Self-assembly and spectroscopic fingerprints of photoactive pyrenyl tectons on hBN/Cu(111)

D. M. Zimmermann, K. Seufert, L. Ðorđević, T. Hoh,S. Joshi, T. Marangoni, D. Bonifazi, W. Auwärter. Beilstein J. Nanotechnol., 2020, 11, 1470–1483. DOI: 10.3762/bjnano.11.130 Abstract The controlled modification of electronic and photophysical properties of polycyclic aromatic hydrocarbons by chemical functio-nalization, adsorption on solid supports, and supramolecular organization is the key to optimize the application of these compounds in (opto)electronic devices. Here, we present a multimethod study comprehensively characterizing a family of pyridin-4-ylethynyl-functionalized pyrene derivatives in different environments. UV–vis measurements in toluene solutions revealed absorption at wavelengths consistent with density functional theory (DFT) calculations, while emission experiments showed a high fluorescence quantum yield. Scanning tunneling microscopy (STM) and spectroscopy (STS) measurements of the pyrene derivatives adsorbed on a Cu(111)-supported hexagonal boron nitride (hBN) decoupling layer provided access to spatially and energetically resolved molecular electronic states. We demonstrate that the pyrene electronic gap is reduced with an increasing number of substituents.Furthermore, we discuss the influence of template-induced gating and supramolecular organization on the energies of distinct molecular orbitals. The selection of the number and positioning of the pyridyl termini in tetrasubstituted, trans- and cis-like-disubstituted derivatives governed the self-assembly of the pyrenyl core on the nanostructured hBN support, affording dense-packed arrays and intricate porous networks featuring a kagome lattice.

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Targeting G Protein‐Coupled Receptors with Magnetic Carbon Nanotubes: The Case of the A3 Adenosine Receptor

F. Pineux, S. Federico, K. N. Klotz, S. Kachler, C. Michiels, M. Sturlese, M. Prato, G. Spalluto, S. Moro, D. Bonifazi. ChemMedChem, 2020, 15, 1909 –1920. DOI: 10.1002/cmdc.202000466 Abstract The A3 adenosine receptor (AR) is a G protein‐coupled receptor (GPCR) overexpressed in the membrane of specific cancer cells. Thus, the development of nanosystems targeting this receptor could be a strategy to both treat and diagnose cancer. Iron‐filled carbon nanotubes (CNTs) are an optimal platform for theranostic purposes, and the use of a magnetic field can be exploited for cancer magnetic cell sorting and thermal therapy. In this work, we have conjugated an A3AR ligand on the surface of iron‐filled CNTs with the aim of targeting cells overexpressing A3ARs. In particular, two conjugates bearing PEG linkers of different length were designed. A docking analysis of A3AR showed that neither CNT nor linker interferes with ligand binding to the receptor; this was confirmed by in vitro preliminary radioligand competition assays on A3AR. Encouraged by this result, magnetic cell sorting was applied to a mixture of cells overexpressing or not the A3AR in which our compound displayed indiscriminate binding to all cells. Despite this, it is the first time that a GPCR ligand has been anchored to a magnetic nanosystem, thus it opens the door to new applications for cancer treatment.

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1,8,10-Trisubstituted anthracenyl hydrocarbons: Towards versatile scaffolds for multiple-H-bonded recognition arrays

S. Forensia, A. Stopin, F. de Leo, J. Wouters, D. Bonifazi. Tetrahedron, 2020, 76, 131299. DOI: 10.1016/j.tet.2020.131299 Abstract In this work, we describe the synthesis of 1,8,10-trisubstituted anthracenyl scaffolds that, bearing boronic acid functionalities, can act as multiple H-bonding donor systems. The trisubstituted anthracenyl derivatives are synthesized following two main synthetic pathways. Whereas in the first approach trisubstituted anthracenyl derivatives are prepared through the regioselective addition of the relevant organomagnesium nucleophile to 1,8-dichloroanthraquinone, in the second avenue a triflate-bearing anthracene is prepared by reduction of the anthraquinone into the anthrone precursor and functionalized through metal-catalysed cross-coupling reactions. Complementary studies of the Na2S2O4-mediated reduction of 1,8-dichloroanthraquinone allowed to shed further light on the possible mechanism of formation of the anthrone precursor, suggesting the presence of a cis-diol intermediate undergoing antiperiplanar elimination. Solid-state X-ray diffraction investigations of the bisboronic acids show that the molecules self-assemble into dimers through the formation of four H-bonds established between the anti–syn conformers of the boronic acid moieties. 1H-NMR titrations between bisboronic acids and tetra H-bond acceptor, diisoquinolino-naphthyridine, showed a significant shift of the -B(OH)2 proton resonances, suggesting the presence of H-bonding interactions between both molecules.

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Revealing the Impact of Heat Generation Using Nanographene-Based Light-Emitting Electrochemical Cells

E. Fresta, J. Dosso, J. Cabanillas-Gonzalez, D. Bonifazi, R. D. Costa. ACS Appl. Mater. Interfaces, 2020, 12, 28426−28434. DOI: 10.1021/acsami.0c06783 Abstract Self-heating in light-emitting electrochemical cells (LECs) has been long overlooked, while it has a significant impact on (i) device chromaticity by changing the electroluminescent band shape, (ii) device efficiency because of thermal quenching and exciton dissociation reducing the external quantum efficiency (EQE), and (iii) device stability because of thermal degradation of excitons and eliminate doped species, phase separation, and collapse of the intrinsic emitting zone. Herein, we reveal, for the first time, a direct relationship between self-heating and the early changes in the device chromaticityas well as the magnitude of the error comparing theoretical/experimental EQEs that is,an overestimation error ofca. 35% at usual pixel working temperatures of around 50°C. This has been realized in LECs using a benchmark nanographene that is, a substituted hexa-peri-hexabenzocoronene as an emerging class of emitters with outstanding device performance compared to the prior art of small-molecule LECs for example, luminances of 345 cd/m2 and EQEs of 0.35%. As such, this work is a fundamental contribution highlighting how self-heating is a critical limitation toward the optimization and wide use of LECs.

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O-Annulation to Polycyclic Aromatic Hydrocarbons: A Tale of Optoelectronic Properties from Five- to Seven-Membered Rings

L. Đorđević, D. Milano, N. Demitri, D. Bonifazi. Org. Lett., 2020, 22, 11, 4283–4288. DOI: 10.1021/acs.orglett.0c01331 Abstract We take advantage of the Pummerer oxidative annulation reaction to extend PAHs through the formation of an intramolecular C-O bond with a suitable phenol substituent. Depending on the peripheral topology of the PAH precursor (e.g., pyrene, boron-dipyrromethene, or perylene diimide) five-, six-, and seven-membered O-containing rings could be obtained. The effect of the O-annulations on the optoelectronic properties were studied by various methods with the pyrano-annulated pyrene and BODIPY derivatives depicting quantitative emission quantum yields.

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Configurational Selection in Azobenzene‐Based Supramolecular Systems Through Dual‐Stimuli Processes

P. Tecilla, D. Bonifazi. ChemistryOpen, 2020, 9, 538 – 553. DOI: 10.1002/open.202000045 Abstract Azobenzene is one of the most studied light‐controlled molecular switches and it has been incorporated in a large variety of supramolecular systems to control their structural and functional properties. Given the peculiar isomeric distribution at the photoexcited state (PSS), azobenzene derivatives have been used as photoactive framework to build metastable supramolecular systems that are out of the thermodynamic equilibrium. This could be achieved exploiting the peculiar E/Z photoisomerization process that can lead to isomeric ratios that are unreachable in thermal equilibrium conditions. The challenge in the field is to find molecular architectures that, under given external circumstances, lead to a given isomeric ratio in a reversible and predictable manner, ensuring an ultimate control of the configurational distribution and system composition. By reviewing early and recent works in the field, this review aims at describing photoswitchable systems that, containing an azobenzene dye, display a controlled configurational equilibrium by means of a molecular recognition event. Specifically, examples include programmed photoactive molecular architectures binding cations, anions and H‐bonded neutral guests. In these systems the non‐covalent molecular recognition adds onto the thermal and light stimuli, equipping the supramolecular architecture with an additional external trigger to select the desired configuration composition.

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Combining high-resolution scanning tunnelling microscopy and first-principles simulations to identify halogen bonding

J. Lawrence, G. C. Sosso, L. Đorđević, H. Pinfold, D. Bonifazi, G. Costantini. Nat. Commun., 2020, 11, 2103. DOI: 10.1038/s41467-020-15898-2 Abstract Scanning tunnelling microscopy (STM) is commonly used to identify on-surface molecular self-assembled structures. However, its limited ability to reveal only the overall shape of molecules and their relative positions is not always enough to fully solve a supramolecular structure. Here, we analyse the assembly of a brominated polycyclic aromatic molecule on Au(111) and demonstrate that standard STM measurements cannot conclusively establish the nature of the intermolecular interactions. By performing high-resolution STM with a CO-functionalised tip, we clearly identify the location of rings and halogen atoms, determining that halogen bonding governs the assemblies. This is supported by density functional theory calculations that predict a stronger interaction energy for halogen rather than hydrogen bonding and by an electron density topology analysis that identifies characteristic features of halogen bonding. A similar approach should be able to solve many complex 2D supramolecular structures, and we predict its increasing use in molecular nanoscience at surfaces.

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Non-covalent bridging of bithiophenes through chalcogen bonding grips

D. Romito, N. Biot, F. Babudri and D. BonifaziNew J. Chem., 2020,44, 6732-6738.DOI: 10.1039/C9NJ06202E Abstract In this work, chalcogen functionalized dithiophenes, equipped on both extremities with chalcogen-bonding recognition heterocycles, have been prepared following two synthetic pathways. The insertion of the chalcogenazolo[5,4-β]pyridine allows the control of the organization at the solid state. X-Ray diffraction analysis of the single crystals, showed that the Te-doped derivatives give the most persistant assemblies, with the molecules arranging at solid-state in wire-like polymeric structures through Te⋯N interactions. As expected, the introduction of the Se and Te atoms, dramatically decreases the emission properties, with the Te-bearing congeners being virtually non emissive.

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Chalcogen-bond driven molecular recognition at work

N. Biot, D. Bonifazi. Coord. Chem. Rev., 2020, 413, 213243. DOI: 10.1016/j.ccr.2020.213243 Abstract Out of the supramolecular toolbox, Secondary Bonding Interactions (SBIs) have attracted in the last decades the attention of the chemical community as novel non-covalent interactions of choice for a large number of chemical systems. Amongst all SBIs, halogen-bonding (XBIs) and chalcogen-bonding (EBIs)interactions are certainly the most important. However, the use of EBIs have received marginal consideration if compared to that of XBIs. By sieving the most significant examples, this review focuses on the theoretical and experimental studies carried out with EBIs in functional systems. In a systematic way the reader is guided through the most recent and representative examples in which chemists have rationally designed molecular modules that, through EBIs, trigger the initiation of chemical reactions,molecular recognition events in solutions and at the solid state to produce self-assembled and self-organised functional materials at different length scales. The study and understanding of the fundamental geometrical and physical parameters ruling EBIs is at its infancy, and it still needs to establish those principles to rationally design and program synthons that, undergoing molecular recognition through EBIs, allow the development of new tailored materials for applications in the field of optoelectronic, sensing, catalysis, and drug discovery.

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Concurring Chalcogen- and halogen-bonding interactions in supramolecular polymers for crystal engineering applications

N. Biot, D. Bonifazi.Chem. Eur. J. 2020, 26, 2904.DOI: 10.1002/chem.201904762 Abstract The engineering of crystalline molecular solids through the simultaneous combination of distinctive non‐covalent interactions is an important field of research as it could allow chemist to prepare materials depicting multiresponsive properties. It is in this contest that, pushed by our will to expand the chemical space of chalcogen‐bonding interactions that, in this work we put forward the concept for which chalcogen‐ and halogen‐bonding interactions can be used simultaneously to engineer multicomponent co‐crystals. Through the rational design of crystallizable molecules, we prepared chalcogenazolo pyridine scaffold (CGP) modules that, bearing either a halogen‐bond acceptor or donor at the 2‐position can interact with suitable complementary molecular modules, undergoing formation of supramolecular polymers at the solid state. The recognition reliability of the CGP moiety to form chalcogen‐bonded dimers allow the formation heteromolecular supramolecular polymers through halogen‐bonding interactions as confirmed by single‐crystal X‐ray diffraction analysis.

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