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ChemMat PhD Projects 2019 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. 02-2019)

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. 03-2019)

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 superconductors. While that was not achieved a new a class of molecular 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. After the first organic superconductors, based on quasi-one dimensional Bechgaard salts (TMTSF)2X (X = ClO4, PF6, AsF6, etc.,), there has been a remarkable development of 2D molecular conducting systems first with salts (BEDT-TTF)2X and then other salts based on derivatives of the electron donor BEDT-TTF.[1] Systems based on double layered structures, potentially more interesting, have however not been explored since very recently by our group [2,3] .

THE NOVELTY:

This project aims at further exploring bilayer conducting systems based on a new BEDT-TTF dissymmetric derivative, as CNB-BEDT-TTF recently prepared in the C2TN group [2], and different inorganic anions. CNB-BEDT-TTF was recently found to self-assemble in double layered structures in charge transfer salts with small anions [3]. However a significant number of different anions remain to been 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 r 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

Different dissymmetrical tetrathiafulvalene type donors with CN groups will be designed, synthetized and investigated in the quest for new bilayer systems. Structural modifications in these donors will be induced either by changes in the CN group position, either by modifications involving the heteroatoms in dissymmetrical tetrathiafulvalene type donors with the coupling of methydithio, dithiin, thiophenic or even chiral units. These modifications will promote modifications in the electronic density distribution of the donor molecule aiming at more efficient interactions between the donor molecules maintaining by self-assembling capability of the donors into bilayer structures.

The second stage of this project is the preparation of the charge transfer salts with different anions (Cl-, Br-, AsF6-, BF4-, NO3-, FeCl4-, GaCl4- ,NiCl4-, CuCl4-, etc. ) of variable size and magnetic moment and the growth of crystals, primarily 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.

The 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 to possible small size of crystals, 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. 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.
  8. D. Graf J. S. Brooks, M. Almeida, et al., Phys. Rev B, 2007, 75, 245101-245108.
  9. N. Kikugawa, L. Balicas, et al., Nature Comm., 2016, 7, 10903.
  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. 13-2019)

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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CoPoS: multifunctional Coordination Polymers for optical Sensing applications (Ref. 24-2019)

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. 27-2019)

Supervisor: Manuela Ramos Silva, (CFisUC/FCT-UCoimbra)  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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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. 30-2019)

Supervisor: Rui Fausto (CQ, FCT-UC) rfausto@ci.uc.pt

Co-Supervisors:  Maria Teresa Duarte (CQE, IST-ULisboa)  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).

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Materials for environmentally friendly and stable organic photovoltaics  (Ref. 31-2019)

Supervisor: Ana Charas (IT)  ana.charas@lx.it.pt

Co-Supervisors:  Adelino Galvão (CQE/IST-UL) adelino@ist.utl.pt

Organic photovoltaics (OPVs) represent a promising renewable energy technology due to enabling to fabricate lightweight, flexible, low cost, and semi-transparent solar cells [1,2]. Nevertheless, improvements are still required for becoming truly competitive, among the conventional inorganic (silicon)-based solar photovoltaic technologies, namely in what concerns to efficiency levels, lifetimes, and toxicity issues related with the fabrication process.

This project aims at investigating organic compounds with advantageous properties, namely, morphologic stability and solubility in non-toxic solvents (ex. water or ethanol) for organic photovoltaic devices. It is proposed to synthesise new organic semiconductors, i.e. conjugated small molecules and polymers, substituted with groups that both provide solubility in water or ethanol and allow for self-assembling, through hydrogen bonding, to form morphologically stable supramolecular structures. Target supramolecular structures are organic semiconductors that self-assemble in structures such that they optimize the charge generation and transport within the device and whose morphologic stability can be transferred from laboratory-scale deposition techniques to R2R techniques, and therefore reach high device efficiencies in real applications [3].

Overall, the workplan includes: i) design, by quantum mechanical calculations, and synthesis of new compounds; ii) investigation of self-assembly in solution and in solid film; iii) photophysical studies of individual compounds and supramolecular assemblies; iv) fabrication of solar cells (laboratory prototypes) and their electrical characterization. The ultimate objective is to obtain efficient and stable devices using the synthesised materials processed from environmentally friendly solvents. The devices will be characterized and their electric performance will be evaluated under simulated sunlight. Accelerating aging tests, to evaluate the operation device lifetimes, will be performed in accordance with ISO regulations for such tests. Another route to explore, aiming at the enlarging of devices´s lifetime, deals with the functionalization of the newly synthesised materials with cross-linkable moieties, so that they can form three-dimensional cross-linked networks of enhanced morphologic stability which will potentially increase operation devices´ lifetimes. Following their synthesis, the materials will be fully characterized in terms of structure, including Nuclear Magnetic Resonance (NMR) spectroscopy, mass spectrometry, elemental analysis, and size-exclusion chromatography in case of polymer materials. Furthermore, electrochemical methods (ex. cyclic voltammetry) will be used to estimate relevant properties for OPV applications, namely, ionization potential and electron affinity. Photophysical studies focusing on photo-induced charge generation mechanisms in the films comprising the new materials will be performed and used to formulate the active layer of OPV cells prototypes. Such formulations will be established also on the basis of morphologic data acquired from films´ characterization using Atomic Force Microscopy. It is proposed that experiments of X-ray spectroscopies will be performed at Karlstad University (Sweden), during a short secondment (ca. 1 month) under the guidance of Prof. Ellen Moons. Complementary photo-physical studies are also proposed to be performed during a secondment at Centre for Materials Physics, at Durham University (UK) under the guidance of Dr. Fernando Dias.

References

  1. H. Zhang, H. Yao, J. Hou, J. Zhu, J. Zhang, W. Li, R. Yu, B. Gao, S. Zhang, J. Hou, Adv. Mater., 30 (2018), pp. 1800613.
  2. “From lab to fab: how must the polymer solar cell materials design change? – an industrial perspective”, R. Po, A. Bernardi, A. Calabrese, C. Carbonera, G. Corso, A. Pellegrino, Energy Environ. Sci., 7, 925 (2014).

 

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Single-Chain Ultra-Small Fluorescent Polymer Nanoparticles for Imaging and Diagnostics (Ref. 32-2019)

Supervisor: José Paulo Farinha (CQFM- IN/IST/ULisboa), farinha@tecnico.ulisboa.pt

Co-supervisor: Jorge Marques (FCTUC), qtmarque@ci.uc.pt

Background

Over the last years we have been interested in imaging and drug delivery using hybrid silica-polymer nanocontainers programed to reach a target tissue or cell and release their cargo in a programable way. [1] While these systems provide excellent control over the morphology, targeting and delivery properties, [2] and we have already reached extremely small sizes, [3],[4] these are still too large for some applications. In particular, imaging of processes in the cell nucleus and delivery of cargo across the nuclear membrane are usually restricted to very small probes.

We have also worked with super bright polymer chains, containing a large number of fluorophores and a biotin end-group for bio-targeting. [5],[6] While this strategy has produced good results, and these probes are small enough, the performance of the dyes attached to the polymer chain is impaired by their exposure to the environment (photobleaching by oxygen, quenching, etc.)

A possible solution to these problems would be to control the polymer conformation so that the polymer collapses to protect the attached dyes without losing colloidal stability (that would lead to aggregation). The way we propose to achieve this is to use molecular self-assembling principles to fold copolymer chains into ultra-small polymeric nanoparticles (usPNs). This topic has been very recently addressed by the group of Bert Meijer, [7],[8] to produce single-chain polymer nanoparticles for catalytic applications. [9],[10]

Objectives

The main GOAL of this project is to develop NOVEL highly fluorescent ultra-small polymeric nanoparticles (usPNs) with diameters of the order of 5 – 10 nm, that can be used as labels in advanced laser-scanning imaging of cell nucleus processes and transport therapeutic agents for delivery inside the nucleus. Our STRATEGY is to use molecular self-assembling principles to fold copolymer chains into usPNs. To this end we will develop block copolymer chains with precise architecture and composition, incorporating two types of side groups: fluorescent dyes and groups that direct the chain folding into a conformation that encapsulates the dyes in a hydrophobic center core, while the outer surface is protected by a hydrophilic polymer domain. To design the copolymer structure, we will perform molecular dynamics simulations of the self-assembling process of model polymer-chains with different side groups in varied positions along the chain. These results will guide us in the synthesis of the appropriate structures containing fluorophores attached to the polymer backbone.

Work plan

The project covers the modeling, design and synthesis of the highly fluorescent copolymer chains that self-assemble into ultra-small single-chain polymeric nanoparticles (usPNs) with diameters of the order of 5 – 10 nm.

The teams, CQFM-IN/IST-UL (José Paulo Farinha) and DQ-UC (Jorge Marques), have complementary expertise in nanomaterials, covering all aspects of the project: modeling of nanosystems and their dynamic processes; synthesis of polymers with precisely controlled size, composition and architecture; self-assembling into nanoparticles; and cell testing and laser scanning imaging.

The PhD workplan comprise five main tasks:

1. Preparation and characterization of block copolymer chains composed by a hydrophilic block (eg. N-acryloylmorpholine, NAM) and a random copolymer block composed by a hydrophobic monomer (eg., butyl acrylate, BA) and a reactive comonomer (N-Acryloxysuccinimide, NAS). The NAS units can used to introduce stechiometric amounts of the dye molecules (eg., Perylene diimide modified with amine groups), with the reminder NAS being finally capped with an amine terminated group that will direct the self-assembling process (eg., alkane, aromatic or other). Self-assembling by solvent exchange to aqueous solution will produce the fluorescent usPNs. The process will be repeated with copolymer chains of different size, architecture and side groups.

2. The self-assembling process of the copolymer chains prepared in task 1 will be studied by employing molecular dynamics simulations in order to validate the theoretical model against the obtained experimental results.

3. The refined model will be used to establish relations between composition, architecture and size of the copolymer and the result of its self-assembling into usPNs, taking into consideration the average distance between dyes in the nanoparticle to predict possible photobleaching and quenching effects. These results will be used to establish design guidelines for the preparation of fluorescent usPNs with the desired properties.

4. Preparation and characterization of the optimized block copolymer chains with a hydrophilic block and a random copolymer block composed by a hydrophobic monomer, fluorescent side groups and side groups to direct the self-assembling process. Self-assembling of the copolymer in aqueous solution to prepare the fluorescent usPNs. Characterization of the nanoparticle size, colloidal stability and photophysical properties (brightness and photoresistance, lifetime).

5. Evaluation of the fluorescent usPNs cytotoxicity (by measuring cell viability at different usNP concentration) and performance in imaging the nucleus of live cells by laser-scanning confocal imaging.

This PhD project will allow the candidate to acquire multidisciplinary and advanced formation in a hot topic, which will provide a wide range of skills from polymer synthesis and characterization to modeling and colloidal characterization, optical characterization and advanced microscopy. The outcomes are expected to allow publication in top scientific journals and possibly originate a patent of the process.

References

  1.     C. Baleizão, J. P. S.* Farinha, Nanomedicine 2015, 10, 2311-2314.
  2.     T. Ribeiro, E. Coutinho, A. S. Rodrigues, C.* Baleizão, J. P. S.* Farinha, Nanoscale 2017, 36, 13485-13494.
  3.     C. Baleizão, J.P.S. Farinha, T. Ribeiro, A. Rodrigues, Process for the Production of Mesoporous Silica Nanoparticles with Diameters Under 100 Nanometers and Precise Control of the Particle Size. International patent PCT/PT2017/000003, 2017.
  4.     S. V. Calderon, T. Ribeiro, J. P. S. Farinha, C. Baleizão, P. J. Ferreira, Small 2018, 1802180.
  5.     P. Relogio, M. Bathfield, Z. Haftek-Terreau, M. Beija, F. D’Agosto, A. Favier, M.-J. Giraud-Panis, B. Mandrand, J. P. S.* Farinha, M.-T.* Charreyre, J. M. G. Martinho, Polymer Chemistry 2013, 4, 2968-2981.
  6.     M.-T. Charreyre, J. P. S. Farinha, B. Mandrand, J. M. G. Martinho, P. Relógio, Fluorescent polymers soluble in an aqueous solution and preparation thereof, International patents US8133411B2 2012, EP1899434 2008, WO2007003781 2007
  7.     G. M. ter Huurne, I. K. Voets, A. R. A. Palmans, E. W. Meijer, Macromolecules 2018, 51, 8853−8861
  8.     G. M. ter Huurne, L. N. J. de Windt, Y. Liu, E. W. Meijer, I. K. Voets, A. R. A. Palmans, Macromolecules 2017, 50, 8562–8569
  9.     Y. Liu, S. Pujals, P. J. M. Stals, T. Paulöhrl, S. I. Presolski, E. W. Meijer, L. Albertazzi, A. R. A. Palman, J. Am. Chem. Soc. 2018, 140, 3423−3433
  10.     Y. Liu, P. Turunen, B. F. M. de Waal, K. G. Blank, A. E. Rowan, A. R. A. Palmans, E. W. Meijer, Mol. Syst. Des. Eng. 2018, 3, 609–618

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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.