Colour polymorphism in molecular crystals

 Colour polymorphism is an intriguing characteristic of chemical systems that entails the manifestation of crystal polymorphs in various hues. Within the realm of organic molecular crystals, this phenomenon remains relatively uncommon, with scant instances documented in literature thus far. However, the potential applications of systems displaying colour polymorphism span across diverse domains, including stimuli responsive pigments development, and sensors technology. Our endeavour involves the strategic design, synthesis, and detailed characterization of novel organic molecular crystals showcasing colour polymorphism. This research has been counting with the collaboration of scientists from the Polytechnical of Milan (Italy).

• “Colour Polymorphism in Organic Crystals”, B. A. Nogueira, C. Castiglioni and R. Fausto, Comm. Chem. - Nature, 3 (2020) 34.
• “Unveiling the Red and Brownish-Green Polymorphs of a Novel ROY Derivative: 2-(4-((3-Cyanothiophen-2-yl)amino)-3-nitrophenyl)acetic acid”, B. A. Nogueira, S. M. M. Lopes, A. C. B. Rodrigues, M. E. S. Eusébio, V. André, T. Duarte, J. A. Paixão, T. M. V. D. Pinho e Melo and R. Fausto, Cryst. Growth Des. 24 (2024) 947.
• “Colour polymorphs of ROY-ol”, B. A. Nogueira, S. M. M. Lopes, A. Milani, V. André, J. A. Paixão, M. E. S. Eusébio, T. M. V. D. Pinho e Melo, T. Duarte, C. Castiglioni and R. Fausto, Cryst. Growth Des., 22 (2022) 5375.
• “Portrayal of the Colour Polymorphism in the 5-Acetyl-derivative of ROY”, B. A. Nogueira, M. Carvalho, J. A. Paixão, M. E. S. Eusébio, S. M. M. Lopes, T. M. V. D. Pinho e Melo and R. Fausto, CrystEngCom, 24 (2022) 1459.

Photochromism, solvatochromism and thermochromism

Solvatochromism, photochromism, and thermo-chromism are fascinating phenomena in the realm of molecular chemistry, referring to the change in colour of a substance due to alterations in the solvent environment, reversible change of a material’s colour upon exposure to light, and changes of colour in response to fluctuations in temperature, respectively. These behaviours offer insights into molecular structure and electronic transitions. Solvatochromism finds applications in solvent polarity assessment and environmental sensing, while photochromic materials can be used in optical devices, such as photochromic lenses and light-sensitive switches, and thermochromic compounds are utilized in indicators for temperature monitoring and security inks. We have been investigating these phenomena in different chemical systems using different experimental and theoretical approaches, specifically UV/VIS absorption, fluorescence, infrared and Raman spectroscopies, together with quantum chemistry calculations. Part of these investigations received the contribution of scientists from the University of Bitlis (Turkey).

• “Photochromism of a Spiropyran in Low-Temperature Matrix. Unprecedented Bidirectional Switching Between a Merocyanine and an Allene Intermediate”, C. M. Nunes, N. A. M. Pereira and R. Fausto, J. Phys. Chem. A. 126 (2022) 2222.
• “Reversal in Solvatochromism, Photochromism and Thermochromism in a New bis-Azo Dye Based on Naphthalen-1-amine”, İ. Sıdır, Y. E. Kara, Y. G. Sıdır, H. Berber and R. Fausto, J. Photochem. Photobiol. A: Chemistry, 446 (2023) 115138.
• “Solvato-, Thermo- and Photochromism in a New Diazo Diaromatic Dye: 2-(p-Tolyldiazenyl)naphthalen-1-amine”, İ. Sıdır, Y. G. Sıdır, H. Berber and R. Fausto, J. Mol. Struct. 1267 (2022) 133595.

Structure of geological and meteoritic objects

Raman spectroscopy is a powerful tool for investigation of geological formations and meteoritic materials. It provides information about the composition, structure and crystallinity of minerals, assisting in mineral identification and understanding geological processes. Together with researchers from Turkey (Istanbul and Izmir) and Russia (Ekaterinburg), we have undertaken detailed morphological, structural and compositional characterization of these types of materials, relating these properties with the processes of formation of the studied objects either in Earth or in the space.

• “Crystallization Kinetics: Relationship between Crystal Morphology and the Cooling Rate - Applications for Different Geological Materials”, N. Aysal, Y. Kurt, H Öztürk, G. O. Ildiz, M. Yesiltas, D. Laçin, S. Öngen, T. Nikitin and R. Fausto, Crystals 13 (2023) 1130.
• “Micro-Raman Spectroscopy and X-ray Diffraction Analyses of the Core and Shell Compartments of an Iron-Rich Fulgurite”, A. Karadag, E. Kaygısız, T. Nikitin, N. Aysal, G. O. Ildiz and R. Fausto, Molecules, 27 (2022) 3053.
• “Bjurböle L/LL4 Ordinary Chondrite Properties Studied by Raman Spectroscopy, X-Ray Diffractions, Magnetization Measurements and Mössbauer Spectroscopy”, A. A. Maksimova, E. V. Petrova, A. V. Chukin, B. A. Nogueira, R. Fausto, Á. Szabó, Z. Dankházi, I. Felner, M. Gritsevich, T. Kohout, E. Kuzmann, Z. Homonnay and M. I. Oshtrakh, Spectrochim. Acta A, 248 (2021) 119196.

Study of cultural heritage artworks, museum objects and objects of forensic interest

Objects with relevance in the domains of cultural heritage, museum collections and forensics are prone to be studied by Raman spectroscopy, considering the essentially non-destructive and portability characteristics of this technique. We have been engaged in the study of these type of objects, in collaboration with different institutions, from the Machado de Castro Museum (Coimbra, Portugal), to the Portuguese Criminal Police Laboratory (Lisbon, Portugal), and from the Archaeology Unit of the University of Coimbra, to the Department of Conservation and Restoration of the Istanbul University (Turkey).

• “Identification of Decorative Pigments in Ceramic and Stone Artefacts from Late Antiquity, Islamic Period and Modern Age belonging to the Archaeological Collection of the Rectory of the University of Coimbra, by Raman Spectroscopy”, U. F. Marques, S. Filipe, H. Catarino, B. A. Nogueira and R. Fausto, in “Current Approaches, Solutions and Practices in Conservation of Cultural Heritage”, (Eds. E. Gulder, A. Yilmaz, G. O. Ildiz, P. Pogliani and R. Fausto, Istanbul University Press, 2024.EISBN: 978-605-07-1592-7

              https://iupress.istanbul.edu.tr/tr/book/current-approaches-solutions-and-practices-in-conservation-of-cultural-heritage/home

Nanomaterials for optoelectronics and sensing

Nanomaterials have emerged as pivotal components in the fields of optoelectronics and sensing, revolutionizing their capabilities and applications. At the nanoscale, materials exhibit unique optical, electrical, and structural properties, making them highly desirable for use in advanced technologies. In optoelectronics, nanomaterials such as quantum dots, nanowires, and nanotubes play critical roles in light emission, detection, and manipulation. Their tunable optical properties enable the development of high-performance light-emitting diodes (LEDs), solar cells, and photodetectors with enhanced efficiency and functionality. Additionally, nanomaterial-based sensors offer exceptional sensitivity, selectivity, and response times, making them ideal for various sensing applications. Nanomaterials can be engineered to detect a wide range of analytes, including gases, chemicals, biomolecules, and environmental pollutants, thereby addressing critical needs in healthcare, environmental monitoring, and security. Furthermore, the integration of nanomaterials into flexible and wearable devices holds promise for the development of portable and real-time sensing platforms. We have been investigating these type of materials as well as other types of compounds which exhibit appropriate characteristics to act as sensors (e.g., hybrid materials of ligand-metal complexes) using a combined experimental and theoretical approach, in which Raman and infrared spectroscopies appear as major tools. These investigations have been carried on in collaboration with colleagues from the Departments of Electric Engineering and of Physics of the Faculty of Sciences and Technology of the University of Coimbra, The Department of Physics of the University of Aveiro, and several research centres in Iran.

• “Graphene-Assisted Chemical Stabilization of Liquid Metal Nano Droplets for Liquid Metal Based Energy Storage”, A. L. Sanati, T. Nikitin, R. Fausto, C. Majidi and M. Tavakoli, J. Adv. Mater. Tech. (2024) 2301428.
• “Nanoscale Study of the Polar and Electronic Properties of a Molecular Erbium(III) Complex Observed via Scanning Probe Microscopy”, M. Ivanov, A. Grempka, A. Buryakov, T. Nikitin, L. L. G. Justino, R. Fausto, P. M. Vilarinho and J. A. Paixão, Crystals 13 (2023) 1331.
• “Sandwich-Type Double-Layer Piezoelectric Nanogenerators Based on One- and Two-Dimensional ZnO Nanostructures with Improved Output Performance”, P. Fakhri, N. Eaianli, R. Bagherzadeh, B. Jaleh, M. Sillanpää and R. Fausto, Sci. Reports - Nature, 13 (2023) 16412.
• Synthesis, Characterization and Sensing Mechanism of a Novel Fluorescence Probe for Fe(III) in Semi-aqueous Solution Based on a Schiff Base Hexadentate Receptor”, F. Ooshall, S. Jamehbozorgi, R. Golbedaghi, L. L. G. Justino, K. M. Feshalame, M. Liyghati-Delshad, H. Anaklari-Ardakani, B. Jaleh and R. Fausto, Inorg. Chim. Acta, 558 (2023) 121761.

Auxiliary diagnosis of neurodevelopmental diseases

In close collaboration with the Raman Spectroscopy Laboratory of the Istanbul Kultur University (RSLab@IKU Lab), we have been using infrared and Raman spectroscopies, combined with chemo-metrics, to develop analytical models for diverse applications, in particular for the early diagnosis of neurodevelopmental diseases, such as autism spectrum disorder, schizophrenia, and bipolar and attention-deficit hyperactivity disorders. In these studies, spectral data obtained from blood serum samples are used as an holistic spectroscopic biomarker of the diseases, thus avoiding the need of identifying specific chemical biomarkers, thus strongly facilitating the analysis.

• “PLS-DA Model for the Evaluation of Attention Deficit and Hyperactivity Disorder in Children and Adolescents through Blood Serum FTIR Spectra”, G. O. Ildiz, A. Karadag, E. Kaygisiz and R. Fausto, Molecules, 26 (2021) 3400.
• “Auxiliary Differential Diagnosis of Schizophrenia and Phases of Bipolar Disorder Based on the Blood Serum Raman Spectra”, G. O. Ildiz, S. Bayari, U. M. Aksoy, N. Yorgunere, H. Bulut, S. S. Yılmaz, G. Halimoğlu, H. Nur Kabuk, G. Yavuza and R. Fausto, J. Raman Spectrosc., 51 (2020) 2233.
• “Blood Serum Infrared Spectra Based Chemometric Models for Auxiliary Diagnosis of Autism Spectrum Disorder”, G. O. Ildiz, S. H. Bayari, N. Yorguner and R. Fausto, in “Neural Engineer Techniques for Autism Spectrum Disorder”, Eds. A. S. El-Baz and A. Mahmoud, Volume 1: Imaging and Signal Analysis, Elsevier Science, Amsterdam (Netherlands), Chapter 10, pp. 185-213, 2021.

Food and related materials

The combined use of spectroscopy (specifically infrared and Raman spectroscopies) and chemometrics have also been adopted to perform the semi-quantitative analyses of mixtures of closely-related compounds (such as sugars), as well as to evaluate the factors determining structural and compositional features of biomaterials and foods, like the impact of oestrogens on hair properties, the influence of species diversity on the lipid-protein-sugar relative composition in crops, the effects of genetic manipulation leading to salt resistance on the chemical composition of soybeans, or the chemical stability of preservatives (e.g., parabens). Some of the studies in this domain have been undertaken in collaboration with different research institutions in Turkey.

• “A Comparative Study of the Yellow Dent and Purple Flint Maize Kernel Components by Raman Spectroscopy and Chemometrics”, G. O. Ildiz, H. N. Kabuk, E. S. Kaplan, G. Halimoglu and R, Fausto, J. Mol. Struct., 1184 (2019) 246.
• “Raman Spectroscopic and Chemometrics Investigation of Lipid/Protein Ratio Contents of Soybean Mutants”, G. O. Ildiz, O. Celik, C. Atak, A. Yilmaz. H. N. Kabuk, E. Kaygisiz, A. Ayan, S. Meriç and R. Fausto, Appl. Spectrosc. 74 (2020) 34.
• “Methylparaben Isolated in Solid Argon: Structural Characterization and UV-Induced Conversion into Methylparaben Radical and Isomeric Ketenes”, N. Kuş, S. H. Bayarı and R. Fausto, J. Phys. Chem. B, 117 (2013) 13543.