Multifunctional Porous Organics Synthesis

Multi operating(a) poriferous Organics SynthesisTITLE OF WORKThe subtraction and characterisation of functionalized holey innatesAbstractLophine establish motifs arrive been studied for some(prenominal) years due to their photochromic nature, new-fangled literature has seen attempts to connect two etymons to hundred based backbones. In this report we impart discuss attaching sextuplet lophine corpuscles to a single backbone which is a phosphazene take a hop. Cyclophosphazene sounds nourish a preposterous con take formation al humbleding for supramolecular architectures to be formed by varying the substituents, these architectures range from 0-2D structures. The hexalophine molecule exhibits 1D channels due its unique descriptor which eliminates to the formation of a porous material. Porous positives atomic turn of events 18 of mettlesome interest in recent literature due to them being a cheaper, less toxic alternative to MOFs as well as having the ability t o be modified and tailored easily due to the simple starting materials. In this report we sh completely verbalise unreal paths from simple molecular build blocks to hexalophine (32%) and two derivatives, complicated 4 (46%) and 5 (15%). These two derivatives amaze the probable to increase pore stability. This report pull up stakes to a fault include the oxidization of hexalophine to its innate species which were found to dis hornswoggle photochromic properties and it is in like manner believed that this material could contain light gated pores which argon closed in the dimer form of the harvest-home but thusly extend upon barb of UV of 365nm.1. introduction1.0 Properties and potential recitations of LophineThis report will feature chemistry based upon the triphenylimidazolyl based prows (TPIRs) as well as the dimer form hexaarylbi glyoxaline (HABI). Lophine (2,4,5-triphenyl-1H-imidazole) is a heterocyclic imidazole derivative where three phenyl lots atomic numb er 18 attached to the imidazole beleaguer (figure 1), these imidazole derivatives are an area of importance due to the many another(prenominal) raise properties it possesses. Lophine has been of interest to inquiryers for many years with its chemiluminescent properties being setoff sight in 1877 by Radziszewski.1 The oxidation of the lophine molecule fol measlys the answer scheme to a lower place, where lophine is alter to the TPIR radical submit via addion of base and treatment with Fe forming one of six dimers two in solution and the solid plead (figure 2). These materials display photochromic, thermochromic and piezochromic properties. The implement of photochromism of the lophine dimer is the homolytic cleavage of the 2C-1N stick with of the dimer by shaft with light, forming two lophine radicals.2 The fast semblance vary associated with this dimer opening means there is a potential use in display screens or as the basis for molecular switches, where peter with light opens the dimer forming the radical in turn switching the external region On/Off. These accomplishable applications have caused a focus on creating methods to keep in line and control the colour of these materials and as well as to increase the wander of switching.3 The colour of the radical form is dependent upon the substituents on the remember, the to a greater extent flux the system the further toward the red side of the spectrum the colour.4 Lophine displays piezochromic properties in its solid state, upon applying insistence lophine crystals the colour change of color to blue/green has been observed, this occurs via the radical disassociation of the 1N-1N dimer bond.5 Other to a greater extent unusual modes have been of dimerization much(prenominal) as the 2C-2C have now as well been isolated, this mode features a unusually long C-C bond.3 examine 1 The structure of Lophine (2,4,5-triphenyl-1H-imidazole)Another interesting lophyl radical derivative is the 1,8 -TPID-naphthalene radical which consists of 2 lophine radicals connected by a naphthalene call. 1,8-TPID-naphthalene has been characte matured in the solid state by Abe et al who studied the photoreactivity of the compound. 1,8-TPID-naphthalene allowed the group to fix two radicals onto a backbone signification that the radicals were in close proximity and could dimerise easily as debate to two radicals not connected via a backbone which first destiny to find eachother in order for dimerization to occur (figure 3). They found that the dimer could be cleaved photochemically giving the diradical and then could be thermally converted back to the dimer.6 They as well as found that the formation of a peroxide bridge was much more common than previous literature had accounted for. This bridging occurred when the 1,8-TPID-naphthalene radical was placed under an O2 atmosphere.7 This peroxide bridge formation is rattling important as when type O quenches the eddy to form the closed s hell peroxide it does so irr constantlysibly meaning the material is no longer photochromic. It was then shown that this peroxide degradation track preempt be generalised for the chromic dimers of TPIR materials, with non-tethered TPIRs forming similar peroxide bridges.8 A recent development by the same research group has too shown how a thiophene substituted phenoxyl-imidazole radical complex (PIC) can generate two non-equivalent radical upon irradiation with UV light. The colour change can be fine-tuned from tens of seconds to nanoseconds, however a sensitivity to lower wavelengths of light meant that applications were limited. This problem was rectified by adding a phenyl group to the 5 postal service of the thiophene ring.9 gauge 2 The six potential dimerization modes of two lophyl radicals.3 witness 3 Illustrates the reversible conversion of 1,8-TPID-naphthalene between its radical and dimer forms.1.1 Hexa-substituted Phophazene Rings, Tectons and Crystal EngineeringA key component of this project was the evolution of the Phosphazene ring as demulcent tecton a tecton is a molecular building block that interacts with sticky sites, formally known as supramolecular synthons, via spatial order of battles to scram the formation of supramolecular aggregates. The search for new tectons is a hot area of research due to the constantly increase field of crystal engineering where the convey is to produce functional single crystal materials apply intermolecular interactions. The arrangement of molecules in solid state structures is largely dependent on hit a fine balance between intramolecular forces and pugilism interactions, acquaintance of these forces is key to the field of crystal engineering.10 In general, hard tectons interact via more robust synthons than soft tectons and therefore usually crystallise with unambiguous geometries. Whereas soft tectons and less robust synthons allow for the formation of supramolecular isomers (figure 4).11 These tectons allow for many functional materials to be formed in a one pot subtraction, they also have the ability to be care encompassingy adjusted to alter and mend upon their functionality.12 Cyclophosphazenes are extremely soft tectons that interact with soft synthons to give a large variety of supramolecular architectures in the solid state. The conformation of the cyclophosphazenes is also very(prenominal) interesting as three substituents reside higher up the plane of the ring and three below (figure 5). It was found that small modifications to the substituents attached to the ring gave supramolecular architectures ranging from 0D to 2D structures (figure 6) such as include monomer, dimer, cyclic hexamer, zigzag chain, linear chain, two-base hit chain, graphite-type sheet, rectangular grid and hexagonal close-packed sheet. Such variety of structures came from the easy rotation about the exocyclic P-N bonds, which allowed variable directionalities for all of the N-H bonds. 11 3a) 3b) normal 4a) Shows benzene-1,4-dicarboxylic panelling a classic object lesson of a hard tecton. 4b) shows a silanetriol a classic soft tecton.Figure 5 Conformation of a Hexa-substituted Phosphazene Ring.Figure 6 Schematic re collapseations of aggregation patterns of (RNH)6P3N3 in the solid state.111.2 Magnetism and magnetized FrustrationThe materials we aim to make during this project once appropriately oxidize should go on to form dimers which when irradiated with UV light form decided radicals containing unmated electrons thus giving each radical an associated magnetised moment. torpid organic radicals tend to be para magnetised and exhibit Curie- Weiss behaviour, where the reel vectors of the unpaired electrons are randomly aligned above the Curie temperature (Tc), which is the critical temperature below which the long ordered state is established, unless a magnetic field is applied. If spin vectors are parallel to each other below the Curie temperature then the material is ferromagnetic, if the spin vectors are aligned antiparallel to one another(prenominal) the material is antiferromagnetic.13Due to the geometry of the phosphazene ring (three substituents pointing up above the plane of the ring and three below) there is the possibility of forming a 2D angular wicket gate of spins if the substituents are organic radicals. This could possibly lead to nonrepresentational magnetic licking due to the fact that the two nearest neighbours to a spin are themselves nearest neighbours and therefore antiferromagnetic couplings cannot be satisfied (figure 7).14 This can lead to very interesting magnetic properties. Most solid state examples of this geometric frustration tend to be transition metal oxides, however, studies have been through with(p) on organic systems that also distribute geometric frustration.13 One example of this is m-MPYNNP+ which is a spin organic radical that upon dimerization forms a 2D triangular grille which demonstrate s the aforementioned geometric frustration.14The issue of spin frustration has been almost for a long time as Quantum spin liquids (QSL) were first theoretically proposed by Anderson many years ago which are now a hot topic of research due to the realisation of these QSLs in organic materials such as k-(ET)2-CH2(CN)3, which has a near perfect triangular lattice with angles very close to 120.15 A QSL is an exotic ground state where interacting spins continuously fluctuate with no formation of low range magnetic order even at sufficiently low temperatures.16Figure 7 Antiferromagnetic coupling cannot be fulfilled causing geometric magnetic frustration.1.3 Porous MaterialsPorous materials are as important as ever due to their wide spread use in several field such as catalysis and swagger absorption,17 meaning they can play a critical role in the route to solving our growing energy shortage problems. Porous materials are instantly associated with materials such as zeolites, metal orga nic framework (MOF) and organic polymers. MOFs are characterised by their tuneable pores and intact flexibility which more classical carbon or oxide based structures do not possess, this gives a wide range of applications for MOFs such as gas storage, separation, drug delivery or catalysis.18 Porous organics have been discovered in nature but are largely created synthetically and approaches often need to be coupled with knowledge of crystal engineering. These materials are often held together by directional forces which form extended frameworks of noncovalent interactions such as - interactions, total heat bonding or coordinate bonding (figure 8).17 Like zeolites and MOFs porous organics have the ability to selectively absorb atoms and molecules in the gas phase.19 There are many positives to these porous organics, they are often cheaper to implicatione and less toxic as well as being far less wakeless than metal containing MOFs.Figure 8 One example of a Porous Organic by Sozz ani et al.1.4 P3N3 HexalophineThe chemistry of P3N3 Hexalophine incorporates much of the chemistry discussed above and has many interesting properties. The P3N3 Hexalophine molecule consists of six lophine substituents attached to the phosphazene ring via a P-O bond (figure 9). Previous work in the Robertson group found that the solid state structure of Hexalophine consisted of a pseudo hexagonal motif giving rise to 1D channels that run parallel to the stacking axis (figure 10). The molecule maintained its D3 amity in the solid state. The phenyl rings twist to maximise pi-stacking interaction and the 3 imidazole nitrogen atoms form hydrogen bonds to a central pee molecule. There are 4 pi-pi interactions that stabilise this structure, the molecules are in a slipped conformation allowing the phenyl and imidazole to rings overlap. Other non-covalent interactions such as van der Waals interactions also help to stabilise the structure. The high symmetry of the structure which comes f rom the hexa substituted phosphazene ring (three above the plane of the ring and three below) gives an equal distribution of intermolecular forces giving a high probability of forming a stable porous structure. IGA measurements with CO2 loading at 195K shows a Type I isotherm with absorption reaching 8cm3g-1 at a closet of 700mmHg confirming the materials microporosity. so far only a small fraction of the void space contained CO2.Figure 9 The structure of Hexalophine.Figure 10 The crystal structure of Hexalophine, illustrating the 1D channels.1.5 account of ProjectThe aim of this project is to combine our knowledge of the chemistry of twain lophine radical systems and cyclophosphazene rings to find elegant synthetic routes which will modify upon the porous properties of hexalophine. This will be done by varying the ring substituents to increase stability of the pores and to improve its gas absorption properties. Three lophine derivatives have been identified as plausible cand idates for thid are where two of the phenyl groups on the lophine will be replaced by two thiophene rings and two pyridine rings respectively, with the position of the nitrogen in the pyridine ring being varied depending upon the synthetic pathway (figure 11). We wish to tax write-offe and fully characterise these derivatives including growing single crystals for morphologic studies via X-ray crystallography. Also a stoichiometric controlled oxidation of the hexalophine material to its neutral radical/dimer pair is demand in order to further ask the properties of hexalophine such as the possibility of creating a photochromic material that has light gated pores that open on irradiation with UV light.R= or orFigure 11 the synthetic targets of this project.2. Results and discussion2.0 Hexa-benzaldehyde SynthesisThe first step in this synthetic project involved attaching six benzaldehyde units to the phosphazene ring via a P-O oxygen bond. This was achieved by reacting the phospho nitrillic chloride trimer along with 6 equivalents of 4-hydroxybenzaldehyde, yard carbonate in ironical THF (figure 12). The reception was monitored with 31P NMR which showed completion when only a vest was present in the spectra indicating full substitution. This produced the compound 1 which was the precursor for many of the consequent reactions. The reaction gave the desired accede in a fairly low yield (45%). Whilst the yield was slightly low the FT-IR showed all of the characteristic absorptions such as C=O (1697cm-1) and railway car-CAr (1585cm-1). 31P NMR was conducted and showed a sharp singlet at 7.08ppm which indicated full substitution on the phosphazene ring as all of the environments are equivalent. 1H NMR was also conducted and show a singlet at 9.87ppm with an integrating of 6Hs which was as expected for the 6 aldehyde protons, two doublets were found in the aromatic region and integrated to 12Hs each which was correct for the number of protons expected. The C HN digest was almost perfect with less than 0.2% difference from the calculated set, this indicated that the product was of high purity. Mass spectometry also indicated that the desired product had been synthesized as a M+Na+ acme was detected at 884.Figure 12 The reaction scheme for the synthesis of 1.2.1 Synthesis of Hexalophine and Hexalophine derivatives2.1.0 Using DiketonesThe synthesis of hexalophine and hexalophine derivatives is important due to their porous properties which can be of great importance in fields such as gas storage and catalysis. The method for attaching six lophine units to the ring was a ring condensation of 1 on the six benzaldehyde units attached to the phosphazene ring using a synthesis based upon Radziszewskis synthesis.1 The product 2 was achieved by reacting 1 along with six equivalents of benzil, ammonium acetate in excess in polar acetic vitriolic (figure 13). The yield for 2 was quite forgetful (32%), the FT-IR showed all of the characteri stic peaks such as CAr-H (3055cm-1), C=N (1604cm-1) and CAr=CAr (1538cm-1) indicating the desired product had been formed. This was further confirmed by both the 31P and 1H NMR, the 31P NMR showed a singlet at 8.36ppm which indicates full substitution on the phosphazene ring. The 1H NMR showed a singlet at 12.65ppm which had an integration equal to 6Hs which is delegate of the 6 imidazole N-Hs, it also showed multiplets in the aromatic region with an integration of 84Hs which is exactly the number of aromatic hydrogens in the desired product. CHN analysis of the product correlated well with the desired structure, especially when three molecules of urine were factored into the calculation. It is unsurprising that this compound also contained water due to its porous nature. NH4OAc Acetic acid(6eq.)Figure 13 The reaction scheme for the synthesis of 2.Another reaction designed based upon the ring condensation reaction was the synthesis of 4. This synthesis builds upon the diketone fu nctionality as above, however, in this reaction the R groups of the diketone thenil were thiophene rings as contrasted to the phenyl rings of benzil. Thenil like benzil was reacted with 1 and ammonium acetate in glacial acetic acid (figure 14). The yield for this compound, whilst better than 2, was still fairly low (46%). FT-IR showed the characteristic peaks such as CAr-H (3071cm-1), CAr=CAr (1643cm-1) and C=N (1607cm-1) indicating the target molecule had been synthesised. The 31P NMR showed a singlet at 8.26ppm over over over again indicating full substitution. The 1H NMR showed a singlet 12.91ppm with an integration of 6Hs representative of the 6 imidazole N-H hydrogens, it also showed multiplets in the aromatic region with an integration of 60 which was again exactly what was required for the number of aromatic hydrogens, indicating the correct product had been synthesised. The CHN analysis was close to the theorectical values required especially when four water molecules we re factored in, again this is unsurprising as this material like 2 is also expected to be porous. NH4OAc Acetic acid(6eq.)Figure 14 The reaction scheme for the synthesis of 4.Like thenil and benzil, pyridil is also a diketone where the two R groups are heterocycles, in this case the two heterocycles are pyridine rings. Pyridil was used again with the classical Radziszewski based synthesis to synthesise the compound 5 (Figure 15). The yield for this compound was very low (15%) due to a lot of clutch lost upon recrystallization and decomposition upon heating. The FT-IR showed the correct absorptions for the key functional groups such as C=N (1600cm-1) and P=N (1158cm-1) indicating that the target compound had been synthesised. as yet large OH absorption band (3349cm-1) was also present showing that the product contained a wide amount of water or ethanol. CHN analysis of the compound showed a vast difference in carbon and nitrogen values when compared to the theoretical values indi cating some impurities in the sample. The fact that the product contained considerable amounts solvent would also skew the result of the CHN analysis somewhat. NH4OAc Acetic acid(6eq.)Figure 15 The reaction scheme for the synthesis of 5.2.1.1 Using Aldehydes for an alternative supplyThe idea of using aldehydes such as pyridine carboxyaldehyde and benzaldehyde as opposed to the diketones used above was born when questioning on how we could stabilise the pores in the materials we wished to synthesise as larger groups could be added to these aldehyde starting materials. An alternative synthesis of 2 using twelve equivalents of benzaldehyde is illustrated in figure 16.The reaction was left(p) to reflux for 7 days however the 31P NMR showed a multiplet indicating that full substitution had not occurred or a mix of products was present. Unfortunately, this was a reoccurring group as the failed synthesis of 3 using twelve equivalents of pyridine carboxyaldehyde (figure 17) also showed a multiplet in the 31P NMR.Benzaldehyde (12 eq.)Figure 16 The reaction scheme for and alternative preparation of 2.Carboxyaldehyde (12 eq.)Figure 17 The reaction scheme for compound 3.2.2 Oxidation of Hexalophine and its derivativesThe oxidation of hexalophine is of great interest due to the potential properties it may possess, such as it possessing photochromic properties which may lead to light gated pores. For this oxidation an excess of potassium hydroxide was used to create the anion before 50 equivalents of the classical oxidising agent potassium ferrocyanide (III) were used to perform a one electron oxidation to the radical species 6, a yellow(a) to orange colour change is associated with the formation of the radical species. This radical species quickly dimerises and an orange to yellow colour change is associated with this. Upon irradiation with UV light (365nm) the dimer opens to form two radicals, the colour change associated with this was yellow to purple displaying t he photochromic behaviour of this compound (figure 18). The radical species is stable for a number of hours in the solid state unless gentle heating is applied which induces dimerization again and the colour change of purple to yellow is associated with this. FT-IR showed characteristic absorbances of CAr-H (2955cm-1), C-N (1301cm-1) and P=N (1198cm-1) which are present in the desired product.The thiophene hexalophine derivative 4 was also oxidised using the same classical oxidation conditions as above to form its radical species 7. Upon separation the system formed 3 layers, an organic layer, an aqueous layer and a solid substance formed which was dissoluble in neither. Both the organic layer and solid substance were irradiated with UV light to test for photochromic properties however neither displayed a colour change and thus further testing of this material via UV/Vis spectroscopy is required to determine its nature.Figure 18 A RBF containing the hexalophine dimer and radical, the purple is the radical species, the yellow is the dimer species.3. Conclusions and further workThe aim of this project was to synthesise and characterise functionalised porous organics based upon hexalophine as well as to perform oxidations to the radical species and try out their properties such as photochromism. For the most part the aim of the project has been met as two derivatives of hexalophine (4 and 5) and hexalophine (2) itself have been synthesised from simple molecular building blocks and characterised using a range of spectroscopic techniques such as NMR, FT-IR and CHN analysis. The next step in the characterisation of these materials would be to gain crystal structures via x-ray crystallography to show the packing arrangement of these molecules and to prove the existence of pores with in the molecule created from the unique conformation of the phosphazene ring. Additionally, once crystal structures have been gained gas absorption test should be taken to test both th e gas uptake properties and selectivity of certain gases. Yields for these experiments were quite low and the aldehyde reactions did not demonstrate full substitution onto the ring, one possible solution would be to try the reaction in a Parr pressure reactor. The oxidation of hexalophine was carried out with great success as the experiment present the proposed photochromic nature of the material, also the stability of this material with respect to air was very surprising. If possible crystal structures for this material should be obtained in order to check into further the possibility of light gated pores which when the molecule is in the dimer form are closed but once in the radical form are open.4. Experimental details4.0 Ma