Bridged fused porphyrin tapes thin films as heterogeneous catalysts

Abstract

The invention concerns bridged fused metalloporphyrin polymer comprising meso-β, β-meso doubly fused and / or meso-meso, β-β, β-β triply fused metalloporphyrin tapes connected by aromatic bridges, their methods of production and uses.

Description

Bridged Fused Porphyrin Tapes Thin Films as Heterogeneous CatalystsField of the Invention

[0001] The present invention generally relates to a polymer made of bridged fused metalloporphyrin tapes, and a preparation method and application thereof. According to the present invention, the bridged fused metalloporphyrin tapes can be directly applied onto a substrate using the preparation method of the invention, and used as heterogeneous catalysts.Background of the Invention

[0002] Metal loporphyrins are ubiquitous in Nature, where they fulfil the two main catalytic phenomena allowing life, i.e. photosynthesis by chlorophylls and respiration by cytochromes (Lesage et al. in Hydrological Sciences Journal 38, 343 to 354 (1993)). Some naturally occurring metalloporphyrins, such as Vitamin B-12, a cobalt porphyrin, can catalyze even more advanced chemical reactions, e.g. isomerisation, dehalogenation or methyl transfer, to enable DNA synthesis and red blood cell formation (Giedyk et al. in Chem. Soc. Rev. 44, 3391-3404 (2015)).

[0003] Therefore, metallorporphyrins stand as highly versatile and stable functional molecules, displaying intriguing physical and chemical properties which fostered their incorporation for various practical applications including photovoltaics (Mathew et al. in Nature Chemistry 2014 6:3 6, 242-247 (2014), and Maree et al. in J Appl Phys 80, 3381-3389 (1996)), photonics (Gharaati, et al. in Chemistry - A European Journal 26, 1003-1007 (2020)), sensing (Boscher et al. in Sens Actuators B Chem 191 , 553-560 (2014), Paolesse et al. in Chem Rev 117, 2517-2583 (2017), Heier et al. in Inorg Chem 53, 11086-11095 (2014), Heier et al. in Dalton Transactions 42, 906-917 (2012), and Rakow et al. in Nature 2000 406:6797 406, 710-713 (2000)) and catalysis (Zhang et al. in Chem Rev 117, 3717-3797 (2017), Lee et al. in J Am Chem Soc 133, 8775-8777 (2011 ), Shan et al. in Energy Environ Sci 11 , 447-455 (2018),Bansal et al. in J. Mater. Chem. A 11 , 5188-5198 (2023), and Wang et al. in Adv Funct Mater 31 , 2009819 (2021 )).

[0004] Constituted of four pyrrole subunits connected through methine bridges, metalloporphyrins can chelate a cation at their centre and be functionalized with side groups attached to one or several of their meso and [3 positions. The careful selectionof the central metal cation and peripheral substituents enables to tune electronic and optoelectronic characteristics of metalloporphyrins (Kesters et al. in Adv Energy Mater 5, 1500218 (2015). The binding affinity to reactants and catalytic activity of metalloporphyrins is mainly governed by the nature of the central cation (Zheng et al. in Journal of Physical Chemistry C 111 , 7084-7090 (2007). Yet, metalloporphyrins’ peripheral substituents, with respect to their electron withdrawing / donating character, can also affect the electronic energy levels and impact the catalytic properties of metalloporphyrins (Rybicka-Jasihska et al. in J Am Chem Soc 138, 15451-15458 (2016)).

[0005] Owing to their highly conjugated structure and central metal ion, that readily interconvert between different oxidation states to accomplish oxidation and reduction reactions, metalloporphyrins have found application in a number of synthetic transformations of great interest for industry, including C-H functionalization, epoxidation, sulfoxidation or oxidation of alcohols to carbonyls, and water splitting (Barona-Castano et al. in Molecules 21 , (2016)).

[0006] Several studies have highlighted the cooperative effect promoted by conjugated bonds between metalloporphyrins on their catalytic properties (Khusnutdinova et al. in ACS Catal 8, 9888-9898 (2018), and Chen et al. in Journal of Physical Chemistry C 114, 8633-8638 (2010)). In addition to a stability increase, metalloporphyrins-based conjugated oligomers and polymers (CPs) exhibit improved catalytic performances for both oxidation (e.g. Oxygen Evolution Reaction, OER; Jia et al. in Chemistry of Materials 27, 4586-4593 (2015)) and reduction reaction (e.g. Hydrogen Evolution Reaction HER or Oxygen Reduction Reaction ORR; Huerta-Flores et al. in ACS Appl Energy Mater 3, 9848-9855 (2020), and Hijazi et al. in J Am Chem Soc 136, 6348-6354 (2014)). The superior catalytic activity of conjugated metalloporphyrins assemblies is associated with their capacity to store multiple charges in order to fulfill multiple-electron processes (Reyes Cruz et al. in ChemElectroChem 8, 3614-3620 (2021 ), as well as their ability to enable a dinuclear radical oxo-coupling (ROC) mechanism at low overpotential (Bansal et al. in J. Mater. Chem. A 11 , 5188-5198 (2023)). Specifically, intermolecular dehydrogenative coupling can significantly enhance the delocalization of charge carriers and reduce recombination. Thus, improved charge transfer in metalloporphyrin-based conjugated polymers promotes their electrocatalytic performances. In consequence, thecontrolled extension of the rr-conjugated system in metalloporphyrins assemblies often yields to a substantial reduction of the required overpotential for electrocatalytic reaction, outperforming monomeric counterparts. Recently, fused Ni(ll) porphyrins tapes have been reported as potent heterogeneous electrocatalysts for OER catalysis, unveiling the significant role of the direct fusion of metalloporphyrins to form preorganized electrocatalysts able to operate at lower overpotentials (Bansal et al. in J. Mater. Chem. A 11 , 5188-5198 (2023)). Precisely, fused Ni(ll) porphyrin tape catalysts showed superior performance than their monomeric counterparts due to the facilitation of a radical oxo coupling (ROC) mechanism operating at lower overpotentials than the fundamental minimum required for the water nucleophilic attack (WNA) pathway, i.e. , 300 mV (Hessels et al. in Chemistry - A European Journal 23, 16413-16418 (2017), and Hessels, J. et al. in ChemSusChem 13, 6629-6634 (2020)).

[0007] Several strategies have been developed to form highly rr-conjugated metalloporphyrin systems, e.g., fused metalloporphyrin tapes (Nakamura, et al. in J. Porphyr. Phthalocyanines 7, 264-269 (2012)), bridged metalloporphyrins polymers (Wang, J. et al. in Adv Funct Mater 31 , 2009819 (2021 )), incorporation into covalent organic frameworks (COFs; Tavakol, E. et al. in J Am Chem Soc 141 , 19560-19564 (2019)), metal-organic frameworks (MOFs; Hamad et al. in J Mater Chem A Mater 3, 23458-23465 (2015)) and hybrid frameworks (e.g., hybrid COF-multi-walled carbon nanotubes framework). Nevertheless, due to the very weak solubility of rr-conjugated metalloporphyrins assemblies and the lack of a synthetic approach, the design and application of rr-conjugated metalloporphyrins assemblies is a largely unexplored topic in view of the plethora of available metalloporphyrin patterns.

[0008] Among the rr-conjugated metalloporphyrin assemblies, directly fused metalloporphyrin tapes have been reported to possess superior electrocatalytic properties than their monomeric counterparts. Fused metalloporphyrin tapes rely on the direct fusion of metalloporphyrin macrocycles via single meso-meso or meso-[3 bonds or multiple meso-[3 / [3-meso or meso-meso / [3-[3 / [3-[3 bonds, using a suitable oxidant (Tanaka et al. in Chem Soc Rev 44, 943-969 (2015), Tsuda et al. in Science 293, 79-82 (2001 ), Baba et al. in European J Org Chem 2019, 2368-2375 (2019), and Brennan et al. in Chemical Communications 47, 10034-10036 (2011 )). Although reported for the first time in 2000, the developed solution-based synthetic approaches towards extended fused metalloporphyrin tapes did not allow the integration and studyof these very weakly soluble compounds for practical applications. In 2019, an oxidative chemical vapor deposition (oCVD) approach for the simultaneous synthesis and deposition of fused metalloporphyrin tapes in thin film on a wide range of substrates was implemented (Bengasi et al. in Chemistry - A European Journal 25, 8313-8320 (2019)).

[0009] WO 2020 / 099385 A1 discloses conductive films of fused porphyrin polymers and methods of forming coated substrates, involving the synthesis of conductive coatings comprising doubly or triply linked fused (poly)porphyrins. The synthesis is carried out by using chemical vapor deposition (CVD) of monomers in the presence of an oxidant (oxidative CVD or oCVD). In WO 2022 / 002891 A1 , the same oCVD process was employed to selectively form doubly fused (meso-[3 and [3-meso) or triply fused ([3- [3, meso-meso and [3- [3) polyporphyrin tapes. The oCVD reaction was controlled by the selection of monomer substituents, reaction temperature and oxidant / monomer ratio.

[0010] Further enhancement of the degree of conjugation of fused metalloporphyrin tapes is considered a promising route to further improve catalytic properties.Summary of the invention

[0011] In a first aspect, the invention relates to bridged fused metalloporphyrin polymers comprising meso-[3, [3-meso doubly fused and / or meso-meso, |3-|3, f3-|3 triply fused metalloporphyrin tapes connected by aromatic bridges, and represented by Formula 1 or Formula 2:Formula 2, wherein "m" and "n" are integers greater than 1 , M is a metal cation selected from the group consisting of metals and transition metals, and R is an aromatic bridge composed of one or more aromatic heterocyclic moieties. Contrary to the fused metalloporphyrin tapes of the state of the art, which consist of a linear (1 D) arrangement of fused metalloporphyrin units, the bridged fused metalloporphyrinpolymers according to the present invention consist of a laminar (2D) array of metalloporphyrin units. According to the invention, the metalloporphyrin units are fused together in one dimension in their [3- and meso-positions. In the case of Formula 1 , the metalloporphyrin units are triply fused (|3-|3, meso-meso, and |3-|3), whereas in the case of Formula 2, the metalloporphyrin units are doubly fused ([3-meso and mesofl). In addition, the metalloporphyrin tapes are connected through bridges composed of one or more aromatic heterocyclic moieties in their positions 10 and 20, thereby forming bridged fused metalloporphyrin polymers which extend in two dimensions.

[0012] According to one embodiment of the present invention, the metal cation M may be selected from the group consisting of Mg(ll), Cr(lll), Mn(lll), Fe(lll), Co(ll), Ni(ll), Cu(ll), Zn(ll), Ru(ll), Pd(ll), Ag(ll), Pt(ll), or a mixture thereof. Selection of M enables to tune electronic and optoelectronic characteristics and the binding affinity to reactants and catalytic activity of the bridged fused metalloporphyrin polymers.

[0013] According to one embodiment of the present invention, the aromatic bridge R may comprise or consist of one or more heterocyclic aromatic compounds selected from substituted or unsubstituted five-membered rings with one heteroatom, such as pyrrole, phosphole, arsenole, stibole, bismole or a chalcogenophene such as furan, thiophene, selenophene or tellurophene, substituted or unsubstituted five-membered rings with two heteroatoms, such as imidazole, pyrazole, oxathiole, isoxathiole, oxazole, isoxazole, thiazole, isothiazole, dithiole, substituted or unsubstituted fivemembered rings with three heteroatoms, such as triazoles, furazan, thiadiazole, dioxazole, dithiazole, or substituted or unsubstituted polycyclic moieties, such as ethylenedioxythiophene, indole, isoindole, indolizine, quinoline, isoquinoline, dibenzopyrrole, dibenzofuran, benzothiadiazole, or mixtures thereof. Selection of R allows for the formation of bridged fused metalloporphyrin polymers with tunable electronic, optoelectronic, chemical or catalytic properties.

[0014] Also part of the present invention is a method for forming bridged fused metalloporphyrin polymers according to the invention. The method comprises the steps of (i) providing a substrate in a vacuum chamber, and (ii) performing on said substrate an oxidative chemical vapour deposition reaction with an oxidant and at least one metalloporphyrin monomer of general formula 3:Formula 3, wherein M is a metal cation selected from the group consisting of typical metals and transition metals, and R’ is an aromatic heterocyclic moiety. M and R’ may be selected in the same way as M and R above, in order to form desired bridged fused metalloporphyrin polymers. R’ is the singly bound hydrogenated analogue of the bridging aromatic heterocyclic moiety R. The method of formation of metalloporphyrin polymers in a vacuum chamber by oCVD has been demonstrated in the past. The application on monomers according to Formula 3 for the formation of novel bridged fused metalloporphyrin polymers has not previously been demonstrated. The step of performing an oxidative chemical vapour deposition reaction on the substrate may comprise sublimating concomitantly but separately the oxidant and the at least one metalloporphyrin monomer of Formula 3 in the vacuum chamber to form gaseous phases respectively and delivering said gaseous phases on the substrate.

[0015] According to one embodiment, the step of performing oCVD on the substrate may additionally comprise sublimation of a composition R” concomitantly but separately from the oxidant and the at least one metalloporphyrin monomer in the vacuum chamber. R” may comprise or consist of one or more heterocyclic aromatic compounds selected from substituted or unsubstituted five-membered rings with one heteroatom, such as pyrrole, phosphole, arsenole, stibole, bismole or a chalcogenophene such as furan, thiophene, selenophene or tellurophene, substituted or unsubstituted five-membered rings with two heteroatoms, such as imidazole, pyrazole, oxathiole, isoxathiole, oxazole, isoxazole, thiazole, isothiazole, dithiole, and substituted or unsubstituted five-membered rings with three heteroatoms, such as triazoles, furazan, thiadiazole, dioxazole, dithiazole, or substituted or unsubstituted polycyclic moieties, such as ethylenedioxythiophene, indole, isoindole, indolizine, quinoline, isoquinoline, dibenzopyrrole, dibenzofuran, benzothiadiazole, or a mixture thereof. In one embodiment, R” comprises the fully hydrogenated analogue of thebridging aromatic heterocyclic moiety R and / or the singly bound hydrogenated moiety R’. It has been found that improved reaction yields may be achieved through concomitant but separate sublimation of composition R”.

[0016] According to one embodiment, the oxidant may be selected from the group consisting of iron(lll) chloride (FeCh), antimony(V) chloride (SbCIs), copper(ll) chloride (CuC ), copper(ll) perchlorate (Cu(CIO4)2), vanadium(V) oxychloride, iron(lll) trifluoromethanesulfonate, and copper(ll) trifluoromethanesulfonate.

[0017] According to one embodiment, the step of performing oCVD on the substrate may be performed at a pressure comprised between 10’4mbar to 10’2mbar and / or at a temperature of 25°C to 350°C, preferentially 100°C to 200°C.

[0018] According to one embodiment, the substrate may be a conductive substrate, preferentially fluorine-doped tin oxide (FTO) coated glass, indium tin oxide (ITO) coated glass, carbon paper (CP), carbon cloth (CC) and nickel foam.

[0019] The present invention further encompasses a device comprising a substrate and a thin conductive coating of bridged fused metalloporphyrin polymers of the invention.

[0020] Finally, the present invention includes the use of the bridged fused metalloporphyrin polymers of the invention in catalytic or electrocatalytic processes, such as water splitting.

[0021] The invention is particularly interesting in that fused metalloporphyrin tapes are crosslinked by conjugated bridges to yield highly conjugated porphyrin assemblies with superior catalytic properties. The bridged fused metalloporphyrin polymers with their highly crosslinked structure exhibit remarkable electrocatalytic activity, promoting low onset overpotential and higher reaction kinetics illustrated by low Tafel slopes.

[0022] In the present document, the verb “to comprise” and the expression “to be comprised of’ are used as open transitional phrases meaning “to include” or “to consist at least of”, not excluding the presence of further features or components. Unless otherwise implied by context, the use of singular word form is intended to encompass the plural, except when the cardinal number “one” is used: “one” herein means “exactly one”. Ordinal numbers (“first”, “second”, etc.) are used herein to differentiate between different instances of a generic object; no particular order, importance or hierarchy is intended to be implied by the use of these expressions. Furthermore, when pluralinstances of an object are referred to by ordinal numbers, this does not necessarily mean that no other instances of that object are present (unless this follows clearly from context). When this description refers to “an embodiment”, “one embodiment”, “embodiments”, etc., this means that the features of those embodiments can be used in the combination explicitly presented but also that the features can be combined across embodiments without departing from the invention, unless it follows from context that features cannot be combined.Brief Description of the Drawings

[0023] By way of example, preferred, non-limiting embodiments of the invention will now be described in detail with reference to the accompanying drawings, in which:Fig. 1 : shows a schematic view of an example of oxidative chemical vapour deposition (oCVD) reactor for the deposition of conjugated porphyrins using an oxidant;Fig. 2: represents the chemical reaction for the formation of a bridged fused metalloporphyrin polymer according to the present invention, wherein the porphyrin monomer units are triply fused, M = Cu, R’ = thiophenyl and the oxidant is copper(ll) chloride;Fig. 3: represents the chemical reaction for the formation of a bridged fused metalloporphyrin polymer according to the present invention, wherein the porphyrin monomer units are triply fused, M is a combination of Cu or Co, R’ = thiophenyl and the oxidant is iron(lll) chloride;Fig. 4: represents the chemical reaction for the formation of a bridged fused metalloporphyrin polymer according to the present invention, wherein the porphyrin monomer units are triply fused, M = Ni, R’ = ethylenedioxythiophenyl and the oxidant is iron(lll) chloride;Fig. 5: shows l(V) curves recorded with voltage sweeps from -4 V to +4 V for pNiDTP (Example 4; cubes), pNiDPP (Comparative Example 1 ; up-sided triangles), and pNiDTDPP (Comparative Example 2; down-sided triangles);Fig. 6: shows linear sweep voltammograms recorded for pNiDTP (Example 4) pNiDPP (Comparative Example 1 ), and pNiDTDPP (Comparative Example 2) in 1 M KOH solution (pH 13.6) with 100 mV s-1scan rate;Fig. 7: shows Tafel plots derived from voltammograms of pNiDTP (Example 4) pNiDPP (Comparative Example 1 ), and pNiDTDPP (Comparative Example 2).Detailed Description of a Preferred Embodiment

[0024] Water splitting is an attractive approach for sustainable fuels production, however the overall process occurs at considerably higher voltages than the theoretical thermodynamic potential (1.23 V) due to the large overpotentials needed to drive the kinetically sluggish water oxidation half-reaction. Therefore, OER catalysts working at low potentials are a fundamental requirement for the implementation of sustainable fuels production systems with low energy cost.

[0025] The bridged fused metalloporphyrin polymer according to the present invention were formed using oxidative chemical vapor deposition (oCVD) techniques known to the skilled person in the art. Fig. 1 represents a typical apparatus for use in oCVD.

[0026] Exemplary reaction schemes are shown in Figs. 2 to 4. In these cases, metalloporphyrin doubly substituted in positions 10 and 20 is sublimated under reduced pressure in the presence of an oxidant to form a bridged fused metalloporphyrin polymer according to the present invention. Typically, the metalloporphyrin is placed into a crucible within the vacuum chamber of an apparatus as shown in Fig. 1 . If solid, the oxidant is placed into a separate crucible within the vacuum chamber of an apparatus as shown in Fig. 1 . If liquid, the oxidant is placed into a jar connected to the vacuum chamber of an apparatus. A substrate is placed on the substrate holder, also within the vacuum chamber. The reaction proceeds by sublimation of the metalloporphyrin and sublimation or evaporation of the oxidant in the vacuum chamber, and leads to the deposition of the reaction product, i.e. the bridged fused metalloporphyrin polymer according to the present invention on the substrate, forming a thin conductive film.

[0027] As illustrated in Figs. 2 to 4, different substituted metalloporphyrins, including mixtures, may be used, and different oxidants may be employed.

[0028] The bridged fused metalloporphyrin polymer according to the present invention provide such desired advantages, as will be shown below.Example 1 : oCVD reaction of copper(ll) 5,15-(di-3-thienyl) porphyrin (CuDTP) withCuCI2

[0029] The oxidative chemical vapor deposition (oCVD) reaction of Cu(ll) 5,15-di(3- thienyl)porphyrins (CuDTP) in the presence of anhydrous copper(ll) chloride (CuCI2) (Fig. 2) was performed in custom build oCVD reactor (Fig. 1 ). Two low temperature evaporators loaded with CuDTP (10 mg) and CuCI2(160 mg) were heated at 255°C and 290°C respectively. The oCVD reaction was performed at stable pressure of 10’3mbar. To promote the oxidative coupling reaction, the substrate temperature was kept at 130°C. The resulting oCVD thin film prepared from the oCVD reaction of CuDTP and CuCI2(pCuDTP) exhibits a grey coloration, contrasting with the orange coloration of the reference thin film of CuDTP monomer deposited in the absence of oxidant under identical conditions (sCuDTP). This indicates the polymerization of CuDTP in presence of CuCI2.

[0030] UV-Vis-NIR absorption studies of oCVD pCuDTP thin film revealed the broadening and bathochromic shift of the Soret band and Q-bands. The absorption of the oCVD pCuDTP thin film extending into the NIR region up to 2500 nm signifies the presence of directly fused metalloporphyrins assemblies. The LDI-HRMS analysis of the oCVD pCuDTP thin film evidences the presence of (CuDTP)2dimers. CuDTP is foreseen to couple by both direct fusion and thienyl bridging to form a bridged fused metalloporphyrins polymer whose highly crosslinked structure prevents the ionization and desorption of oligomers bigger than dimers of only few fragments. Importantly, the oCVD pCuDTP thin film exhibits a superior conductivity and superior hydrogen evolution reaction (HER) catalytic activity (lower onset overpotential and lower Tafel slope) than the oCVD pCuDPP thin film prepared from Cu(ll) 5,15-di(phenyl)porphyrin (CuDPP) under the same conditions.Example 2: oCVD reaction of CuDTP and cobalt(ll) 5,15-(di-3-thienyl) porphyrin (CoDTP) with FeCh

[0031] The oxidative chemical vapor deposition (oCVD) of Cu(ll) 5, 15-di(3-thienyl) porphyrin (CuDTP) and Co(ll) 5, 15-di(3-thienyl) porphyrin (CoDTP) in the presence of iron(lll) chloride (FeCh) as the oxidant agent (Fig. 3), was conducted in a custom-build reactor equipped with three individual low temperature evaporators. Two low temperature evaporators were used to sublime the CuDTP and CoDTP monomers at 255°C and 260°C, respectively, with a load amount of 10 mg each. A third evaporatorwas used to sublime the oxidant at 150 °C, with a load amount of 150 mg. The pressure inside the reactor was kept at 10’3mbar under an argon atmosphere. The substrate holder was kept at 150°C, and the deposition time was set to 30 minutes. A reference coating of the sublimed monomers, s(CuDTP / CoDTP), was obtained under the same conditions, without supplying the oxidant. The oCVD coating obtained from CuDTP and CoDTP in the presence of FeCh, p(CuDTP-CoDTP), exhibits an intense green coloration, notably different from the orange color of the reference sublimed coating s(CuDTPZCoDTP) prepared in the absence of the oxidant. This is indicative of successful oxidative dehydrogenation and polymerization in the presence of FeCh, and the retention of the porphyrin macrocycle upon sublimation.

[0032] The UV-Vis-NIR spectrum of the p(CuDTP-CoDTP) coating depicted broadened and red-shifted Soret and Q bands, and absorption in the NIR spectral region above 1500 nm, pointing to the extension of the rr-conjugated system as result of the dehydrogenative C-C coupling between free meso- and [3- positions of metalloporphyrin building units, and between the thienyl substituents. The highly crosslinked structure of p(CuDTP-CoDTP) was evidenced by a very low number of fragments ionized and desorbed during LDI-HRMS analysis. Analysis of the dimer region of the LDI-HRMS spectrum revealed the presence of heterometallic CuDTP- CoDTP dimers, confirming the co-polymerization of the two different metalloporphyrins, as well as contributions related to fused homometallic species.Example 3: oCVD reaction of nickel(ll) 5,15-di(3,4-ethylenedioxythiophene) porphyrin (NiDEDOTP) with FeCI3

[0033] The oxidative chemical vapor deposition (oCVD) of Ni(ll) 5,15-di(3,4- ethylenedioxythiophene) porphyrin (NiDEDOTP) with iron(lll) chloride (FeCh) as the oxidant (Fig. 4), was undertaken in a custom-build reactor equipped with two low temperature evaporators. Two low temperature evaporators loaded with NiDEDOTP (20 mg) and FeCh (300 mg) were heated at 300°C and 130°C respectively. The oCVD reaction was performed at a substrate temperature of 100°C and a stable pressure of 10’3mbar.

[0034] The UV-Vis-NIR spectrum of the oCVD pNiDEDOTP thin film obtained from the reaction of NiDEDOTP with FeCh revealed broadened and red-shifted Soret and Q bands when compared to the spectrum of a reference sNiDEDOTP thin film obtainedfrom the sublimation of NiDEDOTP. Such a broadening and red-shifting of the Soret and Q bands, and the absorption in the NIR spectral region above 2000 nm, point to the extension of the rr-conjugated system as result of the dehydrogenative C-C coupling between free meso- and [3- positions of metalloporphyrins building units, and between the 3,4-ethylenedioxythiophene substituents. Importantly, the oCVD pNiDEDOTP thin film exhibits excellent oxygen evolution reaction (OER) catalytic properties (low onset overpotential, low Tafel slope, high stability).Example 4: oCVD reaction of nickel(ll) 5,15-(di-3-thienyl) porphyrin (NiDTP) with FeCh

[0035] NiDTP, which is thermally stable up to at least 420°C, was sublimed under reduced pressure (10-3mbar) in a custom-built reactor as illustrated by Fig. 1 in the presence of an excess of iron(lll) chloride (FeCh). Two low temperature evaporators loaded with NiDTP (10 mg) and FeCh (150 mg) were heated at 255°C and 150°C respectively. The oCVD reaction was performed at a substrate temperature of 150°C and a stable pressure of 10’3mbar for 30 minutes. The resulting oCVD thin film obtained exhibits a of grey coloration, contrasting with the orange coloration of the reference thin film of NiDTP monomer deposited in the absence of oxidant under identical conditions. This indicates the polymerization of NiDTP in presence of FeCh

[0036] UV-Vis-NIR absorption studies of oCVD pNiDTP thin film revealed the broadening and bathochromic shift of the Soret band and Q-bands. The absorption of the oCVD pNiDTP thin film extending into the NIR region up to 2500 nm signifies the presence of directly fused metalloporphyrins assemblies. The UV / Vis / NIR spectrum fully shifts from a band spectrum from sNiDTP to a continuous spectrum for pNiDTP, hinting to a superior extension of the rr-conjugated system in pNiDTP.Comparative Example 1 : oCVD reaction of nickel(ll) 5,15-(diphenyl) porphyrin (NiDPP) with FeCh

[0037] NiDPP, which is characterised by the absence of heteroaromatic moieties in its 10- and 20-positions, was expected not to undergo bridging reactions. It was sublimed under reduced pressure (10-3mbar) in a custom-built reactor as illustrated by Fig. 1 in the presence of an excess of iron(lll) chloride (FeCh). Two low temperature evaporators loaded with NiDPP (10 mg) and FeCh (150 mg) were heated at 242°C and 150°C respectively. The oCVD reaction was performed at a substrate temperature of 150°C and a stable pressure of 10’3mbar for 30 minutes. The resulting oCVD thinfilm obtained exhibits a of green coloration, contrasting with the orange coloration of the reference thin film of NiDPP monomer deposited in the absence of oxidant under identical conditions. This indicates the polymerization of NiDPP in presence of FeCh

[0038] UV-Vis-NIR absorption studies of oCVD pNiDPP thin film revealed the broadening and bathochromic shift of the Soret band and Q-bands. The absorption of the oCVD pNiDPP thin film extending into the NIR region up to 2500 nm signifies the presence of directly fused metalloporphyrins assemblies.Comparative Example 2: oCVD reaction of 5,15-(di-3-thienyl) 10,20-(diphenyl) porphyrin (NiDTDPP) with FeCh

[0039] NiDTDPP, which is characterised by the presence of phenyl groups in its meso-positions, was expected not to undergo porphyrin fusion in the meso- and [3- positions. It was sublimed under reduced pressure (10’3mbar) in a custom-built reactor as illustrated by Fig. 1 in the presence of an excess of iron(lll) chloride (FeCh). Two low temperature evaporators loaded with NiDTDPP (10 mg) and FeCh (150 mg) were heated at 300°C and 150°C respectively. The oCVD reaction was performed at a substrate temperature of 150°C and a stable pressure of 10’3mbar for 30 minutes. The resulting oCVD thin film obtained exhibits a brown coloration, contrasting with the yellow coloration of the reference thin film of NiDTDPP monomer deposited in the absence of oxidant under identical conditions. This indicates the polymerization of NiDTDPP in presence of FeCh

[0040] UV-Vis-NIR absorption studies of oCVD pNiDTDPP thin film revealed the broadening and bathochromic shift of the Soret band and Q-bands, suggesting that the thienyl substituents provide amenable positions for the intermolecular dehydrogenative coupling of porphyrins in oCVD.Synthesis: Electrical and Electrocatalytic Properties of films obtained in Example 4 and Comparative Examples 1 and 2

[0041] The electrical properties of pNiDTP (Example 4), pNiDPP (Comparative Example 1 ) and pNiDTDPP (Comparative Example 2) deposited onto chips patterned with interdigitated electrodes were investigated to highlight the benefit of thienyl- bridging on the functional properties of fused porphyrin tapes (Fig. 5). The recorded current-voltage (l(V)) characteristics show ohmic behavior for all oCVD thin films, indicating a resistor-like nature. pNiDTP exhibits the highest conductivity value, at18.57 mS crrr1, significantly higher than pNiDPP (6.94 mS cm’1) and pNiDTDPP (8.11 mS cm’1). DFT calculations show that NiDTP undergoes polymerization through both available meso / p positions and thienyl substituents, resulting in a crosslinked structure.

[0042] The impact of the expansion of the rr-system related to the thienyl bridging of fused porphyrin tapes on their electrocatalytic performance towards the oxygen evolution reaction (OER) of the Ni(ll) porphyrin-based conjugated polymer thin films of Example 4 and Comparative Examples 1 and 2 was investigated: An alkaline solution (1 M KOH with pH 13.6) was selected for electrochemical characterizations. As showed in Fig. 6, pNiDTP and pNiDPP thin films show a reduced onset overpotential (r|pn) with respect the OER potential (1.23 V vs. RHE) of 266 mV and 278 mV, respectively, whereas the value for pNiDTDPP is 302 mV (Fig. 6).

[0043] Fig. 7 shows Tafel plots for the metalloporphyrin polymers obtained in Example 4 and Comparative Examples 1 and 2, indicating higher reaction kinetics of pNiDTP (Tafel slope of 69.9 mV / dec) over pNiDTDPP, and comparable to pNiDPP.

[0044] While specific embodiments and examples have been described herein in detail, those skilled in the art will appreciate that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.

Claims

Claims1. Bridged fused metalloporphyrin polymer comprising meso-[3, [3-meso doubly fused and / or meso-meso, |3-|3, |3-|3 triply fused metalloporphyrin tapes connected by aromatic bridges, and represented by Formula 1 or Formula 2:Formula 2 wherein“m” and “n” are integers greater than 1 ,M is a metal cation selected from the group consisting of typical metals and transition metals, andR is an aromatic bridge composed of one or more aromatic heterocyclic moieties.

2. Bridged fused metalloporphyrin polymer according to claim 1 , wherein M is a metal cation selected from the group consisting of Mg(ll), Cr(lll), Mn(lll), Fe(lll), Co(ll), Ni(ll), Cu(ll), Zn(ll), Ru(ll), Pd(ll), Ag(ll), Pt(ll), or a mixture thereof.

3. Bridged fused metalloporphyrin polymer according to claim 1 or 2, wherein R comprises or consists of one or more heterocyclic aromatic compounds selected from substituted or unsubstituted five-membered rings with one heteroatom, such as pyrrole, phosphole, arsenole, stibole, bismole or chalcogenophene such as furan, thiophene, selenophene or tellurophene, substituted or unsubstituted fivemembered rings with two heteroatoms, such as imidazole, pyrazole, oxathiole, isoxathiole, oxazole, isoxazole, thiazole, isothiazole, dithiole, substituted or unsubstituted five-membered rings with three heteroatoms, such as triazoles, furazan, thiadiazole, dioxazole, dithiazole, or substituted or unsubstituted polycyclic moieties selected from ethylenedioxythiophene, indole, isoindole, indolizine, quinoline, isoquinoline, dibenzopyrrole, dibenzofuran, benzothiadiazole, or mixtures thereof.

4. Method of forming a bridged fused metalloporphyrin polymer thin film on a substrate the method comprising the steps of- providing a substrate in a vacuum chamber, and- performing on said substrate an oxidative chemical vapour deposition reaction with an oxidant and at least one metalloporphyrin monomer of general formula 3:Formula 3 whereinM is a metal cation selected from the group consisting of typical metals and transition metals, andR’ is an aromatic heterocyclic moiety.

5. Method according to claim 4, wherein M is a metal cation selected from the group consisting of Mg(ll), Cr(lll), Mn(lll), Fe(lll), Co(ll), Ni(ll), Cu(ll), Zn(ll), Ru(ll), Pd(ll), Ag(ll), Pt(ll), or a mixture thereof.

6. Method according to claim 4 or 5, wherein R’ comprises or consists of one or more heterocyclic aromatic compounds selected from substituted or unsubstituted five-membered rings with one heteroatom, such as pyrrole, phosphole, arsenole, stibole, bismole or a chalcogenophene such as furan, thiophene, selenophene or tellurophene, substituted or unsubstituted fivemembered rings with two heteroatoms, such as imidazole, pyrazole, oxathiole, isoxathiole, oxazole, isoxazole, thiazole, isothiazole, dithiole, substituted or unsubstituted five-membered rings with three heteroatoms, such as triazoles, furazan, thiadiazole, dioxazole, dithiazole, or substituted or unsubstituted polycyclic moieties selected from ethylenedioxythiophene, indole, isoindole, indolizine, quinoline, isoquinoline, dibenzopyrrole, dibenzofuran, benzothiadiazole or a mixture thereof.

7. Method according to any one of claims 4 to 6, wherein the step of performing on said substrate an oxidative chemical vapour deposition reaction comprises sublimating or evaporating concomitantly but separately the oxidant and the at least one metalloporphyrin monomer in said vacuum chamber to form gaseous phases respectively and delivering said gaseous phases on the substrate.

8. Method according to any one of claims 4 to 7, wherein the step of performing on said substrate an oxidative chemical vapour deposition reaction additionally comprises sublimation of a composition R” concomitantly but separately from the oxidant and the at least one metalloporphyrin monomer in said vacuum chamber, wherein R” comprises or consists of one or more heterocyclic aromatic compounds selected from substituted or unsubstituted five-membered rings with one heteroatom, such as pyrrole, phosphole, arsenole, stibole, bismole or a chalcogenophene such as furan, thiophene, selenophene or tellurophene, substituted or unsubstituted five-membered rings with two heteroatoms, such as imidazole, pyrazole, oxathiole, isoxathiole, oxazole, isoxazole, thiazole,isothiazole, dithiole, substituted or unsubstituted five-membered rings with three heteroatoms, such as triazoles, furazan, thiadiazole, dioxazole, dithiazole, or substituted or unsubstituted polycyclic moieties, such as ethylenedioxythiophene, indole, isoindole, indolizine, quinoline, isoquinoline, dibenzopyrrole, dibenzofuran, benzothiadiazole, or a mixture thereof.

9. Method according to any one of claims 4 to 8, wherein the said oxidant is selected from the group consisting of: iron(lll) chloride (FeCh), antimony(V) chloride (SbCIs), copper(ll) chloride (CuC ), copper(ll) perchlorate (Cu(CIO4)2), vanadium(V) oxychloride, iron(lll) trifluoromethanesulfonate, and copper(ll) trifluoromethanesulfonate.

10. Method according to any one of claims 4 to 9, wherein the step of performing on said substrate an oxidative chemical vapour deposition reaction is performed at a pressure comprised between 10’4mbar to 10’2mbar and / or at a temperature of 25°C to 350°C, preferentially 100°C to 200°C.

11. Method according to any one of claims 4 to 10, wherein the substrate is a conductive substrate such as fluorine-doped tin oxide (FTO) coated glass, indium tin oxide (ITO) coated glass, carbon paper (CP), carbon cloth (CC) and nickel foam.

12. Device comprising a substrate as defined in claim 11 and a conductive coating of bridged fused metalloporphyrin polymers as defined in any one of claims 1 to 4 or obtained according to a method of any one of claims 5 to 10.

13. Use of a conductive coating of bridged fused metalloporphyrin polymers as defined in any one of claims 1 to 4 or obtained according to a method of any one of claims 5 to 10, a substrate as defined in claim 11 or of a device as defined in claim 12 in a catalytic or electrocatalytic process, such as water splitting.

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