Organic chemistry for energy & catalysis
In our group we deal with the synthesis of organic molecules, often perylene-based and their self-assembled nanomaterials, for applications in electronics, catalysis and solar energy conversion.
Perylene tetracarboxylic acid bisimides, in short perylene bisimides (PBIs), are one of the most studied π-conjugated small molecules in chemistry. They present excellent chemical, thermal and photochemical stability, highly oxidative excited states and high fluorescence quantum yields. PBIs are well known dyes colorants, widespread as pigments in industry, due to their insolubility in plenty of solvents, thermal and photo stability. Moreover, a straightforward and simple route towards tuning the properties, like solubility or ionic interactions, is the modification of PBIs both at the core and at imide position: by a proper choice of the substituent, the tuning of their properties can be achieved, from enhanced solubility in a number of solvents to increased formation of aggregates in water. More recent applications of PBIs dyes are in the field of organic electronics (i.e. field effect transistors, photovoltaics devices, etc), among which PBI-based molecules are the best n-type molecular semiconductors available to date. Next to these applications field, in the last years perylene bisimide has gained more attention for its properties emerging in its supramolecular assemblies, which can be exploited for various applications.
Despite their wide range of applicability, the synthesis of these materials presents some limitations: indeed, condensation of perylenebisanhydride with amines requires long reaction times in harsh conditions with non‐common solvents, such as imidazole. In our group we developed a facile and efficient strategy, that involves the use of microwaves irradiation for the synthesis of perylene bisimide. The protocol has been extended to a vast variety of amines, bearing different functional groups, and it was proven to be succesful even with halogenated derivatives confirming its wide applicability. [1]
Another peculiar factor, which can deeply modify the properties of π-conjugated molecules, is the formation of extended structures in solution, due to hydrophobic interactions. This effect is crucial and influences the photophysical features of the final material. In collaboration with Dr. Heinz Amenitsch (responsible of SAXS beamline at Elettra Synchrotron), assemblies of PBIs have been extensively studied and characterized with a number of spectroscopical techniques, disclosing how PBI aggregate under different conditions, e.g., forming highly ordered cylindrical nano-crystals packed along the π-π-stacking direction at high concentration. [2,3] In this context, water-soluble PBIs have been proven to form hydrogels which can conduct electricity even in this nano-crystalline form. [4]
Among the several applications of perylene bisimide, photocatalysis is one of the most interesting one. Indeed, photocatalysis is a type of catalysis that results in the modification of the rate of a photoreaction - a chemical reaction that involves the absorption of light by one or more reacting species - by adding substances (photocatalysts) that are involved in the chemical transformation of the reaction partners. In most cases, photo-catalyzed reactions are promoted by precious metal complexes, which are used in high loading. In the last years, attempts to overcome this issue employing metal-free catalysts have been done: perylene bisimide fulfills many requisities for a photocatalysts, like activity under visible light irradiation, efficiency and low cost. Recently, we found out that PBI can be used as photocatalyst in low loading (0.05% mol) for the iodoperfluoroalkylation reaction of olefins. PBIs work also with continuous flow protocols, under visible light, enhancing the productivity of desired products up to gram scale in few hours. This last protocol has been extended to the preparation of a perfluorinated building block for the synthesis of an anticancer drug, using inexpensive starting compounds. [5,6]
PBIs have gained attention for their behaviour as n-type organic semiconductor, indeed used as acceptor component in organic photovoltaics devices. But few attempts have been done with the use of PBIs in solar fuel cells for water splitting reaction. In collaboration with Prof. Caramori, from University of Ferrara, we demonstrated that bis-cationic PBIs spontaneously adsorb on surfaces of nanocrystalline WO3 via aggregation/hydrophobic forces. Thanks to its intrinsic features, PBI provides one of the strongest and most robust photogenerated oxidants under visible irradiation, thus the combination with WO3 leads to photoanodes where electron injection results in long-lived charge separated state. Indeed if coupled with water oxidation catalysts (WOCs), i.e. IrO2 nanoparticles, they are ascribed to be perfect candidate for photo-oxidative water splitting reaction in photoelectrochemical cells (PECs) for the production of oxygen and hydrogen from water. [7]
In collaboration with the group of Prof. Bonchio, from the University of Padova, water splitting reaction was optimized using PBIs in combination with polyoxometalate (POM), one of the most efficient water oxidation catalysts. In combination with POM, bis-cationic PBIs form supramolecular nanocylinders in which the POM is sorrounded by five PBIs. The PBI/POM assembly forms an ordered lamellar structure in water and is able to efficiently perform water oxidation under visible light, with optimal performances. [8]
Highlighted contributions:
[1] Fast and Efficient Microwave‐Assisted Synthesis of Perylenebisimides.
F. Rigodanza, E. Tenori, A. Bonasera, Z. Syrgiannis, M. Prato. Eur. J. Org. Chem., 5060–5063 (2015). Link
[2] Structural and optical properties of a perylene bisimide in aqueous media.
M. Burian, F. Rigodanza, H. Amenitsch, L. Almásy, I. Khalakhan, Z. Syrgiannis, M. Prato. Chem. Phys. Letters 683, 454–458 (2017). Link
[3] A water-soluble, bay-functionalized perylenediimide derivative – correlating aggregation and excited state dynamics.
K. Dirian, S. Bauroth, A. Roth, Z. Syrgiannis, F. Rigodanza, M. Burian, H. Amenitsch, D. I. Sharapa, M. Prato, T. Clark and D. M. Guldi. Nanoscale 10, 2317-2326 (2018). Link
[4] Inter-Backbone Charge Transfer as Prerequisite for Long-Range Conductivity in Perylene Bisimide Hydrogels.
M. Burian, F. Rigodanza, N. Demitri, L. D̵ord̵ević, S. Marchesan, T. Steinhartova, I. Letofsky-Papst, I. Khalakhan, E. Mourad, S. A. Freunberger, H. Amenitsch, M. Prato, Z. Syrgiannis. ACS Nano 12, 5800−5806 (2018). Link
[5] Highly Performing Iodoperfluoroalkylation of Alkenes Triggered by the Photochemical Activity of Perylene Diimides.
C. Rosso, G. Filippini, P.G. Cozzi, A. Gualandi, M. Prato. ChemPhotoChem 3, 193–197 (2019). Link
[6] Visible-Light-Mediated Iodoperfluoroalkylation of Alkenes in Flow and Its Application to the Synthesis of a Key Fulvestrant Intermediate.
C. Rosso, J. D. Williams, G. Filippini, M. Prato, C.O. Kappe. Org. Lett. 21, 5341−5345 (2019). Link
[7] Modification of Nanocrystalline WO3 with a Dicationic Perylene Bisimide: Applications to Molecular Level Solar Water Splitting.
F. Ronconi, Z. Syrgiannis, A. Bonasera, M. Prato, R. Argazzi, S. Caramori, V. Cristino, C.A. Bignozzi. J. Am. Chem. Soc. 137, 14, 4630-4633 (2015). Link
[8] Hierarchical organization of perylene bisimides and polyoxometalates for photo-assisted water oxidation.
M. Bonchio, Z. Syrgiannis, M. Burian, N. Marino, E. Pizzolato, K. Dirian, F. Rigodanza, G.A. Volpato, G. La Ganga, N. Demitri, S. Berardi, H. Amenitsch, D.M. Guldi, S. Caramori, C.A. Bignozzi, A. Sartorel, M. Prato,. Nature Chemistry 11, 146-153 (2019). Link or Video