Alessio Dessì

Microwave-activated synthesis of thiazolo[5,4-d]thiazoles by a condensation/oxidation sequence

A microwave-assisted preparation of symmetrical thiazolo[5,4-d]thiazoles from the corresponding aldehydes is presented. The two-step reaction sequence comprises the condensation of aldehydes with dithiooxamide followed by oxidation/aromatization with 1,4-benzoquinone derivatives. The new procedure provides the desired products in good yields and in most cases allows reduction of the excess of aldehyde employed in the process compared to previous methodologies. For the first time, application of the reaction both on aromatic and aliphatic aldehydes is demonstrated.

Thiazolo[5,4-d]thiazole-based organic sensitizers with strong visible light absorption for transparent, efficient and stable dye-sensitized solar cells

A small set of thiazolo[5,4-d]thiazole-based D–π–A organic dyes, endowed with bis-pentylpropylenedioxythiophene (ProDOT) moieties in the π-spacer, was designed with the aid of computational analysis, synthesized and characterized. The presence of bulky and electronrich ProDOT groups beside the electron poor thiazolothiazole unit induced optimal physico-chemical properties, including broad and intense visible light absorption. As a consequence, the dyes were particularly suitable for application in thin layer dye-sensitized solar cells (TiO2 thickness: 3.0–6.5 μm). Small-scale (0.25 cm2) devices prepared using standard materials and fabrication techniques gave power conversion efficiencies up to 7.71%, surpassing those obtained with two different reference dyes. Transparent larger area cells (3.6 cm2) also showed good η values up to 6.35%, not requiring the use of a co-adsorbent, and retained their initial efficiency over a period of 1000 h storage at 85 °C. These results make this new family of organic sensitizers promising candidates for successful application in the production of efficient and stable transparent DSSCs for building-integrated photovoltaics.

Towards Sustainable H2 Production: Rational Design of Hydrophobic Triphenylamine-based Dyes for Sensitized Ethanol Photoreforming

Donor-acceptor dyes are a well-established class of photosensitizers, used to enhance visible-light harvesting in solar cells and in direct photocatalytic reactions, such as H2 production by photoreforming of sacrificial electron donors (SEDs). Amines-typically triethanolamine (TEOA)-are commonly employed as SEDs in such reactions. Dye-sensitized photoreforming of more sustainable, biomass-derived alcohols, on the other hand, was only recently reported by using methanol as the electron donor. In this work, several rationally designed donor-acceptor dyes were used as sensitizers in H2 photocatalytic production, comparing the efficiency of TEOA and EtOH as SEDs. In particular, the effect of hydrophobic chains in the spacer and/or the donor unit of the dyes was systematically studied. The H2 production rates were higher when TEOA was used as SED, whereas the activity trends depended on the SED used. The best performance was obtained with TEOA by using a sensitizer with just one bulky hydrophobic moiety, propylenedioxythiophene, placed on the spacer unit. In the case of EtOH, the best-performing sensitizers were the ones featuring a thiazolo[5,4-d]thiazole internal unit, needed for enhancing light harvesting, and carrying alkyl chains on both the donor part and the spacer unit. The results are discussed in terms of reaction mechanism, interaction with the SED, and structural/electrochemical properties of the sensitizers.

The Stille Reaction: Applications in the Synthesis of Organic Dyes for DSSCs

The cross-coupling reaction of organic electrophiles with organostannanes, traditionally known as the Stille reaction, has found renewed interest in the preparation of new organic materials such as conjugated polymers, organic semiconductors and photoactive molecules for use in organic photovoltaics. Moreover, a very recent field in which the Stille reaction has found successful application is that of the design and synthesis of new photosensitizers for dye-sensitized solar cells (DSSCs). DSSCs are considered a promising alternative for energy production from renewable sources. In such devices light harvesting is carried out by a dye which is generally a highly conjugated molecule. Due to the mild operating conditions and the high functional-group compatibility, the Stille reaction proved to be a powerful tool not only for the preparation of photosensitizers, but also to plan their chemical elaboration in order to tune and optimize their photophysical, electrochemical and photovoltaic properties. In this microreview some recent examples of the Stille reaction in the synthesis of organic dyes for DSSC are reported.