Supramolecular Chalcogen-Bonded Semiconducting Nanoribbons at Work in Lighting Devices

D. Romito, E. Fresta, L. M. Cavinato, H. Kählig, H. Amenitsch, L. Caputo, Y. Chen, P. Samorì, J.- C. Charlier, R. D. Costa, D. Bonifazi. Angew. Chem. Int. Ed. 2022, e202202137. DOI: 10.1002/anie.202202137 Abstract This work describes the design and synthesis of a π-conjugated telluro[3,2-β][1]-tellurophene-based synthon that, embodying pyridyl and haloaryl chalcogen-bonding acceptors, self-assembles into nanoribbons through chalcogen bonds. The ribbons π-stack in a multi-layered architecture both in single crystals and thin films. Theoretical studies of the electronic states of chalcogen-bonded material showed the presence of a local charge density between Te and N atoms. OTFT-based charge transport measurements showed hole-transport properties for this material. Its integration as a p-type semiconductor in multi-layered CuI-based light-emitting electrochemical cells (LECs) led to a 10-fold increase in stability (38 h vs. 3 h) compared to single-layered devices. Finally, using the reference tellurotellurophene congener bearing a C−H group instead of the pyridyl N atom, a herringbone solid-state assembly is formed without charge transport features, resulting in LECs with poor stabilities (<1 h).

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Orbital Mapping of Semiconducting Perylenes on Cu(111)

G. Di Santo, T. Miletić, M. Schwendt, Y. Zhou, B. M. Kariuki, K. D. M. Harris, L. Floreano, A. Goldoni, P. Puschnig, L. Petaccia, D. Bonifazi. J. Phys. Chem. C 2021, 125, 44, 24477–24486. DOI: 10.1021/acs.jpcc.1c05575 Abstract Semiconducting O-doped polycyclic aromatic hydrocarbons constitute a class of molecules whose optoelectronic properties can be tailored by acting on the π-extension of the carbon-based frameworks and on the oxygen linkages. Although much is known about their photophysical and electrochemical properties in solution, their self-assembly interfacial behavior on solid substrates has remained unexplored so far. In this paper, we have focused our attention on the on-surface self-assembly of O-doped bi-perylene derivatives. Their ability to assemble in ordered networks on Cu(111) single-crystalline surfaces allowed a combination of structural, morphological, and spectroscopic studies. In particular, the exploitation of the orbital mapping methodology based on angle-resolved photoemission spectroscopy, with the support of scanning tunneling microscopy and low-energy electron diffraction, allowed the identification of both the electronic structure of the adsorbates and their geometric arrangement. Our multi-technique experimental investigation includes the structure determination from powder X-ray diffraction data for a specific compound and demonstrates that the electronic structure of such large molecular self-assembled networks can be studied using the reconstruction methods of molecular orbitals from photoemission data even in the presence of segregated chiral domains.

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Oxygen-Doped PAH Electrochromes: Difurano, Dipyrano, and Furano-Pyrano Containing Naphthalene-Cored Molecules

J. F.- Charles, R. R. Ferreira, M. Abraham, D. Romito, M. Oppel, L. González, D. Bonifazi. Eur. J. Org. Chem., 2021, e202101166. DOI: 10.1002/ejoc.202101166 Abstract In this work, we report the synthesis of O-doped naphthalene-based electrochromes. Exploiting the CuO-mediated Pummerer oxidative cycloetherification reaction, a series of 1,4- and 1,5-disubstituted naphthalene-cored dipyrano, difurano, and furano-pyrano polycyclic aromatic hydrocarbons (PAHs) have been prepared. Steady-state UV-Vis absorption and emission investigations showed that the spectroscopic profile strongly depends on the O-doping topology, with the dipyrano and the difurano derivatives demonstrating the most red-shifted and blue-shifted electronic transition, respectively. Computational investigations revealed that the cycloetherification reaction raises the HOMO energy level (while the LUMO remains largely unaffected), with the dipyrano derivatives displaying the highest values. Spectroelectrochemical measurements showed that, depending on the O-topology and the type of O-ring, different electrochromic responses could be obtained with colour transitions featuring high contrasts involving yellow, pink, orange or blue colours.

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2D materials hybrid heterostructures: achievements and challenges towards high throughput fabrication

L. Maggini, R. Ferreira. J. Mater. Chem. C, 2021, 9, 15721-15734. DOI: 10.1039/D1TC04253J Abstract 2D materials attracted tremendous interest since the discovery of graphene, because of their unique optical/electronic/mechanical properties, and their manipulable bidimensional morphology. Since forthcoming technologies require a stringent yet faceted portfolio of features, hardly feasible by a single pristine material, the demand for property tuning and multifunctionality has led to the development of hybrid 2D materials heterostructures to modulate and exploit the synergy between two or more materials and achieve novel properties. Because of their straightforwardness of implementation and rich variety of possible combinations, these hybrid architectures, held together mostly by non–covalent interactions, virtually allow the fabrication of any kind of assembly offering a unique opportunity for fine–tuning of the materials properties. However, reproducibility, scale–up, assembly into ordered structures and processability are the challenges yet to address to technologically harness their full potential, and enable their integration into mass produced commercial devices. In this perspective article we analyse the recent developments in the automatised production of hybrid solution processed 2D materials heterostructures, especially emphasising on the technologies that are currently closer to achieving low–cost, high–throughput standardised production, namely spray coating, inkjet printing and 3D printing, to sense the direction this research field is taking in pursuit of the development of commercialisable products.

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peri-Xanthenoxanthene (PXX): a Versatile Organic Photocatalyst in Organic Synthesis

C. Pezzetta, A. Folli, O. Matuszewska, D. Murphy, R. W. M. Davidson, D. Bonifazi. Adv. Synth. Catal. 2021, 363, 1-15. DOI: 10.1002/adsc.202100030 Abstract Recent years have witnessed a continuous development of photocatalysts to satisfy the growing demand of photophysical and redox properties in photoredox catalysis, with complex structures or alternative strategies devised to access highly reducing or oxidising systems. We report herein the use of peri-xanthenoxanthene (PXX), a simple and inexpensive dye, as an efficient photocatalyst. Its highly reducing excited state allows activation of a wide range of substrates, thus triggering useful radical reactions. Benchmark transformations such as the addition of organic radicals, generated by photoreduction of organic halides, to radical traps are initially demonstrated. More complex dual catalytic manifolds are also shown to be accessible: the β-arylation of cyclic ketones is successful when using a secondary amine as organocatalyst, while cross-coupling reactions of aryl halides with amines and thiols are obtained when using a Ni co-catalyst. Application to the efficient two-step synthesis of the expensive fluoro-tetrahydro-1H-pyrido[4,3-b]indole, a crucial synthetic intermediate for the investigational drug setipiprant, has been also demonstrated.

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Substituent-Controlled Tailoring of Chalcogen-Bonded Supramolecular Nanoribbons in the Solid State

N. Biot, D. Romito, D. Bonifazi. Cryst. Growth Des. 2021, 21, 1, 536–543. DOI: 10.1021/acs.cgd.0c01318 Abstract In this work, we design and synthesize supramolecular 2,5-substituted chalcogenazolo[5,4-β]pyridine (CGP) synthons arranging in supramolecular ribbons at the solid state. A careful choice of the combination of substituents at the 2- and 5-positions on the CGP scaffold is outlined to accomplish supramolecular materials by means of multiple hybrid interactions, comprising both chalcogen and hydrogen bonds. Depending on the steric and electronic properties of the substituents, different solid-state arrangements have been achieved. Among the different moieties on the 5-position, an oxazole unit has been incorporated on the Se- and Te-congeners by Pd-catalyzed cross-coupling reaction and a supramolecular ribbon-like organization was consistently obtained at the solid state.

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BN-Doped Metal–Organic Frameworks: Tailoring 2D and 3D Porous Architectures through Molecular Editing of Borazines

F. Fasano, J. Dosso, G. Bezzu, M. Carta, F. Kerff, N. Demitri, B. -L. Su, D. Bonifazi. Chem. Eur. J. 2021 , 27, 4124 –4133. DOI: 10.1002/chem.202004640 Abstract Building on the MOF approach to prepare porous materials, herein we report the engineering of porous BN-doped materials using tricarboxylic hexaarylborazine ligands, which are laterally decorated with functional groups at the full-carbon ‘inner shell’. Whilst an open porous 3D entangled structure could be obtained from the double interpenetration of two identical metal frameworks derived from the methyl substituted borazine, the chlorine-functionalised linker undergoes formation of a porous layered 2D honeycomb structure, as shown by single-crystal X-ray diffraction analysis. In this architecture, the borazine cores are rotated by 60° in alternating layers, thus generating large rhombohedral channels running perpendicular to the planes of the networks. An analogous unsubstituted full-carbon metal framework was synthesised for comparison. The resulting MOF revealed a crystalline 3D entangled porous structure, composed by three mutually interpenetrating networks, hence denser than those obtained from the borazine linkers. Their microporosity and CO2 uptake were investigated, with the porous 3D BN-MOF entangled structure exhibiting a large apparent BET specific surface area (1091 m2 g−1) and significant CO2 reversible adsorption (3.31 mmol g−1) at 1 bar and 273 K.

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Harnessing Selectivity and Sensitivity in Ion Sensing via Supramolecular Recognition: A 3D Hybrid Gold Nanoparticle Network Chemiresistor

V. Montes-García, R. F. de Oliveira, Y. Wang, A. Berezin, P. Fanjul-Bolado, M. B. G. García, T. M. Hermans, D. Bonifazi, S. Casalini, P. Samorì. Adv. Funct. Mater. 2020, 2008554. DOI: 10.1002/adfm.202008554 Abstract The monitoring of K+ in saliva, blood, urine, or sweat represents a future powerful alternative diagnostic tool to prevent various diseases. However, several K+ sensors are unable to meet the requirements for the development of point‐of‐care (POC) sensors. To tackle this grand‐challenge, the fabrication of chemiresistors (CRs) based on 3D networks of Au nanoparticles covalently bridged by ad‐hoc supramolecular receptors for K+, namely dithiomethylene dibenzo‐18‐crown‐6 ether is reported here. A multi‐technique characterization allows optimizing a new protocol for fabricating high‐performing CRs for real‐time monitoring of K+ in complex aqueous environments. The sensor shows exceptional figures of merit: i) linear sensitivity in the 10–3 to 10–6 m concentration range; ii) high selectivity to K+ in presence of interfering cations (Na+, Ca2+, and Mg2+); iii) high shelf‐life stability (>45 days); iv) reversibility of K+ binding and release; v) successful device integration into microfluidic systems for real‐time monitoring; vi) fast response and recovery times (<18 s), and v) K+ detection in artificial saliva. All these characteristics make the supramolecular CRs a potential tool for future applications as POC devices, especially for health monitoring where the determination of K+ in saliva is pivotal for the early diagnosis of diseases.

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Organic room-temperature phosphorescence from halogen-bonded organic frameworks: hidden electronic effects in rigidified chromophores

J. Zhou, L. Stojanović, A. A. Berezin, T. Battisti, A. Gill, B. M. Kariuki, D. Bonifazi, R. C. Otero, M. R. Wasielewski, Y. L. Wu. Chem. Sci., 2021, 12, 767-773. DOI: 10.1039/D0SC04646A Abstract Development of purely organic materials displaying room-temperature phosphorescence (RTP) will expand the toolbox of inorganic phosphors for imaging, sensing or display applications. While molecular solids were found to suppress non-radiative energy dissipation and make the RTP process kinetically favourable, such an effect should be enhanced by the presence of multivalent directional non-covalent interactions. Here we report phosphorescence of a series of fast triplet-forming tetraethyl naphthalene-1,4,5,8-tetracarboxylates. Various numbers of bromo substituents were introduced to modulate intermolecular halogen-bonding interactions. Bright RTP with quantum yields up to 20% was observed when the molecule is surrounded by a Br⋯O halogen-bonded network. Spectroscopic and computational analyses revealed that judicious heavy-atom positioning suppresses non-radiative relaxation and enhances intersystem crossing at the same time. The latter effect was found to be facilitated by the orbital angular momentum change, in addition to the conventional heavy-atom effect. Our results suggest the potential of multivalent non-covalent interactions for excited-state conformation and electronic control.

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Synthetic strategies tailoring colours in multichromophoric organic nanostructures

O. Kulyk, L. Rocard, L. Maggini and D. Bonifazi Chem. Soc. Rev., 2020, 49, 8400. DOI: 10.1039/C9CS00555B Abstract 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.

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