thanh Trung Huynh in preparation

Graphene quantum dots (GQDs) have much to offer in the race for new light emitters. Indeed, bottom-up chemistry leads to total control of the structure, allowing the possibility of customizing its optical and spin properties [1–3]. In particular, we have recently shown that GQDs can be efficient sources of single photons [4] whose properties can be tuned by playing with symmetry and size [5]. The full benefit from these opportunities needs to address their intrinsic optical properties. In this talk, I will summarize our recent findings on the influence of the size and symmetry of GQDs on their optical properties [5-9]. This question has been addressed by various optical methods such as absorption, fluorescence, time-resolved fluorescence, and femtosecond transient absorption. It allows us to investigate the transition energies, their relative oscillator strength, and the exciton relaxation rates. The experimental results are compared to theoretical calculations. References [1] M. G. Debije, J. Am. Chem. Soc. 126, 4641 (2004) [2] X. Yan, X. Cui, and L.-s. Li, J. Am. Chem. Soc. 132, 5944 (2010) [3] A. Konishi et al, J. Am. Chem. Soc. 132, 11021 (2010) [4] S. Zhao, J. Lavie, L. Rondin, L. Orcin-Chaix, C. Diederichs, P. Roussignol, Y. Chassagneux, C. Voisin, K. Müllen, A. Narita, S. Campidelli, J.-S. Lauret. Nat. Commun. 9 :3470 (2018). [5] D. Medina-Lopez, T. Liu, S. Osella, H. Levy-Falk, N. Rolland, C. Elias, G. Huber, P. Ticku, L. Rondin, B. Jousselme, D. Beljonne, J.-S. Lauret, S. Campidelli Nat. Commun . 14:4728 (2023). [6] H.Levy-Falk, O. Capelle, T. Liu, D. Medina-Lopez, E. Deleporte, S. Campidelli, L. Rondin, JS Lauret Physica Status Solidi b 260, 2300310 (2023) [7] T. Liu, B. Carles, C. Elias, C. Tonnelé, D. Medina-Lopez, A. Narita, Y. Chasagneux, C. Voisin, D. Beljonne, S. Campidelli, L. Rondin, and JS Lauret Journal of Chemical Physics 156, 104302 (2022) [8] T. Liu, C. Tonnelé, S. Zhao, L. Rondin, C. Elias, D. Medina-Lopez, H. Okuno, A. Narita, Y. Chassagneux, C. Voisin, S. Campidelli, D. Beljonne, and JS Lauret Nanoscale , 14, 3826 – 3833 (2022) [9] S. Quistrebert et al, in preparation

Monolayers of transition metal dichalcogenides (2D TMDs) experience strong modulation of their optical properties when the charge density is varied. Indeed, the transition from carriers composed mostly of excitons at low electron density to a situation in which trions dominate at high density is accompanied by a significant evolution of both the refractive index and the extinction coefficient. Using optical interference reflection microscopy at the excitonic wavelength, this (n, kappa)-q relationship can be exploited to directly image the electron density in operating TMD devices. In this work, we show how this technique, which we call XRM (excitonic reflection microscopy), can be used to study charge distribution in MoS2 field-effect transistors with subsecond throughput, in wide-field mode. Complete maps of the charge distribution in the transistor channel at any drain and gate bias polarization point (V-DS, V-GS) are obtained, at similar to 3 orders of magnitude faster than with scanning probe techniques such as KPFM. We notably show how the advantages of XRM enable real-time mapping of bias-dependent charge inhomogeneities, the study of resistive delays in 2D polycrystalline networks, and the evaluation of the V-DS vs V-GS competition to control the charge distribution in active devices.

Rare-earth elements (REEs) are critical to the production of modern integrated electronic devices that are ubiquitous in our lives. They are also of strategic importance to our economy and security. Unfortunately, although electronic waste contains such elements, its overall low concentration makes its recovery economically impractical, posing a significant challenge to recycling efforts. Hence, this paper proposes changes to the extraction process that focus on the potential for economically viable recovery. In addition, it also reduces the environmental impact of downstream hydrometallurgical processes. More precisely, this study presents novel extraction molecules that exhibit exceptional solubility and extraction efficiencies in supercritical carbon dioxide. This development therefore provides an alternative process to traditional hydrometallurgical processes that is more environmentally friendly and addresses the urgent need for sustainable methods of REE recovery and separation.

Atomically precise on-surface synthesis of graphene nanoribbons (GNRs) with well-defined width and edge configuration has been widely advanced during the past decade. The main bottom-up growth strategy relies on the thermally activated Ullmann-like coupling reaction followed by the cyclodehydrogenation of tailor-made precursors to achieve the desired precision. We present a systematic investigation of the growth mechanism of chevron GNR on the Ag(111), Au(111), and Cu(111) surfaces in ultrahigh vacuum. We found that the multistep reaction follows different pathways with different activation temperatures depending on the supporting surface. The importance of the as-released Br and their potential influence on the growth process are discussed. The different intermediate states were investigated by low-temperature scanning tunneling microscopy in combination with thermal desorption spectroscopy and kinetic Monte Carlo simulations.

Recent advancements in on-surface synthesis have enabled the reliable and predictable preparation of atomically precise low-dimensional materials with remarkable properties, which are often unattainable through traditional wet chemistry. Among these materials, porphyrins stand out as a particularly intriguing class of molecules, extensively studied both in solution and on surfaces. Their appeal lies in the ability to fine-tune their unique chemical and physical properties through central metal exchange or peripheral functionalization. However, the synthesis of pi-extended porphyrins featuring unsubstituted anthracenyl groups has remained elusive. Herein, we report an in vacuo temperature-controlled cyclodehydrogenation of bis- and tetraanthracenyl Zn(II) porphyrins on a gold(111) surface. By gradually increasing the temperature, sequential dehydrogenation leads to the formation of fused anthracenyl porphyrin products. Notably, at high molecular coverage, the formation of bowl-shaped porphyrins occurs, along with transmetalation of Zn with Au. These findings open the door to a variety of pi-extended anthracenyl-containing porphyrin products via cyclodehydrogenation and transmetalation, offering significant potential in the fields of molecular (photo/electro)catalysis, (opto)electronics, and spintronics.

Recent advancements in materials science have shed light on the potential of exploring hierarchical assemblies of molecules on surfaces, driven by both fundamental and applicative challenges. This field encompasses diverse areas including molecular storage, drug delivery, catalysis, and nanoscale chemical reactions. In this context, the utilization of nanotube templates (NTs) has emerged as promising platforms for achieving advanced one-dimensional (1D) molecular assemblies. NTs offer cylindrical, crystalline structures with high aspect ratios, capable of hosting molecules both externally and internally (Mol@NT). Furthermore, NTs possess a wide array of available diameters, providing tunability for tailored assembly. This review underscores recent breakthroughs in the field of Mol@NT. The first part focuses on the diverse panorama of structural properties in Mol@NT synthesized in the last decade. The advances in understanding encapsulation, adsorption, and ordering mechanisms are detailed. In a second part, the review highlights the physical interactions and photophysics properties of Mol@NT obtained by the confinement of molecules and nanotubes in the van der Waals distance regime. The last part of the review describes potential applicative fields of these 1D heterostructures, providing specific examples in photovoltaics, luminescent materials, and bio-imaging. A conclusion gathers current challenges and perspectives of the field to foster discussion in related communities.

The electrochemical oxidation of a polyphenylene-based dendrimer containing 96 sp2 carbon atoms (PPD) allows obtaining a more extended conjugated carbon framework, polymer PPD (pPPD), starting from the parent fused-benzene-based PPD. The structure and electronic properties of the polymeric thin film obtained by electrochemical oxidation have been characterized by Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy. Structural properties of the thin film formed upon electrochemical oxidation of PPD, are characterized by Matrix-Assisted Laser Desorption/Ionization (MALDI-TOF) and Gel-Permeation Chromatography (GPC) measurements. The degree of order of the layers as well as the virtual, and occupied, electronic states are addressed and exploited to obtain information on conjugation and oligomer size within the polymeric pPPD film. The experimental results are compared with DFT, B3LYP/6–31G(d), calculations. The overall results suggest that the thin film formed on the electrode surface is mainly formed by PPD dimer and trimer upon electrochemical oxidation.

Graphene nanostructures, such as Graphene Quantum Dots (G-QDs), Graphene Nanoribbons (G-NRs) and Carbon Nanotubes (C-NTs), combine the unique mechanical and electronical transport properties of sp2- hybridized carbon materials and the optical properties of direct semiconductors provided by the optical gap resulting from the reduction of dimensionally. Here we use transient absorption of 30 fs temporal resolution with polarization-controlled configuration to probe the hot exciton relaxation (internal conversion, Sn→S1) in rectangular G-QDs of various lateral lengths. We selectively excite the different samples at the second optically active electronic transition and, thought the appearance of a photo-induced emission signal at the energy corresponding to the bandedge and red-shifted vibrational replica (i.e. at the position of the steady-state photoluminescence peaks), the dynamics of relaxation were unveiled. The resulting relaxation times range from 100 fs to 175 fs. These results allowed to discuss the mechanism of relaxation, with the effect of the length of the graphene nanoflakes and of the fluence excitation.

Carbon nanomaterials have attracted the attention of the scientific community for more than 30 years now; first with fullerene, then with nanotubes and now with graphene and graphene related materials. Graphene quantum dots (GQDs) are nanoparticles of graphene that can be synthesized following two approaches, namely top-down and bottom-up methods. The top-down synthesis used harsh chemical and/or physical treatments of macroscopic graphitic materials to obtain nanoparticles, while the second is based on organic chemistry through the synthesis of polycyclic aromatic hydrocarbons exhibiting various sizes and shapes that are perfectly controlled. The main drawback of this approach is related to the low solubility of carbon materials that prevents the synthesis of nanoparticles containing more than few hundreds of sp(2) carbon atoms. Here we report on the synthesis of a family of rectangular-shaped graphene quantum dots containing up to 162 sp(2) carbon atoms. These graphene quantum dots are not functionalized on their periphery in order to keep the maximum similarity with nanoparticles of pure graphene. We chose water with sodium deoxycholate surfactant to study their dispersion and their optical properties (absorption, photoluminescence and photoluminescence excitation). The electronic structure of the particles and of their aggregates are studied using Tight-Binding (TB). We observe that the larger particles (GQD 3 and GQD 4) present a slightly better dispensability than the smaller ones, probably because the larger GQDs can accommodate more surfactant molecules on each side, which helps to stabilize their dispersion in water.

Research on graphene based nanomaterials has flourished in the last decade due their unique properties and emerging socio-economic impact. In the context of their potential exploitation for biomedical applications, there is a growing need for the development of more efficient imaging techniques to track the fate of these materials. Herein we propose the first correlative imaging approach based on the combination of radioimaging and mass spectrometry imaging for the detection of Graphene Oxide (GO) labelled with carbon-14 in mice. In this study, 14C-graphene oxide nanoribbons were produced from the oxidative opening of 14C-carbon nanotubes, and were then intensively sonicated to provide nano-size 14C-GO flakes. After Intravenous administration in mice, 14C-GO distribution was quantified by radioimaging performed on tissue slices. On the same slices, MS-imaging provided a highly resolved distribution map of the nanomaterial based on the detection of specific radical anionic carbon clusters ranging from C2˙- to C9˙- with a base peak at m/z 72 (12C) and 74 (14C) under negative laser desorption ionization mass spectrometry (LDI-MS) conditions. This proof of concept approach synergizes the strength of each technique and could be advantageous in the pre-clinical development of future Graphene-based biomedical applications.

In this article, we conduct comparative studies on the optical properties of metallic carbon nanotubes. First, we compare the complex dielectric constant predicted by an analytical model, the linear surface conductivity model, with ab initio calculations based on density functional theory. We highlight the similarities and differences between these two models, with the major discrepancy being the significantly different behavior of the plasma frequency with respect to the carbon nanotube diameter. In the second step, we compare the predictions of these models with experimental measurements of the dielectric function. We demonstrate that the screened plasma frequency serves as a reliable quantifier for distinguishing between the two models. In conclusion, we find that the ab initio calculations more accurately describe the optical properties of metallic carbon nanotubes compared with the commonly used linear surface conductivity model.

Nanographene materials are promising building blocks for the growing field of low-dimensional materials for optics, electronics and biophotonics applications. In particular, bottom-up synthesized 0D graphene quantum dots show great potential as single quantum emitters. To fully exploit their exciting properties, the graphene quantum dots must be of high purity; the key parameter for efficient purification being the solubility of the starting materials. Here, we report the synthesis of a family of highly soluble and easily processable rod-shaped graphene quantum dots with fluorescence quantum yields up to 94%. This is uncommon for a red emission. The high solubility is directly related to the design of the structure, allowing for an accurate description of the photophysical properties of the graphene quantum dots both in solution and at the single molecule level. These photophysical properties were fully predicted by quantum-chemical calculations.

The development of hybrid nanomaterials that preserve and combine the properties of their constituents is a central issue of nanosciences. Herein, we describe the polymerization via coppercatalyzed azide-alkyne cycloaddition (CuAAC) of cobalt(III) corroles around conductive carbon nanotubes to produce chemically robust hybrid catalysts for the oxygen reduction reaction (ORR). A combination of techniques including UV-vis-NIR absorption, Raman and X-ray photoelectron spectroscopies (XPS), and scanning electron microscopy (SEM) was used to characterize the assembly of the two parts of the functional hybrid system for which the activity and the selectivity toward the ORR process in acidic media are obtained by a combination of rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) measurements. The polymerized hybrid (click MWNT-CoCorr) exhibits an overpotential of ca. 230 mV compared to a reference platinum ink; the number of electrons involved in the reduction of oxygen is close to 3 in acidic media, demonstrating that the corrole cobalt centers in the hybrids reduce oxygen via a mixed pathway of twoand four-electrons.

Carbon based light emitters ranging from small organic molecules to carbon nanotubes have been subject of a great attention in the framework of diverse applications such as optoelectronics, bio-imaging, and quantum technologies. In this context, graphene quantum dots (GQD) whose size is between that of small polycyclic aromatic hydrocarbon molecules and of carbon nanotubes, have important assets. In particular the complete control of the structure allowed by their synthesis through bottom-up chemistry opens the way to a wide customization of their electronic, optical, and spin properties [1-3]. The full benefit from these opportunities requires addressing GQD’s intrinsic photophysical properties. To do so, single molecule photoluminescence experiment is a powerful tool [4-6]. Nevertheless, until now, GQDs faced a problem of solubility that has complexified both the study of their intrinsic properties and their use for applications. In this presentation, we will report on the study of new structures that show a quasi-perfect solubility. We will show how this breakthrough allows us studying in depth their photophysics. Finally, we will see that the theoretical predictions of the evolution of the electronic properties of the GQDs with their structure are fully confirmed by the experiments. [1] M. G. Debije, J. Am. Chem. Soc. 2004, 126, 4641 [2] X. Yan, X. Cui, and L.-s. Li, J. Am. Chem. Soc. 2010 132, 5944 [3] A. Konishi et al, J. Am. Chem. Soc. 2010, 132, 11021 [4] S. Zhao et al, Nature Communications, 2018, 9, 3470 [5] T. Liu et al, Nanoscale, 14, 3826 – 3833 (2022) [6] T. Liu et al, Journal of Chemical Physics 156, 104302 (2022) [7] D. Medina-Lopez et al, in preparation