Multifunctional Photoelectroactive Materials for Optoelectronic Applications Based on Thieno[3,4-b]pyrazines and Thieno[1,2,5]thiadiazoles.

In this study, we introduce a novel family of symmetrical thiophene-based small molecules with a Donor-Acceptor-Donor structure. These compounds feature three different acceptor units: benzo[c][1,2,5]thiadiazole (Bz), thieno[3,4-b]pyrazine (Pz), and thieno[1,2,5]thiadiazole (Tz), coupled with electron donor units based on a carbazole-thiophene derivative. Using Density Functional Theory (DFT), we investigate how the molecular geometry and strength of the central acceptor unit impact the redox and spectroscopic properties. Notably, the incorporation of Pz and Tz moieties induces a significant redshift in the absorption and emission spectra, which extend into the near-infrared (NIR) region, simultaneously reducing their energy gaps (~1.4-1.6 eV). This shift is attributed to the increased coplanarity of the oligomeric inner core, both in the ground (S0 ) and excited (S1 ) states, due to the enhanced quinoidal character as supported by bond-length alternation (BLA) analysis. These structural changes promote better π-electron delocalization and facilitate photoinduced charge transfer processes in optoelectronic devices. Notably, we show that Pz- and Tz-containing molecules exhibit NIR electrochromic behavior and present ambivalent character in bulk heterojunction (BHJ) solar cells. Finally, theoretical calculations suggest that these molecules could serve as effective two-photon absorption (2PA) probes, further expanding their potential in optoelectronic applications.

Biobased and Compostable Multiblock Copolymer of Poly(l-lactic acid) Containing 2,5-Furandicarboxylic Acid for Sustainable Food Packaging: The Role of Parent Homopolymers in the Composting Kinetics and Mechanism.

In the last years, the exponential growth in the demand of petroleum-based plastic materials, besides the extreme exploitation of nonrenewable resources, lead to the mismanagement of their disposal and to serious ecological issues related to their dispersion in the environment. Among the possible practical solutions, the design of biobased and biodegradable polymers represents one of the most innovative challenges. In such a context, the eco-design of an aromatic-aliphatic multiblock copolymer based on poly(lactic acid) and containing 2,5-furandicarboxylic acid was carried out with the aim of improving the properties of poly(l-lactic acid) for sustainable packaging applications. The synthetic method followed a novel top-down approach, starting from industrial high-molecular-weight poly(l-lactic acid) (PLLA), which was reacted with 1,5-pentanediol to get hydroxyl-terminated PLLA and then chain-extended with hydroxyl-terminated poly(pentamethylene furanoate) (PPeF-OH). The final copolymer, called P(LLA50PeF50)-CE, was subjected to molecular, structural, and thermal characterization. Tensile and gas permeability tests were also carried out. According to the results obtained, PLLA thermal stability was improved, being the range of processing temperatures widened, and its stiffness and brittleness were decreased, making the new material suitable for the realization of films for flexible packaging. The oxygen permeability of PLLA was decreased by 40% and a similar improvement was measured also for carbon dioxide. P(LLA50PeF50)-CE was found to be completely biodegraded within 60 days of composting treatment. In terms of mechanism, the blocks of PPeF and PLLA were demonstrated to undergo surface erosion and bulk hydrolysis, respectively. In terms of kinetics, PPeF blocks degraded slower than PLLA ones.

Ionic Push-Pull Polythiophenes: A Further Step towards Eco-Friendly BHJ Organic Solar Cells.

Four new conjugated polymers alternating benzothiadiazole units and thiophene moieties functionalized with ionic phosphonium or sulfonic acid salts in the side chains were synthesized by a postfunctionalization approach of polymeric precursors. The introduction of ionic groups makes the conjugated polymers soluble in water and/or polar solvents, allowing for the fabrication of bulk heterojunction (BHJ) solar cells using environmentally friendly conditions. All polymers were fully characterized by spectroscopic, thermal, electrochemical, X-ray diffraction, scanning electron, and atomic force techniques. BHJ solar cells were obtained from halogen-free solvents (i.e., ethanol and/or anisole) by blending the synthesized ionic push-pull polymers with a serinol-fullerene derivative or an ionic homopolymer acting as electron-acceptor (EA) or electron-donor (ED) counterparts, respectively. The device with the highest optical density and the smoothest surface of the active layer was the best-performing, showing a 4.76% photoconversion efficiency.

EQCM Analysis of the Insertion Phenomena in a n-Doped Poly-Alkyl-Terthiophene With Regioregular Pattern of Substitution.

In the present work, we have undertaken the study of the n-doping process in poly-3,3″-didodecyl-2,2':5',2″-terthiophene (poly-33″-DDTT) employing the electrochemical quartz crystal microbalance (EQCM). The present study aims at understanding how cathodic charge in n-doped poly-33″-DDTT is compensated. For this purpose, the in situ analysis of the variations of the polymeric mass has been considered. Poly-33″-DDTT was obtained as a thin coating onto a metallic substrate via the anodic coupling of the corresponding monomer 3,3″-didodecyl-2,2':5',2″-terthiophene (33″-DDTT). When subjected to electrochemical n-doping in the polarization interval -2.5 ≤ E appl ≤ 0 V vs. Ag/Ag+, the films of poly-33″-DDTT varied their mass according to a mechanism of cations insertion during n-doping and cations extraction during polymer neutralization. In fact, the electrochemical doping of polythiophenes requires the accompanying exchange of charged species to maintain the electroneutrality within the structure of the polymer in all states of polarization. At the end of a full electrochemical cycle (consisting of the n-doping and the successive neutralization of poly-33″-DDTT), the polymer retains a fraction of the mass acquired during n-doping, thus manifesting the phenomena of mass trapping. The combined analysis of electrochemical and microgravimetric data suggests that poly-33″-DDTT in the n-doped state undergoes (or electrocatalyzes) uncontrolled electrochemical reactions that are not accompanied by mass variations.

Influence of the Active Layer Structure on the Photovoltaic Performance of Water-Soluble Polythiophene-Based Solar Cells.

A new side-chain C60-fullerene functionalized thiophene copolymer bearing tributylphosphine-substituted hexylic lateral groups was successfully synthesized by means of a fast and effective post-polymerization reaction on a regioregular ω-alkylbrominated polymeric precursor. The growth of the polymeric intermediate was followed by NMR spectrometry in order to determine the most convenient reaction time. The obtained copolymer was soluble in water and polar solvents and was used as a photoactive layer in single-material organic photovoltaic (OPV) solar cells. The copolymer photovoltaic efficiency was compared with that of an OPV cell containing a water-soluble polythiophenic homopolymer, functionalized with the same tributylphosphine-substituted hexylic side chains, in a blend with a water-soluble C60-fullerene derivative. The use of a water-soluble double-cable copolymer made it possible to enhance the control on the nanomorphology of the active blend, thus reducing phase-segregation phenomena, as well as the macroscale separation between the electron acceptor and donor components. Indeed, the power conversion efficiency of OPV cells based on a single material was higher than that obtained with the classical architecture, involving the presence of two distinct ED and EA materials (PCE: 3.11% vs. 2.29%, respectively). Moreover, the synthetic procedure adopted to obtain single material-based cells is more straightforward and easier than that used for the preparation of the homopolymer-based BHJ solar cell, thus making it possible to completely avoid the long synthetic pathway which is required to prepare water-soluble fullerene derivatives.

Effect of regioregularity and role of heteroatom on the chiral behavior of oligo(heteroalkyl thiophene)s.

Novel optically active oligothiophenes bearing electron-donating chiral side chains have been prepared by synthetic methods suitable to achieve regioregular head-to-tail and head-to-head/tail-to-tail derivatives. In particular, the chiral (S)-(2-methyl)butyl moiety was linked at position 3 of the thiophene ring through heteroatoms, such as S or O, to evaluate its effect on the macro molecular aggregation and, consequently, on the chiroptical properties of the material in the solid state. The materials have been fully characterized and investigated by optical and chiroptical methods upon aggregation both from the solution and as cast films. Compared with the related head-to-tail and head-to-head/tail-to-tail poly(3-alkyl)thiophene derivatives, with the same optically active moiety directly linked to the ring and possessing a higher polymerization degree, the chiroptical properties of the newly synthesized oligomers were significant, or even better, and provided insight into the role of intrachain-interchain interactions between the heteroatom and the thienyl sulfur atom.

Multifunctional Platform Based on Electrospun Nanofibers and Plasmonic Hydrogel: A Smart Nanostructured Pillow for Near-Infrared Light-Driven Biomedical Applications.

Multifunctional nanomaterials with the ability to respond to near-infrared (NIR) light stimulation are vital for the development of highly efficient biomedical nanoplatforms with a polytherapeutic approach. Inspired by the mesoglea structure of jellyfish bells, a biomimetic multifunctional nanostructured pillow with fast photothermal responsiveness for NIR light-controlled on-demand drug delivery is developed. We fabricate a nanoplatform with several hierarchical levels designed to generate a series of controlled, rapid, and reversible cascade-like structural changes upon NIR light irradiation. The mechanical contraction of the nanostructured platform, resulting from the increase of temperature to 42 °C due to plasmonic hydrogel-light interaction, causes a rapid expulsion of water from the inner structure, passing through an electrospun membrane anchored onto the hydrogel core. The mutual effects of the rise in temperature and water flow stimulate the release of molecules from the nanofibers. To expand the potential applications of the biomimetic platform, the photothermal responsiveness to reach the typical temperature level for performing photothermal therapy (PTT) is designed. The on-demand drug model penetration into pig tissue demonstrates the efficiency of the nanostructured platform in the rapid and controlled release of molecules, while the high biocompatibility confirms the pillow potential for biomedical applications based on the NIR light-driven multitherapy strategy.

The Importance of Excellent π-π Interactions in Poly(thiophene)s To Reach a High Third-Order Nonlinear Optical Response.

Poly(thiophene)s have an inherently large third-order nonlinear optical (TONO) response, but applications are not straightforward due to unoptimized materials. Therefore, several structure-property relationships (molar mass, branching, regioregularity) are investigated to unravel which structural modifications give the highest TONO response. Poly(3-hexylthiophene) with different molar masses, poly[3-(2-ethylhexyl)thiophene] with different molar masses, and random copolymers with different degrees of regioregularity are synthesized and measured by UV-vis spectroscopy and the third harmonic scattering technique. Every structural modification that leads to an increase in π-π interactions in poly(thiophene)s leads to an increase in the TONO response of the material. Therefore, a material with a high molar mass, an unbranched alkyl side chain, and a high regioregularity degree is preferably tested as a promising TONO material.

Thermodynamically versus Kinetically Controlled Self-Assembly of a Naphthalenediimide-Thiophene Derivative: From Crystalline, Fluorescent, n-Type Semiconducting 1D Needles to Nanofibers.

The control over aggregation pathways is a key requirement for present and future technologies, as it can provide access to a variety of sophisticated structures with unique functional properties. In this work, we demonstrate an unprecedented control over the supramolecular self-assembly of a semiconductive material, based on a naphthalenediimide core functionalized with phenyl-thiophene moieties at the imide termini, by trapping the molecules into different arrangements depending on the crystallization conditions. The control of the solvent evaporation rate enables the growth of highly elaborated hierarchical self-assembled structures: either in an energy-minimum thermodynamic state when the solvent is slowly evaporated forming needle-shaped crystals (polymorph α) or in a local energy-minimum state when the solvent is rapidly evaporated leading to the formation of nanofibers (polymorph ß). The exceptional persistence of the kinetically trapped ß form allowed the study and comparison of its characteristics with that of the stable α form, revealing the importance of molecular aggregation geometry in functional properties. Intriguingly, we found that compared to the thermodynamically stable α phase, characterized by a J-type aggregation, the ß phase exhibits (i) an unusual strong blue shift of the emission from the charge-transfer state responsible for the solid-state luminescent enhancement, (ii) a higher work function with a "rigid shift" of the electronic levels, as shown by Kelvin probe force microscopy and cyclic voltammetry measurements, and (iii) a superior field-effect transistor mobility in agreement with an H-type aggregation as indicated by X-ray analysis and theoretical calculations.

Enantiopure polythiophene nanoparticles. Chirality dependence of cellular uptake, intracellular distribution and antimicrobial activity.

The use of intrinsic chiral molecules opens the door to bio-imaging specific tools and to the development of target-therapy. In this work the synthesis and characterization of polythiophenes with alkyl side chains containing one R or S chiral carbon is reported. Enantiopure chiral nanoparticles (R or S NPs) were prepared from the polymers by a reprecipitation method. UV-vis, photoluminescence and circular dichroism spectroscopy of the NPs are described. In vitro analysis and metabolic assays show that both R and S NPs are efficiently taken-up by fibroblast cells without signs of toxicity. SDS-PAGE experiments show that formation of hard protein 'corona' enhances the chirality difference between nanoparticles. Co-localization experiments demonstrate that the cells are able to discriminate between the enantiomeric R and S nanoparticles. Finally, experiments carried out on Gram negative and Gram positive bacteria show that the enantiomeric NPs display different antibacterial activity.

Poly(3-hexylthiophene) Nanoparticles Containing Thiophene-S,S-dioxide: Tuning of Dimensions, Optical and Redox Properties, and Charge Separation under Illumination.

We describe the preparation of poly(3-hexylthiophene-S,S-dioxide) nanoparticles using Rozen's reagent, HOF·CH3CN, either on poly(3-hexylthiophene) (P3HT) or on preformed P3HT nanoparticles (P3HT-NPs). In the latter case, core-shell nanoparticles (P3HT@PTDO-NPs) are formed, as confirmed by X-ray photoelectron spectroscopy measurements, indicating the presence of oxygen on the outer shell. The different preparation modalities lead to a fine-tuning of the chemical-physical properties of the nanoparticles. We show that absorption and photoluminescence features, electrochemical properties, size, and stability of colloidal solutions can be finely modulated by controlling the amount of oxygen present. Atomic force microscopy measurements on the nanoparticles obtained by a nanoprecipitation method from preoxidized P3HT (PTDO-NPs) display spherical morphology and dimensions down to 5 nm. Finally, Kelvin probe measurements show that the coexistence of p- and n-type charge carriers in all types of oxygenated nanoparticles makes them capable of generating and separating charge under illumination. Furthermore, in core-shell nanoparticles, the nanosegregation of the two materials, in different regions of the nanoparticles, allows a more efficient charge separation.

Novel Random PBS-Based Copolymers Containing Aliphatic Side Chains for Sustainable Flexible Food Packaging.

In the last decade, there has been an increased interest from the food packaging industry toward the development and application of biodegradable and biobased plastics, to contribute to the sustainable economy and to reduce the huge environmental problem afflicting the planet. In this framework, the present paper describes the synthesis of novel PBS (poly(butylene succinate))-based random copolymers with different composition containing glycol sub-units characterized by alkyl pendant groups of different length. The prepared samples were subjected to molecular, thermal, diffractometric and mechanical characterization. The barrier performances to O2, CO2 and N2 gases were also evaluated, envisioning for these new materials an application in food packaging. The presence of the side alkyl groups did not alter the thermal stability, whereas it significantly reduced the sample crystallinity degree, making these materials more flexible. The barrier properties were found to be worse than PBS; however, some of them were comparable to, or even better than, those of Low Density Polyethylene (LDPE), widely employed for flexible food packaging. The entity of variations in the final properties due to copolymerization were more modest in the case of the co-unit with short side methyl groups, which, when included in the PBS crystal lattice, causes a more modest decrement of crystallinity degree.

Chirality induced by microaggregation of regioregular polythiophenes with side-chain optically active substituent.

Two novel optically active terthiophene and bithiophene monomers bearing at the C-ß position of thiophene ring an enantiomerically pure chiral alkyl group, namely 3,3″-di[2-((S)-(+)-2-methylbutoxy)ethyl]-2,2':5',2″-terthiophene and 3,3'-di[2-((S)-(+)-2-methylbutoxy)ethyl]-2:2'-bithiophene, have been synthesized and characterized. Being symmetrically substituted, their polymerization adopting simple and economic method, such as the chemical oxidation with iron (III) trichloride, allowed to obtain regioregular macromolecules. The synthesized polymers have been investigated by CD in solution as well as in the microaggregated state upon gradual addition of a poor solvent. The results display different CD behaviors related to their chemical structure.

Supramolecular chirality and reversible chiroptical switching in new chiral liquid-crystal azopolymers.

The synthesis of chiral liquid-crystalline polymers of well-controlled structure (linear and three-armed star-shaped) with distinct average chain lengths and low polydispersity was achieved by atom transfer radical polymerisation (ATRP) of a new optically active monomer (S)-4-[6-(2-methacryloyloxypropanoyloxy)hexyloxy)]-4'-ethoxyazobenzene [(S)-ML6A], containing the L-lactic residue of one absolute configuration in the side-chain. All the obtained polymeric samples, characterised by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarised optical microscopy (POM), exhibit a smectic A(1/2) (fully interdigitated) liquid-crystalline phase and high cleaning points, with transition temperatures dependent on the average polymerisation degree and the macromolecular structure. The chirality originated at the molecular level by the asymmetric functionality of the L-lactic acid residue provides the polymers, in the smectic phase, of highly homogeneous conformations with a prevailing chirality related to the presence of H-aggregates having conformational dissymmetry of one prevailing screw-sense. By irradiating with circularly polarised light (CPL), it is possible to photomodulate the chiroptical properties of these intrinsically chiral polymeric thin films. Upon irradiation with left-handed CPL (l-CPL), the circular dichroism (CD) spectra of the films show enhancement of ellipticity and a net inversion of sign. The effect is reversible and the mirror image of the CD spectrum can be restored by pumping with right-handed CPL radiation (r-CPL). The results show the ability of l-CPL to invert the supramolecular chirality of the materials and demonstrate the essential role of azoaromatic aggregates.