Raffaella Signorini

Novel heterocycle-based two-photon absorbing dyes.

[structure: see text]. The synthesis and nonlinear optical characterization of two novel heteroaromatic-based chromophores is described. The new dyes present an A-pi-D-pi-A general framework, where A is a pi-deficient heteroaromatic ring (pyridine, quinoline, benzothiazole) and D a pi-excessive pyrrolyl moiety. Both systems exhibit large two-photon absorption (TPA) values in the femtoseconds regime (TPA cross section as high as 150 x 10(-50) cm(4) s photon(-1) molecule(-1) with 150 fs laser pulses). Their TPA-based optical limiting activity is also shown.

Push–Pull Organic Chromophores for Frequency‐Upconverted Lasing

Properly designed organic molecules where a p-conjugated bridge is end-capped by an electron-donor and electron-withdrawing group (push‐pull chromophores) can show, under specific conditions, frequency-upconverted lasing emission. Materials based on these dyes are therefore able to convert the emission of a cheap and easily available infrared (IR) laser (e.g., 800 nm radiation) into more useful visible (vis) laser emission via a two-photon absorption induced fluorescence phenomenon. The design of the molecular structure, the substituent effect, and modulation of the electronic and geometric parameters can be used in order to optimize and tune frequency emission and conversion efficiency. Examples of some of the best dyes reported to-date and organic design strategies employed are discussed in this article.

Novel heteroaromatic-based multi-branched dyes with enhanced two-photon absorption activityElectronic supplementary information (ESI) available: Experimental section. See http://www.rsc.org/suppdata/cc/b3/b305995b/

The first examples of heterocycle-based multi-branched dyes with efficient two-photon absorption (TPA) activity are reported; the novel chromophores exhibit large TPA cross sections (as high as 1600 x 10(-50) cm4 s photon(-1) molecule(-1), measured with 150 fs laser pulses at 800 nm); a strong cooperative enhancement in the branched systems with respect to the one-dimensional sub-units is found.

Linear and nonlinear optical properties of fullerenes in solid state materials

Fullerenes containing nanocomposite materials for optical applications have attracted the attention of many different research groups during the last few years. Great effort has been devoted to finding appropriate solid state materials allowing the inclusion of fullerenes: among them, polymeric, sol–gel and porous matrices have been largely investigated. Particular emphasis has been placed on the synthesis of these nanostructured materials incorporating fullerenes to reach the best control of fullerene interactions in different environments and higher fullerene dispersions in solid environments.

Investigation into the Heterostructure Interface of CdSe-Based Core-Shell Quantum Dots Using Surface-Enhanced Raman Spectroscopy

The structural nature of heterointerfaces in core-shell semiconductor quantum dots (QDs) plays a crucial role in tailoring their optical properties. In this work we have focused on using surface-enhanced Raman spectroscopy as a nondestructive tool to investigate the structural evolution of such interfaces in CdSe/CdS and CdSe/Cd0.5Zn0.5S colloidal QDs. A comparison between the two systems shows significant structural variation across the core-shell interfaces for the two different materials: a smooth interface for the former and an abrupt interface for the latter. This structural difference modifies the electronic structure within the QDs, which directly dictates the confinement behavior of the electrons and holes. The implications of this translate to a better understanding of why graded CdSe/CdS/Cd0.5Zn0.5S/ZnS QDs are so lucrative for linear and nonlinear fluorescence-based applications.

Evaluation of gold nanoparticles toxicity towards human endothelial cells under static and flow conditions.

A new in vitro model system, adding advection and shear stress associated with a flowing medium, is proposed for the investigation of nanoparticles uptake and toxicity towards endothelial cells, since these processes are normally present when nanoparticles formulations are intravenously administered. In this model system, mechanical forces normally present in vivo, such as advection and shear stress were applied and carefully controlled by growing human umbilical vein endothelial cells inside a microfluidic device and continuously infusing gold nanoparticle (Au NPs) solution in the device. The tests performed in the microfluidic device were also run in multiwells, where no flow is present, so as to compare the two model systems and evaluate if gold nanoparticles toxicity differs under static and flow culture conditions. Full characterization of Au NPs in water and in culture medium was accomplished by standard methods. Two-photon fluorescence correlation spectroscopy was also employed to map the flow speed of Au NPs in the microfluidic device and characterize Au NPs before and after interactions with the cells. Au NPs uptake in both in vitro systems was investigated through electron and fluorescence microscopy and ICP-AES, and NPs toxicity measured through standard bio-analytical tests. Comparison between experiments run in multiwells and in microfluidic device plays a pivotal role for the investigation of nanoparticle-cell interaction and toxicity assessment: our work showed that administration of equal concentrations of Au NPs under flow conditions resulted in a reduced sedimentation of nanoparticle aggregates onto the cells and lower cytotoxicity with respect to experiments run in ordinary static conditions (multiwells).

3-(Glycidoxypropyl)-trimethoxysilane–TiO2 hybrid organic–inorganic materials for optical limiting

Abstract A guest–host solid state system based on silica–titania hybrid organic–inorganic materials and fullerene derivatives has been developed for optical limiting applications. The hybrid host matrix has been prepared by sol–gel processing of 3-(glycidoxypropyl)-trimethoxysilane (GPTMS). Titanium butoxide or TiCl4 have been used in two different syntheses as the catalysts of the epoxy ring opening in GPTMS and the polyethylene oxide formation. The microstructure of the hybrid matrix has been studied by Fourier transform infra-red spectroscopy. UV–VIS spectra and optical limiting measurements of the doped materials have shown that in the TiCl4 derived matrix clustering of fulleropyrrolidine (FP) molecules is avoided and optical limiting comparable to solution samples is achieved. In the titanium butoxide derived matrix, instead, the aggregation of FP degraded the optical limiting properties. The laser damage threshold in the TiCl4 synthesized matrix has been also found to be larger than in the titanium butoxide derived material.

Effective two-photon absorption cross section of heteroaromatic quadrupolar dyes: dependence on measurement technique and laser pulse characteristics.

The linear and nonlinear optical properties of the heteroaromatic push-pull-push two-photon absorbing dye N-methyl-2,5-bis[1-(N-methylpyrid-4-yl)ethen-2-yl]-pyrrole ditriflate (PEPEP) are reported. The determination of the two-photon absorption (TPA) cross-section spectrum has been performed with different techniques: femtosecond TPA-white light continuum probe experiments, two-photon-induced fluorescence, and open aperture Z-scan measurements using both nanosecond and femtosecond laser pulses. The measured TPA cross sections and their wavelength dispersion show a marked dependence on the parameters of the laser pulses and on the measurement technique employed. These properties are discussed in terms of the different microscopic mechanisms that can contribute to the multiphoton absorption processes, with different weight depending on the measurement conditions and on the photophysical parameters of the dye.

Optical limiting and non linear optical properties of fullerene derivatives embedded in hybrid sol-gel glasses

Abstract Non linear optical properties of pyrrolidino-fullerenes in sol–gel matrix have been investigated for Optical Limiting (OL) applications. The fullerene functionalization increases the solubility in polar solvent and allows the preparation of solid materials via sol–gel method. It also extends the absorption of fullerenes to the red spectral region, where the maximum of the triplet to triplet absorption spectrum is located and, as a result, the Reverese Saturable Absorption (RSA) mechanism is enhanced. The use of the sol–gel method allows the preparation of samples with controlled thickness, with very good linear and non linear optical properties and with high damage fluences. This is useful to design and prepare a bottleneck structure, in order to optimize a laser protection device. The test of the non-linear optical properties of sol–gel samples containing fullerene derivatives has been made by optical limiting and Z-scan measurements and by comparing the experimental data with the calculated RSA behavior. Fullerene derivatives show good optical limiting performances in the red spectral region, better than fullerene. The pyrrolidino-fullerenes in sol–gel samples still show the same performances as solution samples. The comparison of the experimental data with the theoretical OL curves indicates that RSA is the predominant OL behavior, especially at 690 nm, but other different mechanisms, like non linear scattering, may contribute and are being considered in refining our theoretical model. The control of the propagation beam geometry is one of the critical point for OL measurements as well as for the optimal design of a protecting device.

Optical limiting properties of soluble fullerene derivatives for incorporation in sol–gel materials

The optical limiting properties of fullerene derivatives containing silicon alkoxide functionalities are measured in toluene solution both at 532.0 and 652.0 nm and compare favourably with those of C60.