The Rainbow Arching over the Fluorescent Thienoviologen Mesophases.

Thermofluorochromic materials exhibit tunable fluorescence emission on heating or cooling. They are highly desirable for applications ranging from temperature sensing to high-security anti-counterfeiting. Luminescent matrices based on liquid crystals are very promising, particularly those based on liquid crystals with intrinsic fluorescence. However, only a few examples have been reported, suggesting ample margins for development in the field, due to the wide range of fluorophores and supramolecular organizations to be explored. Moreover, thermofluorochromic liquid crystals can be tailored with further functionalities to afford multi-stimuli responsive materials. For the first time, herein we report the thermofluorochromism of thienoviologen liquid crystals, already known to show bulk electrochromism and electrofluorochromism. In particular, we studied their photophysics in the 25 °C-220 °C range and as a function of the length of the N-linear alkyl chains, m (9 ≤ m ≤ 12 C atoms), and the type of anion, X (X = OTs-, OTf-, BF4-, NTf2-). Interestingly, by changing the parameters m, X and T, their fluorescence can be finely tuned in the whole visible spectral range up to the NIR, by switching among different mesophases. Importantly, by fixing the structural parameters m and X, an interesting thermofluorochromism can be achieved for each thienoviologen in a homologous series, leading to a switch of the emitted light from red to green and from white to blue as a consequence of the temperature-induced variation in the supramolecular interactions in the self-assembled phases.

Developing functionalized Fe3O4-Au nanoparticles: a physico-chemical insight.

Nanotechnology for biomedicine has recently attracted increasing interest from the scientific community. In particular, among the different nanodevices suitable for this application, multifunctionalizable hybrid nanoparticles are one of the most investigated research topics. Here we present a detailed physico-chemical characterization of hybrid magneto-plasmonic iron oxide-gold nanoparticles (NPs) with core-shell structure. In particular, we underline all the synthetic difficulties concerning the preparation of these systems. Based on all our results, after different tests of a commonly reported protocol for the synthesis of the core-shell system, we believe that several issues are still open in the synthetic preparation of these particular NPs. Indeed, at least for the conditions that we adopted, core-shell morphology nanoparticles cannot be produced. However, independent of the core structure, we describe here an optimized and efficient functionalization protocol to obtain stable nanoparticle aqueous suspensions, which can be easily exported to other kinds of metal and metal-oxide NPs and used to develop biocompatible systems. Furthermore, reliable information that could be useful for researchers working in this field is extensively discussed.

A microscopic insight into the deformation behavior of semicrystalline polymers: the role of phase transitions.

The deformation behavior of semicrystalline polymers associated with polymorphic transformations under tensile deformation is discussed in the case of syndiotactic polypropylene. We report a phase diagram of this polymer where the regions of stability of the different polymorphic forms are defined as a function of the degree of stereoregularity and deformation. The values of critical strain corresponding to the structural transformations depend on the stereoregularity that affects the relative stability of the involved polymorphic forms and the state of the entangled amorphous phase.

Synthesis and characterization of high-molecular-weight syndiotactic amorphous polypropylene.

Heterocycle-fused titanium indenyl silylamido dimethyl complexes produce very high molecular weight polypropylene having a prevailingly syndiotactic microstructure with syndiotactic pentad contents rrrr up to 40-55% (sam-PP). The samples are basically amorphous and may slowly develop a low level of crystallinity (16-20%) at room temperature. A structural characterization has shown that sam-PP samples crystallize in disordered modifications of the helical form I of syndiotactic polypropylene (s-PP). The stretching of compression-molded films of sam-PP samples produce oriented crystalline fibers in the trans-planar mesomorphic form of s-PP. The low stereoregularity prevents the formation of the ordered trans-planar form III of s-PP, which instead is obtained in stretched fibers of the highly stereoregular and crystalline s-PP. The trans-planar mesomorphic form, obtained in stretched fibers, in turn transforms into the helical form I upon releasing the tension. The analysis of the mechanical properties has shown that sam-PP samples show good elastic behavior in a large range of deformation with remarkable strength, due to the presence of crystallinity. A comparison with the mechanical properties of less syndiotactic and fully amorphous samples is reported. These fully amorphous samples present lower strength and experience rapid viscous flow of the chains at high deformations and/or by application of stresses for long times. The higher strength in the semicrystalline sam-PP samples makes these materials interesting thermoplastic elastomers showing high toughness and ductility.

Influence of regio- and stereoregularity of propene insertion on crystallization behavior and elasticity of ethene-propene copolymers.

Melting enthalpies of several ethene-propene samples, obtained by different single-center catalytic systems and having widely different constitutions and compositions in the range of industrial interest, are compared. For the first time, a clear evidence of influence of the regio- and stereoregularity of propene insertion on crystallization behavior of ethene/propene copolymers is provided. This influence is in qualitative agreement with the results of simplified energy calculations relative to models of pseudo-hexagonal packing of ethene-propene copolymers.