Publications

Abstract A systematic synthetic study was performed to explain the usual trend in selectivity towards multi-coupling, over mono-coupling, in Suzuki-Miyaura reactions. This preference was observed under different reaction conditions: for various halobenzenes, using substituents on the boronic acid, and changing the catalyst and temperature. Moreover, this reaction selectivity was found to increase for more reactive systems towards oxidative addition and more diluted media. The results constitute experimental evidence that the formation of the totally substituted coupling product is kinetically favoured by a reaction path location-the proximity between the regenerated catalyst and the newly formed coupling intermediate promotes the subsequent reaction.

Abstract Microdroplets and thin films of imidazolium-based ionic liquids (ILs) of different sizes and shapes were used as confining agents for the formation of high-quality perylene crystals by vapor deposition. The role of ILs to control the nucleation and subsequent crystal growth of perylene was investigated by sequential and simultaneous depositions of both materials using indium tin oxide (ITO) as the underlying substrate. The deposition of ILs onto the perylene film surface led to the formation of a complete 2D wetting layer, followed by island growth. Higher adhesion and affinity were found for longer-chain ILs. Inverting the deposition order, the perylene microcrystals were found to grow via the ILs droplets. Additionally, the nucleation and growth of perylene monocrystals enhanced the coalescence mechanisms of the ILs droplets. This wetting process was especially evident for longer-chain ILs. The deposition of perylene onto ITO surfaces fully covered with coalesced ionic liquid films led to the formation of a perylene film with the highest homogeneity as the result of a decrease in surface mobility. The co-deposition of perylene and ILs emphasized the potential application of ILs as crystallization solvents for the formation of thin organic films with improved crystalline quality without compromising the optoelectronic properties.

Abstract The wetting behavior of ionic liquids (ILs) on the mesoscopic scale considerably impacts a wide range of scientific fields and technologies. Particularly under vacuum conditions, these materials exhibit unique characteristics. This work explores the effect of the deposition rate and substrate temperature on the nucleation, droplet formation, and droplet spreading of ILs films obtained by thermal evaporation. Four ILs were studied, encompassing an alkylimidazolium cation (C(n)C(1)im) and either bis(trifluoromethylsulfonyl)imide (NTf2) or the triflate (OTf) as the anion. Each IL sample was simultaneously deposited on surfaces of indium tin oxide (ITO) and silver (Ag). The mass flow rate was reproducibly controlled using a Knudsen cell as an evaporation source, and the film morphology (micro- and nanodroplets) was evaluated by scanning electron microscopy (SEM). The wettability of the substrates by the ILs was notably affected by changes in mass flow rate and substrate temperature. Specifically, the results indicated that an increase in the deposition rate and/or substrate temperature intensified the droplet coalescence of [C(2)C(1)im][NTf2] and [C(2)C(1)im][OTf] on ITO surfaces. Conversely, a smaller impact was observed on the Ag surface due to the strong adhesion between the ILs and the metallic film. Furthermore, modifying the deposition parameters resulted in a noticeable differentiation in the droplet morphology obtained for [C(8)C(1)im][NTf2] and [C(8)C(1)im][OTf]. Nevertheless, droplets from long-chain ILs deposited on ITO surfaces showed intensified coalescence, regardless of the deposition rate or substrate temperature.

Abstract This work reports the formation of silver nanoparticles (AgNPs) by sputter deposition in thin films of three different ionic liquids (ILs) with the same anion (bis(trifluoromethylsulfonyl)imide) and cation (imidazolium), but with different alkyl chain lengths and symmetries in the cationic moiety ([C(4)C(1)im][NTf2], [C(2)C(2)im][NTf2], and [C(5)C(5)im][NTf2]). Ionic liquid (IL) films in the form of microdroplets with different thicknesses (200 to 800 monolayers) were obtained through vacuum thermal evaporation onto glass substrates coated with indium tin oxide (ITO). The sputtering process of the Ag onto the ILs when conducted simultaneously with argon plasma promoted the coalescence of the ILs' droplets and the formation, incorporation, and stabilization of the metallic nanoparticles in the coalesced IL films. The formation/stabilization of the AgNPs in the IL films was confirmed using high-resolution scanning electron microscopy (SEM) and UV-Vis spectroscopy. It was found that the IL films with larger thicknesses (600 and 800 monolayers) were better media for the formation of AgNPs. Among the ILs used, [C(5)C(5)im][NTf2] was found to be particularly promising for the stabilization of AgNPs. The use of larger IL droplets as capture media was found to promote a better stabilization of the AgNPs, thereby reducing their tendency to aggregate.

Abstract Diels-Alder cycloaddition is a common synthetic approach to functionalize fullerenes. However, the stability of such fullerene adducts is hampered by the existence of the Retro Diels-Alder (RDA) reaction. Herein, the RDA reactions in the solid phase of the mono and bisadducts of C60 with indene, IC60MA and IC60BA, were studied by differential scanning calorimetry and thermogravimetric analysis. The RDA reaction in solid IC60MA occurs at a higher temperature than in IC60BA. IC60MA decomposition follows a first-order rate law and in IC60BA it is described by two consecutive first-order reaction steps. The decomposition of both adducts yields a metastable C60 solid. The higher decomposition temperature of IC60MA is due to higher activation energy, Ea, and lower preexponential factor, A. The values of Ea for the RDA reactions differ due to crystal packing efficiency in the solids. The measured A values were found to reflect the statistical weight of C60-Indene bonds that can be broken. A reaction mechanism was proposed for the decomposition of the fullerene adducts. The enthalpies of sublimation of IC60MA and IC60BA were estimated based on the enthalpies of their respective RDA reactions. Additionally, the heat capacities of the solid fullerenes (C60, IC60MA, and IC60BA), at T = 298.15 K, were measured by highprecision heat capacity drop calorimetry, indicating that the rotational motion of C60 in the crystal increases its expected heat capacity.

Abstract Decaphenylbiphenyl (1) and 2,2',4,4',6,6'-hexaphenylbiphenyl (2) are bulky molecules expected to be greatly destabilized by steric crowding. Herein, through a combined experimental and computational approach, we evaluate the molecular energetics of crowded biphenyls. This is complemented by the study of phase equilibria for 1 and 2. Compound 1 shows a rich phase behavior, displaying an unusual interconversion between two polymorphs. Surprisingly, the polymorph with distorted molecules of C-1 symmetry is found to have the highest melting point and to be the one that is preferentially formed. The thermodynamic results also indicate that the polymorph displaying the more regular D-2 molecular geometry has larger heat capacity and is probably the more stable at lower temperatures. The melting and sublimation data clearly reveal the weakening of cohesive forces in crowded biphenyls due to the lower molecular surface area. The experimental quantification of the intramolecular interactions in 1 and 2 indicated, using homodesmotic reactions, a molecular stabilization of about 30 kJ mol(-1). We attribute the origin of this stabilization in both compounds to the existence of two parallel-displaced pMIDLINE HORIZONTAL ELLIPSISp interactions between the ortho-phenyl substituents on each side of the central biphenyl. Computational calculations with dispersion-corrected DFT methods underestimate the stabilization in 1, unless the steric crowding is well balanced in a homodesmotic scheme. This work demonstrates that London dispersion forces are important in crowded aromatic systems, making these molecules considerably more stable than previously thought.

Abstract Perovskite solar cells (PSCs) have emerged as a promising technology for renewable energy generation due to their low cost and low carbon footprint compared to traditional silicon-based solar cells. However, some main challenges associated with PSCs lie ahead, namely their toxicity and lack of stability, particularly under factors such as light, temperature, oxygen, and humidity. This review focuses on the lack of stability of PSCs and the various ways it can be mitigated. We explore different methodologies, solution and vapor based, and different strategies for PSC production and enhancing. Furthermore, the potential of ionic liquids (ILs) as promising materials for improving the stability and performance of PSCs is highlighted. ILs have advantageous physicochemical properties that make them suitable as an additive or interfacial layer in PSCs. They optimize the interface contact, improve energy level matching, suppress ion migration, and increase hydrophobicity, which inhibits the decomposition of the device in humid environments. ILs have also been used as precursors in the solution-based fabrication of perovskite thin films for PSC applications, assisting in the perovskite crystallization. Several studies have shown that the incorporation of ILs in PSCs can increase stability, lifetime, and efficiency. The existing research indicates that ILs hold great promise as materials for improving the stability and performance of PSCs, which could have significant implications for the development of low-cost, renewable energy technologies. © 2023, Universidade do Porto - Faculdade de Engenharia. All rights reserved.

Abstract Evaluationof the sustainability of using vineyard pruningwaste extracts as natural additives for biodiesel production is discussed,along with comparative impacts with butylated hydroxytoluene. The control of the oxidative stability of biodiesel andblendsof biodiesel with diesel is one of the major concerns of the biofuelindustry. The oxidative degradation of biodiesel can be acceleratedby several factors, and this is most critical in the so-called secondgeneration biodiesel, which is produced from low-cost raw materialswith lower environmental impacts. The addition of antioxidants isimperative to ensure the oxidative stability of biodiesel, and theseare considered products of high commercial value. The antioxidantscurrently available on the market are from synthetic origin, so theexistence/availability of alternative antioxidants of natural origin(less dependent on fossil sources) at a competitive price presentsitself as a strong business opportunity. This work describes and characterizesa sustainable alternative to synthetic antioxidants used in the biodieselmarket developed from extracts of vineyard pruning waste (VPW), whichare naturally rich in phenolic compounds with antioxidant properties.A hydrothermal extraction process was applied as a more efficientand sustainable technology than the conventional one with the potentialof the extracts as antioxidant additives in biodiesel evaluated inRancitech equipment. The VPW extract showed comparable antioxidantactivity as the commercial antioxidant butylated hydroxytoluene (BHT)typically used in biodiesel. The stability of the biodiesel is dependentfrom the amount of the extract added. Further, for the first time,the assessment of the environmental impacts of using natural extractsto control the oxidative stability of biodiesel in the productionprocess is also discussed as a key factor of the process environmentalsustainability.