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New indeno[1,2-c]pyran-3-ones bearing different substituents at the pyran moiety were synthesized and their photophysical properties were investigated. In solution all compounds were found to be blue emitters and the trans isomers exhibited significantly higher fluorescence quantum yields (relative to 9,10-diphenylanthracene) as compared to the corresponding cis isomers. The solid-state fluorescence spectra revealed an important red shift of λmax due to intermolecular interactions in the lattice, along with an emission-band broadening, as compared to the solution fluorescence spectra.

The versatility of the surface chemistry of carbon dots (CDs) can generate high flexibility in engineering their surface functionality for a wide and precise array of applications. In respect of this, we perform for the first time the surface passivation of carboxylated carbon nanoparticles with p-phenylenediamine to prepare water soluble photoluminescent CDs exhibiting intriguing physicochemical properties. The new strategy used to engineer the surface functionality allows us to synthesize CDs with a stable excitation independent green photoluminescence with a quantum yield of 14% and lifetime of 11.8 ns, suitable for application in bioimaging, sensing and optoelectronics.

The unique photoluminescent properties of carbon dots (CDs) continue to encourage a great interest in their development for a wide range of applications in energy conversion, optoelectronics or sensing. Engaging carbon dots in resonance energy transfer processes with organic dyes could enable the design of functional materials to greatly enhance the performance of solar cells and other optoelectronic devices, or to create new types of sensors. In this work, CDs were functionalized with Rhodamine B (RhB) isothiocyanate, (CD–PEG1500N–Rh) via a simple procedure after surface modification of bare carbon nanoparticles with poly(ethylene glycol) bis(3-aminopropyl) (PEG1500N). The morphology of CD–PEG1500N was ascertained using HR-TEM while the covalent linkage of Rhodamine B at the surface of PEG1500N capped CDs was proved by spectroscopic analysis. The overlap between the emission spectra of CDs and the absorption spectrum of RhB molecules favoured fluorescent (Forster) resonance energy transfer (FRET) from the CDs to the dye molecules. The FRET mechanism was firstly demonstrated by steady-state fluorescence measurements and its efficiency was estimated by photoluminescence lifetime measurements, using the time correlated single photon counting (TCSPC) method with the excitation of picosecond pulse lasers. The synthetic accessibility and the transfer efficiency of these conjugates make them reliable candidates for fluorescent materials to be later used in FRET based sensing platforms and photovoltaic devices.

International audience; We describe herein the synthesis of new profluorescent nitroxides based on 2,5-disubstituted-1,3,4-oxadiazoles as fluorescent moieties and the 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO) as paramagnetic probes. The synthesis and optical and electronic properties of the oxadiazole-based precursors of the profluorescent nitroxides, as well as the nitroxides and their reduced forms are also described. Physical investigations (i.e. absorption and emission spectroscopy, cyclic voltammetry) indicate a different luminescence behaviour function to the oxadiazole substituent. A linear response to reducing agents, i.e. sodium ascorbate, monitored by fluorescence spectroscopy, suggests the possibility of using the synthesized compounds as potent active probes in detection of various analytes of interest.

Carbon ‘quantum’ dots or carbon dots have emerged as a new class of luminescent nanomaterials. While photoluminescence properties of carbon dots had targeted optical imaging and related usage, their unique excited state redox processes responsible for the luminescence emissions may find potentially significant optoelectronic applications. In this regard, we investigated the electroluminescence properties of the carbon dots integrated into multilayer light emitting diode devices. The devices emitted white light with a slight blue color, visible to naked eyes, thus validating the expectation that carbon dots may potentially serve as a new platform for electroluminescent nanomaterials.

A series of novel 2,5-disubstituted 1,3,4-oxadiazin-6-ones and their N-aroylhydrazone precursors were synthesized and characterized by NMR and UV–Vis spectroscopy. The electronic properties of 2-aryl-5-phenyl-1,3,4-oxadiazin-6-ones are mainly dependent on the 2-aryl substituent and their absorption maxima exhibit a red shift in dichloromethane. Single crystal X-ray diffraction on four acylhydrazones indicated the isolation of isomer with Z configuration of the C N double bond. Intermolecular interactions through strong H-bonding and C H⋯π contacts serve to link the molecules into a three-dimensional supramolecular network.

International audience; Donor–acceptor molecules (D-π-A) built by connecting a diphenylhydrazone block to a dicyanovinyl acceptor group via various thiophene-based π-conjugating spacers (1–5) were synthesized from mono- or dialdehydes by a simple metal-free procedure. Cyclic voltammetry and UV/Vis absorption spectroscopy show that the extension and/or increase of the donor strength of the spacer produces a decrease of the HOMO and LUMO energy level, a red shift of the absorption spectrum and an increase of the molecular absorption coefficient. Compared to solutions, the optical spectra of spin-cast thin films of compounds 1–3 show a broadening and red shift of the absorption bands, consistent with the formation of J-aggregates. In contrast the blue shift observed for the EDOT-containing compounds 4 and 5 suggests the presence of H-aggregates. Solution-cast and vacuum-deposited films of donors 1–5 were evaluated in solar cells with fullerene C60 as acceptor. A power-conversion efficiency among the highest reported for bilayer devices of basic configuration was obtained with compound 2. On the other hand, the results obtained with 4 and 5 suggest that the presence of EDOT in the structure can have deleterious effects on the organization and performances of the donor material.

International audience