Lorenzo Zani

Direct addition of alkynes to imines and related C=N electrophiles: A convenient access to propargylamines

Propargylic amines are highly useful building blocks in organic synthesis, and the corresponding structural motif has been found in various natural products and compounds of pharmaceutical relevance. This article provides an overview of the most significant advances in the preparation of propargylic amines via the direct addition of alkynes to imines and related carbon-nitrogen electrophiles in the presence of metal catalysts or promoters.

Excited State Geometries and Vertical Emission Energies of Solvated Dyes for DSSC: A PCM/TD-DFT Benchmark Study

The ability of Time-Dependent Density Functional Theory (TD-DFT) to provide excited state geometries and reproduce emission energies of organic D-π-A dyes designed for DSSC applications is evaluated. The performance of six functionals (CAM-B3LYP, MPW1K, ωB97X-D, LC-BLYP, LC-ωPBE, and M06-HF) in combination with three basis sets (cc-pVDZ, 6-31+G(d,p), and 6-311+G(2d,p)) has been analyzed. Solvent effects have been taken into account by means of a Polarizable Continuum Model in both LR and SS formalisms. Our LR-PCM/TD-DFT results show that accurate emission energies are obtained only when solvent effects are included in the computation of excited state geometries and when a range separated hybrid functional is used. Vertical emission energies are reproduced with a mean absolute error of at most 0.2 eV. The accuracy is further improved using the SS-PCM formalism.

Base-promoted elaboration of aziridines

The base-promoted isomerization of aziridines to allyl amines is still an almost unknown reaction. However, the use of superbasic reagents has shown to be able to promote a regio- and stereoselective conversion of monocyclic and bicyclic sulfonyl aziridines. Moreover, the use of alkoxy substituted aziridines opens new routes to non-natural α- and β-amino acids.

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.

Design and synthesis of organic sensitizers with enhanced anchoring stability in dye-sensitized solar cells

Abstract D-π-A dyes have received a special attention in the field of dye-sensitized solar cells (DSSCs). In this kind of molecules, the acceptor group (A) generally acts as an anchor, enabling the adsorption of the dye onto the metal oxide substrate (TiO2) and providing a good electron injection. The search for new anchors represents a critical factor for the development of improved DSSCs and in recent years has been a very active research field. This mini-review focuses especially on our work on pyridine-derived anchoring groups for D-π-A dyes, with a special regard on the preparation and characterization of three different families of dyes and a critical evaluation of their stability and efficiency.

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.