Synthetic strategies tailoring colours in multichromophoric organic nanostructures

There has never been a time when colour did not fascinate humanity, inspiring an unceasing manufacturing of a kaleidoscopic variety of dyes and pigments that brought about great revolutions in art, cosmetics, fashion, and our lifestyle as a whole. Over the centuries these tints evolved from raw earths to molecular masterpieces devised by expert chemists whose properties are now being exploited far beyond traditional applications. Mimicking Nature, a timely challenge, regards the preparation of innovative and highly efficient multi-coloured architectures structured at the molecular and nanoscopic scale with specific light-absorbing and light-emitting properties. This tutorial review provides an overview on the chemical strategies developed to engineer and customise these ingenious coloured nanostructures tackling the current performance of organic matter in cutting edge technological sectors, such as solar energy conversion

Programming artificial antennas through templated assembly of chromophores

One of the main challenges for the creation of artificial light harvesting systems is to develop high-yielding and easy-to-implement protocols for the assembly of chromophores into spatially organized architectures. The use of a template bearing pre-programmed receptor sites accommodating selectively specific chromophores appears to be a very attractive synthetic approach. In this manuscript, pre-programmed peptides will guide the spatial arrangement of different dyes, acting as energy donors and acceptors and absorbing over the whole visible spectrum. The self-assembly of the chromophores into the scaffold can be achieved through the engineering of orthogonal recognition motifs. The employed method, described in Chapter 2, relies on the development of simultaneous multireaction systems. A triorthogonal system involving three reactions of dynamic covalent chemistry, namely disulfide exchange, boronate and acyl hydrazine formations, is first optimized for the design of triorthogonal recognition motifs. The complexity of the system is then increased by incrementally adding reactions: the strain promoted azide-alkyne cycloaddition and the inverse electron demand Diels-Alder cycloaddition between s-tetrazine and trans-cyclooctene leading to tetra- and pentaorthogonal recognition motifs. Chapters 3 and 4 address the creation of a library of multichromophoric architectures with tailored yellow, red and blue chromophores through the three simultaneous reactions of dynamic covalent chemistry. In this respect, the design and synthesis of various α-helix peptides bearing disulfide, diol and hydrazide acting as receptor sites at given positions and chromophoric units with complementary sticky sides are detailed, as well as the dyes assembly leading to excitation energy transfer within the colored structure. Finally, Chapter 5 focuses on the extension of the absorption range of the colored architectures by selectively incorporating additional dyes following their energy gradient to favor the unidirectionality of the energy transfer. This will be achieved through the introduction of the tetra- and pentaorthogonal recognition motifs within the peptide and the dyes (Figure 1)

An Efficient Imine Photocyclization as an Alternative to the Pictet-Spengler Reaction for the Synthesis of AzaBenzannulated Perylenediimide Dyes

AzaBenzannulated PDI (AzaBPDI) dyes were synthesized in high yields via a new reaction sequence involving an imine condensation followed by visible light-induced photocyclization. The large scope and efficiency of this alternative to the Pictet-Spengler reaction is demonstrated, and allows the easy preparation of dimeric AzaBPDI as potential non-fullerene acceptors for organic solar cells

A Divergent Synthetic Strategy Based on the Regioselective Reductive Ring-Opening of a Cyclic 1,2-p-Methoxybenzylidene Acetal

International audienceDibenzyl-1-[(4R)-2-(4-methoxyphenyl)-1,3dioxolan-4-yl]ethanamine is obtained in five steps from an abromo-a¢-(R)-sulfinyl ketone and is used as a common intermediate for the synthesis of the p-methoxybenzyl-protected primary and secondary alcohols, (2R,3S)-3-(dibenzylamino)-2-[(4-methoxybenzyl)oxy]butan-1-ol and (2R,3S)-3-(benzylamino)-1-[(4-methoxybenzyl)oxy]butan-2-ol, respectively. These alcohols are further exploited as precursors for the synthesis of a fully protected syn-3amino-2-hydroxybutanoic acid and an N-benzyl 2-hydroxymethylaziridine

Templated Chromophore Assembly on Peptide Scaffolds:A Structural Evolution

The use of a template bearing pre‐programmed receptor sites selectively accommodating chromophores at given positions is an attractive approach for engineering artificial light‐harvesting systems. Indulging this line of though, this work tackles the creation of tailored antenna architectures with yellow, red and blue chromophores exploiting three dynamic covalent reactions simultaneously, namely disulfide exchange, acyl hydrazone and boronic ester formations. The effect of various structural modifications, such as the chromophores as well as their spatial organization (distance, orientation, order), on the energy transfer within the antennas was studied by means of steady‐state UV‐Vis absorption and fluorescence spectroscopies. This systematic study allowed a significant improvement of the energy transfer efficiencies across the chromophores to a noticeable 22 and 15%, for the yellow and red donors to the blue acceptor, respectively. Metadynamics simulations suggested that the conformational properties of the antennas are driven by intramolecular chromophoric stacking interactions that, forcing the a‐helix to fold on itself, annul any effects deriving from the programming of the spatial arrangement of the receptor sides in the peptide backbon

CCDC 1850843: Experimental Crystal Structure Determination

Related Article: Lou Rocard, Darren Wragg, Samuel Alexander Jobbins, Lorenzo Luciani, Johan Wouters, Stefano Leoni, Davide Bonifazi|2018|Chem.-Eur.J.|24|16136|doi:10.1002/chem.201803205,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 1850844: Experimental Crystal Structure Determination

Related Article: Lou Rocard, Darren Wragg, Samuel Alexander Jobbins, Lorenzo Luciani, Johan Wouters, Stefano Leoni, Davide Bonifazi|2018|Chem.-Eur.J.|24|16136|doi:10.1002/chem.201803205,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.