Small gold nanoparticles capped with 4trimethylsilylethynyl-1-acetylthiobenzene (SEB) were prepared with spherical shape and different mean sizes (5−8 nm). The functionalized gold nanoparticles (AuNPs-SEB) were deposited onto TiO 2 substrates, and the interaction at the molecule−gold interface, the molecular layer thickness, and the ligand organization on the surface of Au nanospheres were investigated by means of synchrotron radiation induced X-ray photoelectron spectroscopy (SR-XPS) and angular dependent near edge X-ray absorption spectroscopy (NEXAFS) at the C K-edge. In order to obtain better insight into the molecular shell features, the same measurements were also carried out on a self-assembling monolayer (SAM) of SEB anchored on a "flat" gold surface (Au/Si(111) wafer). The comparison between angular dependent NEXAFS spectra collected on the self-assembling monolayer and AuNPs-SEB allowed for successfully probing the molecular arrangement of SEB molecules on the gold nanospheres surface. Furthermore, DFT calculations on the free SEB molecule as well as bonded to a small cluster of gold atoms were developed. The comparison with experimental results allowed better understanding of the spectroscopic signatures in the experimental absorption spectra and rationalization of the molecular organization in the SAM, NPs having a thin molecular shell, and NPs covered by a thick layer of ligands.

Gold nanoparticles stabilized by two novel bifunctional fluorenyl thiols, generated in situ from 9,9-idodecyl-2,7-bis(acetylthio) fluorene (1) and 9,9-didodecyl-2,7-bis(acetylthiophenylethynyl) fluorene (2), exhibit bridged structures which self-assemble in parallel lines. The size, shape and structure of the AuNPs have been determined by means of dynamic light scattering (DLS), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). AuNPs modified with fluorenyl thiol derivatives show diameters in the range of 3-7 nm. The linkage between the nanoparticles can be envisaged with the formation of dyads supported by TEM analysis and XPS measurements. Remarkably, investigation by scanning electron microscopy of the AuNP films revealed an ordered distribution of well-separated individual nanoparticles to form a 2D network. The formation of interconnected networks between AuNPs with different distances, depending on the nature of the thiol linkers (1) or (2), and the photoluminescence properties open perspectives for applications in optical devices and electronics

A series of three novel ZnPc-C60 conjugates (Pc=phthalocyanine) 1 a-c bearing different spacers (single, double, and triple bond) between the two electroactive moieties was synthesized and compared to that of ZnPc-C60 conjugate 2, in which the two electroactive moieties are linked directly. The synthetic strategy- towards the preparation of 1 a-c- involved palladium-catalyzed cross-coupling reactions over a monoiodophthalocyanine precursor 4 to introduce the corresponding spacer, and subsequent dipolar cycloaddition reaction to C60. Detailed photophysical investigations of 1 a-c and 2 prompted an intramolecular electron transfer that evolves from the photoexcited ZnPc to the electron-accepting C60. In particular, with the help of femtosecond laser photolysis charge separation was indeed confirmed as the major deactivation channel. Complementary time-dependent density functional calculations supported the spectral assignment, namely, the spectral identity of the ZnPc(*+) radical cation and the C60 (*-) radical anion as seen in the differential absorption spectra. The lifetimes of the correspondingly formed radical ion-pair states depend markedly on the solvent polarity: they increase as polarity decreases. Similarly, although to a lesser extent, the nature of the linker impacts the lifetime of the radical ion-pair states. In general, the lifetimes of these states tend to be shortest in the system that lacks any spacer at all (2), whereas the longest lifetimes were found in the system that carries the triple-bond spacer (1 a).

Two series of tetrahedral phthalocyanine-based systems presenting a central carbon or silicon atom have been synthesized and fully characterized. Ethynyl spacers connect the peripheral Pc units to the central core. Some of the structures contain four identical Pc moieties, whereas other ones bear either an electron-withdrawing or an electron releasing group in the fourth subunit. The synthetic strategy consisted in metal mediated coupling reactions between tri-tert-butylethynylphthalocyanine and the corresponding methane or silane derivatives. A second-order nonlinear optical (NLO) study, through hyper-Rayleigh scattering measurements, reveals that, by combining centrosymmetrical moieties that are not second-order NLO active by themselves, in an octupolar fashion, a large second-order NLO response is achieved, in contrast to classical octupolar combinations of donor-acceptor NLO active dipolar moieties. In particular, the C-centered tetramer exhibits a large beta(HRS) value, which is among the highest reported so far for octupolar Pc-based molecules. Interestingly, carbon-centered molecules show a better NLO response with respect to the silicon-centered ones, probably due to a different effective symmetry, largely T(d) for the C-centered compounds and D(2d) for the Si-centered systems. While other design strategies for second-order NLO effects have always fundamentally kept on relying on the old dipolar paradigm (even though the resulting molecular structure was octupolar--the most striking exponent of this is the octupolar 1,3,5-triamino-2,4,6-trinitrobenzene molecule, a simple octupolar expansion of the dipolar p-nitroaniline), we here present for the first time that the octupolar symmetry by itself, realized by four nondipolar moieties in a tetrahedral arrangement, results also in a large second-order nonlinear response.