Noémi Jordão

Novel Bipyridinium Ionic Liquids as Liquid Electrochromic Devices

Novel mono and dialkylbipyridinium (viologens) cations combined with iodide, bromide, or bis(trifluoromethanesulfonyl)imide [NTf2] as anions were developed. Selective alkylation synthetic methodologies were optimized in order to obtain the desired salts in moderate to high yields and higher purities. All prepared mono- and dialkylbipyridinium salts were completely characterized by (1)H, (13)C, and (19)F NMR spectroscopy, Fourier-transform IR spectroscopy, and elemental analysis (in the case of NTf2 salts). Melting points, glass transition temperatures by differential scanning calorimetry (DSC) studies, and decomposition temperatures were also checked for different prepared organic salts. Viscosities at specific temperatures and activation energies were determined by rheological studies (including viscosity dependence with temperature in heating and cooling processes). Electrochemical studies based on cyclic voltammetry (CV), differential pulsed voltammetry (DPV), and square-wave voltammetry (SWV) were performed in order to determine the redox potential as well as evaluate reversibility behavior of the novel bipyridinium salts. As proof of concept, we developed a reversible liquid electrochromic device in the form of a U-tube system, the most promising dialkylbipyridinium-NTf2 ionic liquid being used as the electrochromic material and the room-temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)-imide [EMIM][NTf2], as a stable and efficient electrolyte.

Deep eutectic solvents (DESs) as low-cost and green electrolytes for electrochromic devices

The application of deep eutectic solvents based on choline chloride or lithium chloride with ethylene glycol and glycerol as low-cost, recyclable and green electrolytes for electrochromic devices is reported. Reversible electrochromic devices incorporating DESs as alternative electrolytes and bipyridinium electrochromic probes have been tested and compared to conventional systems.

Reversible systems based on CO2, amino-acids and organic superbases

A group of amino-acids from a chiral pool in combination with two organic superbases (DBU or TMG) and CO2 was used to prepare carbamate-based ionic liquids and molten salts. The compounds obtained were characterized by 1H NMR, 13C NMR, FTIR, solubility profiles in reference solvents and DSC thermal analysis, including their decomposition temperature evaluation, which permitted us to check the stability/reversibility of the carbamate based salts. Its possible to tune the temperature of CO2 release according to the superbase tested as cation and the characteristics of the side chains of the amino-acids. Moreover, it was possible to solubilize a considerable variety of these carbamate functionalized amino-acids in conventional solvents.

Switchable electrochromic devices based on disubstituted bipyridinium derivatives

Gel switchable electrochromic devices based on disubstituted bipyridinium derivatives have been developed. The type of substituent from the 4,4′-bipyridinium cation and counter-ions can influence the reversibility and switching of colours of these electrochromic systems. Three switching colours (yellow, blue and red or violet) can be obtained for iodide salts due to dimer formation. In the case of bistrifluoromethanesulfonylimide [NTf2] salts only two reversible colour switches (transparent and blue) were observed. Complementary electrochromic performance including chromatic contrast (ΔT%); transition times between the bleached and coloured states; colouration efficiencies (CE), colour coordinates (CIE L*a*b*) and preliminary cycling stability studies of the devices have been performed. The higher coloration efficiency is observed in the case of [(C10)2bpy][NTf2]2 (186.9 cm2 C−1), which is similar to other bipyridinium systems already reported in the literature.

Tetramethylguanidine-based gels and colloids of cellulose

Novel and stable gels of cellulose were produced. These gels are prepared at room temperature by combination of cellulose and tetramethylguanidine (TMG) in different ratios (1:1, 1:2, 1:3 in equivalents of alcohol groups of cellulose per number of molecules of TMG). Detailed NMR, SEM, rheological and XRD studies of these gels were carried out. The concentration of cellulose in the gel, temperature, frequency of oscillation and shear rate were used as variables in order to understand the fundamentals and optimize operational conditions, considering their possible use as matrices for CO2 capture. Cellulose recovery from a specific gel was performed using ethanol as precipitating agent, leading to a lower crystallinity, which permits to consider this polymer in further studies associated to physical/chemical modification of cellulose.