bluuebunny/crossref_metadata_2025 huggingface dataset:
Layered Tin Chalcogenide Electrochemistry: Fundamentals and Implications on Energy-Related Applications
Authors: Chia Xinyi , Lazar Petr , Sofer Zdeněk , Luxa Jan , Pumera Martin
Published: February 2020

Despite the prominent applications of layered tin (Sn) chalcogenides in batteries and supercapacitors, there is limited discourse on the relevance of Sn valence or structural differences to their electrochemical and electrocatalytic properties. To address this gap in literature, we investigate the electrochemistry of layered Sn chalcogenides; orthorhombic SnS and hexagonal SnS2, and establish implications to catalytic applications in oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Between the two layered Sn chalcogenides, which show distinct signals in the cathodic region, the inherent electrochemistry is more accentuated in SnS2. SnS2 manifests three characteristic signals placed in juxtaposition to a single reduction peak in SnS. Therefore, SnS shows a wider inert operating window compared to SnS2. In the aspect of heterogeneous electron transfer (HET) rates, SnS2 is an order of magnitude faster than SnS. Due to the high onset potentials and low current, both SnS and SnS2 are rendered unsuitable catalysts for ORR and OER. Conversely, both Sn chalcogenides are moderate catalysts for HER that outperform the bare glassy carbon (GC) electrode. In particular, SnS2 emerged a stronger contender for HER than SnS given the lower HER overpotential required in SnS2. However, it is important to recognise that the overpotential of SnS2 is remote from the ideal Pt catalyst. We perform electrochemical impedance spectroscopy (EIS) and density function theory (DFT) calculations to elucidate the variations in the HER performance of the layered Sn chalcogenides. By EIS study, SnS2 unveiled strikingly lower charge transfer resistance and hence, faster HER kinetics that could have contributed to its higher HER catalytic efficiency. Likewise, DFT studies disclose favourable Gibbs free energy of adsorbed hydrogen (∆GH) at the S edges for SnS2 whereas ∆GH at all edges of SnS are incompatible for HER. Our findings offer fundamental insights to layered Sn chalcogenides and provide an initial assessment of their electrochemical properties that would be beneficial for their future development in energy-related applications.
(Invited) In Situ scanning Tunneling Microscopy Studies of hBN Layer Growth Kinetics and the Influence of Substrate on Electronic Structure of the Layers
Authors: Arias Pedro , Abdulslam Abdulfattah , Ebnonnasir Abbas , Ciobanu Cristian V , Kodambaka Suneel
Published: February 2020

Two-dimensional (2D) layered materials, owing to a wide range of properties (e.g., graphene is metallic, hBN is insulating, and MoS2 is semiconducting), have attracted considerable attention over the past decade. hBN is isostructural to graphene and is considered an ideal dielectric for the fabrication of vertical 2D layered heterostructures with potential applications in optoelectronics and nanoelectronics. hBN layers are commonly grown on metal substrates. In contrast to free-standing hBN layers, substrate-supported hBN can be metallic, semiconducting, or insulating, depending on the chemistry and electronic structure of the hBN/substrate interface. Moreover, due to relatively weak van der Waals interactions between the 2D layer and the substrate, orientational registry of the layers with the substrate is not expected and is often difficult to control. While the growth and electronic structure of graphene layers have been fairly well studied, relatively little is known concerning the mechanisms underlying the growth of the hBN layers and the influence of hBN domain orientation (with respect to the substrate) on its electronic properties.

Using in situ ultra-high vacuum scanning tunneling microscopy (UHV STM), we investigated the chemical vapor deposition (CVD) kinetics of hBN on Pd(111). STM images are acquired during CVD of borazine as a function of substrate temperature, borazine flux, and deposition time. We observe the nucleation and growth of chemisorbed borazine islands on the Pd surfaces. Furthermore, we investigated the surface structure of hBN domains on Pd(111) using STM, scanning tunneling spectroscopy (STS), and density functional theory (DFT) calculations. STM images acquired from the hBN/Pd(111) sample reveal moiré patterns with at least four different periodicities λ corresponding to four rotational domains of hBN. From the STM images, we measured the surface corrugations in each of the moiré patterns and found that the corrugation amplitude Δz depends on the tunneling bias and increases with increasing λ. We suggest that Δz is a measure of hBN-Pd(111) interaction strength and attribute the higher corrugation amplitudes to stronger interactions between the hBN domains and the Pd(111). We expect that similar approach could be used to investigate growth kinetics and orientation-dependent interactions in other substrate-supported 2D layers with large lattice mismatch with respect to the substrate.
(Invited) Epitaxy of 2D Transition Metal Dichalcogenide Monolayers and Heterostructures
Authors: Zhang Xiaotian , Choudhury Tanushree , Chubarov Mikhail , Redwing Joan M.
Published: February 2020

There is growing interest in monolayer transition metal dichalcogenides (TMDs) such as MoS2 and WSe2 and related 2D heterostructures due to their compelling electronic and photonic properties. The majority of this work has been carried out using ultra-thin flakes exfoliated from bulk chalcogenide crystals but future device development requires the ability to synthesize large area single crystal films and heterostructures. Our research is aimed at the development of an epitaxial growth technology for layered dichalcogenides, similar to that which exists for III-V and other compound semiconductors, based on gas source chemical vapor deposition (CVD). This approach provides a high overpressure of chalcogen species needed to maintain stable growth at elevated temperature and excellent control of the precursor partial pressures to achieve layer-by-layer and heterostructure growth.

Our recent studies have focused on the epitaxial growth of WSe2 and WS2 monolayer films and heterostructures using metal hexacarbonyl and hydride chalcogen precursors on substrates including sapphire and hexagonal boron nitride (hBN). A multi-step precursor modulation growth method was developed to independently control nucleation density and the lateral growth rate of WSe2 and WS2 monolayer domains on the substrate. This approach also enables measurement of W-species surface diffusivity and domain growth rate as a function of growth conditions providing insight into the fundamental mechanisms of monolayer growth. Using this approach, coalesced monolayer and few-layer TMD films were obtained on sapphire substrates up to 2” in diameter at growth rates on the order of ~ 1 monolayer/hour. In-plane X-ray diffraction demonstrates that the films are epitaxially oriented with respect to the sapphire resulting from a merging of an equal mixture of 0o and 60o oriented domains. WSe2 also grows epitaxially on hBN single crystal flakes but in this case the domains exhibit a predominant direction resulting in a reduced density of anti-phase boundaries. Applications and challenges of this approach in the growth of 2D heterostructures will also be discussed.
(Invited) Graphene-Based Membranes for Nanofiltration
Authors: Grossman Jeffrey C
Published: February 2020

Nanoporous graphene-based films have recently emerged as promising materials for separations. Graphene-oxide is a 2D material with high mechanical strength, chemical resilience, favorable surface properties, and the potential for scalable low-cost manufacturing. In this talk, I will highlight our computational and experimental work on the properties, synthesis, and performance of graphene-oxide based membranes.
Investigation of HF Treatment Effect on the Structure and Electrical Conductivity of Carbonized Metal–Organic Frameworks
Authors: Zhang Zhao-Quan , Li Bing-Han , Lin Chia-Her , Lee Szetsen
Published: February 2020

Metal-organic frameworks (MOFs) containing Fe, Cr, Ni, and Cu were calcined under nitrogen flow. The formation of carbonized MOFs (CMOFs) was monitored by electrical conductivity, powder X-ray diffraction, and Raman spectroscopic techniques. To remove metallic residues in CMOFs, HF treatment was performed. Powder X-ray diffraction analysis showed that only Ni, but not Fe, Cr and Cu, could be completely removed from CMOFs after HF treatment. Raman spectroscopic data indicated that well-stacked graphene layers structures were present only in Fe and Ni-containing CMOFs. The electrical conductivity, powder X-ray diffraction, and Raman data were correlated. The effect of acid treatment on the structure of CMOFs and the performance of CMOFs as electrode materials were evaluated.
Synthesis of Optically Uniform Single Layer WS2 for Tunable Photoluminescence
Authors: Park Juhong , Kim Minsu , Cha Eunho , Kim Jeongyong , Choi Wonbong
Published: February 2020

Two-dimensional transition metal dichalcogenides (2D TMDs) are promising materials for next-generation opto-electronic and nano-electronic devices due to their unique tunable bandgap as a function of the number of layers. Especially, single-layer tungsten disulfides (WS2) is a direct band gap semiconductor with a gap of 2.1eV featuring strong photoluminescence and large exciton binding energy. Although synthesis of MoS2 and their layer dependent properties have been studied rigorously, little attention has been paid to the formation of single-layer WS2 and its layer dependent properties. Here we report the scalable synthesis of uniform single-layer WS2 film by a two-step chemical vapor deposition (CVD) method followed by a laser thinning process. As-synthesized few-layer WS2 film shows 3.8 nm thickness considered to be 4 – 6 layers, and the post-laser irradiation enables systematic layer-by-layer thinning of the as-synthesized WS2 down to single-layer. The PL intensity increases six-fold, while the PL peak shifts from 1.92 eV to 1.97 eV during the laser thinning from few-layers to single-layer. We also find WS2 layer dependent intensity variation of the exciton complexes in PL emission. Both a neutral exciton and a trion increases with decreasing WS2 film thickness; however, the neutral exciton is predominant in single-layer WS2. The tunable optical properties by precise control of WS2 layers could empower a great deal of flexibility in designing atomically thin optoelectronic devices.

Figure 1
(Invited) Resonance Raman Spectroscopy in New 2D Materials
Authors: Pimenta Marcos A
Published: February 2020

The pioneering experiments with graphene in 2004 opened the new area of two-dimensional (2D) systems in science. Several new 2D systems have been studied, such as the semiconducting transition metal dichalcogenides MX2 (M = Mo, W and X = S, Se, Te), and a phosphorus crystalline halotropic called black phosphorus. The behavior of the electrons in these materials depends not only on the atoms in the crystalline structure but also on the number of layers and the form of stacking. We have in recent years studied some of these 2D materials by Raman spectroscopy, which provides us with information about phonons and their interactions with electrons and excitons. In this work, I will initially present Raman spectroscopy results in MoS2, [1,2], WS2 and WSe2 [3] compounds, which show that Raman modes are intensified by resonances with excitons, allowing us to obtain dependence of their energies with the number of atomic layers. We observed that the electron-phonon coupling is dependent on the symmetry of the excitons and phonons [1] and we could evidence electron scattering processes between different valleys by acoustic phonons [2]. Finally, I will present results on black phosphorus, which has peculiar anisotropic electronic bands. Different edges of black phosphorus were studied using Raman spectroscopy and the results show the appearance of new modes at the edges of the sample, which depend on the atomic structure of the edges (zig-zag or armchair). Theoretical simulations confirm that the existence of new modes is due to edge phonons, which are originated by the atomic rearrangements at the crystalline terminations [4]..

[1] B. R. Carvalho, Phys. Rev. Letters 114, 136403 (2015)

[2] B. R. Carvalho et al. Nature Comm. (2017)

[3] E. del Corro et al, Nano Letters 16 (4), pp 2363–2368 (2016)

[4] H. B. Ribeiro et al, Nature Comm. vol 7, 12191 (2016)
Colloidal, Nanoelectronic State Machines Based on 2D Materials for Aerosolizable Electronics
Authors: Koman Volodymyr , Liu Pingwei , Kozawa Daichi , Liu Albert Tianxiang , Cottrill Anton , Strano Michael S
Published: February 2020

A here-to- fore unexplored property of 2D electronic materials such as graphene, hexagonal boron

nitride, and MoS2 is the ability to graft electronic circuits, transistors, memory, and sensors onto

colloidal particles. Such particles can access local hydrodynamics in fluids to impart mobility and can

otherwise access spaces inaccessible to conventional electronics. Herein, we develop a 2D material

transfer approach combined with conventional lithography to pattern completed, functional circuits on

SU-8 particles (100x100x1 µm3 ) that function as fully autonomous state machines. The circuits are

powered by a p-n heterojunction of MoS2 and WSe2 operating as a photodiode, which powers, as a

chemiresistor circuit element, a distinct MoS2 monolayer for the detection of VOCs or carbon

particulates. Finally, the electrical output is irreversibly stored in a memristor device placed in series

consisting as a distinct MoS2 flake sandwiched between Au and Ag electrodes and protected from the

environment by hBN monolayer. These colloidal state machines are capable of operation after

aerosolization and hydrodynamic propulsion to a target over 0.6 m away. The devices can successfully

detect the presence of select analytes while aerosolized, storing this information in memory on the

particle for retrieval upon capture. An incorporated retroreflector design of the system allows for facile

position location using optical detection. Such state machines, enabled by 2D nanoelectronics, may find

widespread application as probes in the human digestive tract, oil and gas conduits, chemical and

biosynthetic reactors, and as autonomous environmental sensors.
(Invited) Emerging Two-Dimensional Materials for Electronic and Photonic Device Applications
Authors: Wang Han
Published: February 2020

In this talk, I will discuss our recent work in developing novel electronic and photonic devices based on the emerging two-dimensional (2D) materials. I will first present our work in understanding the fundamental electronic and optical properties of low-symmetry 2D materials such as black phosphorus (BP) using a newly developed scanning ultrafast electron microscopy (SUEM) technique. Our recent study of bandgap tuning in BP and the demonstration of BP based optical detectors will also be presented. In the second half of my talk, I will discuss our work on developing an atomically-thin resistive memory device based on two-dimensional materials that demonstrates record low current/power operation with promising potential applications in ultra low power computation and memory.
(Invited) 2D Materials Heterostructures for Electronic Applications
Authors: Fiori Gianluca
Published: February 2020

In this talk, I will present the perspectives of two-dimensional material heterostructures devices for electronic applications. To this purpose, we will exploit really accurate multi-scale, multi-physics numerical simulations able to predict device performance under different working conditions.

This is indeed a powerful approach, in order to assess which solutions are the most promising, and those that will never meet industry requirements.

I will also provide some perspectives regarding 2DMs inkjet printed devices, as an interesting solution to print on-demand and on flexible substrates electronic systems.
(Invited) All-Carbon Interconnects - from 1D to 3D
Authors: Yang Cary Y
Published: February 2020

Continuous downward scaling in silicon integrated circuit technology into the sub-20 nm regime has created critical challenges in chip manufacturing, among them, reliability and performance of on-chip interconnects. Current interconnect materials, Cu and W, face increased reliability challenges in the nanoscale as a result of electromigration failures at high current densities. Materials such as nanocarbons, metal silicides, and metallic nanowires are being considered as potential replacements for Cu and W. In particular, due to its superior electrical and mechanical properties as well as much higher current-carrying capacities, carbon nanotube (CNT) is a serious contender to replace Cu and W in on-chip interconnect via. However, the main challenge to functionalizing CNT vias is the metal-CNT contact resistance. To mitigate such challenge, a seamless three-dimensional all-carbon interconnect structure has been fabricated by growing CNTs directly on one or few layers of graphene (MLG). This 3D structure can potentially yield low resistance due to the strong C-C sp2 bonding in CNT and graphene and across the CNT-graphene interface. While such growth has been demonstrated, the CNT/graphene interfacial nanostructure and how it impacts the electrical properties of the 3D structure are far from being understood.

Our test structure consists of MLG grown by annealing a Ni thin film in H2/CH4 ambient inside a low-pressure PECVD chamber, before being transferred onto an oxide-covered silicon substrate. Vertically aligned CNTs are then grown on the transferred MLG in a PECVD system using a similar recipe as in our previous work on CNT vias, resulting in a 3D all-carbon interconnect structure. Scanning and transmission electron microscopy images reveal CNT alignment and interfacial nanostructure comparable to the CNT-Cr interface in CNT via. The measured resistance of the 3D structure is compared with those of sub-100 nm linewidth CNT vias. Our results demonstrate the feasibility of fabricating a 3D CNT/graphene device, which can serve as the building block for all-carbon interconnects. Enhanced understanding of the relationship between interfacial nanostructure and device resistance can lead to eventual functionalization of contacts between CNT vias and a graphene-based planar interconnect network in the most advanced technology nodes.
(Invited) Impacts of Nanostructures and Interfaces on Perovskite Solar Cell Performance
Authors: Cao Guozhong
Published: February 2020

Organometallic halide perovskite materials have a variety of remarkable optoelectronic properties, such as suitable band gap (1.5eV), high absorption coefficient, long carrier diffusion lengths and lifetimes. All these unique characters pave the way for perovskite-based devices, especially the photovoltaic cells. This presentation will start with the variation of the surface potential, photo-generated voltage, and photocurrent networks of perovskite solar cells (PSCs) with different film topography has been studied by coupling scanning Kelvin probe force microscopy (SKPM) and photoconductive atomic force microscopy (pcAFM). Then a series of TiO2 compact films was prepared by sol-gel method with different sol aging time resulting in change of, thickness, surface roughness and compactness. High roughness of the films benefits the light absorption of perovskite layer and the injection efficiency at interface. The films with better compactness perform better hole blocking effect. The Ag@TiO2 nanoparticles made by polyol solution method are embedded in perovskite films, resulting in an enhanced short-circuit current density due better light absorption and reduced charge recombination. Finally, both excess CH3NH3Cl and thiourea were introduced into the pristine CH3NH3PbI3 precursor for antisolvent precipitation at low temperature and fabricated high quality perovskite films with desired morphology, crystallinity and optical properties. CH3NH3Cl exerted significant impacts on the perovskite crystallization process by controlling the delivery speed of PbI2 from the intermediate phase CH3NH3I2Cl. Further tuning the chemical composition with controlled film growth condition resulted in an average power conversion efficiency above 21% under the standard light illumination condition.
(Invited) Influence of Nanoscale Surface Structure of TiO2 Single Crystal Electrode on Water Photooxidation Reaction Process
Authors: Imanishi Akihito
Published: February 2020

The oxygen photoevolution reaction on TiO2 and related metal oxides has attracted strong attention from the point of view of solar water splitting. In our previous study, we have proposed a new reaction model in which generated holes are consumed not only by the O2 evolution reaction but also by three competitive paths possibly occur at different surface sites; photoluminescence, surface roughening (i.e. photocorrosion), and nonradiative recombination [1,2]. Actually, we found that the branch ratio for these paths on TiO2 (110) changed by the density and the direction of steps (i.e. atomic leveled surface structure) [3]. On the other hand, it is expected that the nano-sized structure of the TiO2 surface also affect the branch ratio of 4 competitive photooxidation reactions. Thus, in this study, we investigated oxygen photoevolution efficiency on a nanostructured TiO2 electrode that exposes different facets.

A Pt wire and an Ag/AgCl/sat.KCl electrode were used as a counter and a reference electrode, respectively. An n-type TiO2 (110) doped with 0.05wt% Nb was used as a working electrode. The j−U curves were measured in 0.1 M HClO4 (pH 1.1) under UV irradiation.

Nanostructured TiO2(110) surfaces were prepared by photoetching in 0.05 M H2SO4 [4]. We obtained the nanostructured surfaces on which shallow grooves are regularly arranged. We should note that formed surface of the nanostructure is composed by (100) facet faces [4]. Photocurrent generated along with the O2 evolution from H2O on the nanostructured TiO2 (110) was apparently different from that on the flat TiO2 (100). The onset potential of nanostructured TiO2 electrode was shifted toward negative voltage, indicating that the activation energy of oxygen evolution reaction was smaller than that on the flat surface. In addition, the consumption ratio of the photogenerated holes by above mentioned 4 competitive reactions was largely different from that on the atomically flat (100) surface. Considering the fact that the photoetched TiO2(110) surface is composed by (100) microfacets[4], this result can be attributed to the nanostructuring effect. We also carried out the same experiment using the some other TiO2 electrode those have different nanostructure on their surfaces, and found that the nanostructuring effect (1. Branch ratio of 4 competitive photooxidation reactions, 2. Activation energy of O2 evolution reaction) depends on the nano-sized surface morphology of the TiO2 electrode.

[1] A. Imanishi, T. Okamura, N. Ohashi, R. Nakamura, Y. Nakato, J. Am. Chem. Soc., 129 (2007) 11569.

[2] A. Imanishi, K. Fukui, J. Phys. Chem. Lett., 5 (2014) 2108.

[3] M. Kadono, Master’s thesis, Osaka Univ. (2013).

[4] A. Imanishi, H. Suzuki, K. Murakoshi, Y. Nakato, J. Phys. Chem. B, 110 (2006) 21050.
(Invited) Fast CO2 Sorption Kinetics Using Nanowire Based Materials
Authors: Sunkara Mahendra Kumar , Nambo Apolo , Atla Veerendra , Zain Muhammed
Published: February 2020

Capture and utilization of carbon dioxide is one of the important strategies for reducing greenhouse gas emissions. The capture of CO2 onto solid sorbents is receiving increasing attention. In recent years, different lithium ceramics have been tested as possible CO2 adsorbents. However, majority of materials systems exhibit sorption capacities much lower than the corresponding theoretical capacities and slow kinetics necessary for practical use. Here, nanowire forms of several lithiated ceramics have been tested for their carbon dioxide sorption capacities and kinetics. The nanowire morphology provides smaller length scale in diameter for complete lithium utilization for carbon dioxide capture.

Li4SiO4 nanowire (NWs) powders exhibited an uptake of 0.35 g g–1 of CO2 at an ultrafast adsorption rate of 0.22 g g–1 min–1 at 650–700 °C.1 The time scales for CO2 sorption using nanowires are approximately 3 min and two orders magnitude faster compared to those obtained using lithium silicate powders with spherical morphologies and aggregates. Furthermore, Li4SiO4 nanowire powders showed reversibility through sorption–desorption cycles indicating their suitability for CO2 capture applications.

The presentation will also highlight our recent results with other nanowire materials with CO2 sorption at temperatures around 100 C.

Acknowledgements: Support from National Science Foundation (NSF) EPSCoR program (1355438).

References:

Nambo, J. He, V. Atla, T. Q. Nguyen, T. Druffel, and M. Sunkara, “Ultrafast carbon dioxide sorption kinetics using lithium silicate nanowires”, 17 (6), 3327–3333, Nano Letters (2017).
A Stream-Lined Approach to Evaluating New Ru(II)-Bodipy Complexes for Photodynamic Therapy
Authors: Swavey Shawn
Published: February 2020

Photodynamic therapy is a more targeted treatment modality; utilizing light, oxygen, and a photosensitizer (prodrug) to induce cell damage and ultimately cell death. Current photosensitizers have many limitations leading to extensive studies over the past decade to develop the next generation of this prodrug. Two promising paths have focused on boron dipyrromethenes (BODIPY) and ruthenium(II) polypyridyl complexes; however, BODIPY dyes do not exhibit efficient singlet to triplet intersystem crossing (necessary for generating reactive oxygen species) and ruthenium(II) polypyridyl complexes have weak or no absorption within the PDT window (600-850 nm). By coordinatively combining Ru(II) polypyridyl complexes with pi-extended BODIPY dyes we have shown the ability to generate singlet oxygen within the PDT window and thus have generated a new class of photosensitizer.
Direct and Mediated Spectro-Electrochemistry of Highly Oxidized Heme Species in Horseradish Peroxidase
Authors: Proshlyakov Denis A. , LeVasseur Grant , Chen Dawei , Zhang Zipin , Swain Greg M
Published: February 2020

Highly oxidized iron species play key role in the catalysis of many heme and non-heme enzymes due to their ability to activate substrates via electron or hydrogen atom transfer. Their high reactivity also makes them unstable and typically transient in nature, which hinders their structural and mechanistic investigation. Furthermore, generation of ferryloxo states typically requires addition of either oxygen and reductants or partially reduced oxygen equivalents, followed by irreversible oxygen activation. This unidirectional reaction effectively excludes investigation of associated structural changes in the protein moiety by such sensitive techniques as infrared spectroelectrochemistry, for example. Here we report on our effort to develop novel approaches toward reversible generation of ferryloxo species in horseradish peroxidase and other heme and non-heme iron proteins. We demonstrate reversible, sequential formation and quenching of Compounds I and II of HRP using several mediators in optically transparent thin layer electrochemical cell and a novel bulk optical transmission electrochemical cell. We also show that pre-conditioning of carbon-based electrodes enables generation of highly oxidized species without the use of mediators or oxygen. Following predictions of kinetically limited pre-equilibrium computational modelling and taking advantage of our chemical-free approach, we investigated the mechanisms of spontaneous quenching of highly oxidized species in HRP, the role of solvent, and the effect of pH, which yielded an unexpected result. General rules and potential pitfalls in electrochemistry of highly oxidized species in metalloenzymes will be outlined.

Figure 1
Quantum-Interference-Enhanced Thermoelectricity in Single-Molecule Junctions
Authors: Lambert Colin John
Published: February 2020

Experimental evidence of the effect of quantum interference on the room-temperature electrical conductance of single-molecules 1 opens the possibility of manipulating quantum interference in single molecules and self-assembled molecular layers.

In this talk, I will present a brief outline of current understanding of quantum interference in single-molecules2 and then discuss our recent works3 demonstrating how quantum interference can be exploited to increase the thermoelectric performance of single molecules and assemblies of molecules connected to nano-gap electrodes. Results will be presented for the thermoelectric properties of metallo-porphyrins, endohedral fullerenes and oligoynes.

Am. Chem. Soc., 2011, 133, 11426; Nature Nano. 2012, 7, 305; Nat. Nano., 2012, 7, 663, Phys. Rev. Lett. 2012, 109, 056801;
Nano. Lett. 2012, 6, 1643-1647; JACS 2012, 134, 5262; Beil
stein J. Nanotech. 2011, 2, 699 and refs. therein

Lambert C.J., Soc. Rev.
44, 875-888 (2015); Geng, et al., J. Am. Chem. Soc. 137, 4469 (2015); Sangtarash et al., J. Am. Chem. Soc. 137 11425 (2015); D. Manrique, et al., Nature Comm. 6 6389 (2015); Berritta et al, Nanoscale 7 1096 (2015)

Evangeli et al., Nano Letters
13, 2141-2145 (2013); Garcia-Suarez et al, Nanotechnology
25, 205402 (2014); Sadeghi et al, Nano Lett. 15, 7467-7472 (2015); Manrique et al., Lett.
16, 1308−1316 (2016); Ismael et al, Nanoscale 7 17338 (2015); Rincón-García at al, Nature Materials, 15, 289–293 (2016); Han et al., Nature Comm.
7 11281 (2016); M. Noori et al, Nanoscale 9 (16), 5299-5304 (2017); Q. Al-Galiby et al, Nanoscale 9 (14), 4819-4825 (2017)
Inter-Digitated Photo-Active Strands
Authors: Rein Regis , Solladie Nathalie
Published: February 2020

In natural photosynthetic systems, the solar energy is collected by pigment molecules attached to the light harvesting complexes. In these units, the chlorophylls are held in a favored spacing and orientation by fairly short a-helical polypeptides.1 When a photon hits one of the chlorophylls, the absorbed energy spreads extremely rapidly to the others until the reaction center is reached within the cell membrane, where the solar energy is converted into chemical energy used by the cell to grow. In this way, the energy contained in a single photon is conducted in a very short time and with minimal loss of energy from the point where it is absorbed to where it is needed. The extraordinary efficiency of the energy migration over long distances with minimal loss of energy is ascribed to the favored spacing and orientation of the chlorophylls which are held in an appropriate parallel conformation. Beyond the control of the structure of multi-chromophoric arrays, monitoring the spatial orientation of the chromophores in artificial light harvesting devices is a challenge of growing interest. Indeed, multi-porphyrinic arrays attract more and more attention for the elaboration of photonic and electronic wires.2

An octapeptide3 and an hexadecapeptide4 derived from the L-lysine and functionalized with porphyrins have been prepared. Beyond a certain degree of oligomerisation, we observed the development of a secondary structure such as a 310 helix which forces the porphyrins to arrange in a defined spatial arrangement. Due to the overlap of the porphyrins in such a conformation, the chromophores undergo a sufficient electronic coupling to favor a good exciton migration.5

The ability of these peptides to accomodate guests was investigated through ligand binding studies carried out in dichloromethane with DABCO as bidentate base. The complexation of DABCO by these peptides was monitored by UV-visible spectrophotometric titration in CH2Cl2. We showed that the enhanced stability of the complexe octapeptide/DABCO can be ascribed to a pre-organization of the octapeptide forming cavities, and provides convincing evidence that the bidentate base is inserted into the cavities of the octapeptide via host/guest interactions.

Acknowledgements

This work was supported by the CNRS and the French Ministry of Research.

References

W. Kühlbrandt, Nature
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a) R. W. Wagner, J. S. Lindsey, J. Seth, V. Palaniappan, D. F. Bocian, J. Am. Chem. Soc.
1996, 118, 3996-3997 and ref. cited therein. b) M. J. Crossley, P. L. Burn, S. J. Langford, J. K Prashar, J. Chem. Soc., Chem. Commun.
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Unpublished results.

a) M. Fujitsuka, M. Hara, S. Tojo, A. Okada, V. Troiani, N. Solladié, T. Majima, J. Phys. Chem B.
2005, 109, 33-35. b) M. Fujitsuka, D. W. Cho, N. Solladié, V. Troiani, H. Qiu, T. Majima, J. Photochem.
Photobiol. A
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Figure 1
Β-Arylamino Functionalized Porphyrins: Regioselective Synthesis, Structural, Photophysical and Electrochemical Properties
Authors: Sankar Muniappan , Prakash Kamal
Published: February 2020

Among the different approaches for β-functionlization of poprhyrins, a limited number of β-arylamino functionalized poprhyirns were reported.1 Porhyrins and metallopoprhyrins that consist arylamino group have exhibited unique physiochemical and electrochemical redox properties and utilized for various applications such as dye-sensitized solar cells (DSSCs), catalysis, and nonlinear optics.2
In this regard, we report the regioselective synthesis of 2-arylamino-12,13-dibromo-5,10,15,20-tetraphenylporphyrins and their metal (Cu(II) and Zn(II)) complexes (Fig. 1a). The palladium catalyzed coupling reaction of tetrabromoporphyrin with substituted anilines yielded various mono-β-arylamino substituted poprhyrins. All β-arylamino porphyrins were characterized by UV-Vis, fluorescence, 1H NMR spectroscopic techniques and cyclic voltammetry studies. β-arylamino porphyrins exhibited broadened absorption spectra which consist one Soret and two Q bands as shown in Fig. 1b. Notably, β-arylamino porphyrins exhibited multiple oxidations and reductions due to 'push-pull' β-substituents which alters the energy levels of frontier molecular orbitals. DFT studies revealed that these porphyrins are having quasiplanar confirmation. In this presentation, we will discuss about the regioselective synthesis, spectral, electrochemical redox properties of β-arylamino functionalized porphyrins in detail.

Figure 1
Porphyrinic Metal-Organic Frameworks As Chemoselective Catalysts
Authors: Su Cheng-Yong , Zhang Li
Published: February 2020

Owing to the designable structure, large surface area, high porosity et al, metal-organic frameworks (MOFs) as heterogeneous catalysts have aroused a lot of interests. By reasonable design of the components (e.g. metal node, ligand and guest), cavity, topology, etc., MOFs can be widely applied in a variety of reactions. With the aid of diffusion-controlment, host-guest recognition, and confinement effect of the coordination space of MOFs, they can display chemoselectivity, including shape-, size-, regio- and enantio-selectivitiy, and even inverted chemeoselectivity compared to conventional molecular catalysts. Considering that various elements such as transition metals and main group elements can be implanted into the central ring of porphyrin, porphyrinic metal-organic frameworks (PMOFs) have emerged as powerful MOF-based heterogeneous catalysts and applied in a variety of reactions, including photocatalysis, electrocatalysis, CO2 conversion, carbene insertion, etc. Our group has recently worked on the design and synthesis PMOFs based on noble metals (e.g. Ru, Rh, Ir, Pd, and Pt). Catalytic results show that our PMOFs can induce selective X-H (X = Si, N) insertion reaction.

Figure 1
Hydrogen and Oxygen Evolution Reactions Catalyzed By Single Site Metal Porphyrins and Corroles
Authors: Cao Rui
Published: February 2020

Catalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are key steps involved in artificial photosynthesis for solar-energy conversion for the production of clean, carbon-free, and renewable energy sources, and thus they are considered to be appealing ways to eliminate the energy and environmental problems caused by burning fossil fuels. Extensive efforts have been made to develop efficient and robust catalysts for these two processes. Research on mononuclear metal complexes has attracted increasing attention recently because not only they are capable of catalyzing HER and OER as efficiently as multinuclear metal complexes, but also there are several advantages in synthesis and mechanism studies by using single site catalysts. In this talk, we will introduce hydrogen and oxygen evolution reactions catalyzed by single site metal porphyrins and corroles.1-6

References

(1) Zhang, W.; Lai, W. Z.; Cao, R. Energy-Related Small Molecule Activation Reactions: Oxygen Reduction and Hydrogen and Oxygen Evolution Reactions Catalyzed by Porphyrin- and Corrole-Based Systems. Chem. Rev.
2017, 117, 3717-3797.

(2) Han, Y. Z.; Fang, H. Y.; Jing, H. Z.; Sun, H. L.; Lei, H. T.; Lai, W. Z.; Cao, R. Singly Versus Doubly Reduced Nickel Porphyrins for Proton Reduction: Experimental and Theoretical Evidence for a Homolytic Hydrogen-Evolution Reaction. Angew. Chem. Int. Ed.
2016, 55, 5457-5462.

(3) Lei, H. T.; Fang, H. Y.; Han, Y. Z.; Lai, W. Z.; Fu, X. F.; Cao, R. Reactivity and Mechanism Studies of Hydrogen Evolution Catalyzed by Copper Corroles. ACS Catal.
2015, 5, 5145-5153.

(4) Lei, H. T.; Liu, C. Y.; Wang, Z. J.; Zhang, Z. Y.; Zhang, M. N.; Chang, X. M.; Zhang, W.; Cao, R. Noncovalent Immobilization of a Pyrene-Modified Cobalt Corrole on Carbon Supports for Enhanced Electrocatalytic Oxygen Reduction and Oxygen Evolution in Aqueous Solutions. ACS Catal.
2016, 6, 6429-6437.

(5) Han, Y. Z.; Wu, Y. Z.; Lai, W. Z.; Cao, R. Electrocatalytic Water Oxidation by a Water-Soluble Nickel Porphyrin Complex at Neutral pH with Low Overpotential. Inorg. Chem.
2015, 54, 5604-5613.

(6) Sun, H. L.; Han, Y. Z.; Lei, H. T.; Chen, M. X.; Cao, R. Cobalt Corroles with Phosphonic Acid Pendants as Catalysts for Oxygen and Hydrogen Evolution from Neutral Aqueous Solution. Chem. Commun.
2017, 53, 6195-6198.

Figure 1
Synthesis of Carbazole-Based Porphyrin Oligomers
Authors: Maeda Chihiro
Published: February 2020

Fused porphyrins show NIR absorption because they have larger p-conjugation system than regular porphyrins. General fused porphyrins have been synthesized by the peripheral oxidative fusion reaction of the porphyrin skeleton. On the other hand, we successfully synthesized carbazole-based porphyrin via the annulation reaction of butadiyne-bridged carbazole dimer and the subsequent oxidation of the isophlorin. The carbazole-based porphyrin shows strong NIR absorption due to the effect of the quadruple benzo-fusion.

We have synthesized several carbazole-based porphyrins, and effective substituent effect was observed at the carbazole moieties. Therefore, we then tried to oligomerize the carbazole-based porphyrin at the carbazole moieties. Four kinds of carbazole-based diporphyrins were synthesized, and their photophysical properties were investigated. As a result, thiophene-bridged diporphyrin was found to show strong intramolecular electron coupling. Furthermore, cyclic porphyrin trimer and tetramer with thiophene linkages were synthesized.

All the molecules show NIR absorption. It is worth to note that the spectra of oligomers show broad and red-shifted NIR band as compared to the monomer, which indicates strong intramolecular electronic interaction.

Figure 1
Assemblies of Expanded and Contracted Oligopyrroles: On-Surface Synthesis, Reactions, and Electronic Properties
Authors: Gottfried J. Michael
Published: February 2020

Oligopyrroles and their metal complexes are versatile materials for surface and interface functionalization [1]. While monolayers of these molecules can sometimes be prepared by physical vapor deposition under vacuum conditions, this approach is limited to chemically and thermally stable species. An interesting alternative is the on-surface synthesis, which provides access to monolayers of species that are too fragile for vapor deposition or that cannot be made by solution-based synthesis at all. In this contribution, I introduce several strategies for the on-surface synthesis of oligopyrroles: (1) On-surface metalation of pre-deposited free-base porphyrin, phthalocyanine, or corrole ligands. With this approach, surface-stabilized complexes with metal centers in unusual oxidation states can be prepared. The attachment of additional ligands on the metal center can lead to bonding competition such as the surface trans effect. (2) Phthalocyanines, naphthalocyanines and their expanded homologs can be prepared by template-directed on-surface synthesis from suitable dinitrile-based precursors. (3) On-surface synthesis also gives access to linear open-chain counterparts of phthalocyanines, which represent a novel class of non-cyclic oligopyrroles. Structure, electronic properties and reactivities of the oligopyrrole monolayers will be discussed on the basis of extensive experimental and theoretical results.

[1] J.M. Gottfried, Surface Chemistry of Porphyrins and Phthalocyanines, Surf. Sci. Rep. 70 (2015) 259-379.
Subphthalocyanines Axially Substituted with Electroactive Moities
Authors: Torres Tomas , Guldi Dirk M. , Bottari Giovanni , Winterfeld Kim A. , Lavarda Giulia , Sekita Michael , Lissau Henriette , Labella Jorge , Guilleme Julia
Published: February 2020

Among the molecular building blocks used for the construction of light-powered, electroactive ensembles, subphthalocyanines (SubPcs) hold a privileged position due to their outstanding photophysical properties. These singular cone-shaped, aromatic molecules show a strong absorption in the 550-650 nm region with excitation energies above 2.0 eV, high fluorescence quantum yields, a rich redox chemistry, and low reorganization energies. As part of our systematic investigation in the preparation and study of novel SubPc-based D–A systems, we decided to use 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) as partner for SubPcs. Thus, a 1,1,4,4-tetracyanobuta-1,3-diene (TCBD)-aniline moiety has been introduced, for the first time, at the axial position of two subphthalocyanines (SubPcs) peripherally substituted with hydrogen (H12SubPc) or fluorine atoms (F12SubPc). Single-crystal X-ray analysis of both SubPc-TCBD-aniline systems showed that each conjugate is a racemic mixture of two atropisomers resulting from the almost orthogonal geometry adopted by the axial TCBD unit, which were separated by chiral HPLC.

Figure 1
Nitrogen-Doped Graphene Based Nanostructures for Energy & Catalytic Applications
Authors: Kim Sang Ouk
Published: February 2020

Carbon nanotubes (CNTs) and graphene attract enormous research attention for their outstanding material properties along with molecular scale dimension. Optimized utilization of the graphene based materials in various application fields inevitably requires the subtle controllability of their properties according to a specified target application. In this presentation, our recent research works associated to nitrogen-doped graphene based nanomaterials will be presented. Substitutional doping of CNTs and graphene with nitrogen (N) heteroelement could be achieved via pre- or post-synthetic treatment. The resultant N-doped CNTs and graphene demonstrate tunable workfunction, modulated charge carrier density and remarkably enhanced surface activity, including catalytic behavior, which could be employed for many different graphene based functional nanostructure or heterostructure formation. N-doped CNTs could be hybridized with metallic nanoparticles to accommodate plasmonic properties with charge selective carrier transport, which can be utilized for the effective enhancement of device efficiency of organic and perovskite solar cells. Various catalytic oxides or other ceramics, such as amorphous molybdenum sulfides, can be directly deposited at the surface of N-doped graphene based materials without any intermediate adhesive layer for high performance hybrid photocatalysts or electrocatalysts for oxygen reduction or hydrogen evolution reaction. N-dopant sites can initiate damage-free unzipping of graphene plane to greatly enlarge the surface area of N-doped CNT array, whose facile carrier transport along the highly crystalline unzipped nanoribbon structure can be utilized for ultrahigh power supercapacitors and so on.
Syntheses and Optoelectronic Applications of Porphyrins and Porphyrinoids
Authors: Xie Yongshu , Li Qizhao , Wei Pingchun , Wang Yueqiang
Published: February 2020

Pyrrole based linear oligopyrroles, porphyrins and porphyrinoids have exhibited rich structural diversity and interesting properties applicable in a variety of fields.1 We have synthesized novel linear oligopyrroles and porphyrinoids, and applied them as fluorescent sensors for detecting ions with biochemical and environmental relevance.2 Meanwhile, We have synergistically improved the photovoltage and photocurrent of dye-sensitized solar cells by optimizing the porphyrin dye structures in combination with an effective co-sensitization approach, thus achieving a high photovoltaic efficiency of 11.5%.3

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Figure 1
Correlating Redox and Photophysical Properties of Donor-Acceptor (aza)BODIPY-Based Dyads and Triads with Their Electronic Structures Toward a Rational Design of New Light-Harvesting Material
Authors: Nemykin Victor V. , Zatsikha Yuriy V. , Kovtun Yuriy P. , Blank David A.
Published: February 2020

Redox and photophysical properties of a large number of the BODIPY-, aza-BODIPY-, and BOPHY-based donor-acceptor dyads and triads (with representative examples given in Figure 1) have been investigated by the variety of steady-state and time-resolved spectroscopic methods. An influence of the catechol bridge between organic chromophore and the nanocarbon-based acceptor was studied in details and correlated with the electronic structures of new compounds investigated by the Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) methods. It was found that catechol bridge is quite efficient electron-donor, which hinders the photo-induced electron-transfer processes in dyads and triads.

Fig. 1. Representative examples of BODIPY-, aza-BODIPY-, and BOPHY-based dyads and triads.

Figure 1