Assunta Marrocchi

Flow approaches towards sustainability

Green chemistry and flow chemistry are ideal partners for accessing novel chemical spaces and define highly efficient synthetic tools. In this review article contributions have been selected according to the advantages offered in terms of features that are not immediately related to classic green metrics such as minimization of reaction time, optimization for time screening, waste minimization, safety improvement, process intensification and easy scale up, energy and cost efficiency. Such features make processes in flow highly interesting in terms of developing a green and sustainable chemistry.

Poly(3-hexylthiophene): synthetic methodologies and properties in bulk heterojunction solar cells

Poly(3-hexylthiophene) (P3HT) remains of significant importance as a prototypical benchmark hole conductor material in Organic Photovoltaics (OPVs). In this review we discuss synthetic strategies to P3HT, particularly focusing on those leading to the regioregular form and discussing key physical and morphological properties. Finally, a survey and a brief discussion of P3HT performance in bulk-heterojunction (BHJ) OPVs are also provided.

Conjugated anthracene derivatives as donor materials for bulk heterojunction solar cells: olefinic versus acetylenic spacers

Substituting olefinic for acetylenic pi-spacers in anthracene-based conjugated semiconductor donors leads to appreciable increases in the power conversion efficiencies of the resulting bulk heterojunction solar cells.

Acetylene-Based Materials in Organic Photovoltaics

Fossil fuel alternatives, such as solar energy, are moving to the forefront in a variety of research fields. Organic photovoltaic systems hold the promise of a lightweight, flexible, cost-effective solar energy conversion platform, which could benefit from simple solution-processing of the active layer. The discovery of semiconductive polyacetylene by Heeger et al. in the late 1970s was a milestone towards the use of organic materials in electronics; the development of efficient protocols for the palladium catalyzed alkynylation reactions and the new conception of steric and conformational advantages of acetylenes have been recently focused the attention on conjugated triple-bond containing systems as a promising class of semiconductors for OPVs applications. We review here the most important and representative (poly)arylacetylenes that have been used in the field. A general introduction to (poly)arylacetylenes, and the most common synthetic approaches directed toward making these materials will be firstly given. After a brief discussion on working principles and critical parameters of OPVs, we will focus on molecular arylacetylenes, (co)polymers containing triple bonds, and metallopolyyne polymers as p-type semiconductor materials. The last section will deal with hybrids in which oligomeric/polymeric structures incorporating acetylenic linkages such as phenylene ethynylenes have been attached onto C60, and their use as the active materials in photovoltaic devices.

A biomass-derived safe medium to replace toxic dipolar solvents and access cleaner Heck coupling reactions

γ-Valerolactone (GVL) is an excellent reaction medium, derived from biomasses, which can replace classic dipolar aprotic media such as DMF or NMP. In this contribution, we have investigated the use of GVL in the palladium-catalyzed Heck reaction and accessed the clean synthesis of several small molecules. Furthermore, we optimized a GVL-based protocol to synthesize a poly(phenylenevinylene) (PPV) derivative in high yields and purity, and with very low Pd-content. Finally, we demonstrated that GVL is superior to conventional dipolar media in terms of controlling palladium impurities, which may influence the performance of certain optoelectronic devices such as organic solar cells and field-effect transistors.

γ-Valerolactone as an alternative biomass-derived medium for the Sonogashira reaction

γ-Valerolactone (GVL) can be used as an efficient and practical alternative to the banned and commonly used dipolar aprotic solvents. In this contribution GVL has been used as a non-toxic, biodegradable, biomass-derived medium, for the definition of a simple and general protocol for the Sonogashira cross-coupling reaction. The chemical efficiency of GVL as a medium is excellent and the best results have been obtained using DABCO as the base allowing the isolation of products 3a–q in 60–96% yields. These results represent an example which proves that biomass-derived safer solvents can be used efficiently in common transformations reaching higher greenness/sustainability as well as high chemical efficiency.

Current methodologies for a sustainable approach to π-conjugated organic semiconductors

The most effective synthetic methodologies currently employed for producing polymeric semiconductors are affected by cost, safety, and environmental issues which may seriously prevent their large-scale production. In this regard, the application of principles of green chemistry for the development of waste-minimized and cleaner synthetic approaches to semiconductor synthesis is essential for propelling the field of organic electronics. In this review, selected advances in the development of synthetic green strategies for the preparation of poly(arylene) families as well as their implication in the performance of selected opto-electronic devices such as organic thin-film transistors and bulk heterojunction solar cells are summarized.

Molecular-Shape-Controlled Photovoltaic Performance Probed via Soluble π-Conjugated Arylacetylenic Semiconductors

The synthesis and characterization of a new series of anthracene-based derivatives and their use as donors in bulk-heterojunction solar cells is reported. It is found that when using well-defined building blocks in constructing the chromophore, the donor molecular shape dramatically affects organic photovoltaic (OPV) performance in a previously unrecognized way.

Comprehensive Photophysical Behaviour of Ethynyl Fluorenes and Ethynyl Anthracenes Investigated by Fast and Ultrafast Time-Resolved Spectroscopy

Detailed investigations by time-resolved transient absorption and fluorescence spectroscopies with nano- and femtosecond time resolutions are carried out with the aim of characterising the lowest excited singlet and triplet states of three ethynyl fluorenes (1-3) and three ethynyl anthracenes (4-6) in solvents of different polarity. The solvent is found to modify the deactivation pathways of the lowest excited singlet state of compounds 1-4, thus changing their fluorescence, intersystem crossing and internal conversion efficiencies. The fluorescence and triplet yields gradually decrease, while the internal conversion quantum yield increases upon increasing the solvent dielectric constant. These experimental results, coupled with the marked fluorosolvatochromic effect, point to the involvement of an emitting state with a charge-transfer (CT) character, strongly stabilised by polar solvents. This is proved by ultrafast spectroscopic studies in which two transients, distinguished by characteristic spectral shapes assigned to locally excited (LE) and CT states, are detected, the CT state being the longer lived and fluorescent one in highly polar solvents. The intramolecular LE→CT process, operative in highly polar media, becomes particularly fast (up to ≈300 fs) in the case of the NO(2) derivative 1. No push-pull character is found for 5 and 6, which exhibit different photophysical behaviour; indeed, the solvent polarity does not modify significantly the dynamics of the lowest excited singlet states. Quantum mechanical calculations at the TDDFT level are also used to determine the state order and nature of the lowest excited singlet and triplet states and to rationalise the different photophysical behaviour of fluorine and anthracene derivatives, particularly concerning the intersystem crossing process.

High Pressure Diels-Alder Reactions of 2-Vinyl-3,4-Dihydronaphthalene. Synthesis of Cyclopenta[c]- and Indeno[c]Phenanthrenones.

Abstract A new shorter synthesis of 2-vinyl-3,4-dihydro-naphthalene has been described. The Diels-Alder reactions of this diene with 4-acetoxy-2-cyclopenten-1-one, 3-bromoindan-1-one and inden-1-one under high pressure conditions are reported. A two step synthesis of cyclopenta[c]-and indeno[c]phenanthrenones is discussed. Structure analysis by 1 H and 13 C NMR spectroscopy is presented.