Dye-sensitized photocatalytic hydrogen generation is emerging as a promising process to produce fuels using a clean and abundant energy source such as sunlight. In the first part of this work, three organic dyes featuring a dithieno[3,2-b:2′,3′-d]silole heterocyclic unit (OB1−OB3), bearing different substituents on various parts of the molecular scaffold, were synthesized, characterized, and used as sensitizers for the commercially available benchmark TiO 2 (P25), first in dye-sensitized solar cells and then for the photocatalyzed production of hydrogen with triethanolamine as a sacrificial electron donor. In the second part of the study, aiming to improve the efficiency of the photocatalytic system, P25 was replaced with the less investigated brookite TiO 2 polymorph. The photocatalyst obtained upon sensitization with the best performing dye, OB2, still in the presence of Pt as co-catalyst, displayed an enhanced performance in hydrogen production compared to that based on P25 at a lower dye loading. Extended time experiments confirmed that the catalyst was still significantly active after 1 week under continuous illumination, providing a maximum TON of 4201. The higher efficiency of the brookite-based catalytic system and its prolonged stability are especially significant in the perspective of the practical application of the dye-sensitized photocatalytic H 2 production technology.

Photocatalytic hydrogen production has recently emerged as a promising process for the long-term storage of solar energy. In this work, we studied the application of a series of heterogeneous photocatalysts obtained by sensitizing Pt/TiO2 nanoparticles with 10 different D-π-A organic dyes containing the benzo­[c]­[1,2,5]­thiadiazole (BTD) heterocyclic moiety in H2 generation. Starting from the known DSSC sensitizer RK-1, our approach involved the systematic and simultaneous alteration of several important structural features, such as steric bulk and hydrophobicity/hydrophilicity in different parts of the molecules, giving rise to a set of compounds with diverse physico-chemical properties. Visible light-driven H2 generation studies conducted with the dye-sensitized photocatalysts together with different sacrificial electron donors (SEDs) revealed that both their overall hydrogen production efficiency and their relative order of performances could be altered by the choice of SED and the corresponding reaction conditions. In particular, the best results were obtained with dyes having a strongly hydrophobic central core and a hydrophilic donor section in combination with ascorbic acid as the electron donor. In addition, the effect of changing the dye loading and extending the reaction time was examined, resulting in a stable three-component photocatalytic system displaying high activity up to 72 h of experiment.

The preparation and spectroscopic characterization of some symmetrical small molecules containing the disubstituted (E)-3,3′-bifuranylidene-2,2′-dione chromophore (the so-called Pechmann lactone) and featuring an extended conjugation are reported. The synthetic approach of such compounds is based on the Stille–Migita coupling reaction, which is carried out in very mild conditions, suitable to be applied with the very sensitive Pechmann core. The absorption and emission spectra of the new molecules obtained have been recorded in solution and clearly show how their photophysical properties can be modulated by a proper choice of the (hetero)aromatic terminal groups. The compounds prepared in this study (or close analogues thereof) have interesting optical properties and could find application as semiconductors in organic electronics or as near-IR fluorescent dyes.

Luminescent solar concentrators (LSCs) are a class of optical devices able to harvest, downshift, and concentrate sunlight, thanks to the presence of emitting materials embedded in a polymer matrix. Use of LSCs in combination with silicon-based photovoltaic (PV) devices has been proposed as a viable strategy to enhance their ability to harvest diffuse light and facilitate their integration in the built environment. LSC performances can be improved by employing organic fluorophores with strong light absorption in the center of the solar spectrum and intense, red-shifted emission. In this work, we present the design, synthesis, characterization, and application in LSCs of a series of orange/red organic emitters featuring a benzo[1,2-b:4,5-b′]dithiophene 1,1,5,5-tetraoxide central core as an acceptor (A) unit. The latter was connected to different donor (D) and acceptor (A′) moieties by means of Pd-catalyzed direct arylation reactions, yielding compounds with either symmetric (D–A–D) or non-symmetric (D–A–A′) structures. We found that upon light absorption, the compounds attained excited states with a strong intramolecular charge-transfer character, whose evolution was greatly influenced by the nature of the substituents. In general, symmetric structures showed better photophysical properties for the application in LSCs than their non-symmetric counterparts, and using a donor group of moderate strength such as triphenylamine was found preferable. The best LSC built with these compounds presented photonic (external quantum efficiency of 8.4 ± 0.1%) and PV (device efficiency of 0.94 ± 0.06%) performances close to the state-of-the-art, coupled with a sufficient stability in accelerated aging tests.