Multi Stimuli-responsive Organic Salts: From preparation to functional device application

The discovery of novel and efficient stimuli-responsive materials that change their properties according to external stimuli and therefore, adjust to our demands become an interesting research topic for several potential applications. The integration of the most promissory stimuli-responsive materials in devices for antiglare car mirrors, smart windows, sunglasses, sensors, among others has been applied. In this thesis, the development and application of stimuli-responsive materials containing ionic photochromic or electrochromic units have been explored. In general, it is possible to incorporate specific scaffolds possessing pH, temperature, and light or electron-transfer stimuli-responsive behaviour in the cation or anion structures. Also, ionic polymers based on these structures have been investigated. In this context, 4,4’-bipyridinium, diarylethenes and flavylium were selected as electrochromic and photochromic units, respectively. For the preparation of the selected organic salts including polymers, different synthetic routes and purification processes have been followed. Detailed characterization of all prepared salts by spectroscopic techniques in order to elucidate their structures and purities has been performed. Thermal, rheological, photochemical and electrochemical properties of some prepared salts were also studied. It is important to focus that the adequate selection of the counter-ions can be crucial to achieve ionic liquids as well as to tune their final properties. The most promissory electrochromic salts based on 4,4’-bipyridinium symmetrical and non-symmetrical di and tetra-cations as well as ionic polymers were tested in liquid, gel or solid electrochromic devices. The substituents from bipyridinium scaffold as well as counter-ions can significantly influence the electrochromic performance in particular its reversibility; stability; colour contrast and transition times. Photochromic Room Temperature Ionic Liquid based on the combination of diarylethene derivative anion with tri-octyl methylammonium ([ALIQUAT]) cation was developed and characterized. Additionally, a new thermal, pH and photo-stimuli responsive co-polymer containing N-isopropylacrylamide and flavylium derivative have been prepared. The chemical versatility of the prepared ionic photo- and electrochromic materials opens excellent perspectives for future applications as efficient and reversible multi stimuli-responsive materials

Estudos de estabilidade térmica e fotoquímica de compósitos de Au/PtBA

Mestrado em Engenharia QuímicaEste projecto teve como objectivos principais a síntese de compósitos de poli(acrilato de tert-butilo) com nanopartículas de ouro, e sua caracterização através de análises térmicas e ensaios de estabilidade fotoquímica. Estes nanocompósitos foram preparados através de dois métodos: um por mistura simples dos componentes (ex situ) e o outro por miniemulsão (in situ). A síntese das nanopartículas de ouro baseou-se numa adaptação do método do poliol. O tamanho das nanopartículas, o tipo de síntese do nanocompósito e a razão entre nanopartículas / polímero influencia as características do nanocompósito. Verificou-se que a temperatura de transição vítrea (Tg) é influenciada pelo método de preparação e que decresce com a presença das nanopartículas de ouro. Comprovou-se que a presença das nanopartículas de ouro ajudam a melhorar a estabilidade térmica deste polímero. Quanto ao estudo da estabilidade fotoquímica, confirmou-se que nas condições investigadas não ocorreu modificação da estrutura do polímero.The main objectives of this project were the synthesis of composites of poly(tert-butyl acrylate) with gold nanoparticles and their characterization by thermal and photochemical stability. These nanocomposites were prepared by two distinct methods: the first is film casting (ex situ) and the other by miniemulsion (in situ). The synthesis of gold nanoparticles was based on the adaptation of polyol method. The size of nanoparticles, the type of synthesis the nanocomposite and ratio nanoparticles / polymer influenced the characteristics of nanocomposite. This study shows that glass transition temperature (Tg) is influenced by the preparation method, and that Tg decreases with the presence of gold nanoparticles. Besides, the presence of gold nanoparticles improves thermal stability for the polymer. Regarding the photochemical stability the structure of the polymer doesn’t show any changes using the conditions investigated

Alkali Iodide Deep Eutectic Solvents as Alternative Electrolytes for Dye Sensitized Solar Cells

PTDC/QEQ- QFI/1971/2014 POCI- 01-0145-FEDER-016387Different alkali deep eutectic solvents (DES), such as LiI:nEG, NaI:nEG, and KI:nEG, have been tested as electrolytes for dye sensitized solar cells (DSSCs). These DSSCs were prepared using pure DES or, alternatively, DES combined with different amounts of iodine (I2). The most important parameters, such as open circuit voltage (VOC), short circuit current density (JSC), fill factor (FF), and the overall conversion efficiency (η), were evaluated. Some DES seem to be promising candidates for DSSC applications, since they present higher VOC (up to 140 mV), similar FF values but less current density values, when compared with a reference electrolyte in the same experimental conditions. Additionally, electrochemical impedance spectroscopy (EIS) has been performed to elucidate the charge transfer and transport processes that occur in DSSCs. The values of different resistance (Ω·cm2) phenomena and recombination/relaxation time (s) for each process have been calculated. The best-performance was obtained for DES-based electrolyte, KI:EG (containing 0.5 mol% I2) showing an efficiency of 2.3%. The efficiency of this DES-based electrolyte is comparable to other literature systems, but the device stability is higher (only after seven months the performance of the device drop to 60%).publishersversionpublishe

Effect of Iodide-Based Organic Salts and Ionic Liquid Additives in Dye-Sensitized Solar Cell Performance

Funding Information: This work was performed under the project PTDC/QUI-QOR/7450/2020 “Organic Redox Mediators For Energy Conversion” through Fundação para a Ciência e a Tecnologia I. P.-FCT. Additional support includes the Associate Laboratory for Green Chemistry–LAQV, financed by national funds from FCT/MCTES (UIDB/50006/2020 and UIDP/50006/2020). FCT/MCTES is also acknowledged for the National NMR Facility (RECI/BBB-BQB/0230/2012 and RECI/BBB-BEP/0124/2012,) and Ph.D. grants 2020.09047.BD (J.S.), PD/BD/135087/2017 (A.L.P.) and PD/BD/145324/2019/ (G.M.). Publisher Copyright: © 2022 by the authors.The use of ionic liquid and organic salts as additives for electrolyte systems in dye-sensitized solar cells have been widely described in recent years. The tunability of their physical-chemical properties according to the cation–anion selection contributes toward their high efficiencies. For this purpose, several iodide-based organic salts including imidazolium, picolinium, guanidinium and alkylammonium cations were tested using acetonitrile/valeronitrile electrolytes and their photovoltaic parameters were compared. A best efficiency of 4.48% (4.15% for the reference) was found for 1-ethyl-2,3-dimethylimidazolium iodide ([C2DMIM]I) containing electrolyte, reaffirming the effectiveness of these additives. 4-tertbutylpyridine was included into the formulation to further improve the performance while determining which iodide salts demonstrate the highest synergy with this additive. [C2DMIM]I once again proved to be the superior additive, achieving an efficiency of 6.48% (6% for the reference). Electrochemical impedance spectroscopy was employed to elucidate the effects of the various additives, demonstrating the relevance of the counter electrode resistance on device performance. Finally, several computational descriptors for the cationic structures were calculated and correlated with the photovoltaic and resistance parameters, showing that properties related to polarity, namely relative positive charge, molecular polarizability and partition coefficient are in good agreement with the counter-electrode resistance.publishersversionpublishe

Development of cellulose-based polymeric structures using dual functional ionic liquids

Funding Information: This work was supported by the Associate Laboratory for Green Chemistry – LAQV which is nanced by national funds from FCT/MCTES (UIDB/50006/2020 and UIDP/50006/2020); Linking Landscape, Environment, Agriculture and Food Research Centre (LEAF), which is nanced by national funds from FCT/ MCTES (UID/AGR/04129/2020) and the national project “PTDC/ CTM-CTM/29869/2017”, which is nanced by Fundação para a Ciência e a Tecnologia (FCT). The NMR spectrometers are part of The National NMR Facility, supported by FCT/MCTES (RECI/ BBB-BQB/0230/2012). Funding Information: NMR spectra were done on a Bruker AMX 400 instrument operating at 400.13 MHz (1H), 100.61 MHz (13C). The NMR spectrometers are part of The National NMR Facility supported by Fundação para a Ciência e a Tecnologia (RECI/BBB-BQB/0230/2012). Publisher Copyright: © The Royal Society of Chemistry 2021.Carboxylate ionic liquids (ILs) combining benzethonium (BE) and didecyldimethylammonium (DDA) as cations have been explored to be used for the first time as dual functional solvents for microcrystalline cellulose (MCC) dissolution and, subsequently development of polymeric structures. Considering that some ILs can remain in the polymeric structures after phase inversion, these ILs can offer advantages such as antibacterial/antimicrobial response and ability to disrupt H-bonds. In this context, all tested ILs have been able to dissolve MCC up to a concentration of 4% (w/w), resulting in different polymeric structures, such as gel-like or films, depending on the type of IL and the ratio between MCC and IL. Furthermore, FTIR spectroscopy showed that some IL remains in the polymeric structures, which can enhance their application in the biomedical field.publishersversionpublishe

Synthesis, Characterization and an Electrochemical Study

This study was funded in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001 and FCT-CAPES project (2019–2020). The authors also thank the funding agencies FAPERJ, CNPq and Fundação para a Ciência e Tecnologia (PTDC/QUI-QOR/32406/2017, PEst-C/LA0006/2013, RECI/BBBBQB/0230/2012 as well as “SunStorage—Harvesting and storage of solar energy”, with reference POCI-01-0145-FEDER-016387. The NMR spectrometers are part of the National NMR Network (PTNMR) and are partially supported by Infrastructure Project N° 022161 (co-financed by FEDER through COMPETE 2020, POCI and PORL and FCT through PIDDAC). Ž.P. and H.C. acknowledge Fundação para a Ciência e a Tecnologia, MCTES, for the Norma Transitória DL57/2016 Program contract. A.F.M.S. also thanks FCT-MCTES for the PhD Grant (SFRH/BD/132551/2017).Ferrocene-based porous organic polymers (FPOPs) were prepared fromphenol-formaldehyde polymer (Bakelite) and phenol as starting materials; and two possible mechanisms for polymerization were discussed. Solid-state 13C CP-MAS NMR, FTIR, powder XRD, elemental analysis and ICP (Fe, Na, B) were performed to characterize the prepared materials. The two synthetic approaches produced polymers with different pore sizes: the FPOP synthesized through Bakelite presented a higher surface area (52 m2 g1) when compared to the one obtained by the bottom-up polymerization from phenol (only 5 m2 g1). Thermogravimetric analysis confirmed the thermal stability of the material, which decomposed at 350 C. Furthermore, cyclic voltammetry (CV) of the new FPOP on modified electrodes, in ACN and 0.1 M TBAP as an electrolyte, showed fully reversible electron transfer, which is similar to that observed for the ferrocene probe dissolved in the same electrolyte. As a proof-of-concept for an electrochromic device, this novel material was also tested, with a color change detected between yellow/brownish coloration (reduced form) and green/blue coloration (oxidized form). The new hybrid FPOP seems very promising for material science, energy storage and electrochromic applications, as well as for plastic degradation.publishersversionpublishe