Marina Alloisio

Functionalized Au/Ag nanocages as a novel fluorescence and SERS dual probe for sensing.

We obtained chitosan-protected Au/Ag nanocages (NCs), i.e., hollow and porous metallic nanoparticles, by galvanic replacement reaction. Subsequently, we functionalized the NCs with a fluorescent derivative of 4-methoxy-1,8-naphtalimide (NAFTA6). The plasmonic properties of these structures, which exhibit an extinction maximum in the 700-800 nm range, allowed their use as SERS active substrates for excitation at 785 nm and an efficient identification of the vibrational bands of NAFTA6, in spite of the low ligand concentration (<10(-5) M). Furthermore, NAFTA6 could also be identified from its fluorescence emission. The proposed functionalization with fluorescent compounds opens the way to the application of metal NCs using double-wavelength detection. Namely, Raman spectroscopy in the near infrared and fluorescence emission in the visible region, with considerable potential especially for in vivo medical applications, as the plasmonic band is centered in the visible light region where biological fluids and tissues are transparent.

Polydiacetylenes for photonic application: chemical modulation of optical properties

Abstract Highly soluble alkyl-substituted derivatives of the polycarbazolyldiacetylene, with a particularly large value of the off-resonance third-order non-linearity have been obtained in our laboratories. In order to investigate the role played by the electron-donating character of the carbazolyl groups on the optical and electronic properties of the material, we have synthetized diacetylenic monomers carrying electron-withdrawing acyl-substituents on the carbazolyl rings. Acyl-substituents CH 3 (CH 2 ) n CO– with n =10,14,16 were introduced. The polymers derived by thermal polymerization of the microcrystalline monomers are sparingly soluble and only very dilute solutions are stable at room temperature. However, thin films of the polymers of excellent optical quality are obtained by solution casting of a monomer layer on various substrates, followed by thermal polymerization. These films have been characterized by spectroscopic techniques and by preliminary measurements of third-order susceptibility. Particular attention has been dedicated to the study of both their thermal and photochemical behavior.

Photoinduced absorption spectra in polydiacetylenes for non linear optical applications

Abstract We report on the absorption, photoluminescence and photoinduced absorption of polydiacetylenes (PDAs) having in the side groups the photoconductive carbazolyl rings substituted by acyl CO(CH 2 ) n CH 3 chains ( n =10, polyDLCHD; n =14, polyDPCHD). A novel feature in the absorption spectra is detected and assigned on the basis of theoretical calculation including the electron correlation. Different features are observed in the photoexcitations spectra of thin and thick samples and a preliminary interpretation is proposed.

Synthesis of Fluorescent Core-Shell Metal Nanohybrids: A Versatile Approach

A flexible way of fabricating core-shell noble metal-organic nanohybrids with tailored chemical and spectroscopic properties is proposed here. The synthetic protocol consists of a multi-step procedure able to guarantee acceptable reproducibility of core size and shape as well as control of the organic outer layer. The proposed method highlights limitations in obtaining highly controllable products, although the heterogeneity degree of the nanostructures is in line with that expected from bottom-up approaches in solution. Selective functionalization of the nanohybrids with properly-substituted fluorescent dyes under variable experimental conditions allowed the preparation of composite systems of tunable spectroscopic properties to be employed as nanoprobes in sensing or photonic applications. To this end, preliminary investigation on embedding the nanohybrids in compatible polymeric matrices is also reported.

Optical and electronic properties of thin PDAs films with very narrow excitonic bandwidth

Soluble polycarbazolyldiacetylene systems (PCDAs) having long alkyl chains on the carbazolyl substituents have been recently prepared. In these systems, PCDAs chains in the solid state are assembled in hexagonal columnar structures. Thin films of these PCDAs show a very high value for the third order susceptibility. In order to study the effect of the substituents in the electronic properties of PCDAs we have inserted -CO(CH 2 ) n CH 3 groups on the carbazolyl rings, thus decreasing the electron-donor effect of carbazole. Non-birefringent thin films of excellent optical quality are obtained whose optical and electronic properties are here reported.

Optoelectronic properties of oligomers based on tetrazine, benzothiadiazole, benzodithiophene and thiophene moieties for photovoltaic applications: a theoretical study

Herein, a theoretical design addressed to the synthesis of new conjugated co-polymers for organic photovoltaic devices based on tetrazine, benzothiadiazole, dithiophene and thiophene moieties has been applied. This theoretical investigation aims to explore which combination of these molecules could be the most promising for photovoltaic applications, by studying their intrinsic electronic properties. In particular, the simulated values of the band gap energy and the open circuit voltage are the parameters to be taken into account for the selection of potential materials for solar cell devices. The results shows that the most suitable combination, giving rise to low band gaps, higher absorption coefficients and with an interesting offset of the HOMO and LUMO energy levels, is the bridge-linked copolymer which alternates the benzodithiophene and the benzothiadiazole moieties, likely because of their push–pull effect.

Soluble polydiacetylenes: molecular properties and solid state organization

Abstract The solution properties of a novel soluble polydiacetylene, poly[1,6-bis(3,6-dihexadecyl- N -carbazolyl)-2,4-hexadiyne] (polyDCHD-HS), have been investigated by use of spectroscopic (UV–VIS absorption, fluorescence and FT-Raman) and light scattering techniques in benzene and toluene. The unique spectroscopic and molecular properties of these solutions are reported and discussed in relation to the particular interactions of the polymer substituents with aromatic solvents. The introduction of the long alkyl-substituents on the carbazolyl side groups not only improves the processability relative to the parent unsubstituted polymer but also suppresses the chromic effects observed in other soluble polydiacetylenes. The side groups are also responsible for the peculiar supramolecular organization observed in the powder phase of the red form.

INVESTIGATION OF NANOSTRUCTURED METAL/POLYMER INTERFACES BY SURFACE ENHANCED RAMAN SCATTERING

Surface Enhanced Raman Scattering (SERS) experiments were performed on different interfaces consisting of nanostructured metals and ultra-thin layers of conjugated polymers. The Raman electromagnetic enhancement ensured by the surface roughness of different metals (Au, Ag or Al) permitted the monitoring of the optical and spectroscopic properties of ultra-thin polymer layers. In particular, in the case of a novel carbazolyldiacetylene deposited by self assembling on rough silver films or used as a capping agent for gold nanoparticles and subsequently polymerized by UV radiation, SERS experiments permitted detection of two polymer phases, characterized by a different degree of order in the polymer backbone: the highly conjugated blue phase and the less-extended red conformation.

Vibrational properties of novel diacetylenic monomers

The frequency and intensity of the infrared and Raman CC modes have been investigated for a large number of molecules. A series of symmetrical and asymmetrical substituted diacetylenic monomers having the carbazole group attached directly or indirectly to the diacetylenic backbone have been studied in their microcrystalline or liquid state. A qualitative assignment has been proposed and particular attention has been given to those systems for which a peculiar behaviour of the infrared and Raman intensities has been observed. This behaviour is found when the diacetylenic skeleton is directly attached to either the 9H-carbazolyl or triethylsilyl group.