ChemMat PhD Projects 2018 ed.

List of PhD research projects to be choosen by the candidates. Further details on the research projects can be requested by e-mail to the Programme Director or directly to the project supervisors.

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Study and Development of New Lanthanide Complexes  as Single Molecule Toroics (Ref. 02-2018)

Supervisor: Laura C.  J. Pereira  (C2TN/IST-UL), lpereira@ctn.tecnico.ulisboa.pt

Co-Supervisor: Abílio Sobral (FCTUC),  asobral@ci.uc.pt

Coordination compounds of f-elements, particularly those of lanthanides have accounted for some of the most eye-catching advances in molecular magnetics such as Single Molecule Magnets (SMM) [1]. In SMMs an anisotropy barrier obstructs the reversal of the molecular magnetic moment at very low temperatures [2].

More recently molecules with a toroidal magnetic state, (SMTs: single-molecule toroics) provided a new paradigm of SMMs, more promising for future applications such as quantum computing, high-density information storage and as multiferroics materials with magnetoelectric effect [3]. So far, SMTs have been made by assembly of wheel-shaped complexes in clusters of high symmetry with strong intra-molecular dipolar interactions between anisotropic metal ions. The advantage of lanthanides for obtaining SMTs is the strong uniaxial magnetic anisotropy of the ions in common low-symmetry ligand environments [4]. Large values of local magnetic moments afford strong intramolecular dipolar coupling, which was found to be responsible for the toroidal moment of the ground states of all investigated SMTs. While a wide range of synthetic chemistry has been used to create new SMMs, SMTs compounds are so far restricted to a small group of complexes with dysprosium [4]. The identification of relaxation processes is straightforward to obtain from AC susceptibility measurements but the precise description of the mechanism involved remains challenging, and a theoretical quantum mechanics modeling has just started to be pursued. By analogy with SMMs, lanthanide ions other than Dy are also good candidates to the assembling of SMTs. Our aim is therefore to extend these studies to a variety of new lanthanide compounds with different structural and electronic characteristics and fully characterize them establishing a correlation between their magnetic behaviour and the chemical structure and identifying the key features for the slow relaxation in magnetic toroidal systems. O-donor chelate ligands (based on O-donors, namely phenolate, carboxylate, acetylacetonate, alkoxides) and phosphine oxide derivatives or N-donor chelate ligands like poliazolates derivatives and Schiff base ligands will be used to prepare the SMT clusters.

The synthesis and structural characterization of these new materials will be done at the Physics and Chemistry Dept./FCTUC using different techniques such as X-ray Diffraction, Infrared spectroscopy, Differential Scanning Calorimetry, X-ray Fluorescence. Once the synthesized compounds are structurally characterized, magnetization measurements will be made. The facilities to perform the magnetic data are available in the C2TN/IST. Both static and dynamic magnetic properties of all the synthesized compounds will be characterized by magnetization and AC susceptibility measurements in extended temperature range down to 03K and under magnetic fields up to 12T. The effective magnetic moment, transition temperatures and paramagnetic Curie temperatures will be studied. These measurements will be done in the absence and in applied external magnetic fields, by varying temperature, frequency and time. When possible, Ab initio calculations in collaboration with international partners will be performed in order to elucidate the nature of the electronic states and calculate the toroidal moment.

  • [1]. Gatteschi, D.; Sessoli, R.; Villain, J. Molecular Nanomagnets; Oxford University Press: New York, 2006; Monteiro B. et al., J. Inorg. Chem. (2013) 5059.
  • [2]. Ishikawa N. et. al., J. Am. Chem. Soc. 2003, 125, 8694–8695; Martín-Ramos P. et al., J., Eur. J. Inorg. Chem, (2014) 511–517; Pineda E.M. et al., Nature Comm., 5, 5243.
  • [3]. Spaldin N.A. et al., J. Phys Cond. Matter, 2008, 20, 434203.
  • [4]. Ungur, L. et al.,Chem. Soc. Rev. (2014), 43, 6894-6905; Xue S. et al., Inorg Chem. (2012), 51, 13264-13270.

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Molecular Magnetic Conducting Bilayers (Ref. 03-2018)

Supervisor: Sandra Rabaça (C2TN/IST-UL), sandrar@ctn.tecnico.ulisboa.pt

Co-Supervisor: José António Paixão (CFisUC/FCTUC),  jap@pollux.fis.uc.pt

INTRODUCTION:

Organic conductors were initially proposed as possible high temperature superconductivity materials. While that was not achieved a new a class of materials immerged with a very rich diversity of ground states, ranging from antiferromagnets, insulators, to 2D metals, superconductors and physical phenomena that are very sensitive to magnetic field, pressure, and temperature. Since the first family of organic superconductors, the quasi-one dimensional Bechgaard salts (TMTSF)2X (X = ClO4, PF6, AsF6, etc.,), and after the quasi-two dimensional compounds (BEDT-TTF)2X there has been a remarkable development of bidimensional molecular conducting systems in particular with other derivatives of the electron donor BEDT-TTF.[1] Systems based on double layered structures, potentially more interesting, have however not been explored until recently [2].

THE NOVELTY:

This project aims at exploring bilayer conducting systems based on new cyano substituted BEDT-TTF derivatives as recently prepared in the C2TN group [2], and different inorganic anions including paramagnetic and SMM. These new organic donor were recently found to self-assemble in double layered structures in charge transfer salts with small anions [3]. However the whole range of different anions is far from been fully explored, namely paramagnetic anions which can lead to conducting magnetic materials where anomalous magneto resistance, quantum interference effects [4] and even superconductivity induced by magnetic fields [5] or the coexistence of SMM and conductivity [6] can take place. There is a variety of mechanisms for magnetoresistance (the change the electrical resistance by a magnetic field) which reflects the electronic structure and may be applied in different devices. Besides the common positive magnetoresistance of metals, there is a negative magnetoresistance in ferromagnets and since 1980′s large magnetoresistive in multilayer systems (e.g. magnetic tunnel junctions) gained importance. However low dimensional molecular metals reveal at low temperatures specific phenomena such as anomalous angle dependent magnetorresistence [7] or Shubnikov de Haas oscillations and other quantum interference effects [8] which are sensitive to the anisotropy and details of the electronic structure [9]. A more recent challenge are the effects resulting from conductions electrons and single molecule magnet centers [10].

The structural complexity of the double layer arrangement, usually associated to large unit cells, are not known in detail, and the physical properties of the bilayer systems, having as metallic systems two closely spaced Fermi-surfaces remain essentially unexplored. This project combines different areas of knowledge: organic chemistry in the synthesis of the donor; the use of electrochemical techniques for the preparation of charge transfer salts as single crystals; crystal engineering principles for correlation of structure-properties relationships, X‑ray diffraction using conventional and synchrotron sources for the analysis of complex structures and specialised measurements of magnetic and electrical transport properties to be correlated with quantum chemistry electronic band structure calculations.

WORK PLAN

The first stage of this project is to expand the preparation of the charge transfer salts of cyano substituted TTF donors with new anions (Cl-, Br-, NO3-, FeCl4-, GaCl4- ,NiCl4-, CuCl4-, ReF6, M(SCN)n) of variable size and magnetic moment and the growth of crystals by electrocrystallisation, with size and quality suitable for structural and physical characterisation studies. Different solvents and crystallisation conditions leading to different polymorphic structures will be explored.

Next step will be the characterization by single crystal X-ray diffraction, a crucial step for the understanding of the physical properties and their correlation with solid state structure. Due the large unit cells and the possible superstructures associated with anionic arrangements in different layers and intergrowth phenomena, the structural analysis will not be a trivial task. It is anticipated that in addition to standard single crystal diffractometers using laboratory sources, it will be required the use of synchrotron radiation at dedicated beamlines in European Large Scale Facilities such as the ESRF in Grenoble.

The last experimental task in this research programme is the measurement of electrical and magnetic properties of these systems. The magnetic properties of the materials, will be determined both using single crystals and polycrystalline samples both by DC magnetization and AC susceptibility under different magnetic fields up to 12 T and in a temperature range from room temperatures down to 0.3 K, using a variety of specialised instruments (Maglab and SQUID magnetometers) available at Low Temperature and High Magnetic Field Laboratory (LTHMFL) of C2TN. The electrical transport properties will be measured in single crystals also in the LTHMFL, in a first stage by four probe electrical resistivity and thermoelectric power measurements. In a second stage magneto resistance will be measured in selected single crystals and configurations under fields up to 18T and at very low temperatures (down to 0.3 K) in order to characterise the Fermi surface topology and the coherency of intra- and inter-layer electronic transport regime. Finally the measured physical properties in the different compounds will be compared with the predictions based on theoretical electronic band structure calculated for each of the different crystal structures, based on extended Huckel and DFT approaches.

  1. a) E. Coronado, P. Day, Chem. Rev. 2004, 104, 5419-5448; b) T. Mori, Chem. Rev. 2004, 104, 4947-4969.
  2. S. Oliveira, M. Almeida, S. Rabaça, et al. Beilstein J. Org. Chemistry, 2015, 11, 951-956.
  3. S. Oliveira et al., Inorg. Chem., 2015, 54, 6677-6679; b) S. Rabaça, et al. Inorg.Chem., 2016, 55, 10343–10350; c) S. Rabaça et al., Crystal Growth and Design, 2017, 17, 2801-2808.
  4. K. Clark, et al. Nature Nanotechnology, 2010, 5, 261-265.
  5. a) Uji, S, H, Kobayashi et al. Nature (London) 410, 908 (2001); b) Balicas L, et al. Phys. Rev. Lett. 2001 87(6):067002.
  6. a) N. D. Kushch, et al , Inorg. Chem., 2018, 57, 2386–2389 7- D. Graf J. S. Brooks, M. Almeida, et al., Phys. Rev. B, 2009, 80, 155104-1551108.
  7. 8- D. Graf J. S. Brooks, M. Almeida, et al., Phys. Rev B, 2007, 75, 245101-245108.
  8. 9- N. Kikugawa, L. Balicas, et al., Nature Comm., 2016, 7, 10903.
  9. 10- G. Cosquer, Y. Shen, M Almeida, M. Yamashita, Dalton Trans., 2018, DOI: 10.1039/c8dt01015c.

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Iron (III) polynuclear clusters as single-molecule magnets (Ref. 13-2018)

Supervisor: Manuela Ramos Silva (FCT/Univ. Coimbra), e-mail: manuela@pollux.fis.uc.pt

Co-supervisor: João Carlos Waerenborgh (C2TN/IST-UL), e-mail: jcarlos@ctn.ist.utl.pt

Single molecule magnets (SMM) consist of ion clusters with unpaired electrons, surrounded and bridged by organic ligands. The metal ions interact strongly intramolecularly and very weakly intermolecularly so that each molecule can be considered independent. The identical molecules are self-assembled in a periodic three-dimensional lattice. They possess a high spin ground state and strong Ising type magnetic anisotropy so that the magnetisation can be retained after the removal of the magnetic field. At very low temperatures the magnetization can be retained for several months [1,2].

SMMs can be applied in the storage of information with each molecule stocking one bit of information. In a suitable disk support, these molecules can be nanoscale magnetic particles of a sharply defined size and increase the current storage capacity by 10 000. SMMs are also strong candidates for the construction of quantum computers. They offer two main advantages when compared with other candidate systems for quantum computation: chemical synthesis provides a large number of identical nano-objects in a cheap straightforward way and molecules/clusters being larger than single ion impurities relax constraints for a local read out. Fe(III) polynuclear clusters [3] have recently attracted interest in this field due to their structural and redox stability in air [4].

The aim of this project is to obtain new Fe(III)SMMs with larger metal-metal interactions so that the critical temperature would be higher and the blocking temperatures, i.e., temperatures below which the magnetization remains for several months, would also be higher. Different ligands such assiliconcarboxylate or Schiff bases and synthesis strategies such as building clusters of higher dimensionality based on trimers of magnetic ions bridged by aminoacids will be used. All complexes will be characterized by single crystal X-ray diffraction. Magnetization studies will be done in a SQUID magnetometer in the 300 mK – 300 K temperature range. All materials will be studied by Mössbauer spectroscopy in the 2-300 K temperature range in order to obtain information on the Fe(III) spin states. A theoretical study will accompany the experimental work (synthesis, structuralcharacterization, magneticevaluation, etc.) so that magneto-structural correlations can be established.

The experimental work will take place at the Physics Department of FCT Univ. Coimbra and at C2TN, Instituto Superior Técnico, Loures.

The student should enrol in the University of Coimbra.

  • [1] R. Sessoli, D. Gatteschi, A. Caneschi, M. A. Novak, Nature 1993, 365, 141.
  • [2] M. Ramos Silva, P. Martín-Ramos, J. T. Coutinho, L. C. J. Pereira, J. Martín-Gil, Dalton Trans. 2014, 43, 6752-6761.
  • [3] M. Ramos Silva, J. N. J. Nogueira, P. A. O. C. Silva, C. Yuste-Vivas, L. C. J. Pereira, J. C. Waerenborgh, Solid State Phenomena 2013, 194 162-170.
  • [4] Y.-Y. Zhu, T.-T. Yin, S.-D. Jiang, A.-L. Barra, W. Wernsdorfer, P. Neugebauer, R. Marx, M. Dörfel, B.-W. Wang, Z.-Q. Wu, J. Slageren, S. Gao, Chem. Commun., 2014, 50, 15090-15093.

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Heterometallic Metal-Organic and Supramolecular Networks for Magnetically-Driven Applications (Ref. 16-2018)

Supervisor: Alexander Kirillov (CQE/IST-UL), kirillov@tecnico.ulisboa.pt

Co-supervisor: Laura Cristina Pereira (C2TN/IST-UL),   lpereira@ctn.tecnico.ulisboa.pt

 

This project proposes to design new heterometallic metal-organic frameworks (MOFs) and related supramolecular networks (SNs) for applications driven by their intrinsic magnetic properties.

The research on MOFs and SNs is an intensively growing area in crystal engineering, coordination, supramolecular, and materials chemistry. It attracts high attention due to the structural and practical characteristics of such materials, namely their high structural diversity, porosity, hydrogen bonding, interesting molecular sorption, ion exchange, host-guest, and magnetic properties, usually different from simple discrete metal-organic molecules [1-4].

Although great progress has been achieved in the synthesis and applications of homometallic MOFs, the metal-organic and supramolecular networks which bear two different metal ions are less common, while the heterotrimetallic compounds are limited to single cases. The presence of different types of metals within one molecule often leads to a remarkable synergic effect that may dramatically alter their magnetic and other properties. Hence, this feature of synergic effect is a key inspiring point in designing novel heterometallic materials. Another feature of such materials consists in the possibility of altering their properties by external stimuli (e.g., temperature, pH, magnetic field, light, exposure to solvents or gases) or modifying their structure and functionality during the self-assembly synthesis or crystallization steps.

The key objectives of the present project will be focused on:

(A) Synthesis of new hetero(di- and tri-)metallic coordination or related supramolecular networks bearing various combinations of transition metals (Cu, Fe, Co, Ni, Mn, etc.) by self-assembly and post-synthetic modification methods;

(B) Full structural and topological characterization of the obtained compounds and investigation of their specific properties (porosity, stability, host-guest interactions);

(C) In-depth investigation of magnetic properties of the obtained compounds by magnetic susceptibility techniques, followed by modelling and theoretical interpretation of magnetic behavior. Novel single molecule magnets (SMMs), single-chain magnets, or spin crossover compounds will also be explored and their magnetic properties will be studied and compared before and after their incorporation into MOFs and related host-guest systems [4];

(D) Optimization of selected systems, preparation of tuned compounds, and composite materials therefrom; search for advanced magnetically-driven applications of the most promising materials (molecular magnets, magnetically recoverable catalysts, or bioactive nanocomposites).

The principal synthetic advantages for the heterometallic MOFs and SNs will include the mild reaction conditions, the use of inexpensive metal sources (typically salts or oxides of transition metals) and commercially available and biorelevant chemicals as main building blocks (e.g., aminoalcohols, aminophosphines, N-heterocycles), and spacers/auxiliary ligands (aromatic carboxylates, simple metal-complex ions [M(CN)6]n-, or inorganic anions capable of transmitting magnetic interactions). Besides, a special attention will be paid to the implementation of principles of green chemistry, namely by using mild reaction conditions and water as a preferable reaction medium.

It is expected that the prospective student will get a good experience in the self-assembly synthesis, crystallization methods, and characterization of various heterometallic coordination compounds, as well as in the investigation of their magnetic properties and advanced applications.

This PhD work plan involves two research units, CQE and C2TN of IST-UL. The proponents are Alexander Kirillov (CQE) with expertise in Coordination Chemistry and Crystal Engineering and Laura Pereira (C2TN) with expertise in Solid State Chemistry and Physics and Magnetic Materials. The experimental work will take place mainly at CQE. The magnetic characterization of the materials will be performed at C2TN. The student will be enrolled in a PhD Program of IST.

References

  • [1] Metal-Organic Framework Materials (Eds.: L. R. MacGillivray, C. M. Lukehart), Wiley, 2014, 592 pp.
  • [2] S. R. Batten, D. R. Turner, S. M. Neville, Coordination Polymers: Design, Analysis and Application, RSC, 2009, 300 pp.
  • [3] Y. Cui, B. Li, H. He, W. Zhou, B. Chen, G. Qian,Acc. Chem. Res. 2016, 49, 483.
  • [4] D. Aulakh, J. B. Pyser, X. Zhang, A. A. Yakovenko, K. R. Dunbar, M. Wriedt, J. Am. Chem. Soc. 2015, 137, 9254.

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Multifunctional cobalt oxide nanofoams: novel electrode materials for supercapacitors and electrocatalytic oxygen reactions (FOAM4ENER) (Ref. 18-2018)

Supervisor: Diana Fernandes (LAQV-Requimte, FC-U. Porto) diana.fernandes@fc.up.pt

Co-supervisores: Maria Teresa Duarte (CQE – CTBM group / IST-UL) teresa.duarte@tecnico.ulisboa.pt

BACKGROUND: Electrochemical energy storage devices have become key players in the development of efficient solutions for energy management. Asymmetric supercapacitors (SCs) pave the way to boost electrical mobility and efficiency of storage systems, combining the “best of a battery” with the “best of a SC” to deliver enhanced energy and high power density, but still require important electrode materials developments to increase charge storage capacity and long-term stability. Zn-air batteries have raised interest due to low price and high energy density, but face important challenges that prevent its widespread application and require more efficient air electrode electrocatalysts, namely bifunctional electrodes for both oxygen reduction (ORR) and oxygen evolution (OER) reactions. Novel functional materials are the key to enable these 2 storage technologies.

Metallic nanofoams (MNFs) display high specific areas and a variety of pore sizes, being topmost choice for designing porous electrodes1. MNFs can be fabricated by electrodeposition, a low-cost route that takes advantage of the dynamic template formed by hydrogen bubbling that occurs simultaneously with metal deposition2.

Co-NFs have been rarely reported, but the team has been optimizing this material that can be oxidized to pseudocapacitive Co oxides and used as positive electrode in redox SCs and electrocatalyst for ORR and OER3. Concerning SCs, Co oxides are only electroactive in a narrow potential window, which limits its energy density. Functionalization with synergistic combinations of species containing multivalent cations enlarges that window, resulting in higher energy density thanks to multiple reversible redox processes. Co species are also good electrocatalysts for ORR, but still require dedicated functionalization to serve as bi-functional electrodes.

Functionalization of MNFs includes coating4, thermal treatment, decoration with oxides/hydroxides5, noble metals (Pt/Pd)6 and graphene7. A new class of materials that can be used to functionalize foams are polyoxometalates, which have gained increasing interest in energy production/conversion/storage, sensing and catalysis8. They have unique redox behaviour that can be finely tuned on purpose, by changing composition and structure. Graphene (GF) and its analogous have attracted interest in energy-related applications, mainly due to large surface areas, high conductivity and good mechanical properties. In particular, GF-based materials doped or co-doped with several heteroatoms (e.g N, B, S, P) have demonstrated to be effective bifunctional ORR/OER electrocatalysts9  and high capacity and rate capability electrode material for supercapacitors10 .

Objectives: the project FOAM4ENER aims at designing and preparing a novel generation of highly porous 3D Co-nanofoams (CoNFs) and Co-graphene nanofoams (Co-GF NFs) that after functionalization with polyoxometalates and graphene species can serve as high performance electrodes for energy storage in asymmetric supercapacitors (SCs) and as bifunctional electrocatalysts for the oxygen reduction reaction and oxygen evolution reaction in rechargeable metal air batteries.

CoNFs and Co-GF NFs will be produced by electrodeposition to tailor the morphology and the porosity of the deposited materials. The foams will be functionalized by 3 different routes: (i) oxidation at high temperatures to tailor Co oxides composition; (ii) deposition of POMs to form 3D nanostructures, exploring multiple redox responses; and (iii) POMs/doped-GF nanostructures tailored for enhanced pseudocapacitive behavior in SCs and electrocatalytic response towards ORR and OER.

Novelty: FOAM4ENER delivers novel solutions for electrochemical energy storage: high capacity electrodes for asymmetric SCs that can replace or support batteries for engine cranking and high power input, and high efficiency electrocatalysts for oxygen reactions, which are crucial for the large-scale implement of rechargeable metal-air batteries in electrical vehicles for smart mobility and stationary power generation. The team involves researchers from 2 research centers –LAQV-REQUIMTE (UPorto) and CQE (ULisbon) – that have experience in Electrochemistry, Chemistry and Material Chemistry and scientific records in the study of properties of functional films and nanocomposites for energy storage, hydrogen and oxygen production and electrocatalysis.

Workplan: The PhD workplan comprises five main tasks:

Task 1 – Fabrication of Co foams by electrodeposition: this task is centered on the production of Co foams, without and with GF incorporation by electrodeposition onto stainless steel (foils or mesh) substrates (e.g. AISI 304), a stable and corrosion resistant material adequate for low-cost and low weight current collectors. The resulting materials will be characterized by several techniques.

Task 2 – Tailoring of POMs, doped-GF and POM/doped-GF by chemical routes: this task is centered on the preparation and characterization of doped-GF, electroactive POMs and POM/doped-GF. It comprises synthesis of POMs, doped-graphene (N, S, P and B), and their bi-components (POM/doped-GF), with the final goal of producing multifunctional high performance electrocatalysts and pseudocapacitive materials.

Task 3: Functionalization of the CoNFs: The materials CoNFs and Co-GF NFs produced in task 1 will be submitted to temperature conditioning, and subsequently used for the immobilization of the materials produced in taks 2. The resulting materials will be characterized with several techniques.

Task 4: Energy storage ability of the composites: this task involves the study of the electrochemical response of the functional materials as electrodes for energy storage in asymmetric supercapacitor applications.

Task 5: ORR and OER electrochemical performances of the composites: this task involves the study of the electrocatalytic activity of the functional materials on OER and ORR.

 References:

    1. Jiang, B., et al., Sci Rep (2015) 5, 8
    2. Niu, J. C., et al., Int. J. Electrochem. Sci. (2015) 10 (9), 7331
    3. Schoeberl, C., et al., Int. J. Hydrog. Energy (2015) 40 (35), 11773
    4. Gao, G. X., et al., Small (2015) 11 (7), 804
    5. Qiu, K. W., et al., Electrochim. Acta (2015) 157, 62
    6. Kolaczkowski, S. T., et al., Catal. Today (2016) 273, 221
    7. Yang, J., et al., ACS Appl. Mater. Interfaces (2016) 8 (3), 2297
    8. Song, Y. F., and Tsunashima, R., Chem. Soc. Rev. (2012) 41 (22), 7384
    9. Lin, Z. Y., et al., Carbon (2013) 53, 130
    10. Sliwak, A., et al., Appl. Surf. Sci. (2017) 399, 265

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CoPoS: multifunctional Coordination Polymers for optical Sensing applications (Ref. 24-2018)

Supervisor: Carlos Baleizão (CQFM-IN/IST/ULisboa), carlos.baleizao@tecnico.ulisboa.pt

Co-supervisor: Alexander Kirillov (CQE/IST/ULisboa), kirillov@tecnico.ulisboa.pt

The main GOAL of the “CoPoS” proposal is to prepare new coordination polymers incorporating ruthenium phenanthroline complexes as active materials for temperature and oxygen optical sensing.

The INNOVATION of this project is combine the modular structural properties of coordination polymers with the sensing ability of ruthenium phenanthroline complexes in the same material.

Oxygen, being essential for life, is an immensely important chemical species. Determination of oxygen levels is required in numerous areas, including medicine, biotechnology, and aerospace. Temperature is a basic physical parameter, and its measurement is often required both in scientific research and in industrial applications. Real-time temperature monitoring is of paramount importance in industrial testing and manufacturing and also in many biomedical diagnostic and treatment processes. Among the many optical methods employed for sensing, luminescence has attracted special attention because it is sensitive and versatile. In comparison with contact sensors, luminescence-based sensors have advantages in applications where electromagnetic noise is strong or it is physically difficult to connect a wire as there is no contact with the medium in the sensing process. Additional advantages of a luminescence-based thermometer are the usually fast response and the spatial resolution that can extend from the macroscale (in the case of luminescent paints) down to the nanoscale (such as in fluorescence microscopy).[1]

The luminescences of ruthenium(II) phenanthroline and related polypyridyl complexes exhibit a strong temperature dependence and are very sensitive toward the presence of oxygen. The luminescence of such Ru(II) complexes is quenched by oxygen, and ruthenium(II) tris(4,7-diphenyl-1,10-phenanthroline) (Ru(dpp)3) is one of the most sensitive luminescence oxygen sensors due to the long luminescence lifetime. However, if the Ru complex (e.g., ruthenium(II) tris(1,10-phenanthroline); Ru(phen)3) is incorporated in an oxygen impermeable matrix, the Ru complex luminescence exhibits a strong temperature dependence. The photostability of such complexes is high and they can be excited in the visible region. These complexes exhibit luminescence lifetimes in the micro second range, allowing the use of simple measurements set-up.[2]

Coordination polymers (CPs) are typically compounds composed of metal cations and organic ligands that extend “infinitely” into one, two, or three dimensions. The design of new CPs is an intensively growing interdisciplinary research field, which attracts special attention due to unique structural and functional characteristics of such metal-organic materials, as well as many potential applications that also include molecular recognition and sensing.[3] The presence of multiple ligands and/or multinuclear metal centers in the same moiety, and the possibility to adjust the porosity and the particle size, motivate us to propose CPs as key material in the development of new temperature and O2 sensing materials. The objective is to use the versatility of CPs and ruthenium(II) polypyridyl complexes to obtain new sensing materials with improved characteristics and applicability.

As a STRATEGY, the “CoPoS” project comprises the following tasks:

  1. Synthesis and characterization of a series of multifunctional organic building blocks comprising 1,10-phenanthroline, 2,2’- and 4,4’-bipyridine and related cores with carboxylic acid groups.
  2. Application of these organic N,O-blocks for the self-assembly or solvothermal generation of ruthenium-based coordination polymers or discrete complexes. Use of the obtained compounds as secondary building units or precursors for the generation of more complex coordination polymers by introducing additional metal nodes selected from Ru or other metals (e.g., Cu, Fe, Co, Zn).
  3. Full structural and topological characterization of the obtained CPs, as well as the investigation of their thermal, host-guest, and luminescence properties. Selection of the most promising structures for sensing applications.
  4. The materials with higher porosities, and consequently high oxygen permeability, will be tested in the sensing of oxygen (trace analysis / partial pressure, 0-21% O2). The parameters to follow are the relative sensitivity, response time, and long term stability. This data will be compared against reference sensors.
  5. The temperature sensing evaluation will use the materials with higher degree of network condensation and reduced porosity, to decrease (or even avoid) the oxygen penetration. Due to the high thermal stability of CPs, we expect to cover a high range of temperatures (-100ºC up to 100ºC).
  6. The final task of the project will test the best materials in real applications, such as mapping the oxygen concentration in cells (cancer cells exhibit lower oxygen concentration) or measuring the temperature in fuel tanks for security reasons.

The ORIGINALITY and NOVEL concepts in this proposal are demanding and require high commitment from the team. This way, the supervisors combine expertise covering all areas of the project from organic synthesis, to CPs preparation and characterization, and sensing performance evaluation. Carlos Baleizão, is Principal Researcher at IST with expertise and a strong background in the development of new optical sensing systems and synthesis of new photoactive molecules.[4] Alexander Kirillov, Assistant Professor at IST, brings to the proposal a large experience in the design and assembly of functional multinuclear complexes and coordination polymers, and topological analysis of such materials.[5]

  • [1] R. Narayanaswamy, O. S. Wolfbeis, Optical Sensors for Industrial, Environmental and Clinical Applications, Springer, Berlin, 2004.
  • [2] J. N. Demas, B. A. DeGraff, Coord. Chem. Rev., 2001, 211, 317-351; X.-D. Wang, O. S. Wolfbeis, Chem. Soc. Rev., 2014, 43, 3666-3761
  • [3]  A. Morsali, L. Hashemi, Main Group Metal Coordination Polymers: Structures and Nanostructures, Wiley, 2017.
  • [4] C. Baleizão et al., Anal. Chem., 2008, 80, 6449-6457; C. Baleizão et al., RSC Advances, 2017, 7, 4627-4634.
  • [5] A. M. Kirillov et al., Inorg. Chem., 2016, 55, 125-135;   A. M. Kirillov, Coord. Chem. Rev., 2011, 255, 1603-1622.

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Novel lanthanide-based emitters for circularly polarized organic light-emitting diodes  (Ref. 27-2017)

Supervisor: Manuela Ramos Silva, (CFisUC/FCTUC),  manuela@pollux.fis.uc.pt

Co-Supervisor: Laura Pereira (C2TN/IST-ULisboa),  lpereira@ctn.tecnico.ulisboa.pt

Objectives

This Ph.D. Thesis aims at to be a contribution within the bounds of the interdisciplinary area constituted by the interrelation between Chemistry, Physics, Materials and Electrical Engineering, insofar as the main results of the proposed research would be related to the development of materials and devices which can open up new perspectives for applications of rare earth elements and OLEDs in chiral Optoelectronics and Photonics.

The goal is the development of lanthanide-based complexes and manufacturing of prototypes for proof-of-concept. Lanthanide-based complexes will –in addition of their inherent advantages over purely organic molecules in terms of narrow emission bands, large Stokes shift, and a long excited state lifetime–also feature circularly polarized (CP) emission at crucial wavelengths in the visible (for Tm(III), Tb(III) and Eu(III)) and in the near infrared (for Nd(III), Pr(III), Yb(III) and Er(III)). Such emitting materials must be chiral and non-racemic, in addition to all the expected features for electroluminescent devices. Consequently, the suggested approach will be mostly focused on the use of beta-diketonates, given their excellent properties for lanthanide sensitization by antenna effect, although camphor-based systems or polynuclear systems based on bipyridine-carboxylate ligands, for example, may also be considered.

Investigation of the magnetic properties of the novel compounds and specially the effect of a chiral environment in the magnetic properties (such as energy barrier to moment inversion) will also be pursued.

Framework

Polarized luminescence has attracted widespread attention owing to potential applications in optical information displays, processing and storage. The state of the art of materials and devices that rely on uniaxially oriented emitting species and generate linearly polarized light is quite advanced and technological exploitation may be seen in the near future. On the other hand, circularly polarized emission of light is more challenging to generate and comparatively little research effort has been devoted to this subject to date. CPL is typically achieved with helically arranged luminophores. This helical arrangement of the chromophores is very difficult to influence or promote by an external force field and, consequently, has to be achieved by self-assembly or self-orientation of the optically active materials.

The novel lanthanide-based light-conversion molecular devices developed in this Thesis will be suitable for the manufacturing of solution-processed OLED devices with high intrinsic circularly polarized emission (level of polarization>70%) and excellent spectral purity, fulfilling the requirements for stereoscopic 3D-displays. Moreover, the visible CP emitters –and their near infrared counterparts- may also be promising for other applications in Photonics (e.g., CP-light detectors and emitters in optical communication devices, molecular photoswitches, optical data storage, optical quantum information and spintronics) and in other fields (such as chirality sensing or enhanced image contrast in advanced medical imaging techniques).

Tasks

The candidate will cover all the stages of the novel materials development according to a highly interdisciplinary approach. Key aspects of his/her work will be the synthesis, structural elucidation by X-ray diffraction and characterization by VCD, DSC, FTIR, Raman, NMR and EPR spectroscopies, UV-Vis-NIR absorption, excitation and photoluminescence of highly coordinated lanthanide complexes. Detailed attention will be given to the identification of magnetic relaxation processes from AC susceptibility measurements, and on the origin of the anisotropic barrier. Of particular interest will also be the manufacturing and characterization of solution-processed CP-OLED devices on flexible substrates, resorting to technologies such as arc-erosion nano-patterning to pave the way to the manufacturing of large area CP-OLEDs by cost-effective methods. Training will be provided in all these aspects from within our groups and through collaboration with several European research centers (Universidad de Zaragoza, Universidad Rey Juan Carlos, Universidad de La Laguna, Universidad de Valladolid, University of Amsterdam and Max Planck Institute for the Structure and Dynamics of Matter).

Research centre/lab or R&D unit hosting the thesis project: Universidade de Coimbra

University to which the thesis project will be presented: Universidade de Coimbra

 

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Light-Responsive Organic-Inorganic Hybrid Nanomaterials for High-Performance Photochromic Textiles  (Ref. 28-2018)

Supervisor: : Clara Pereira (REQUIMTE/LAQV, DQB, FCUP), e-mail: clara.pereira@fc.up.pt

Co-Supervisors: Carlos Baleizão (IN-CQFM, IST, UL,  carlos.baleizao@tecnico.ulisboa.pt

Background: Over the years, there has been a growing interest on the development of photoresponsive materials, owing to their remarkable optical properties, namely by undergoing reversible color changes (photochromic)1,2 or presenting  high performance fluorescence properties (photoactive)3 in response to electromagnetic radiation (e.g., UV, visible light). This triggered optical response has been revolutionizing the design of smart devices with sensing, protection and optical memory functionalities. In particular, photochromic and fluorescent materials are potential building blocks for the production of photoresponsive textiles for anti-counterfeiting, military camouflage, UV-protection, NIR reflectance and fashion.4,5

Among photochromic organic compounds, spiropyrans, spirooxazines and naphthopyrans deserve special attention due to the possibility of obtaining a photochromic response in a wide range of wavelengths in the visible spectrum, easy preparation, fast color reversibility and good fatigue resistance.1,6 Their photochromism typically involves pericyclic reactions, cis-trans isomerizations, intramolecular hydrogen/group transfers, dissociation processes and electron transfers. However, it strongly depends on the environment properties, such as the polarity, pH, solubility or temperature, which hampers their technological application. Moreover, these dyes cannot withstand the temperatures used in textile dyeing and spinning processes without suffering degradation. The continuous fabric exposure to sun and washing may also promote the dyes degradation.6

On the other hand, inorganic photochromic compounds such as V2O5, WO3 and MoO3, can overcome these limitations due to their higher thermal, chemical and mechanical stability.1,2,7 Their light-induced color switching properties typically arise from their redox properties, ability to change stoichiometry or to create electron/hole pairs by interaction with the surrounding environment. However, they present slower coloration/discoloration photoresponse and lower color tunability than organic photochromic compounds.1

Perylenediimide (PDI) derivatives have attracted strong interest as imaging and fluorescent agents, due to their excellent photostability, high absorptivity, easily tunable energy levels, NIR reflectance and high quantum yield. These properties can be modulated by introducing appropriate substituents in the imide group (to change solubility or allow immobilization) or in the perylene core (bay or ortho positions, affecting the electronic and optical properties).8,9

To overcome the limitations of both organic and inorganic photochromic compounds and fluorescent dyes, they can be combined into a single material – the so-called organic-inorganic hybrids.1,4 The synergy between both components allows fine-tuning the optical properties of the hybrid en route to innovative photochromic or fluorescent systems with enhanced performance.

The main challenge on materials design continues to be the fabrication of light-responsive hybrid nanomaterials with multicolor photochromism that combine fast photochromic response, high reversibility and a wider color palette. 1 Several issues still need to be addressed: a) development of strong colors upon UV and visible light irradiation (higher contrast); b) controllable fading rates; c) stability and constant response upon multiple coloration/decoloration cycles; d) wider color variety. Moreover, understanding the mechanism underlying the photochromism of these multifunctional complex systems and the factors that govern their optical response is of prime importance.

 Objectives: The main GOAL of this project is to design novel UV and light-responsive hybrid organic-inorganic multichromic nanomaterials with tunable photoresponsive properties, high photostability and a wider color palette for application in smart textiles with sensing and protection features.

To achieve that goal, photochromic V2O5, MoO3 and WO3 nanomaterials will be assembled with spirooxazine, naphthopyran or PDI derivatives via non-covalent and covalent bonding. The influence of the structure, inorganic:organic components ratio and type of interactions on the optical contrast, photochromic response, NIR reflectance, fluorescence properties, reversibility and photostability upon multiple cycles will be assessed. The most promising hybrids will then be immobilized on mesoporous silica nanoparticles (NPs) with tunable size and porosity by post-grafting, co-condensation or electrostatic interactions.6,7,10 This step is of prime importance to improve the affinity of the hybrids to the fabrics and their photostability during textile processing/washing steps. Silica NPs will be the selected matrix due to their high surface area, thermal/UV stability and robustness that they impart to the grafted compounds.6,11,12 Finally, the nanomaterials will be incorporated on fabrics by dyeing, screen-printing and fiber spinning processes to achieve photoactive textiles with efficient performance, high comfort and washing fastness.

Work plan: The project covers the design, fabrication and characterization of light-responsive organic-inorganic hybrid materials with tailored photoresponsive properties under UV and visible light irradiation. The most efficient nanomaterials will be incorporated on textiles through dyeing and advanced processes in collaboration with CeNTI and CITEVE technological transfer centers. The teams, REQUIMTE/FCUP (C. Pereira)6,7,12 and CQFM/IST-UL (C. Baleizão),9,10,11 have complementary expertise in Materials Chemistry & Nanotechnology, ranging from the fabrication and characterization of metal oxides, synthesis of new photoactive molecules, hybrid silica NPs and functional textiles to advanced optical characterization.

The PhD workplan comprise five main tasks:

  1. Preparation and characterization of organic-inorganic hybrid photochromic materials through the incorporation of spirooxazines, naphthopyrans and PDI derivatives on V2O5, MoO3, WO3 NPs.
  2. Evaluation of the photoresponsive properties and establishment of relation composition/structure/chemical bonding/optical contrast/coloration-fading kinetics/cyclability.
  3. Immobilization of the hybrids on silica NPs with tunable size and porosity. Optimization of hybrid loading, bonding type and location/distribution towards preserving the photoresponsive performance.
  4. Fabrication of photoactive smart textiles by dyeing, screen-printing and fiber spinning processes.
  5. Evaluation of the photoresponsive performance and washing fastness. Assessment of the most suitable processes for the incorporation of the photoactive nanomaterial onto textiles.

This PhD project will allow the candidate to acquire multidisciplinary and advanced formation in an ever-growing hot topic, which will provide vital skills for future employability. It will bring a helpful contribution to the design of innovative smart nanomaterials with improved optical functionalities.

References:

  1. S. Parola et al., Adv. Funct. Mater. 2016, 26, 6506–6544;
  2. R. Pardo et al., Chem. Soc. Rev. 2011, 40, 672–687;
  3. F. Würthner et al., Chem. Rev. 2016, 116, 962–1052;
  4. M. A. Chowdhury et al., J. Eng. Fibers Fabr. 2014, 9, 107–123;
  5. D. Sriramulu et al., Sci. Rep. 2016, 6, 35993;
  6. T. V. Pinto et al., ACS Appl. Mater. Interfaces 2016, 8, 28935–28945;
  7. T. V. Pinto et al., Dalton Trans. 2015, 44, 4582–4593;
  8. C. Huang et al., J. Org. Chem. 2011, 76, 2386-2407;
  9. R. Pinto et al., J. Am. Chem. Soc. 2015, 137, 7104-7110;
  10. T. Ribeiro et al., Dyes and Pigments 2014, 110, 227–234;
  11. T. Ribeiro et al., Nanoscale 2017, 9, 13485–13494;
  12. C. Pereira et al., ACS Appl. Mater. Interfaces 2011, 3, 2289–2299.

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A Gateway to Ferromagnetic-Luminescent Bifunctional Materials: Structure, Spectroscopy, Thermal and Magnetic Properties of Compounds of Europium(II) and Related Elements with Nitrogen-Containing Heterocycles  (Ref. 30-2018)

Supervisor: Rui Fausto, CQ, FCT-UC, e-mail: rfausto@ci.uc.pt

Co-Supervisors:  Maria Teresa Duarte (CQE, IST-ULisboa) , e-mail: teresa.duarte@tecnico.ulisboa.pt

 

Materials exhibiting simultaneously ferromagnetic and luminescent properties may receive use in areas where magnetic/electronics and optical responses appear relevant (e.g., magneto-optoelectronics, spintronics).1-3 Compounds based on Eu(II) have been shown to be promising candidates for this sort of applications. Eu(II) oxide, for example, is a semiconductor with a band gap of 108 kJ mol–1 and, below 69.3 K, is a ferromagnet with a large magnetic moment (7.9 μB). Doping of the material may transform it in efficient photoluminescent phosphors covering a wide range of wavelengths.4 Very recently, the synthesis and characterization of a Eu(II) guanidinate, Eu(CN3H4)2, which exhibits paramagnetism at high temperatures and ferromagnetic exchange interactions below 6 K, were reported.5 Interestingly, this compound shows also polymorphism, with 3 different polymorphs being observed in the 25-70 ºC temperature range.

Among the divalent lanthanides, Eu(II) has the most accessible divalent oxidation state because of its half-filled 4f7 electronic configuration and, consequently, a high stabilization from exchange energy. Despite oxidation (to Eu(III)) and oligomerization present obstacles to the preparation and characterization of Eu(II)-containing complexes, the exceptional electronic properties of Eu(II) have spurred a great deal of research. Indeed, besides its unique luminescence properties (in the blue region), this divalent ion shows also a high magnetic moment (7.63–8.43 μB), associated with the seven unpaired electrons in its 8S7/2 ground-state configuration.

The present Ph.D. research program aims to develop Eu(II)-based compounds with nitrogen-containing heterocycles, as a gateway to ferromagnetic-luminescent bifunctional materials. As organic components, 5-membered nitrogen-containing rings, such as hydantoins, imidazoles, oxazoles, isoxazoles and pyrroles, bearing ionisable substituents, will be first considered. These types of compounds have been extensively studied in the laboratories of the proponents of this Ph.D. research program. Regarding the metal core, besides Eu(II) other species will also be tested, such as transition metals and other lanthanides in oxidation state (II) and group 2 elements.

The candidate will cover all the stages of the novel materials development according to a highly interdisciplinary approach, from synthesis, structural elucidation by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and polarized light thermal microscopy (PLTM), and characterization by infrared, Raman and NMR spectroscopies. Optical properties will be investigated by UV-Vis absorption, excitation and photoluminescence measurements, and magnetic properties studied by the Vibrating Sample Magnetometer techniques. The experiments will be complemented by theoretical studies using contemporary quantum chemical methods, including simulation of crystalline state by using periodic boundaries conditions. On the whole, this is an interdisciplinary project between chemistry, physics and materials sciences, which can provide the candidate a solid, eclectic background.

The research will be done in the specialized laboratories of the Department of Chemistry of the University of Coimbra and of the Department of Chemical Engineering of the IST-University of Lisbon, under supervision of Profs. Rui Fausto and Maria Teresa Duarte, respectively. Training will be provided in all referred to above areas required for project development, and will also involve collaboration with several European research centers, in particular the Polytechnic Institute of Milan and the Kultur University of Istanbul, as well as with other research units within the universities of Coimbra and Lisbon.

Research Centre/lab or R&D unit hosting the thesis project: Centro de Química de Coimbra /Universidade de Coimbra

University to which the thesis project will be presented: Universidade de Coimbra

References

  1. H. Li, X. L. Chen, B. Song, H. Q. Bao, and W. J. Wang, Copper-doped AlN polycrystalline powders: A class of room-temperature ferromagnetic materials, Solid State Commun. 151, 499–502 (2011).
  2. H. Li, G. M. Cai, and W. J. Wang, Room temperature luminescence and ferromagnetism of AlN:Fe, AIP Adv., 6, 065025 (2016).
  3. A. P. Black, K. A. Denault, J. Oro-Sole, A. R. Goniac, and A. Fuertes, Red luminescence and ferromagnetism in europium oxynitridosilicates with a beta-K2SO4 structure, Chem. Commun., 51, 2166–2169 (2015).
  4. P. M. Jaffe, Eu2+ luminescence in the ternary EuO-Al2O3-SiO2 system, ECS J. Electrochem. Soc., 116, 629–633 (1969).
  5. A. L. Görne, J. George, J. van Leusen, and R. Dronskowski, Synthesis, crystal structure, polymorphism, and magnetism of Eu(CN3H4)2 and first evidence of EuC(NH)3, Inorganics, 5, 10–24 (2017).

 

Institutions
ChemMat is a partnership between different research units in three different Universities: Instituto Superior Técnico (proponent institution). Faculdade de Ciências da Universidade de Coimbra. Faculdade de Ciências da Universidade do Porto. Centro de Ciências e Tecnologias Nucleares (C2TN). Centro de Química Física Molecular (CQFM). Centro de Química Estrutural (CQE). Instituto de Telecomunicações-Lisboa (IT Lisboa).
Scope
ChemMat is a PhD programme in Materials Chemistry with emphasis on optic electric and magnetic functionalities. It aims at providing advanced education and training in Chemistry including on advanced preparative tools, with a deep knowledge of electrical optical and magnetic properties of materials in order to address the most recent challenges in the development of advanced materials with emphasis on nanostructured and multifunctional materials.