Noble metal anisotropic nanostructures have achieved a growing interest in both academic and industrial domains mostly because of their shape-dependent plasmonic properties in the near-infrared region. In this paper, gold and gold-silver anisotropic nanostructures were synthesized in very high shape-yields through a wet, seed-mediated approach based on the use of nearly spherical silver nanoparticles as seeds and chitosan as stabilizing agent. Two chitosans of different origin and molecular properties were selected for the synthetic pathway, leading to the formation of variously sized and shaped end products. In detail, quite homogeneous nanoplatelets of about 25-nm size and 7-nm thickness or nearly spherical, highly porous nanocages of about 50-nm size were obtained, depending on the type of polysaccharide employed. The shape transition towards anisotropic morphologies occurred through a slow, spontaneous process, in which the chitosan nature seemed to play a key role. As expected, both nanoplatelets and nanocages exhibit shape-dependent plasmonic features and surface properties tunable for a variety of application fields. To prove this point, the nanostructures were successfully post-functionalized with poly(10,12-pentacosadiynoic acid) (PCDA), a carboxylic-endowed diacetylene able to anchor on noble metal substrates, to obtain versatile, chromic platforms suitable for sensing and spectroscopic purposes.

Poly(vinyl alcohol) nanofibrous mats containing ad hoc synthesized gold nanostructures were prepared via a single-step electrospinning procedure and investigated as a novel composite platform with several potential applications. Specifically, the effect of differently shaped and sized gold nanostructures on the resulting mat physical-chemical properties was investigated. In detail, nearly spherical nanoparticles and nanorods were first synthesized through a chemical reduction of gold precursors in water by using (hexadecyl)trimethylammonium bromide as the stabilizing agent. These nanostructures were then dispersed in poly(vinyl alcohol) aqueous solutions to prepare nanofibrous mats, which were then stabilized via a humble thermal treatment able to enhance their thermal stability and water resistance. Remarkably, the nanostructure type was proven to influence the mesh morphology, with the small spherical nanoparticles and the large nanorods leading to thinner well defined or bigger defect-rich nanofibers, respectively. Finally, the good mechanical properties shown by the prepared composite mats suggest their ease of handleability thereby opening new perspective applications.

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.

Absorption, photoluminescence, and photoinduced absorption (PIA) spectra of films of red phase polycarbazolyldiacetylenes (polyCzDAs) carrying selected acyl (polyDPCHD) or alkyl (polyDCHD-HS) groups are reported. The absorption spectrum of polyDCHD-HS, which is almost independent of the temperature down to 20 K, shows an excitonic absorption followed by an inhomogeneously broadened vibronic progression. Very different is instead the case of polyDPCHD whose thin films show a very sharp excitonic transition and a vibronic progression with a lower electron-phonon (el-ph) coupling with respect to that of polyDCHD-HS. These peculiar characteristics allow the detection of additional features in the spectra, which are assigned on the basis of quantum chemical calculations to string modes of the backbone. As far as thick films of polyDPCHD are concerned, broad electronic spectra are observed. Raman spectroscopy studies suggest that this broadening is due to the presence of two forms of the polymer. Unlike other polydiacetylenes (PDA’s) including polyDCHD-HS films, polyDPCHD films are also strongly luminescent, thus suggesting a different ordering of the dipole forbidden and allowed states. For these materials, the photoinduced absorption spectra are dominated by triplet excitons. Effects of different forms in acyl substituted polymers are observed also in the PIA spectra. The rise and decay of the triplet signal for polyDCHD-HS are accounted for through a dynamical model, which includes saturation effects in the monomolecular decay regime. A more complex kinetics is instead observed for polyDPCHD. From the study of the kinetics of the PIA spectra both the triplet generation efficiency and the density of traps are evaluated.