Self-assembly is the most promising approach to build organic nanostructures on surfaces, leading to hybrid organic-inorganic materials. The idea behind this approach is to exploit the thermodynamic control and reversibility of self-assembly for the error-free generation of 3D architectures, like coordination cages, directly on surfaces, which is one of the key requirements for the development of nanotechnology and molecular electronics. The extension of the self-assembly protocol to technologically interesting surfaces, like silicon, allows to build hybrid inorganic-organic structures featuring selective inclusion and other useful properties. The generation of such complex organic architectures on silicon will be pivotal in developing new integrated devices presenting peculiar optic, magnetic and sensing properties.

Selected publications

• S. Levi, P. Guatteri, F.C.J.M. van Veggel, G.J. Vancso, E. Dalcanale, D.N. Reinhoudt, Direct Observation of Surface Controlled Self-assembly of Coordination Cages by an AFM as Molecular Ruler, Angew. Chem. Int. Ed. 2001, 40, 1892-1896.
• E. Menozzi, R. Pinalli, E.A. Speets, B.J. Ravoo, E. Dalcanale, D.N. Reinhoudt, Surface-Confined Single-Molecules: Assembly and Disassembly of Nanosize Coordination Cages on Gold (111), Chem. Eur. J. 2004, 10, 2199-2206.
  
• M. Busi, M. Laurenti, G. G. Condorelli, A. Motta, M. Favazza, I. L. Fragalà, M. Montalti, L. Prodi, E. Dalcanale, Self-Assembly of Nanosize Coordination Cages on Si(100) Surfaces, Chem. Eur. J.2007, 13, 6891-6898.
  
• G. Condorelli, A. Motta, M. Favazza, I. L. Fragalà, M. Busi, E. Menozzi, E. Dalcanale, L. Cristofolini, Grafting cavitands on the Si(100) surface, Langmuir 2006, 22, 1126-1133.
  
• E. Biavardi, M. Favazza, A. Motta, I. L. Fragala, C. Massera, L. Prodi, M. Montalti, M. Melegari, G. G. Condorelli, E. Dalcanale, Molecolar Recognition on a Cavitand-Functionalized Silicon Surface, J. Am. Chem. Soc. 2009, 131, 7447-7455.
  
• F. Tancini, D. Genovese, M. Montalti, L. Cristofolini, L. Nasi, L. Prodi, E. Dalcanale, Hierarchical Self-Assembly on Silicon, J. Am. Chem. Soc. 2010, 132, 4781-4789.
  

Single Molecule Magnets (SMMs) are among the most promising molecular systems for the development of novel molecular electronics based on the spin transport. However, the development of a SMM-based technology is hampered by the intrinsic chemical fragility of most polynuclear SMMs and the evanescence of the SMM behaviour, which make the retention of the molecular magnetic bistability at the nanoscale far from trivial. Another issue related to the technological fruition of SMMs is the development of suitable methods for their stable and robust integration into technologically relevant substrates like silicon.
This research activity addresses these issues by designing, synthetizing and grafting chemically engineered TbIII-bisphtalocyaninato SMM on silicon wafers, covering also the structural and magnetic characterization of the resulting material. So far the research activity has led to:

• A new, versatile multiple peripheral functionalization of Terbium double decker phthalocyanines TbPc2. The introduction of iodine substituents on the Pc ligands does not alter the magnetic properties of the corresponding Tb complexes. These iodinated TbPc2 undergo multiple Sonogashira coupling reactions in high yield in a simple, effective way. This mild and versatile procedure paves the way for the highly sought TbPc2 post-functionalization. The application of this new synthetic protocol for TbPc2 functionalization allows to introduce a wide range of functionalities on LnPc2, necessary prerequisites for the development of SMM-based technologies.




• A reliable methodology for the grafting on silicon of a functionalized TbIII-bisphtalocyaninato SMM. The thermal hydrosilylation procedure employed leads to the formation of thermally and a hydrolytically stable SMM monolayer on silicon, making it solvent and sonication-resistant. The resulting Si-integrated SMM monolayer shows for the first time a surface enhancement of the magnetic bistability, rather than the commonly observed suppression of it. The unprecedented use of chemical design to realize a covalent grafting on silicon has at the same time maximized the robustness of the grafted monolayer as well as enhanced the magnetic memory effect as a result of the electronic effect induced by the grafting on silicon.

Selected publications

• L. Bogani, C. Danieli, E. Biavardi, N. Bendiab, A.-L. Barra, E. Dalcanale, W. Wernsdorfer, A. Cornia, Single-Molecule-Magnet Carbon-Nanotube Hybrids, Angew. Chem. Int. Ed. 2009, 48, 746-750.
• M. Mannini, F. Bertani, C. Tudisco, L. Malavolti, L. Poggini, K. Misztal, D. Menozzi, A. Motta, E. Otero, P. Ohresser, P. Sainctavit, G. G. Condorelli, E. Dalcanale, R. Sessoli, Magnetic behaviour of TbPc2 single-molecule magnets chemically grafted on silicon surface, Nat. Commun. 2014, 5, article # 4582
  
• G. Cucinotta, L. Poggini, A. Pedrini, F. Bertani, N. Cristiani, M. Torelli, P. Graziosi, I. Cimatti, B. Cortigiani, E. Otero, P. Ohresser, P. Sainctavit, A. Dediu, E. Dalcanale, R. Sessoli, M. Mannini, Tuning of a vertical spin valve with a monolayer of single molecule magnets, Adv. Funct. Mater. 2017, 27, 1703600.
  
• A. Pedrini, L. Poggini, C. Tudisco, M. Torelli, A. E. Giuffrida, F. Bertani, I. Cimatti, E. Otero, P. Ohresser, P. Sainctavit, M. Suman, G. G. Condorelli, M. Mannini, E. Dalcanale, Self-Assembly of TbPc2 Single-Molecule Magnets on Surface through Multiple Hydrogen Bonding, Small 2018, 14, 1702572.
  

The fast, widespread and reliable monitoring of carcinogenic compounds at very low concentrations in air constitutes a mandatory goal for environmental and health organizations and a major challenge for the chemical community. Multidisciplinary, innovative solutions are required to overcome the present limits, particularly in benzene detection.

The supramolecular approach to analytical sampling materials can be seen as a noteworthy improvement by imparting selectivity to analytical techniques from one side and by tailoring selectivity of the adsorbed material towards the desired class of analytes from the other side, thus allowing to achieve remarkable analytical results.

Molecular recognition is a recurrent theme in chemical sensing because of the importance of selectivity for sensor performances. The popularity of molecular recognition in chemical sensing has resulted from the progress made in mastering weak interactions, which has enabled the design of synthetic receptors according to the analyte to be detected. However, the availability of a large pool of modular synthetic receptors so far has not had a significant impact on sensors used in the real world. This technological gap has emerged because of the difficulties in transferring the intrinsic molecular recognition properties of a given receptor from solution to interfaces and in finding high fidelity transduction modes for the recognition event. The research activity proposed fills this gap in the case of environmental monitoring of toxic aromatic VOC.

Selective monitoring of airborne aromatic volatile organic compounds (VOC) in air, namely BTEX (benzene, toluene, ethyl benzene and xylenes), is both socially relevant and technologically challenging, since high-precision measurement at trace concentrations of these nonpolar molecules is generally interfered with by overwhelming amounts of aliphatic hydrocarbons. Presently, real-time air monitoring is performed by bulky conventional laboratory equipment that incurs high operating costs and requires trained users. Simple low-cost systems based on solid state gas sensors were recently proposed, the most important being Metal OXide sensors (MOX), Quartz MicroBalances (QMB), Surface Acoustic Waveguides (SAW), and polymeric sensors. These technologies have often reached sufficient sensitivity for the detection of the target gas species, but generally their selectivity is limited and not sufficient for reliable quantification or early-warning systems. However, these are not viable solutions for stand-alone sensors for urban monitoring. Multisite urban monitoring of benzene needs simple yet selective systems to be embedded in traffic lights or lampposts, without maintenance service. The exploitation of molecular receptors as sensing materials is particularly attractive to address the selectivity issue. The progress made in designing synthetic receptors enables the modulation of the sensor selectivity towards different classes of compounds by mastering the weak interactions occurring between the sensing material and the analytes. The selective aromatic hydrocarbon complexation properties of tetraquinoxaline cavitands (QxCav) have been exploited in our group to fabricate low-cost systems with sub-ppbv detection limits of toxic volatile organic compounds (VOCs) in the presence of other airborne pollutants. The performance of this prototype is enabled by a pre-concentrator unit filled with Quinoxaline Cavitand (QxCav) molecules capable of selectively trapping aromatic vapors at the gas-solid interface. The receptor cavity is able to discriminate aromatic from aliphatic hydrocarbons due to the formation of specific interactions like CH-p and p-p interactions. The selective hosting properties of tetraquinoxaline cavitands (QxCav) towards aromatic hydrocarbons have been proven in gas phase as well as in the solid state. Rational design of QxCav molecular structures offers the possibility to further improve both the sensitivity and the selectivity of the preconcentrator. Our research results gave rise to the commercial device PyxisGC in collaboration with Pollution. Our cavitands are used as preconcentrators inside the instrument.

Selected publications

• S. Zampolli, P. Betti, I. Elmi, E. Dalcanale, A Supramolecular Approach to Sub-ppb Aromatic VOC Detection in Air, Chem. Commun. 2007, 2790-2792. (Inside cover and Chemical Technology Highlight)
• F. Bianchi, M. Mattarozzi, P. Betti, F. Bisceglie, M. Careri, A. Mangia, L.Sidisky, S. Ongarato, E. Dalcanale, Innovative Cavitand-based Sol-gel Coatings for the Environmental Monitoring of Benzene and Chlorobenzenes via Solid-phase Microextraction, Anal. Chem. 2008, 80, 6423-6430.
  
• S. Zampolli, I. Elmi, F. Mancarella, P. Betti, E. Dalcanale, G. C. Cardinali, M. Severi, Real-time Monitoring of Sub-ppb Concentrations of Aromatic Volatiles with a MEMS-enabled Miniaturized Gas-chromatograph, Sens. Actuators B 2009, 141, 322-328.
  
• G. G. Condorelli, A. Motta, M. Favazza, E. Gurrieri, P. Betti, E. Dalcanale, Molecular recognition of halogen-tagged aromatic VOCs at the air-silicon interface, Chem. Commun. 2010, 46, 288-290.
  
• F. Maffei, P. Betti, D. Genovese, M. Montalti, L. Prodi, R. De Zorzi, S. Geremia, E. Dalcanale, Highly Selective Chemical Vapor Sensing via Molecular Recognition: Specific C1-C4 Alcohols Detection with a Fluorescent Phosphonate Cavitand, Angew. Chem. Int. Ed. 2011, 50, 4654-4657.
  
• F. Bianchi, A. Bedini, N. Riboni, R. Pinalli, A. Gregori, L. Sidisky, E. Dalcanale, M. Careri,Cavitand-based solid-phase microextraction coatings for the selective detection of nitroaromatic explosives in air and soil, Anal. Chem. 2014, 86, 10646−10652.
  
• F. Bertani, N. Riboni, F. Bianchi, G. Brancatelli, E. S. Sterner, R. Pinalli, S. Geremia, T. M. Swager, E. Dalcanale, Triptycene-roofed quinoxaline cavitands for the supramolecular detection of BTEX in air, Chem. Eur. J. 2016, 22, 3312-3319 (hot paper and cover of the issue).
  
• J. W. Trzciński, R. Pinalli, N. Riboni, A. Pedrini, F. Bianchi, S. Zampolli, I. Elmi, C. Massera, F. Ugozzoli, E. Dalcanale, In Search of the Ultimate Benzene Sensor: The EtQxBox Solution, ACS Sensors 2017, 2, 590-598.
  
• M. Giannetto, A. Pedrini, S. Fortunati, D. Brando, S. Milano, C. Massera, R. Tatti, R. Verucchi, M. Careri, E. Dalcanale, R. Pinalli, Environmental sensing of halogenated aromatic hydrocarbons in water with a cavitand coated piezoelectric device, Sens. Actuators B 2018, 276, 340-348.
  
• R. Pinalli, A. Pedrini, E. Dalcanale, Environmental gas sensing with cavitands, Chem. Eur. J. 2018, 24, 1010-1019. (featured as Frontispiece)
  

Design and preparation of supramolecular polymers is a topic at the forefront of contemporary chemistry, due to its potential fallout in scientific discoveries and technological applications. The essential feature of this class of polymers is the reversibility of the interactions holding together the constituent monomers.

Such reversibility confers two important properties to supramolecular polymers: (i) responsiveness to external stimuli; (ii) self-healing properties. Both features are highly in demand in materials science. We devised and tested a bimodal self-assembly protocol for the generation of a dual-coded supramolecular polymer. Combination of two orthogonal and reversible interactions, namely solvophobic aggregation and metal-coordination, allows precise control at each step of the self-assembly cycle, leading to the formation of rod-like supramolecular architectures.

Following a different approach, we prepared a new class of supramolecular polymers whose self-assembly is driven by the outstanding complexing properties of tetraphosphonate cavitands toward methylpyridinium guests. Cavitand monomers presenting the host functionality at the upper rim and the guest unit at the lower rim self-assemble in solution to give the corresponding homopolymer (see crystal structure below). The remarkable supramolecular plasticity of this system has been proven by the competitive guest triggered reversibility and template driven conversion from linear to star branched polymer (see image below).

The same host-guest association mode was employed for the formation of copolymers, featuring the interesting temperature driven cyclic to linear polymer interconversion.

Selected publications

• L. Pirondini, A.G. Stendardo, S. Geremia, M. Campagnolo, P. Samorì, J.P. Rabe, R. Fokkens, E. Dalcanale, Angew. Chem. Int. Ed. Engl. 2003, 42, 1384-1387.
• R. M. Yebeutchou, F. Tancini, N. Demitri, S. Geremia, R. Mendichi, E. Dalcanale, Angew. Chem. Int. Ed. Engl. 2008, 47, 4504-4508. (Featured as frontispiece).
• F. Tancini, R. M. Yebeutchou, L. Pirondini, R. De Zorzi, S. Geremia, O. A. Sherman, E. Dalcanale, Chem. Eur. J. 2010, 16, 14313-14321 (Inside Cover picture).
• F. Tancini, E. Dalcanale, Polymerization with Ditopic Cavitand Monomers, Supramolecular Polymer Chemistry (Ed. A. Harada), Wiley-VCH Verlag Gmbh & Co. KGaA, Weinheim, Germany, 2012, 71-93.
• A. E. Fruh, F. Artoni, R. Brighenti, E. Dalcanale, Strain field self-diagnostic PDMS elastomers, Chem. Mater. 2017, 29, 7450-7457.
• J. Tellers, S. Canossa, R. Pinalli, M. Soliman, J. Vachon, E. Dalcanale, Dynamic Cross-Linking of Polyethylene via Sextuple Hydrogen Bonding Array, Macromolecules 2018, 51, 7680-7691.
• A. Zych, A. Verdelli, M. Soliman, R. Pinalli, A. Pedrini, J. Vachon, E. Dalcanale, Strain-reporting pyrene-grafted polyethylene, Eur. Pol. J. 2019, 111, 69-73.
• A. Zych, A. Verdelli, M. Soliman, R. Pinalli, J. Vachon, E. Dalcanale, Physically cross-linked polyethylene via reactive extrusion, Polym. Chem. 2019, 10, 1741-1750.
• J. Tellers, R. Pinalli, M. Soliman, J. Vachon, E. Dalcanale, Reprocessable Vinylogous Urethane Cross-linked Polyethylene via Reactive Extrusion, Polym. Chem. 2019, 10, 5534-5542.
• A. Devi Das, G. Mannoni, A. Früh, D. Orsi, R. Pinalli, E. Dalcanale, Damage-Reporting Carbon Fiber Epoxy Composites, ACS Appl. Polym. Mater. 2019, 1, in press (Highlighted in the ACS Editors’ Choice on October 4, 2019).

Chemical sensors play an increasingly important role in our everyday life: environmental monitoring, industrial process control, quality control of food and beverages, hazardous chemicals, explosives detection and workplace monitoring are just a few examples of their widespread use. In all cases the driving force behind the development of sensor technology is the need for immediate and accurate analyses.

A long-standing problem with chemical sensors is their tendency to give false responses. In sensors that use chemically sensitive coating layers, such false responses are caused by inadequate selectivity towards target molecules. The search for selectivity is therefore one of the key issues in developing new chemical sensors with a significant applicative impact.

False responses are caused by inadequate selectivity towards target molecules.

Advances in supramolecular chemistry offer many opportunities to design and prepare molecules endowed with superior molecular recognition properties to be used in chemical sensors. Unfortunately, in most cases the complexation properties of synthetic receptors have been optimized in solution, while their use for gas sensing requires mastering molecular recognition at the gas-solid interface. Molecular recognition in the liquid phase cannot be automatically transferred to vapour and gas sensing, since in moving from the vapour to the condensed phase the analyte experiences a dramatic increase in non-specific dispersion interactions, which are negligible in solution.
Our recent review deals with the design of synthetic molecular receptors capable of recognition at the gas-solid interface, to be used in gas sensors. Cavitands, synthetic organic compounds with enforced cavities of molecular dimensions, have been chosen as a case study to highlight all the necessary steps to prepare an effective supramolecular sensor for organic vapours. The major obstacle in the development of supramolecular sensors using mass transducers is that both specific binding events that occur within the receptor cavity and non-specific dispersion interactions that occur elsewhere in the layer give rise to responses. The competing presence of non-specific dispersion interactions partially overrides the weak specific ones, threatening sensor selectivity. Another essential feature is the reversibility of the responses, which requires the recourse to weak interactions, since the formation of ionic or covalent bonds would result in an irreversible saturation of the chemical layer. Moreover, the design of the supramolecular receptors for gas and vapour sensing demands the appropriate choice of the weak interactions to be implemented in function to the analytes to be detected.

Molecular recognition in the liquid phase cannot be automatically transferred to vapour and gas sensing.

For all these reasons a precise receptor design is required, together with a detailed study of the complexation phenomena both in the gas and solid phase. Several steps are needed: first, compelling evidence of analyte complexation within the receptor layer must be obtained via adsorption isotherm measurements. Then, a molecular level understanding of the receptor-analyte interactions has to be acquired. The combined use of mass spectrometry and X-ray crystallography will respectively provide information about the gas phase and solid state interaction modes. If the dominant interactions in the two phases coincide, the knowledge assumes a predictive value for the receptor performances in sensors.
One of the available options to minimize non-specific interactions is the reduction of the receptor layer thickness in connection with an appropriate transducer. Thin layers or, even better, monolayers of molecular receptors have been employed in connection with SPR (surface plasmon resonance) transducers. SPR is an optical phenomenon that provides a safe, remote and non-destructive means of sensing. Thanks to its increased selectivity with respect to the other transduction schemes, SPR can detect vapour interactions with monolayers of molecular receptors. In our review the effectiveness of supramolecular SPR sensing has been shown using cavitands as receptors for volatile aromatic organic vapours. The same approach has been undertaken recently to develop supramolecular SPR sensors to detect a nerve gas simulant with the aim of producing a selective sensor for chemical warfare agents.

Cover gallery:

Selected publications

• R. Pinalli, F.F. Nachtigall, F. Ugozzoli, E. Dalcanale, Supramolecular Sensors for the Detection of Alcohols, Angew. Chem. Int. Ed. Engl. 1999, 38, 2377-2380.
• M. Suman, M. Freddi, C. Massera, F. Ugozzoli, E. Dalcanale, Rational Design of Cavitand Receptors for Mass sensors, J. Am. Chem. Soc. 2003, 125, 12068-12069.
• R. Paolesse, C. Di Natale, S. Nardis, A. Macagno, A. D’Amico, R. Pinalli, E. Dalcanale, Investigation of the Origin of Selectivity in Cavitand-Based Supramolecular Sensors, Chem. Eur. J. 2003, 9, 5388-5395.
• S. M. Daly, M. Grassi, D. K. Shenoy, E. Dalcanale, Supramolecular Surface Plasmon Resonance (SPR) Sensors for Organophosphorus Vapor Detection, J. Mater. Chem. 2007, 17, 1809-1818.
• S. Zampolli, P. Betti, I. Elmi, E. Dalcanale, A Supramolecular Approach to Sub-ppb Aromatic VOC Detection in Air, Chem. Commun. 2007, 2790-2792.
• L. Pirondini, E. Dalcanale, Molecular recognition at the gas-solid interface: a powerful tool for chemical sensing, Chem. Soc. Rev. 2007, 36, 695-706.
• M. Melegari, M. Suman, L. Pirondini, D. Moiani, C. Massera, F. Ugozzoli, E. Kalenius, P. Vainiotalo, J.-C. Mulatier, J.-P. Dutasta, E. Dalcanale, Supramolecular Sensing with Phosphonate Cavitands, Chem. Eur. J.2008, 14, 5772-5779.
• G.G. Condorelli, A. Motta, M. Favazza, E. Gurrieri, P. Betti, E. Dalcanale, Molecular recognition of halogen-tagged aromatic VOCs at the air-silicon interface, Chem. Commun. 2010, 46, 288-290.
• M. Dionisio, G. Oliviero, D. Menozzi, S. Federici, R. M. Yebeutchou, F. P. Schmidtchen, E. Dalcanale, P. Bergese, Nanomechanical Recognition of N-Methylammonium Salts, J. Am. Chem. Soc. 2012, 134, 1392–1398.
• M. Dionisio, J. M. Schnorr, V. K. Michaelis, R. G. Griffin, T. M. Swager, E. Dalcanale, Cavitand-Functionalized SWCNTs for N-Methylammonium Detection, J . Am. Chem. Soc., 2012, 134, 6540–6543.
• E. Biavardi, S. Federici, C. Tudisco, D. Menozzi, C. Massera, A. Sottini, G. G. Condorelli, P. Bergese and E. Dalcanale, Cavitand-Grafted Silicon Microcantilevers as a Universal Probe for Illicit and Designer Drugs in Water, Angew. Chem., Int. Ed. 2014, 53, 9183–9188.
• N. Bontempi, E. Biavardi, D. Bordiga, G. Candiani, I. Alessandri, P. Bergese and E. Dalcanale, Probing lysine mono-methylation in histone H3 tail peptides with an abiotic receptor coupled to a non-plasmonic resonator, Nanoscale 2017, 9, 8639–8646.
• R. Pinalli, G. Brancatelli, A. Pedrini, D. Menozzi, D. Hernández, P. Ballester, S. Geremia, E. Dalcanale, The origin of selectivity in the complexation of N-methyl amino acids by tetraphosphonate cavitands, J. Am. Chem. Soc. 2016, 138, 8569-8590.
• R. Pinalli, A. Pedrini, E. Dalcanale, Biochemical sensing with macrocyclic receptors, Chem. Soc. Rev. 2018, 47, 47, 7006-7026.