Margherita Durso

Graphene–organic hybrids as processable, tunable platforms for pH-dependent photoemission, obtained by a new modular approach

We describe a new approach to attach organic dyes to graphene oxide (GO) sheets with high loading and minimal perturbation of the electronic and optical properties of the dye. The dye unit used (a pH-sensitive terthiophene) is grafted to GO using a new modular synthetic approach, passing through a C6-aminic linker which makes GO more soluble in different organic solvents and allows straightforward attachment at high yield not only of terthiophene but of many commercially available amino-reactive dyes. The covalent engraftment to GO does not perturb the absorption and emission properties of the dye, and in particular the pH sensing capability through amidic group reversible protonation. This approach can allow (i) high solubility of the GO intermediate in organic solvents, (ii) convenient coupling with commercial, stable amino-reactive dyes under mild conditions, (iii) easy control of the spacer length between the GO and oligothiophene dye and finally (iv) high (up to 5 wt%) dye functionalization loadings.

Silk doped with a bio-modified dye as a viable platform for eco-friendly luminescent solar concentrators

The potential of fluorescent silk fibroin (SF) as a fully water-processable platform for an application in luminescent solar concentrators (LSCs) is shown. SF preserves its mechanical properties when doped with a bio-modified dye and the dye shows enhanced fluorescence when embedded in silk. These features, combined with high optical transparency and high refractive index, make SF a viable eco-friendly matrix for LSCs.

Structure–property relationships in multifunctional thieno(bis)imide-based semiconductors with different sized and shaped N-alkyl ends

The relationships between the molecular structure, packing modalities, charge mobility and light emission in organic thin films is a highly debated and controversial issue, with both fundamental and technological implications in the field of organic optoelectronics. Thieno(bis)imide (TBI) based molecular semiconductors provide an interesting combination of good processability, tunable self-assembly, ambipolar charge transport and electroluminescence, and are therefore an ideal test base for fundamental studies on the structure–property correlation in multifunctional molecular systems. Herein, we introduce a new class of thieno(bis)imide quaterthiophenes having alkyl side chains of different shapes (linear, cyclic, branched) and lengths (C1–C8). We found that contrarily to what is generally observed in most molecular semiconductors, the length of the alkyl substituent does not affect the optical, self-assembly and charge transport properties of TBI materials. However, different electroluminescence powers are observed by increasing the alkyl side, this suggesting a potential tool for the selective modulation of TBI functionalities. A deep experimental and theoretical investigation on this new family of TBI materials is provided.

A time-temperature integrator based on fluorescent and polymorphic compounds

Despite the variety of functional properties of molecular materials, which make them of interest for a number of technologies, their tendency to form inhomogeneous aggregates in thin films and to self-organize in polymorphs are considered drawbacks for practical applications. Here, we report on the use of polymorphic molecular fluorescent thin films as time temperature integrators, a class of devices that monitor the thermal history of a product. The device is fabricated by patterning the fluorescent model compound thieno(bis)imide-oligothiophene. The fluorescence colour of the pattern changes as a consequence of an irreversible phase variation driven by temperature, and reveals the temperature at which the pattern was exposed. The experimental results are quantitatively analysed in the range 20–200°C and interpreted considering a polymorph recrystallization in the thin film. Noteworthy, the reported method is of general validity and can be extended to every compound featuring irreversible temperature-dependent change of fluorescence.

Synergic effect of unsaturated inner bridges and polymorphism for tuning the optoelectronic properties of 2,3-thieno(bis)imide based materials

2,3-Thieno(bis)imide (N) ended oligomers are emerging as valuable molecular materials for applications in organic electronics. Here, we report the synthesis and characterization of three new 2,3-thieno(bis)imide ended oligothiophenes (T) bearing unsaturated ethylene (E), azomethine (I) and ethinyl (A) inner bridges (NTE, NTI and NTA, respectively). The effect of the unsaturated bridge on the π-conjugation extent, molecular conformation and overall aromaticity is related to the functional optoelectronic and morphological properties and compared to the properties of the linear analogue (NTT) with a bithiophene inner moiety. Optical spectroscopy and cyclovoltammetry analysis show a strong red shift of the absorption and an increased energy band gap on going from NTI and NTE to NTA. The HOMO level decreases in the order NTE > NTI > NTA. Moreover, while the LUMO of NTE and NTA have almost the same energy, NTI has a LUMO energy about 0.1 eV lower, likely due to the electron withdrawing effect of the azomethine moiety. Morphological investigation of solution cast thin deposits shows that the unsaturated bridges promote the formation of concomitant polymorphs with the simultaneous presence of microcrystals with different morphology and fluorescence properties. Moreover, irreversible conversion of one polymorph to the other was achieved by thermal treatments for NTA and NTE and by exploiting this feature, we realized a time temperature integrator (TTI) device based on NTE material. This device allowed to monitor temperature evolutions in the range between RT and 200 °C by means of a red to yellow fluorescence switch that was detectable by optical microscopy.

Selective MW-assisted surface chemical tailoring of hydrotalcites for fluorescent and biocompatible nanocomposites

ZnAl based hydrotalcite nanoparticles (ZnAl-HTlc NPs) were covalently modified by an organic oligothiophene fluorescent compound (T4Si) by using direct microwave (MW)-assisted silylation. Morphological and optical characterization proved that the MW-assisted method enables efficient grafting of the target fluorescent dye on the nanoparticles (NPs) surface in a few minutes with a predefined loading ratio only depending by the MW irradiation time. Moreover, the presented approach preserved the HTlc interlayer region, allowing further functionalization. Filmability, fluorescent properties, and biocompatibility of the silylated compound was also demonstrated highlighting the potential of the so-obtained lamellar NPs in applications broadening from diagnostic biomedical tools to photonics and sensing.

APTES mediated modular modification of regenerated silk fibroin in a water solution

Silk fibroin (SF) is a natural polymer of increasing interest for applications ranging from tissue engineering to optoelectronics. Here, we report a new mild and facile strategy targeted on hydroxylic pendants of serine and tyrosine residues, to functionalize SF in water, based on the use of amino(propyl)triethoxysilane (APTES), a common silylating agent. APTES is exploited as a bifunctional linker to bind SF through the triethoxysilane α-ends and to simultaneously graft species of interest, even hydrophobic ones, by means of the end γ-amino groups. By using a fluorescent oligothiophene bearing amino reacting end groups (T3) we monitor the process simply through fluorescence detection and we demonstrate the value of the proposed method to achieve chemically modified SF materials. Moreover, we show that the new SF based biocomposite retains silk filmability and transparency but also shows T3 fluorescence and markedly enhanced mechanical robustness.