The photochromic diarylethene derivative 1,2-bis(5-(4-ethynylphenyl)-2-methylthiophen-3-yl)perfluorocyclopentene (1) was submitted to photochemical, thermal stability and fatigue resistance studies in acetonitrile, also to evaluate its possible application as a new actinometer. This photochromic system covers a wide spectral absorption range, with intense bands in the UV and visible regions for the open-ring and closed-ring isomers, respectively. Very high ring-closure quantum yield values were obtained, in contrast with the low ring-opening quantum yields, which are nevertheless high enough to exploit 1 as an actinometer. The procedure required to determine the photon flux of an irradiation source with this fatigue resistant compound is indeed very simple.

In this letter, we report a chemical route for synthesizing SiO 2 @Au core-shell nanoparticles. The process includes four steps: i) preparation of the silica cores, ii) grafting gold nanoparticles over SiO 2 cores, iii) priming of the silica-coated gold nanoparticles with 2 and 10 nm gold colloids and finally iv) formation of complete shell. The optical extinction spectra were experimentally measured and compared to numerical calculations in order to confirm the dimensions deduced from SEM images. Finally, the potential of such coreshell nanoparticles for biosensing was probed by means of Surface Enhanced Raman Scattering measurements and revealed higher sensitivities with much lower gold quantity of such core-shell nanoparticles compared to Au nanoparticles exhibiting similar diameters.SiO 2 core-Au shell nanoparticles have attracted much attention for the past ten years due to potential applications in various fields such as cancer imaging and treatment (Loo et al., 2004), Surface-Enhanced Raman Spectroscopy (SERS) detection of molecules (Wang et al., 2006, Maurer et al., 2013, catalytic degradation of environmental pollutants (Ma et al., 2009) or even fabrication of SPASER (Surface Plasmon Amplification by Stimulated Emission of radiation) devices when the silica is dye-doped (Stockman, 2008). However, the growth of a complete gold shell around silica nanoparticles is very hard to achieve. Recently, most reports have been limited to the grafting of many Au small colloids onto silica cores (Hiramatsu and Osterloh, 2003, Osterloh et al., 2004, Shi and Asefa, 2007, Zhang et al., 2007. In this case, the more Au colloidal particles surround silica cores, the more red-shifted are their Localized Surface Plasmon Resonances (LSPR), which are typically between 500 nm and 550 nm. The optical signature of a complete gold shell depends in fact on the SiO 2 core diameter. When the SiO 2 cores are large enough (typically larger than 150 nm), the completion of the gold shell is evidenced by the apparition of two LSPR modes in the visible and near-infrared range (Oldenburg et al., 1998), which both blue-shift when the gold shell thickness increases. However, when the SiO 2 cores exhibit lower diameters, only one LSPR peak can be observed in the extinction spectra, which also blue shifts with larger shell thickness. Surprisingly, it seems that there has been no successful report of complete shell growth since the Halas and coworkers study fifteen years ago (Oldenburg et al., 1998). The basics of the synthesis process was indicated but not detailed: i) synthesis of the SiO 2 cores via the Stöber method (Stöber et al., 1968), ii) grafting of previously prepared very small gold colloids (Loo et al., 2004) via organosilane molecules and iii) growth of additional gold onto the colloids via chemical reduction. Therefore, the complete gold shell synthesis around silica cores is far from being easy to achieve.In this paper, we report a detailed process that allows growing a complete gold shell around silica cores. This process presen...

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We have investigated the photophysical and photochemical features of a luminescent heteroleptic Ru(II)-polypyridyl probe and of its corresponding Ru(II)-Cu(II) dinuclear complex formed upon the analyte binding through extensive density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The molecular probe contains the tailored imidazo[4,5-f]-1,10-phenanthroline (IIP) ligand for simultaneously binding the Ru(II) core and the target metal ion in aqueous solution. We have rationalized the static photoluminescence quenching observed upon the Cu(II) coordination, on the grounds of distinct excited state deactivation mechanisms which are absent in the free Ru(II) complex probe. Additionally, the emission quenching found upon increasing the solution pH has also been investigated. When coordinated IIP deprotonates, the nature of the lowest excited state of its complex changes from (3)MLCT to (3)LLCT/(3)IL. The strong base-induced emission quenching can be understood in terms of both the energy-gap law, since the (3)LLCT/(3)IL states lie at a significantly lower energy than the (3)MLCT state increasing the contribution of non-radiative mechanisms, and the expected slower radiative rates from such (3)LLCT/(3)IL states. After Cu(II) binding, the lowest triplet excited state is similar to the analyte-free probe in both energy and electronic nature. However, Cu-centered non-radiative excited states, populated after photoinduced electron transfer and intersystem crossing processes, are responsible for the population drainage of the emissive state.