Anthocyanins are the main polyphenolic dyes found in young red wines, which are transformed into more stable structures such as pyranoanthocyanins, during wine ageing and maturation. While anthocyanins practically lose their red color between pH 1 and 5, as a result of the formation of colorless hemiketals, pyranoanthocyanins practically do not change their color intensity. For that they constitute a photosensitizer family with great potential for bio-inspired dye-sensitized solar cells (DSSCs). In this work, a series of pyranoanthocyanin derivatives were designed, synthesized and applied for the first time as dye sensitizers in DSSCs. A relation was established between dye structure and cell efficiency. Specifically, the influence of different linker units, carboxyl and catechol, was studied in terms of their influence in the various parameters related to DSSC efficiency. The presence of the catechol unit was shown to be essential for efficient electron injection of the dye into the TiO 2 semiconductor, since carboxylic units showed a deleterious effect in electron injection due to their electron withdrawing character. An overall efficiency of 1.15% was obtained for the best performing compound, 10-catecholpyrano-3',4',5,7tetrahydroxyplavylium, with no further optimization.

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Deep eutectic solvents (DES) composed of lithium, sodium, or potassium iodide salts in suitable combination with ethylene glycol (EG), glycerol (Gly), or polyethylene glycol (PEG) have been developed. All prepared DES were characterized by thermal analysis (DSC and TGA) and its complex conductivity (σ*) and impedance (Z*) frequency were evaluated through dielectric relaxation spectroscopy (DRS). Two-and three-electrode electrochemical studies of all DES have been performed. All DES avoid crystallization, exhibiting conductivity values in a range from 10 −4 to 10 −2 S cm −1 at room temperature and electrochemical windows higher than 1 V (on the order of 3−4 V), fulfilling the usual suitability criteria for utilization in electrochromic devices (ECD). The most promissory DES as electrolytes were tested for ECD. Being suitable candidates for further application in batteries.

The pyranoanthocyanins present in red wine display great potential as photosensitizers in bio-inspired Dye-Sensitized Solar Cells (DSSCs). Following a biomimetic approach, a series of amino-π-bridgepyranoanthocyanin derivatives were employed as dye sensitizers in DSSCs. The dimethylamine group was selected to take advantage of its electron-donor character and the possibility of 'dual-mode anchoring' (-OH vs. dimethylamino) to titanium dioxide. The increase in π-conjugation via insertion of C=C bonds affected molecule flexibility, electron-donor ability and the pH-dependent equilibria of the pyranoanthocyanin derivatives. The current vs. potential properties of photoanodes using these dyes pointed to essential features of the relationship between power conversion efficiency and dye structure. These included the influences of the dimethylamine group, of π-conjugation and of substitution in ring B on the adsorption of the dyes to TiO2 and on the overall performance of the DSSCs prepared from them with and without added acid. An overall efficiency of 2.55% was obtained for the best performing compound, 4-(dimethylamino)-cinnamyl-pyranocyanidin-3-O-glucoside (JO3), which consolidates the importance of this family of compounds as potential dye-sensitizers for DSSC applications.

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A set of 3-ethynylaryl coumarin dyes with mono, bithiophenes and the fused variant, thieno [3,2-b] thiophene, as well as an alkylated benzotriazole unit were prepared and tested for dye-sensitized solar cells (DSSCs). For comparison purposes, the variation of the substitution pattern at the coumarin unit was analyzed with the natural product 6,7-dihydroxycoumarin (Esculetin) as well as 5,7-dihydroxycomarin in the case of the bithiophene dye. Crucial steps for extension of the conjugated system involved Sonogashira reaction yielding highly fluorescent molecules. Spectroscopic characterization showed that the extension of conjugation via the alkynyl bridge resulted in a strong red-shift of absorption and emission spectra (in solution) of approximately 73–79 nm and 52–89 nm, respectively, relative to 6,7-dimethoxy-4-methylcoumarin (labs = 341 nm and lem = 410 nm). Theoretical density functional theory (DFT) calculations show that the Lowest Unoccupied Molecular Orbital (LUMO) is mostly centered in the cyanoacrylic anchor unit, corroborating the high intramolecular charge transfer (ICT) character of the electronic transition. Photovoltaic performance evaluation reveals that the thieno [3,2-b] thiophene unit present in dye 8 leads to the best sensitizer of the set, with a conversion efficiency (η = 2.00%), best VOC (367 mV) and second best Jsc (9.28 mA·cm−2), surpassed only by dye 9b (Jsc = 10.19 mA·cm−2). This high photocurrent value can be attributed to increased donor ability of the 5,7-dimethoxy unit when compared to the 6,7 equivalent (9b).

Different 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%).

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