Boîtes quantiques de graphène dans un cristal moléculaire

Graphene quantum dots (GQDs) are nanoscale objects composed of hundreds of carbon atoms. These novel quantum emitters operate in the visible range and hold great promise for applications in optoelectronics, biosensing, and quantum technologies. Their synthesis using bottom-up chemistry enables precise control over the shape and size of GQDs, allowing us to explore how their optical and electronic properties depend on their structure. Recently, a new family of rod-shaped GQDs was synthesized using bottom-up chemistry approach. This particular family contains four distinct molecules: C₇₈-tBu₆, C₉₆-tBu₈, C₁₁₄-tBu₁₀ and C₁₃₂-tBu₁₂. Previous studies have focused on the optical properties of C96-tBu8 at the single-molecule level. This thesis builds upon those earlier works by shifting the focus from C₉₆-tBu₈ to C₁₁₄-tBu₁₀. The first part of this thesis shows the PL study at single-molecule level of C₁₁₄-tBu₁₀ embedded in polystyrene matrix. This investigation shows C₁₁₄-tBu₁₀ is a stable and bright single photon source at room temperature. Despite the success of using polystyrene in embedding C₁₁₄-tBu₁₀, the drawbacks of polystyrene matrix are highlighted. First, the emission intensity from C₁₁₄-tBu₁₀ molecules embedded in polystyrene decreases with a decrease of pressure. Secondly, the spectral linewidth of molecules embedded in polystyrene is measured of few orders of magnitude higher than the lifetime limited emission linewidth at cryogenic temperature. This broadening is mostly due to the coupling of the electronic states of the GQD with the vibration modes of the host matrix. Therefore, it is crucial to use a host matrix other than polystyrene to achieve the lifetime-limited linewidth of C₁₁₄-tBu₁₀ molecule. Our current objective is to identify a new host-environment so that C₁₁₄-tBu₁₀ molecules is completely decoupling from their host. Research from the quantum optics community indicates that at cryogenic temperatures, various molecule-host combinations allow molecules to effectively decouple within the crystals. Therefore, the second part of this thesis focuses on the PL study of C₁₁₄-tBu₁₀ in molecular crystals made of C₇₈ dendrimer. The synthesis and characterization of these original molecular crystals and the protocol to embed the C₁₁₄-tBu₁₀ molecule are presented. Results from the PL experiments at both room temperature show interesting influences of C₇₈d crystals on the lifetime of single C₁₁₄-tBu₁₀ molecule. At cryogenic temperature, the vibrational modes of the C₁₁₄-tBu₁₀ molecule are detected and show good agreement with the TDDFT calculation. In particular, the linewidth of single C₁₁₄-tBu₁₀ molecule in C₇₈d crystals measured at cryogenic temperature reaches the spectrometer resolution.