Materials Chemistry Frontiers Blog

Thermoelectric materials enable the direct conversion of thermal to electric energy, and as such, have received considerable attention as a source of sustainable clean energy. The performance of a thermoelectric material is characterized by the dimensionless figure of merit, zT = S²σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. Achieving high zT requires careful design of low thermal conductivity and high power factor (PF = S²σ). Typically, thermoelectric materials with a high zT are heavily doped semiconductors, which have been extensively studied at medium and high temperatures, but less so at near room temperature. Recently, orthorhombic Ag₂Se has attracted much interest for near-room-temperature thermoelectric applications as they are anticipated to catalyze tremendous growth in energy harvesting for advancing internet of things appliances, self-powered wearable medical systems, and self-powered wearable intelligent devices. In order to optimize the thermoelectric performance of orthorhombic Ag₂Se, it is vital to understand the correlation between composition, structure, and transport properties. A variety of methods have been successfully developed for the preparation of Ag₂Se thermoelectric materials, including high-temperature solid-state reactions, room-temperature grinding, high‐energy mechanical milling, and pulsed hybrid reactive magnetron sputtering techniques. In comparison, solution‐based approaches are relatively less investigated for the synthesis of Ag₂Se, though widely used for generating CdSe, ZnSe and Cu_2-xSe compounds, as these methods offer the unique advantage of excellent control over material stoichiometry with high production throughputs at ambient conditions.

Recently, researchers at the Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), and Tianjin University, demonstrated a high ZT value of near unity at near-room-temperature through compositionally tuned hybridization of n-type Ag⁰:Ag₂Se (Fig. 1). A series of n-type Ag⁰:Ag₂Se materials has been systematically prepared through a surfactant-free, aqueous solution-based approach under ambient conditions. This strategy enables fine control over phases and compositions through nanoscale hybridization, yet remains applicable to large-scale production methods. By prolonging reaction times, the synthetic process is carefully developed/optimized to adjust the stoichiometry of Ag and Se by modulating the oxidation states of Ag and Se in the reaction medium, producing a series of Ag⁰:Ag₂Se (Ag⁰ excess at 50.86%, 45.80%, 15.97%, 6.10%, 4.31% and 1.96%) with enhanced thermoelectric properties.

Fig. 1 Schematic synthesis of Ag0:Ag2Se hybrids for a period of 7 days at room temperature under aqueous condition, with different molar ratios of Ag:Se.

After hot-processing the powder by spark plasma sintering, the temperature-dependent electrical conductivity of 45.80% Ag⁰:Ag₂Se prepared by reaction for 1 day was significantly higher than the rest of the Ag⁰:Ag₂Se samples, which relates to its augmented carrier concentration due to hybridization with more Ag⁰. When the reaction time was prolonged, more Ag₂Se was converted from Ag⁰, resulting in a drastic decrease in electrical conductivity for all the Ag⁰:Ag₂Se samples including 6.10%, 4.31%, and 1.96% Ag⁰ from 3, 5 and 7 days of reaction, respectively. The temperature-dependent trends in Seebeck coefficient of Ag⁰:Ag₂Se are opposite to those of electrical conductivity. These attributes lead to the lowest power factor for 45.80% Ag⁰:Ag₂Se, in comparison to the rest of the Ag⁰:Ag₂Se samples (Fig. 2a). In conjunction with fine-grained structure, which effectively scattered phonons at grain boundaries, the optimal excessive Ag⁰ of 1.96% after 7 days of reaction exhibited a high ZT value of close to unity (Fig.  2b).

Fig. 2 (a) Temperature dependence of power factors of the hot- pressed pellets of 45.80%, 6.10%, 4.31%, and 1.96% Ag0:Ag2Se, synthesized after reactions for 1, 3, 5, and 7 days. (b) Temperature dependence of ZT value of the 1.96% Ag0:Ag2Se pellet in comparison with the 4.31% Ag0:Ag2Se pellet.

Instead of doping or alloying, our work presents an effective way to organize different nanoscale building blocks by precise hybridization at nanoscale, preserving the intrinsic properties of Ag₂Se without incorporating different elements. On this basis, it would be of great interest in extending this solution strategy to the synthesis of hybridized multinary silver-based chalcogenides for further enhancing thermoelectric properties. Additionally, this solution approach could also find uses in the general synthesis of other metal chalcogenides, particularly useful for large-scale production.

Corresponding authors:

Tee Si Yin obtained her PhD in Biomedical Engineering from National University of Singapore. Currently, she is working as a research scientist at the Institute of Materials Research and Engineering, A*STAR. Her research focuses on the development of functional metal and semiconductor nanostructures for biomedical, environmental and energy applications.

Han Ming-Yong worked with IBM and Indiana University, followed by time spent at the National University of Singapore as a faculty member, before his current appointments with the Institute of Materials Research and Engineering and Tianjin University. His research addresses problems at the interfaces of nanoscience, nanotechnology, biotechnology and energy/biomedical applications. He has published >220 papers and filed >100 patents including national entries, with ~28,000 citations and >300 research highlights. He is a Fellow of the Royal Society of Chemistry (FRSC) and a Web of Science / Scopus highly cited researcher.

Emerging Investigator: Guangxue Feng

Position           Professor Postdoc           2016–2017  National University of Singapore Education        2011–2016  National University of Singapore        Ph.D.                         2007–2011  National University of Singapore        B.Eng. ORCID            0000-0003-4344-3517

Read Guangxue Feng’s Emerging Investigator Series article in Materials Chemistry Frontiers and learn more about him.

	Cationic AIE-active photosensitizers for highly efficient photodynamic eradication of drug-resistant bacteria
	Yuewen Yu,‡ Yubo Liu,‡ Yitao Chen, Jinke Chen, Guangxue Feng * and Ben Zhong Tang *
	A cationization and cyano introduction molecular engineering strategy is reported to develop AIE-active photosensitizers for high-efficiency PDT eradication of drug-resistant bacteria.
	From the themed collection: Frontiers Emerging Investigator Series
	The article was first published on 21 Nov 2022
	Mater. Chem. Front., 2023, Advance Article
	https://doi.org/10.1039/D2QM01043G

My research interests

10 Facts about me

Click to find out our Emerging Investigators and their work

Supramolecular self-assembly can be described as a spontaneous process of association of individual molecules to construct complex and large architectures with distinct features from the corresponding monomers. Encouraged by the natural self-assembly processes, creating new artificial self-assembled systems with desired properties has become a pressing research area of interest. Accordingly, during the last few decades, the scientific community has invested enormous effort in searching and constructing novel self-organized organic architectures with diverse functionalities, which have registered their potential in a wide range of applications, such as biosensing, drug delivery, tissue engineering, organic electronics, catalysis, and others.

During the last few decades, pyrene, a small polyaromatic hydrocarbon, has captured an immense attention to the scientific community as a unique blue emissive fluorophore. Pyrene has been an outstanding choice in organic functional materials because of its superb photophysical characteristics and versatile applications, and the possibility of synthetic modifications on the pyrene core. In comparison to systems that only enable self-assembly, the examples of pyrene-based transient assembly and further disassembly remain elusive in the past literature. Transient assembly is an out-of-equilibrium process which is thermodynamically unstable, and hence it dissociates into monomers via the disassembly process.

In the search of such assembly–disassembly system, the group of Prof. Apurba Lal Koner of the IISER Bhopal, India, in collaboration with Prof. Anup Pramanik at Sidho-Kanho-Birsha University, have developed a new biogenic amine (BA)-induced pyrene-based transient assembly and spontaneous disassembly system to access blue emissive Py-BA conjugated monomers which exhibited solid-state emissive property in addition to lysosomal targeting application (Figure 1).

Figure 1. Representation of reaction-based transient assembly and disassembly and demonstration of solid-state emission and bioimaging application of the monomers.

The group has demonstrated that the nucleophilic reaction between BA and pyrene-anhydride led to form open polar conjugates which created the transiently assembled network driven by strong π–π and multiple H-bonding interactions. The evolution of transient assembly via ground-state pre-association was fully established by a combination of spectroscopic and microscopic techniques in addition to computational study. Addition of BA such as 1,4-DAB in probe solution governed to generate an intense excimer band near 550 nm (yellow emission) in fluorescence spectra which further showed quenching with BA concentration as well as time (Figure 2a–b).

Figure 2. (a) UV-Vis. and (b) fluorescence spectra of Py-DA (5 µM) with increasing concentration of 1,4-DAB (0–50 µM), inset showing the change of O.D. and fluorescence intensity with concentration. (c) representation of temporal intensity changes in excimer and monomer band in CHCl₃. (d) plot of change of I₅₄₅/ I₄₀₅ ratio with time; inset cuvette images showing transformation of fluorescence color from excimer to monomer species.

Moreover, time-dependent quenching of excimer band with concomitant enhancement of monomer emission near 400 nm signified dissociation of yellow-emissive excimer/ aggregation to blue-fluorescent monomers in solution (Figure 2c–d). SEM study for Py-1,4-DAB conjugate unravelled temporal evolution of larger bulk aggregates at initial time which were transformed to interconnected network morphology due to disassembly (Figure 3a–c). Two types of products, i.e., Py-BA monomers and dimer were mainly responsible for demonstrating such assembly–disassembly phenomenon in solution as evident from NMR and mass spectrometry. The blue-emissive monomer conjugates exhibited yellowish-orange emission in solid-state (Figure 3d) which can be highly useful for fabricating light-emitting devices in the future. Interestingly, the newly formed water-soluble selective Py-BA conjugates were found to be of potential significance as lysosome targeting fluorophores (Figure 3e–f). Their lysosomal staining property provided a great advantage to monitor the lysosomal membrane degradation in a time-dependent manner.

Figure 3. (a)–(c) Time-dependent SEM images of Py-1,4-DAB conjugate in CHCl₃ showing morphological change with time. (d) CIE-coordinate of Py-1,4-DAB solid-state emitter; inset shows fluorescence image of thin-film captured upon illuminating at 365 nm. CLSM images of live BHK-21 cells: (e) merge image of Py-Spermine and lysotracker red (f) scatter plot with Pearson’s correlation coefficient 0.96 ± 0.02 (scale bars: 20 µm).

The work represents an intriguing example of harvesting water-soluble fluorophores with multifunctional features from reaction-induced transient assembly–disassembly processes.

Read the full article in Materials Chemistry Frontiers:

Prof. Apurba Lal Koner (Indian Institute of Science Education and Research Bhopal, India)

Apurba Lal Koner is an associate professor in the Department of Chemistry at the Indian Institute of Science Education and Research Bhopal (India). He received his PhD in Chemistry from Jacobs University Bremen (Germany) in 2009. From 2009 to 2012 he did postdoctoral studies at the University of Oxford (UK). Professor Apurba Lal Koner’s research team is working at the interface of chemistry, biology, and emissive materials and their applications in various research domains. He is the author of more than 95 articles of international repute and cited more than 2600 times with an index H = 25.

Web Page link: https://bionanolab.wixsite.com/akoner-iiserb

Emerging Investigator: Jintao Zhang

Position         Professor Postdoc         2013–2015  Case Western Reserve University (USA)                       2012–2013  Nanyang Technological University (Singapore) Education      2008–2012  University of Singapore                      Ph.D. ORCID          0000-0002-1029-3404

Read Jintao Zhang’s Emerging Investigator Series article in Materials Chemistry Frontiers and learn more about him.

	Hollow CoOX nanoparticle-embedded N-doped porous carbon as an efficient oxygen electrocatalyst for rechargeable zinc–air batteries
	Maomao Yang,‡ Siyu Ding,‡ Xinxin Shu, Wei Pan and Jintao Zhang *
	The porous carbon embedded with hollow cobalt oxide nanoparticles was prepared via a spray-drying method followed by carbonization, which endows rechargeable zinc–air batteries with the improved bifunctional catalytic activity.
	From the themed collection: Frontiers Emerging Investigator Series
	The article was first published on 24 Oct 2022
	Mater. Chem. Front., 2022, Advance Article
	https://doi.org/10.1039/D2QM00858K

My research interests

Key words: interface electrochemistry, electrocatalysis, energy conversion and storage

My research interests include the rational design and the synthesis of advanced electrode materials for electrocatalysis, electrochemical energy storage and conversion. Typically, with the fundamental understanding of interface electrochemical reactions in combination with in situ electrochemical methods, model electrode materials are rationally designed for advanced electrocatalysis and energy storage devices, such as carbon dioxide reduction reaction, oxygen reduction and iodine oxidation reactions for advanced rechargeable batteries.

10 Facts about me

Click to find out our Emerging Investigators and their work

When a molecule absorbs light, electrons can be excited to higher energy states. Multiple ways exist for the extra energy to be released, including emitting photons in radiative processes. The competition between radiative and nonradiative relaxation pathways dictates that the faster the process is, the more likely it is to occur. As such, for light emitting devices, the radiative decay needs to be fast to decrease losses in non-radiative relaxation. On the other hand, for light harvesting devices, it is important that the radiation is suppressed. Hence, it is crucial to control the radiative rate to achieve higher efficiency in light emitting or harvesting devices. Besides altering the chemical structures of fluorophores, the design of their dielectric environment provides a straightforward means of altering their fluorescent properties. Control of radiative rate has been thoroughly achieved and understood for inorganic photonic structures, whereas it is less so for organic ones. However, for the future of flexible devices, it is important to explore this effect in polymer structures so that they can be easily integrated in device design. A promising polymer photonic structure is a microcavity formed by two polymer dielectric mirrors sandwiching a very thin layer of fluorescent material as schematized in Fig. 1a. The dielectric mirrors consist of alternating thin layers of materials with high and low refractive index, which form a photonic crystal with high reflectance that can be engineered in the desired spectral range, making them more efficient than metallic ones. Additionally, they are easy to fabricate from solution.

Recently, researchers at the Rely photonics group at the University of Genoa and their collaborators at the National Research Council in Genoa demonstrated radiative rate change in microcavities incorporating an NIR emitting dye (Fig. 1b). The cavities employ dielectric mirrors consisting of the low-index fluorinated polymer Aquivion and a high-index polyvinyl carbazole, which together present the highest dielectric contrast reported so far for polymer mirrors. The samples are almost completely transparent to visible light (Fig. 1c), but strongly reflect light from 750–870 nm (Fig. 1d). This has been designed to reflect the fluorescence of a stable dye of choice. However, there is an allowed microcavity mode that has lower reflectance intensity at 850 nm.

Figure 1. (a) Schematic of the microcavity structure. (b) Structure of the NIR dye used. (c) Photo of an NIR-Reflecting microcavity. (d) Transmittance spectrum of microcavity.

The dielectric mirrors change the density of states available for photons, making it highly intensified at the microcavity mode (red arrow in Fig. 1d at 850 nm), and change the fluorescence intensity and kinetics. A series of references were fabricated in order to compare the effects of the microcavity. Compared to a film of the dye in polyacrylic acid matrix, the fluorescence intensity in the microcavity is nearly completely suppressed except at the cavity mode where it is amplified 15 times as strongly. (Fig. 2a).

Figure 2. Comparison between fluorescence of the dye/polymer film and the microcavity regarding (a) spectral intensity and (b) fluorescence lifetime.

Fluorescence intensity amplification at the microcavity wavelength is a commonly reported phenomenon. On the other hand, change in the fluorescence lifetime is rarely reported. However, it has been observed in this work (Fig. 2b), where lifetime decreased in the cavity compared to the reference film. Further measurements exclude any unintended effects and confirm that indeed the radiative rate does decrease due to cavity effects.

This significant change in the lifetime was achievable thanks to the high refractive index contrast achieved by the researchers. The system is highly promising for future implementation in devices. Further development of structures achieving higher contrast and using sharper emitters is needed to increase the radiative rate in order to improve performance of light emitting devices.

Corresponding author:

Prof. Davide Comoretto
University of Genoa

Davide Comoretto was born in Milano, Italy, in 1963. He graduated with a major in Physics in 1988. In 1993 he obtained a PhD in Chemical Sciences and was then enrolled as Research Scientist at the Department of Chemistry and Industrial Chemistry of the University of Genoa where he is now Full Professor of Industrial Chemistry. During his research activity, he worked at the Institute of Macromolecular Chemistry – CNR (Milan, Italy), the Department of Physics “A. Volta” (University of Pavia, Italy) and at the Institute for Polymers and Organic Solids at the University of California Santa Barbara (USA) in the group chaired by Prof. A. J. Heeger. He is the Team Leader of the Rely Photonics research group focusing on design and fabrication of functional solution-processed photonic crystals and spectroscopy. The main topics are related to emission control, sensing, thermal shielding, engineering and fabrication of metamaterials, light harvesting enhancement in photovoltaics, and photocatalysis.

Website: https://www.rely-photonics.it/people

Photochromic dyes are a specific class of molecules that can undergo reversible transformations under exposure to light between isomers that possess different optical properties. This peculiar feature makes them appealing for a myriad of applications, ranging from bioimaging, data storage, sensing or optical lenses.

Very recently, they have been employed in photovoltaics. Few photochromic dyes have been investigated as photosensitizers in dye-sensitized solar cells (DSSCs) and the only photochromes that have demonstrated a fully reversible photochromic process with polychromatic light once embedded in solar cells are diphenyl-naphthopyran derivatives, as reported by the group of Renaud Demadrille of CEA Grenoble in France and collaborators of the University Pablo de Olavide in Spain. Using this class of dyes, they demonstrated the fabrication of semi-transparent smart photovoltaic devices capable to self-adapt their transparency to the ambient light. Recently, they have designed and synthesized a series of spiro-indoline naphthoxazine (SINO) and spiro-indoline naphthopyran (NIPS) with a donor-photochrome-acceptor (D-p-A) chemical structure for their use in DSSCs.

Figure 1. General structure of the new dyes and the interconversion reaction between their close (CF), merocyanine (MC) and protonated merocyanine forms (MCH).

The interconversion process and optical properties of the two SINO and two NIPS dyes synthesized in this work have been proven more complex to unravel than the ones of diphenyl-naphthopyrans, as they are not only photochromic but also acidochromic. The interactions of the molecules with both stimuli, i.e. H⁺ and light, have been studied separately or simultaneously, in solution or after grafting onto the surface of TiO₂. A positive photochromism in solution characterized by extremely fast thermal discoloration kinetics has been observed for some of the compounds. All the dyes demonstrated acidochromic properties, but in the presence of acid, only NIPS derivatives showed a negative photochromism, i.e. a fast bleaching under illumination.

Figure 2. (a) Normalized discoloration curves of SINO-1, SINO-2 and NIPS-1 and (b) coloration curve of NIPS-1 after the addition of HCl and bleaching with light (2 x 10^-5 solutions at 25 °C, irradiation source: 200-600 nm/200 W xenon lamp).

After unraveling the photochromic and acidochromic properties of the new molecules, they were employed in the fabrication of dye-sensitized solar cells. The choice of the electrolyte was found to be critical, due to the pH-driven optical behavior of the dyes. If a low-pH electrolyte is used, a non-photochromic protonated open form was mainly produced, which was mostly avoided in the case of a neutral electrolyte. This work highlights that the photochromic properties of the dyes can be conserved when going from the solution to the devices for some of the dyes.

Figure 3.(a) J-V curves (dashed lines recorded in the dark, solid lines recorded under illumination) of opaque NIPS-2-based DSSCs using our acidic homemade electrolyte (black) and Iodolyte (red) and (b) transmittance spectrum of the transparent device together with a picture of the NIPS-2/Iodolyte device (standard irradiation conditions AM 1.5 G, 1000 W m⁻²; 25 °C; active area= 0.36 cm²).

This study is the first to investigate in detail the complex relationships between photochromic, acidochromic and photovoltaic properties for these classes of dyes. The structure-property relationships established will undoubtedly be useful for the development of new photochromic compounds with optimized optoelectronic properties for applications in various fields, including photovoltaics.

Corresponding authors:

Dr. José María Andrés Castán (Interdisciplinary Research Institute of Grenoble, CEA-Grenoble)

José María Andrés Castán is a postdoctoral fellow in the Molecular Systems and nanoMaterials for Energy and Health (SyMMES) at the Atomic and Alternative Energies Commission (CEA) in Grenoble, France. He received his PhD in Materials Science in 2018 at the Université d’Angers in France. His research is focused on the synthesis of photochromic dyes for their use in Dye-Sensitized Solar Cells. He is the author of more than 20 indexed publications.

Dr. Renaud Demadrille (Interdisciplinary Research Institute of Grenoble, CEA-Grenoble)

R. Demadrille is a team leader at the Atomic and Alternative Energies Commission (CEA) in France. He received his PhD in organic chemistry in 2000 from the University of Aix-Marseille with a grant from PPG Industries and Essilor International before to join the R&D department of an international chemical company to work on functional polymer materials. Then he moved to CEA as a postdoctoral fellow to develop semiconducting polymers for organic photovoltaics before being appointed in 2005 as a permanent researcher. His research focuses on the synthesis and the characterization of new pi-conjugated molecules and polymers for organic and hybrid photovoltaics and electronics. In 2018, he was recipient of the “Chemistry Energy” prize of the French Society of Chemistry, and in 2019, he was awarded of an ERC Advanced Grant to develop photochromic solar cells. Since 2020, he is Associate Editor of Journal of Materials Chemistry C and Materials Advances. He is the author of 8 patents, 2 book chapters and more than 90 articles indexed by SCI.

Controllable defects and interface engineering are perceived as promising routes to develop efficient noble-metal-free electrocatalysts for oxygen evolution reaction (OER), the bottleneck of overall water splitting. Recently Metal-organic frameworks (MOFs) have received particular attention for their remarkable OER performance because of their vast surface area, ability to tune porosity, and functionalization with mixed metals/ligands. Among various MOFs, Prussian blue analogs (PBAs) have been extensively studied for their potential in catalyzing the OER process. However, pristine PBA cubes suffer from low conductivity and exhibit insufficient OER activity, resulting in high overpotential and limiting their OER electrocatalytic applicability.

PBAs’ components, topologies, and surface engineering can be modified to improve their catalytic properties to address these limitations. One common structural alteration is the introduction of vacancies (defects) within the PBA cubes to facilitate ion diffusion, often accomplished through chemical etching that can change the local electronic configuration to boost the OER kinetics. There are only a few works on the selective etching of PBAs to enhance their performance; therefore, modification of the PBAs by the chemical etching process is a trending topic in OER electrocatalyst designing.

Recently, the Zidki’s research group at Ariel University highlighted the significance of combining the PBA etching effect with the decoration of molybdenum disulfide (MoS₂) on the edges and surfaces of Co-Fe PBA for catalyzing the OER kinetics. They proposed using an ethanol-water mixture as a mild etchant, eliminating the need for a capping or stabilizing agent.

Figure 1. (i) Synthetic scheme of Etched-PBA-MoS2 nanoframes. (ii) HR-SEM images of PBA nanocubes (a), Etched-PBA nanocages (c), and Etched-PBA-MoS2 nanoframes (e), and their corresponding TEM images (b,d, and f).

The Etched-PBA-MoS₂ nanoframes presented superior OER performance, requiring an overpotential as low as 260 mV on carbon cloth substrate to obtain the current density of 10 mA cm⁻² with a corresponding Tafel slope of 55 mV dec^-1 (Fig. 2a and b). The Etched-PBA-MoS₂ nanoframes also outperform with a lower charge transfer resistance (R_ct) value (smallest semicircle), indicating its faster charge-transfer kinetics (Fig. 2c). The catalyst retains its catalytic activity for a long-term stability test, proving its OER in a real-time application (Fig. 2d).

Figure 2. (a) LSV curves; (b) Tafel plots; (c) EIS-Nyquist plots measured at 1.5 V vs. RHE in 1.0 M KOH; (d) OER stability test of Etched-PBA-MoS2/CC.

This work demonstrates that the excellent electrocatalytic activity arises from two primary factors: (1) hollowing PBA nanocubes by the etching process increases the density of active sites to promote mass transport; (2) binding MoS₂ on the surface of PBA nanocages induces a synergistic effect – the electronic interactions among the active components tune the electronic structures of Co, Fe, and Mo sites. Their work renders a feasible pathway to optimize the etching effect and fasten different metal sulfide heterostructures on PBAs to achieve an excellent OER performance.

Corresponding author:

Dr. Tomer Zidki received his Ph.D. degree in 2010 from the Chemistry Department, Ben-Gurion University, Beer Sheva, Israel, in the field of radical reactions with nanoparticle catalysts. He pursued postdoctoral research at the Brookhaven National Laboratory, NY, USA, where he gained experience in redox catalytic processes. Dr. Zidki is an Assistant Professor in the Chemical Sciences Department, Ariel University, Israel, where he leads the Nanoparticle Catalysts group. He is also the Head of the Linear Electron Accelerator Facility for fast chemical reactions. Dr. Zidki has guided ten Ph.D. and three M.Sc. students. His research focuses on redox catalyzed reactions by nanoparticles and photo- & electrocatalytic water splitting reactions using non-precious catalysts. In addition, Dr. Zidki’s group studies the kinetic mechanisms of redox reactions and radical reactions using the electron accelerator. Another field of interest of Dr. Zidki is Environmental Chemistry, in which he wrote two patents on nitrogen and sulfur oxides removal from flue gases.

Organic molecule-based crystalline dielectric materials have attracted broad attention from chemists in recent years to develop new organic electronic devices. In their designing strategy, the molecular motion induced by the external dielectric field is required to maximize the polarization effect in the materials to realize a large dielectric constant.

When people pay attention to the molecular motion in curved-π aromatics and their supramolecular complexes, it is assumed that the “curve-to-curve” contact in the curved-π aromatics will afford the smooth molecular motion in the solid state. Sumanene (1) is one of the representative buckybowls and is known to show unique properties such as bowl inversion behaviour derived from its unique bowl shape and is recognised as the potential molecular switch (Figure 1a). However, another feature of 1 to form unidirectionally arraigned π-stacking columns in the solid state makes the bowl inversion behaviour of 1 useless for the switching applications due to the large bowl-inversion energy in the 1D-column formation.

Figure 1. a) Molecular structures of 1 and 2 and schematic diagrams of the features of 1. b) Pendulum-like in-plane motion of 2 exhibiting a dielectric response in an electric field.

Recently, the group of Osaka University and collaborators of Tohoku University, Tokyo Institute of Technology and Kyoto University have demonstrated that the in-plane motion of disfluorinated sumanene 2 in the solid state is applicable as the source of stimuli responsive function instead of the bowl inversion to bring out the dielectric response (Figure 1b).

The group has focused that 2 possesses two fluorine atoms on the same benzylic carbon on pristine sumanene to possess a large dipole moment along the in-plane direction and gives the isostructural crystalline packing to 1. Thermal analyses, variable temperature X-ray diffraction and IR measurements indicated the presence of pendulum-like in-plane motion of 1 at high temperature region although no clear phase transition was involved. Indeed, the dielectric measurement using its both powder and single crystal clearly showed that both real (ε₁) and imaginary (ε₂) parts of the dielectric constant were enhanced above ~360 K at 1 MHz with a Debye-type dielectric relaxation, confirming the in-plane motion of 2 induced by the external electric field (Figure 2).

Figure 2. a) Schematic model of the relationship between the single-crystal shape of 2 and the applied electric field. b) to e) Temperature dependence of b), d) the real part (ε1) and c), e) the imaginary part (ε2) of the dielectric constant of 2 in a single-crystalline form measured at various frequencies. The direction of the electric field applied for b) and c): parallel to the c axis; for d) and e): orthogonal to the c axis.

These results, focusing on the in-plane molecular motion in the π-stacking column of a buckybowl, will help to provide a better understanding of the dynamics of solid-state curved-π systems and will accelerate their application in functional materials.

Corresponding author:

Yumi Yakiyama is an associate professor in the Division of Applied Chemistry at Osaka University (Japan). She got a PhD degree in Chemistry at Osaka University in 2010. From 2010 to 2015 she did postdoctoral studies at POSTECH (Korea). The research field of Professor Yumi Yakiyama is physical organic chemistry especially about functional organic crystals as well as metal-organic and pure organic frameworks.

https://researchmap.jp/yumiyakiyama

https://www-chem.eng.osaka-u.ac.jp/~sakurai-lab/

Deep blue electroluminescence is highly required for organic light-emitting diode (OLED) technology. However, designing fluorophores displaying adequate CIE coordinates and particularly a low CIEy is far from an easy task. We report in this work the synthesis, the physico-chemical properties and the application in OLED of deep blue emitters constructed on the dibenzosuberene (DBS) molecular fragment. Three emitters, SPA-DBS, SIA-DBS and SQPTZ-DBS, have been constructed following a similar molecular design strategy that is the spiro connection of an electron rich unit, namely N-phenylacridine (PA), indoloacridine (IA) or quinolinophenothiazine (QPTZ) to the DBS core. The PA, IA and QPTZ fragments are known to be efficient hole injecters due to their strong electron-rich character. Through a structure/properties relationship study, the group of Prof Cyril Poriel (Institut des Sciences Chimiques de Rennes- UMR 6226, Rennes) reports the electrochemical, photophysical and thermal behaviours of these three emitters.

The resulting organic materials display similar LUMO levels lying at ca -2.30 eV and different HOMO levels driven by the donor unit comprised between -5.22 and -5.48 eV. The spiro-configuration allows maintaining high T_g and T_d in accordance with OLED application. SPA-DBS displays a deep-blue emission with CIE of (0.16, 0.04), reaching an EQE of ca 1% and possessing a very low CIEy coordinate of 0.04. This CIEy coordinate fits the NSTC, ITU and EBU standards. This work not only reports a deep blue emitter for OLED but also shed light on interesting properties displayed by the DBS fragment, such as its low LUMO energy level, ca -2.3 eV, which is significantly decreased compared to its counterpart fluorene. This particularity can be advantageously used in further designs to favour the electron injection in electronic devices.

Corresponding Author:

Cyril Poriel received his PhD in 2003 from the University of Rennes 1. After a postdoctoral stay at the University of Exeter (UK), he joined the CNRS (Institut des Sciences Chimiques de Rennes) in 2005, where he is currently CNRS Research Director. His main research interest deals with the design of π-conjugated architectures for Organic Electronics. He is author/co-author of more than 120 publications, reviews and book chapters.

There are a number of natural product extracts that contain pharmaceutically active ingredients or APIs. These APIs are extracted alongside a host of other compounds such as terpenes, fatty acids, sterols and waxes that naturally occur within the plant. A very topical example are the family of cannabinoids found in hemp extract. Isolating these cannabinoids is a multi-step, energy and solvent intensive process.

Recent work at the Green Chemistry Centre of Excellence, University of York, has shown that mesoporous materials made from naturally derived alginic acid, known as Starbons, work incredibly well at isolating cannabinoids in a single step. Here the Starbon is used in solid phase extraction (SPE) to purify a host of cannabinoids by solvent selection (Figure 1).

Figure 1 – Simple depiction of isolation of cannabinoids from hemp extract

Starbons are able to act in highly selective SPE for two reasons, the first being that their mesopores are large enough (2-50 nm) for complex compounds to enter and leave. The second is the temperature at which they are pyrolysed allows tuning of surface chemistry from hydrophilic to hydrophobic. By screen Starbons produced at 300, 450 and 800 °C, adsorption and desorption solvents (hexane and ethanol respectively) and contact time (30 seconds), we were able to isolate 93% of cannabinoids (by GC-FID) from the extract in a single step (Figure 2). The process was also validated using in line extraction and isolation in supercritical carbon dioxide, where the feedstock was hemp dust. This was especially interesting as the cannabinoid content in this industrial by-product is significantly lower than in hemp top flowers.

Figure 2 – GCchromatograph of hemptops; Crude C. sativa extract, Desorption phase (ethanol)after passing through A300.

Corresponding Author:

Dr Con Robert Mcelroy

Dr Con Robert McElroy (Rob) is a senior researcher at the Green Chemistry Centre of Excellence, Department of Chemistry, University of York. Rob gained his Ph.D in 2007 at Keele University working on the production of composite materials from copolymers incorporating renewable resources. He was a postdoc working on carbonate chemistry for two years at Ca Foscari University of Venice and joined the Green Chemistry Centre of Excellence, University of York as a PDRA in 2011. His current role is as Deputy Director of the Circa Renewable Carbon Institute which focuses on reactions and/or applications of levoglucosenone and the bio-derived solvent Cyrene (developed at the University of York and which he is a co-inventor of). He has published 3 book chapters, 39 papers, 4 reviews and 3 patents and has a H index of 20.

In 2019 he became chief technical officer of Starbons Ltd in which time it has become revenue generating, award winning and has won funding/made sales in relation to projects he managed.

https://www.researchgate.net/profile/Con-Mcelroy