bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Highly Water-Soluble Fullerene Derivatives for Durable Polymer Electrolyte Membrane Fuel Cells
Authors: Matsuo Yutaka , Miwa Kazuhira , Balgis Ratna , Kawasumi Masaya
Published: August 2024

Recently, the focus of proton-exchange membrane fuel cell (PEMFC) applications has shifted from fuel cell vehicles (FCVs) to heavy-duty vehicles (HDVs), necessitating enhanced fuel cell durability. The degradation of carbon-supported metal nanoparticle catalysts and electrolyte membranes are the primary factors responsible for fuel cell durability. Particularly in the context of HDVs, augmenting the chemical stability of electrolyte membranes, such as Nafion, stands as a crucial factor in improving fuel cell lifetime. The degradation mechanism of Nafion is believed to involve the cleavage of polymer chains by OH∙ radicals, formed by crossover hydrogen and crossover oxygen in the presence of trace transition metal ions. A common strategy to mitigate Nafion's chemical degradation involves adding radical quenchers like cerium ion (Ce+) to Nafion. However, Ce+ may migrate out of Nafion during fuel cell operation, leading to a decline in its highly efficient radical quenching ability over extended operational periods.

In this study, we demonstrate that a fullerene-derived radical quencher with multiple hydroxy groups significantly contributes to enhancing the durability of Nafion. Our approach involves synthesizing fullerene derivatives with various kind of hydroxy and functional groups for remarkable water solubility to realize their homogeneous dispersion within the Nafion membrane. The abundant functional groups also aid in improving proton conductivity. Moreover, the chelating effect of the spherically distributed functional groups immobilizes themselves, preventing any observed leakage from the Nafion membrane. These fullerene-derivative radical quenchers effectively enhance fuel cell durability and hold promise for future applications in HDVs.

This study was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan (JPNP20003).
(Invited) Fullerenes for Bio-Applications: The Way of Water
Authors: Porfyrakis Kyriakos
Published: August 2024

Nano-materials are emerging as important components for a series of bio-applications. In this context, carbon nanostructures such as graphene, carbon nanotubes and fullerenes have unique chemical and physical properties that make them attractive for such applications. Carbon nanomaterials have been used in tissue engineering, biosensing and drug delivery. They have also shown anti-microbial activity. They can be loaded with drugs for controlled local delivery. More importantly, the surface of carbon nanomaterials can be functionalised to enhance their biocompatibility by increasing their water-solubility.

In this talk, I will present an update on our work in using fullerenes and their derivatives for developing bio-nanomaterials. I shall focus on the combination of carbon nanostructures and polymeric materials which can result in supramolecular hydrogels with interesting properties. Hydrogels are emerging as important materials in applications such as cellular scaffoldings in regenerative medicine/tissue engineering, tissue replacements, wound dressings, etc.

I will present the synthesis of supramolecular hydrogels made from fullerenes of different sizes (C60, C84 and C90–92) that have been hydroxylated and functionalised with hydrophilic oligoethylene glycol chains. To the best of our knowledge, there have been no attempts made at incorporating higher fullerenes and their derivatives into such extended supramolecular structures, before now.

I will also show possibilities for extending our approach to endohedral fullerenes such as N@C60. I will show how we can use advanced techniques including AFM to characterise the elasticity of the hydrogels formed. The ability to incorporate endohedral fullerenes in hydrogels may be important in extending the possibility for using these materials as sensors in vitro or even in vivo, exploiting the quantum properties of such molecular systems such as their extended electron and nuclear spin lifetimes.
(Invited) Metal-Metal Bond and Metal-Cage Interaction in Endohedral Actinidofullerenes
Authors: Rodriguez-Fortea Antonio , Roselló Yannick , Abella Laura , Poblet Josep M.
Published: August 2024

Since the isolation and characterization of the first metallofullerene containing an actinide, Th@C82,1 many other mono-actinidofullerenes as non-IPR U@C80, Th@C80; IPR U@C76, U@C2n (2n=82-86), Th@C2n (2n=82-86); di-actinidofullerenes U2@C80, Th2@C80; and mixed actinido-lanthanidofullerenes ThDy@C2n (2n = 72, 76-80) and ThY@C2n (2n = 72, 78) have been characterized.2 In mono-actinidofullerenes, the actinide usually shows oxidation state +4, which involves important metal-cage interactions with significant covalent contributions, in contrast to lanthanofullerenes where the lanthanide shows oxidation state +3. In di-actinidofullerenes and mixed actinido-lanthanidofullerenes, the cage plays the role of a nanocontainer that makes possible the formation of the metal-metal bond. We here discuss on the nature of those actinide-actinide and actinide-lanthanide bonds, as well as on the particular actinide-cage interaction in these systems.

References

Wang, Y.; Morales-Martínez, R.; Zhang, X.; Yang, W.; Wang, Y.; Rodriguez-Fortea, A.; Poblet, J. M.; Feng, L.; Wang, S.; Chen, N.J. Am.
Chem. Soc.
2017, 139, 5110-5116.

a) Cai, W.; Abella, L.; Zhuang, J.; Zhang, X.; Feng, L.; Wang, Y.; Morales-Martínez, R.; Esper, R.; Boero, M.; Metta-Magaña, A.; Rodriguez-Fortea, A.; Poblet, J. M.; Echegoyen, L.; Chen, N. J. Am. Chem. Soc.
2018, 140, 18039-18050; b) Yao, Y.-R.; Roselló, Y.; Ma, L.; Puente Santiago, A. R.; Metta-Magaña, A.; Chen, N.; Rodriguez-Fortea, A.; Poblet, J. M.; Echegoyen, L. J. Am. Chem. Soc.
2021, 143, 15309-15318; c) Zhang, X.; Wang, Y.; Morales-Martínez, R.; Zhong, J.; de Graaf, C.; Rodriguez-Fortea, A.; Poblet, J. M.; Echegoyen, L.; Feng, L.; Chen, N. J. Am. Chem. Soc.
2018, 140, 3907-3915; d) Zhuang, J.; Morales-Martínez,R.; Zhang, J.; Wang, Y.; Yao, Y.-R.; Rodríguez-Fortea, A.; Wang, S.; Echegoyen, L.; de Graaf, C.; Poblet, J. M.; Chen, N. Nat.
Commun.
2021, 12, 2372; e) Yan, Y.; Abella, L.; Sun, R.; Fang, Y.; Roselló, Y.; Shen, Y.; Jin, M.; Rodríguez-Fortea, A.; de Graaf, C.; Meng, Q.; Yao, Y.-R.; Echegoyen, L.; Wang, B.-W.; Gao, S.; Poblet, J. M.; Chen, N. Nat.
Commun.
2023, 14, 6637.
(Invited) 1. Chalcogen-Substituted PC61/71BX Derivatives in Perovskite Solar Cells
Authors: Delgado Juan L
Published: August 2024

Taking into account the outstanding electronic and physical properties of fullerenes, novel functionalized fullerenes are synthesized, with adapted structures aimed at improving the efficiency and stability of inverted PSC architectures.

By means of [2+1] cycloadditions, chalcogen-substituted fullerene C60 and C70 derivatives were successfully synthesized using tosylhydrazone derivatives containing thiophene, selenophene, and furan. These derivatives were based on the chemical structures of PC71BM and PC61BM, resulting in the preparation of PC71BX: T70, S70, and F70, and PC61BX: T60, S60 and F60. The chemical structure of the synthesized mono-adducts PC61/71BM was confirmed through 1H and 13C NMR spectroscopy, MALDI-TOF mass spectroscopy, UV-Vis spectroscopy, and cyclic voltammetry.

Inverted PSCs were fabricated employing the synthesized chalcogen-substituted PC61/71BM as dopant-free ETLs. In the current presentation we will comment on the data obtained in this photovoltaic study and the explanation for the different behaviour of these PC61BX and PC71BX materials.

Figure 1
(Invited) Magnetism of Tb3N@C80 Endofullerenes
Authors: Greber Thomas , Yu Lebin , Jin Huaimin , Stalder Urs , Therampilly Sam , Bigler Laurent , Braun Hans-Benjamin , Yang Shangfeng
Published: August 2024

Tb3N@C80 was one of the first trimetallic endofullerenes to be studied in view of its magnetization where the microscopic picture of 3 Tb magnetic moments non-collinearly aligned by the ligand field of the central nitrogen ion was proposed [1]. The triangular geometry results in a net molecular magnetization of two Tb3+ ions or 18 μB. Today, this is confirmed with 23 possible pseudospin arrangements of the 3 Tb magnetic moments, resulting in a frustrated magnetic ground state with fluctuating pseudospins [2]. This picture does not include coherent tunneling of the magnetization, which is predicted within an 8-dimensional Hamiltonian and can be tested with low temperature magnetization measurements. Experimentally, we find a low temperature hysteresis that identifies Tb3N@C80 as a single molecule magnet. More surprisingly, we observe room temperature ferromagnetism in cubic single crystallites of the molecules using SQUID magnetometry. Since the magnetic interaction between adjacent carbon cages is expected to be dipolar it is neglected in the explanation of magnetic order above 3 K [3] and it is challenging to explain this finding with endofullerene magnetism. We present a series of analytical chamistry results of samples with and without room temperature ferromagnetism.

[1] M. Wolf et al. Angew. Chem. Int. Ed. 44, 3306 (2005).

[2] R. Westerström et al. Phys. Rev. B, 89, 060406(R) (2014).

[3] A. Kostanyan et al. Phys. Rev. B, 101, 134429 (2020).
Photo-Modulation of Atomically Thin Molybdenum Diselenides Functionalized with Photochromic Molecules
Authors: Park Sewon , Ji Jaehoon , Cunningham Connor , Pillai Srajan , Fang Mengqi , Yang Eui-Hyeok , Andréasson Joakim , You Jeong Ho , Choi Jong Hyun
Published: August 2024

Two-dimensional (2D) transition metal dichalcogenide semiconductors have garnered significant attention due to their extraordinary electrical and optical properties. It has been increasingly important to develop strategies for modulating their properties. A number of methods have been introduced, including doping, electric and magnetic fields, mechanical strain, etc. Herein, we report a novel approach of using photochromic molecules to modulate optoelectronic properties of monolayer MoSe2 with light. We have synthesized photochromic diarylethene (DAE) molecules that can switch between two isomeric forms, referred to as open and closed, under UV and visible light, respectively. The DAE molecules formed a uniform layer with a thickness of approximately 2 nm on monolayer MoSe2. Our density functional theory (DFT) calculations suggest that the TMD and DAE will align their band energy levels such that UV irradiation moves the lowest unoccupied molecular orbital (LUMO) energy of DAE in between the conduction band minimum (CBM) and valence band minimum (VBM) of MoSe2. This will facilitate photoexcited electron transfer from MoSe2 to DAE LUMO. Experimentally, we have confirmed our predictions by observing a strong quenching of photoluminescence (PL) and an increase of electrical conductivity in MoSe2. In contrast, visible light induced isomerization to the open form of DAE and expanded its energy levels, moving the LUMO level above the MoSe2 CBM. Therefore, the PL was retained and there was no significant change in electrical conductivity. We showed that this photoswitching can dynamically modulate the optoelectronic properties by demonstrating multiple cycles of PL emission and quenching, by alternating UV and visible light repeatedly. Lastly, our Kelvin probe force microscopy (KPFM) revealed that the potential of MoSe2 monolayers can also be modulated with photochromic molecules and external light irradiation. Our work elucidates photo-processes and exciton mechanisms at the hybrid interfaces and lays the foundation for novel applications including new phototransistors and other 2D optoelectronic devices.
The Aspects of Dimensionality in the Analysis of Raman Spectra of 2D Materials
Authors: Mamedov Sergey
Published: August 2024

Two-dimensional crystals are a class of materials in which an individual layer is indefinitely extended in two dimensions. Each layer is the molecular unit in the crystalline lattice. The nature of interlayer/intermolecular interaction is poorly understood. However, it defines physical properties such as carrier mobility, thermal conductivity, photoluminescence, etc. The vibrational properties of 2D materials are described based on triperiodic space groups. However, the triperiodic space groups do not apply to the description of these structures. The 17 two-dimensional groups in triperiodic space groups do not allow the existence of a third dimension. Therefore, if structures are not planar, the approach is inappropriate. The way to describe such structures is using the diperiodic groups in three dimensions. The well-known 2D materials are graphite, graphene, chalcogenide of Ga, Mo, W, and other elements. The crystalline As2S3 belongs to a class of 2D materials. The unit cell contains two layers with ten atoms in each layer, and it is similar to a structure of metal chalcogenide (MoS(Se)2, WS(Se)2). A bond length of 2.24 A is within the layer, and 3.56 A is between the layers. This interlayer/intralayer bond length ratio (= 1.59) corresponds to a significant difference in bond strengths. Center-zone optical phonons in crystalline As2S3 have been investigated by Raman scattering in a wide temperature range for two polarizations in the layer plane (ac). The crystal's and individual layers' symmetry are different, defining different selection rules for optical phonons. According to the crystallographic data, crystal symmetry is monoclinic with 20 atoms in a unit cell and is P21/n (C2h
5). The axis b, perpendicular to the layers, is the only unique axis of the crystal. Therefore, all phonons in the ac plane should be indistinguishable. The layer symmetry is orthorhombic in the diperiodic space group in three dimensions, in which a, b, and c axes are axes of symmetry with a space group of Pnm21 (C2v
7). The intensity of Raman bands in the layer plane shows strong polarization dependence, indicating layer symmetry's dominance. Interlayer interaction is weak, and as a result, low-frequency Raman bands appear in the spectra. The position of these bands defines the strength of interlayer interaction. The data presented provides an understanding of the structural motives of 2D As2S3 and may predict the optical/electronic properties of similar 2D materials based on Raman spectra.
(Invited) On the Optical Response of Layered Materials Exfoliated in Liquid Phase: Evidence of Functional Groups and Size-Dependent Features
Authors: Olaya Daniel , Rico Julian , Cardenas-Chirivi Gabriel , Navarrete Cristina , Hernandez Yenny
Published: August 2024

Liquid phase exfoliation of layered materials has proven successful for a range of applications [1]. However, the range of organic solvents needed, and the broad distribution of thicknesses [2] can be aided by applying intercalation steps such as electrochemical or solvothermal expansion which leads to thinner crystals in the dispersion [2, 3]. In this talk I will present the effect of electrochemical exfoliation on the basal functionalization of graphene and a proposal for a more accurate determination of the optical extinction coefficient based on oxidation levels for standardization [4]. I will also present a few examples of MoS2 and WS2 exfoliated via ultrasonication which display non-linear optical effects in fluorescence spectroscopy [5] and the effect of crystal-size selection on the piezoresistive and photoconduction response of MoS2 and WS2 exfoliated via lithium intercalation.

[1] Yenny Hernandez, et al, Nature Nanotechnology, 3, 563–568 (2008)

[2] Jonathan N. Coleman et al. Science 331, 568-571 (2011)

[3] Zhongfen Ding, et al, J. Mater. Chem., 2009, 19, 2588-2592 (2009)

[4] Khaled Parvez, et al, ACS Nano 2013, 7, 4, 3598–3606 (2013)

[5] J Rico, et al, J. Phys.: Condens. Matter 34 105701 (2022)

[6] Gabriel Cardenas-Chirivi, et al, Optical Materials, 133,112890 (2022)
(Invited) Designer 2D Materials and Machine-Learning Assisted Characterization
Authors: Huang Shengxi
Published: August 2024

2D materials offer enormous opportunities to build designer structures with widely tunable properties. The precise atomic engineering and quick characterization approach are critical to advance the application of designer 2D materials. This talk will introduce new optical features of designer 2D materials [1-4] with a focus on atomic substitution in monolayer WS2 [1]. The engineering of 2D materials presents unique opportunities for optoelectronic device and quantum information platform. When designing optoelectronic devices of 2D materials, spectroscopic permittivity of 2D material is a key parameter. While ellipsometry has been used to measure permittivity, it requires simple device structure, non-trivial parameter fitting, and special setup. This talk will also present a new machine-learning assisted approach to measure permittivity of 2D materials embedded in complex device structures without model fitting, which can facilitate a quick, accurate, and in-situ characterization of 2D and other thin film materials [5].

References

[1] Q. Qian, et al. “Photoluminescence Induced by Substitutional Nitrogen in Single-Layer Tungsten Disulfide,” ACS Nano, 16 (5), 7428-7437 (2022).

[2] K. Zhang, et al. “Enhancement of van der Waals Interlayer Coupling Through Polar Janus MoSSe,” Journal of the American Chemical Society, 142 (41), 17499-17507 (2020).

[3] K. Zhang, et al. “Spectroscopic signatures of interlayer coupling in Janus MoSSe/MoS2 heterostructures,” ACS Nano, 15 (9), 14394-14403 (2021).

[4] Q. Qian, et al. “Chirality-Dependent Second Harmonic Generation of MoS2 Nanoscroll with Enhanced Efficiency,” ACS Nano, 14 (10), 13333–13342 (2020).

[5] Z. Wang, et al. “Measuring complex refractive index through deep-learning-enabled optical reflectometry,” 2D Materials, 10, 025025 (2023).
(Invited) Engendering Non-Noble Metal Catalysts for Electrolyzers: From Fundamentals to Devices
Authors: Mukerjee Sanjeev , Yang Kevin , Kendrick Ian , Friedman Ariel
Published: August 2024

In memory of Prof. Sri Narayanan, this presentation will showcase the electrocatalysis of hydrogen evolution reaction (HER) and oxygen reduction in the context of oxygen depolarization cathode (ODC) for electrolyzer applications. Fundamentals of HER/HOR in alkaline pH will be presented in the context of various theories proposed to rationalize pH, cations, and structure effects. It will be shown that none of them can effectively explain all observations. In this presentation, four schools of thought for HER/HOR will be discussed, focusing on the strengths and shortcomings of each hypothesis and highlighting the magnitude of electrochemical interface structure in hydrogen electrocatalysis. Translation of these fundamental concepts into a durable electrocatalyst will be presented as a functionalized mono-metallic Ni catalyst concept. Durability results will be presented from both steady-state operation and uncontrolled shutdown conditions. These will be presented in conjunction with anion exchange membranes such as VersogenÒ, OrionÒ. Another cathodic process in the context of electrolysis is the oxygen-depolarized cathode, typically paired with anodic processes, such as chlorine generation. ODC cathode using coordinated Fe-N-C catalysts will be presented in the context of hydrochloric acid recovery, where activity and durability in the context of both fundamentals of oxygen reduction reaction mechanism and effects of uncontrolled shutdown will be presented.
Covalent Patterning of Graphene: from Sophistication to Simplicity
Authors: Perez Emilio M
Published: August 2024

Patterning of graphene (functionalizing some areas while leaving others intact) is challenging, as all the C atoms in the basal plane are identical, but it is also desirable for a variety of applications, like opening a bandgap in the electronic structure of graphene. Several methods have been reported to pattern graphene, but most of them are very technologically intensive. For example, some groups have explored electron beam lithography,[1] or laser writing.[2]

Here, we will present the two approaches that we have studied. First, we describe a method to functionalize graphene covalently under ultra-high vacuum conditions and characterized with scanning tunnelling microscopy.[3] We achieve exquisite (>97%) atomic selectivity and yield (92%). The periodic landscape is provided by a single monolayer of graphene grown on Ru(0001) that presents a moiré pattern due to the mismatch between the carbon and ruthenium hexagonal lattices. The moiré contains periodically arranged areas where the graphene–ruthenium interaction is enhanced and shows higher chemical reactivity. Furthermore, we will show how this type of functionalized graphene acts as a catalyst for an unusual and reversible C-C bond forming reaction.[4] Secondly, we will describe easy and scalable protocol for the covalent patterning of graphene based on using microemulsions as templates.[5] This method is technologically trivial and can achieve resolution in the µm range.

[1] M. C. Rodríguez González, A. Leonhardt, H. Stadler, S. Eyley, W. Thielemans, S. De Gendt, K. S. Mali, S. De Feyter, ACS Nano
2021, 15, 10618-10627.

[2] K. F. Edelthalhammer, D. Dasler, L. Jurkiewicz, T. Nagel, S. Al-Fogra, F. Hauke, A. Hirsch, Angew. Chem., Int. Ed.
2020, 59, 23329-23334; T. Wei, S. Al-Fogra, F. Hauke, A. Hirsch, J. Am. Chem. Soc.
2020, 142, 21926-21931.

[3] J. J. Navarro, S. Leret, F. Calleja, D. Stradi, A. Black, R. Bernardo-Gavito, M. Garnica, D. Granados, A. L. Vazquez de Parga, E. M. Perez, R. Miranda, Nano Lett.
2016, 16, 355-361; J. J. Navarro, F. Calleja, R. Miranda, E. M. Pérez, A. L. V. d. Parga, Chem. Commun.
2017, 53, 10418--10421.

[4] J. J. Navarro, M. Pisarra, B. Nieto-Ortega, J. Villalva, C. G. Ayani, C. Díaz, F. Calleja, R. Miranda, F. Martín, E. M. Pérez, A. L. Vázquez de Parga, Science Advances
2018, 4, eaau9366.

[5] A. Naranjo, N. Martín Sabanés, M. Vázquez Sulleiro, E. M. Pérez, Chemical Communications
2022, 58, 7813-7816.
(Invited) Low Temperature Atomic Layer Deposition Processes for Large-Area Synthesis of 2D Transition Metal Dichalcogenides
Authors: Bol Ageeth Anke
Published: August 2024

2D materials have been the focus of intense research in the last decade due to their unique physical properties. This presentation will highlight our recent progress on the large-area synthesis of two-dimensional transition metal chalcogenides for nanoelectronics using advanced atomic layer deposition cycle schemes. First, how we can use advanced cycle schemes to deposit wafer-scale polycrystalline MoS2 thin films at very low temperatures down to 100 °C. We have identified the critical role of hydrogen during the plasma step in controlling the composition and properties of molybdenum sulfide films. By increasing the H2/H2S ratio or adding an extra hydrogen plasma step to our ALD process, we are able to deposit pure polycrystalline MoS2 films at temperatures as low as 100 °C. To the best of our knowledge, this represents the lowest temperature for crystalline MoS2 films prepared by any chemical gas-phase method.[1]

The most dominant methods for preparing MoS2 via ALD is to alternately expose a substrate to a metalorganic precursor and a hydrogen sulfide (H2S) or a plasma containing H2S. H2S is a corrosive, toxic, and flammable gas that is heavier than air, which makes it hazardous and expensive to store, install, and transport. Alternative sulfur precursors in the solid or liquid phase would be beneficial in terms of cost and safety and would require the installation of no additional hardware for most ALD reactors. In the second half of this contribution, the widely researched ALD process using bis(tert-butylimido)bis(dimethylamino)molybdenum(IV) ((tBuN)2(NMe2)2Mo) and H2S plasma is compared to a novel ALD process using (tBuN)2(NMe2)2Mo, hydrogen plasma, and di-tert-butyl disulfide (TBDS), which is an inexpensive, liquid-phase sulfur precursor.

[1] M. Mattinen et al., Chem. Mater. (2022), 34, 5104
(Invited) Delayed Fluorescence from Inverted Singlet and Triplet Excited States
Authors: Aizawa Naoya
Published: August 2024

Hund’s multiplicity rule states that for a given electronic configuration, a higher spin state has a lower energy. Rephrasing this rule for molecular excited states predicts a positive energy gap between singlet and triplet excited states (∆E
ST). Although there is general agreement that ∆E
ST must be positive, the potential for negative ∆E
ST in phenalene analogues, such as cycl[3.3.3]azine and heptazine has been discussed during the last two decades.1–4 In this presentation, we report a fluorescent heptazine analogue HzTFEX2 that disobeys Hund’s rule, possessing negative ∆E
ST of –11 meV (Fig. 1).5 The energy inversion of the singlet and triplet excited states results in delayed fluorescence with short time constants of 0.2 μs, which anomalously decrease with decreasing temperature due to the emissive singlet character of the lowest-energy excited state. Organic light-emitting diodes using this molecule exhibit a fast transient electroluminescence decay with a maximum external quantum efficiency of 17%, demonstrating potential implications for optoelectronic devices.

(1) W. Leupin, J. Wirz, J. Am. Chem. Soc. 102, 6068–6075 (1980).

(2) W. Leupin, D. Magde, G. Persy, J. Wirz, J. Am. Chem. Soc. 108, 17–22 (1986).

(3) J. Ehrmaier, E. J. Rabe, S. R. Pristash, K. L. Corp, C. W. Schlenker, A. L. Sobolewski, W. Domcke, J. Phys. Chem. A
123, 8099–8108 (2019).

(4) P. de Silva, J. Phys. Chem. Lett. 10, 5674–5679 (2019).

(5) N. Aizawa, Y.-J. Pu, Y. Harabuchi, A. Nihonyanagi, R. Ibuka, H. Inuzuka, B. Dhara, Y. Koyama, K. Nakayama, S. Maeda, F. Araoka, D. Miyajima, Nature
609, 502 (2022).

Figure 1
(Invited) Structural and Dynamics Analysis of Organic Semiconducting Materials by Solid State NMR
Authors: Suzuki Katsuaki , Kaji Hironori
Published: August 2024

Our group have successfully developed several highly efficient blue and green thermally activated delayed fluorescence (TADF) emitters, which show the reverse intersystem crossingfrom triplet to singlet excited states. However the conformation and dynamics of TADF emitters related to RISC process in amorphous states is still unclear, because the experimental approach toward these information is limited due to difficulty of application of diffraction technique . Thus we have carried out multiscale simulations and solid-state NMR (ssNMR) analysis of organic amorphous thin films. The ssNMR is one of the powerful technique to obtain the structural and dynamics information of amorphous aggregated materials. In this presentation, we demonstrate structural and dynamics analysis of amorphous organic semiconducting materials using ssNMR.
(Invited) Dynamic Relaxation of Charge Carrier Mobilities in Organic Photovoltaics
Authors: Saeki Akinori
Published: August 2024

A non-fullerene small molecular acceptor (NFA) is a prominent molecule that shows moderate electron mobility and a narrow bandgap complementary to middle-bandgap p-type conjugated polymers, which leads to great improvement in the performance of organic photovoltaic (OPV) cells. However, little is known about the relaxation of charge carriers, which is key to efficient charge transport. Herein, we report simultaneous time-of-flight (TOF) and time-resolved microwave conductivity (TRMC) measurements[1] employing benzodithiophene-based polymer (PBDB-T):soluble C70-fullerere (PCBM) and PBDB-T:NFA (ITIC or Y6) blends, as benchmark systems[2, 3]. In addition to the conventional TOF mobilities, relaxation of the hole and electron mobility was evaluated by TRMC under an external electric field. Although PBDB-T:ITIC exhibited much faster relaxation than PBDB-T:PCBM, the relaxation in PBDB-T:Y6 was considerably moderate. This is consistent with the energetic disorder estimated from the photoabsorption onset. Interestingly, the slower relaxation of the electrons compared to the holes in PBDB-T:Y6 is in line with the preferred normal device structure. Our work deepens the understanding of the energetics of polymer:NFA blends and offers a basis for achieving efficient NFA properties.

Reference

[1] Y. Shimata, A. Saeki, J. Phys. Chem. C 121 (2017) 18351.

[2] F. Hamada, A. Saeki, ChemSusChem 14 (2021) 3528.

[3] S. Li, F. Hamada, R. Nishikubo, A. Saeki, Sustainable Energy Fuels 6 (2022) 756.
(Invited) Molecular Mechanisms That Enhance Charge Separation at Donor-Acceptor Interfaces in Non-Fullerene Organic Photovoltaics
Authors: Tamura Hiroyuki
Published: August 2024

We analyze molecular mechanisms that enhance charge separation at donor-acceptor interfaces in non-fullerene organic photovoltaics by means of molecular dynamics calculations, quantum chemistry, and QM/MM approach. We consider interfaces of π-conjugated polymers (PM6) and non-fullerene acceptors (Y6 and ITIC) as a model system. We clarified the effect of molecular disorders at the interface on the charge separation efficiency.
(Invited) Photochemistry of Metal-Assisted Electron Donor-Acceptor Assemblies
Authors: Yuasa Junpei
Published: August 2024

Here, we demonstrate a metal-ion assisted electron donor(D)-acceptor(A) arrangement. In this context, recently, we have reported that the zinc-ion assisted one-dimensional arrangement (A/D/A) of electron donor and acceptor (JACS 2020). Here, the present work studied on zinc-ion assisted circular arrangement, cyc-A/D-D-A/D-D.
(Invited) Comprehensive Analysis of Exciton Diffusion with Time-Resolved Fluorescence Spectroscopy, Anisotropy and Imaging
Authors: Sotome Hikaru
Published: August 2024

Excitons produced in materials play a crucial role in photo-energy conversion such as photovoltaics and electroluminescence devices. The temporal and spatial diffusion of excitons is a key factor for dominating the fundamental performance of optoelectronic materials. In this context, analysis of the exciton diffusion dynamics is an important issue for obtaining the rational design of the materials. Excitons diffusing in materials can be characterized by several parameters such as the energy level, orientation of the transition dipole moment and spatial distribution, and the detection of these properties is required for the comprehensive analysis. In the present study, we show time-resolved fluorescence methods for detecting the above relevant properties of excitons.

First, time-resolved fluorescence spectroscopy is a basic technique for analyzing the exciton diffusion dynamics. Fluorescence intensity is detected as functions of observation wavelength and time, and the spectral intensity and shift of fluorescence bands provide information on the population of excitons and their energy level. For example, dynamic Stokes shift indicates downhill energy migration and excitons are trapped by the defective site in molecular aggregates. Second, fluorescence anisotropy can be a good indicator for tracking the exciton diffusion in amorphous materials. Fluorescence anisotropy is sensitive to orientation change in transition dipole moments (TDMs) between absorption and fluorescence. In systems where the relative orientation of adjacent molecules is different from each other, such as amorphous solids, the exciton diffusion is accompanied with the change in TDM. Thus, appropriate modeling of molecular alignment enables quantitative estimation of the exciton diffusion coefficient and diffusion length from the anisotropy signal. Finally, time-resolved imaging is a combination of time-resolved spectroscopy and super-resolution microscopy, and an emergent technique for visualizing real-space propagation of excitons in materials. The diffraction-limited excitation beam produces excitons in several hundreds of nanometers and the subsequent exciton diffusion is evaluated by the spatial width of the fluorescence spot. The temporal broadening of the fluorescence spot directly reflects the exciton distribution and we can intuitively obtain the diffusion coefficient and length. Unlike the conventional methods for bulk materials, the advantage of the time-resolved imaging is the applicability to materials with nano- and meso-scale heterogeneous structure and it enables site-selective evaluation of the exciton transport capability. In the conference site, we will also show the application of the above methods to supramolecular polymers and thermally activated delayed fluorescence materials.

Figure 1
(Invited) Semiconductor Facet Effects Toward Photocatalysis
Authors: Huang Michael H.
Published: August 2024

Photo-induced charge transfer has been found to strongly depend on the exposed semiconductor surfaces. For instance, {110}-bound Cu2O rhombic dodecahedra exhibit a high photocatalytic activity toward dye degradation, but {100}-terminated Cu2O cubes are inert. Photocatalytic behaviors of Cu2O-based semiconductor heterostructures, such as Cu2O-ZnS and Cu2O-ZnO composites, can both enhance and suppress photocatalytic activity depending on the contacting planes at the heterojunction. Significantly, Cu2O photocatalytic activity can be greatly enhanced by functionalizing with conjugated molecules such as 4-nitrophenylacetylene (4-NA) to tune the surface band structure. This can turn the inactive cubes to possess a superior photocatalytic activity. Recently, Cu2O rhombic dodecahedra with and without 4-NA modification have been employed in photocatalytic hydroxylation of boronic acids, aryl sulfide oxidation, and amine coupling. SrTiO3 truncated rhombic dodecahedra were also found to be effective in amine coupling. Oxidative cyclization of thioamides is the latest example of surface control to photocatalytic organic transformations.
(Invited) From PL-Inactive to PL-Active: Synthesis and Properties of Novel PL-Active 2D Lead-Free Double Perovskites Based on (PA)4AgInBr8
Authors: Wong Andrew Barnabas
Published: August 2024

In this work, novel two-dimensional lead-free double perovskites ((R)4MaMbMcX8, a+b+c=2) were synthesized to achieve novel compositional and dimensional tunability. Specifically, manganese (Mn2+) is incorporated into (PA)4AgInBr8 (PA = CH3(CH2)2NH3+) to form (PA)4Ag1-0.5xMnxIn1-0.5xBr8 (0 ≤ x ≤ 1). These samples were tuned to be PL-emissive under room temperature via this manganese alloying strategy. Three emission pathways can be investigated: band edge emission, emission stemming from self-trapped excitons, and the energy transfer processes associated with Mn2+ center energy levels. Temperature-dependent PL elucidates two emissive modes: self-trapped exciton emission as well as Mn-center emission based on analysis of the associated Huang-Rhys factors. Overall, this work informs the development of additional light-emissive 2D lead-free double perovskites.
(Invited) Semiconductor Quantum Dots: From Trap States to Single Photon Purity
Authors: Thomas K. George
Published: August 2024

The semiconductor quantum dots (QDs) at the single-particle level exhibit mysterious episodes of photoluminescence (PL) intermittency, often called PL blinking, represented by ON-, GRAY-, and OFF-states which occur due to the trapping of charge carriers and Auger recombination. The first part of the presentation will discuss single-particle charge carrier dynamics in various QDs by employing various time-resolved PL measurements and strategies for controlling the undesirable OFF-states.1,2 Approaches for estimating single exciton and biexciton quantum yield in QDs and nanoplatelets, along with synthetic strategies for controlling exciton purity will be presented in the second part of the presentation.3 The presentation will also cover newer strategies for enhancing PL of QDs through plasmon resonance coupling.4 The last part of the presentation will focus on the potential applications of QDs in energy5 and electron transfer processes.6-8 By following various time-resolved transient absorption spectroscopic methods, we have demonstrated that the presence of deep hole trap states in InP QDs retards the charge recombination to a sub-millisecond timescale, which is seven orders of magnitude lower than that in CdSe QDs having shallow trap states.7 The role of the size of InP QDs on indium to phosphorous stoichiometry and the trap state distribution will also be discussed.8

K. Vishnu, A. A. K. Nair, K. George Thomas, J. Phys. Chem. C, 125, 25706 (2021).

M. Thomas, N. Pradhan, K. George Thomas, ACS Energy Lett., 7, 2856 (2022).

K. Vishnu, A. A. K. Nair, K. George Thomas (under publication 2023).

M. Thomas, C. L. Cortes, L. Paul, S. K. Gray, K. George Thomas, Phys. Chem. Chem. Phys., 24, 17250 (2022).

Manoj, S. M. Somasundaran, D. Rajan, S. Thirunavukkuarasu, K. George Thomas, J. Phys. Chem. B
126, 2635 (2022).

Sandeep, B. Manoj,K. George Thomas,J. Chem. Phys.,152, 044710 (2020).

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3, 2368 (2018).

Manoj, D. Rajan, K. George Thomas, J. Chem. Phys.,
158, 174706 (2023).
(Invited) Optical Excitations and Growth in Layered Organic Metal Halide Semiconductors
Authors: Chabinyc Michael
Published: August 2024

Hybrid organic metal halides, such as CH3NH3PbI3, have garnered attention because they are earth-abundant, solution-processable materials that can be used to form solar cells with high power conversion efficiency (>20%). There are significant questions about the unusual electronic properties of this class of materials because of the coupling between excitations and the lattice. We will present our work investigating the optoelectronic properties of layered organic metal halide systems and the relationship to structure and growth conditions. We will discuss the nature of optical excitations in layered compounds of the class R2PbX4 where R is an organic cation and X is a halide. These systems show signatures of unusually strong optical frequency magnetic dipole transitions that can be understood through self-trapped exciton formation. We will then discuss how mechanical strain during growth influences broad photoluminescence in a model layered system based on the large cation ethylammonium (EA) with the structure (EA)2(EA)n-1PbnBr3n+1. In this system the emission is strongly impacted by growth-induced strain in thin films quantified using X-ray scattering. Our results suggest that broad emission, relevant for LEDs, can be tuned in thin films. Recent work on how growth impacts the behavior of low dimensional system will also be presented.
(Invited) Phase Engineering for Enhanced Stability of Perovskite Nanowire Optoelectronics
Authors: Ho Johnny C
Published: August 2024

The crystallization of halide perovskites (HPs) into one-dimensional structures has generated considerable research interest for their promising prospects in studying electron transport characteristics and multifunctional nanoscale devices. Various strategies have been developed to achieve in-plane growth of one-dimensional (1D) structures, including epitaxy, capillary-bridge-manipulated graphoepitaxy, and van der Waals epitaxy. Typically, the VLS growth mode, which involves the initial seeding of metallic catalytic nanoparticles to facilitate the process, has realized the out-of-plane and bottom-up synthesis route, opening up a new pathway for the one-dimensional perovskite electronics and optoelectronics.

Among many recent advances, Zinc (Zn) has become a significant suppressor of vacancy formation in halide perovskites, establishing its pivotal role in defect engineering for these materials. Herein, we report the Zn-catalyzed vapor-liquid-solid (VLS) route to render black-phase CsPbI3 nanowires operationally stable at room temperature. Based on ﬁrst-principle calculations, the doped Zn2+ can not only lead to the partial crystal lattice distortion but also reduce the formation energy value from the black phase to the yellow phase, improving the stability of the desired black phase. A series of contrast tests further confirm the stabilization effect of the Zn-doped strategy. Besides, the polarization-sensitive characteristics of black phase CsPbI3 nanowires were revealed. Our work highlights the importance of phase stabilization engineering for CsPbI3 nanowires and their potential applications in anisotropic optoelectronics.
(Invited) Features of Photocatalysis on Non-Metallic Plasmonic Nanostructures
Authors: Jain Prashant K
Published: August 2024

Plasmonics is proving to be a powerful strategy for interfacing photons with molecules and activating chemical transformations. Thus far, most examples and implementations of plasmonic catalysis use metallic nanostructures. Recently, we have begun exploring catalysis by non-metallic plasmonic nanostructures, specifically those comprised of oxides laden with oxygen vacancies. I will describe the features of photocatalysis on non-metallic nanostructures, explore similarities and differences vis-à-vis photocatalysis on metal nanostructures, and point to possible electronic structure descriptors of photocatalysis.
(Invited) Three Decades of Polymer Electrolyte Based DMFC: A Perspective
Authors: Karuppaiah Chockkalingam
Published: August 2024

Direct Methanol Fuel Cell, where liquid Methanol is used as fuel and directly oxidized electrochemically to generate power, enables energy generation devices with high energy density. Hence these systems have been developed and evaluated for applications where remote and distributed generation of electrical energy are desired1. While methanol electro oxidation can in fact be achieved at temperatures in the range of 60 to 80 C, it faced two key challenges: a) The intermediate species formed during the electrooxidation poisoning the catalyst2 and b) The crossover of methanol to cathode resulting in mixed potential situation on the cathode and thus reducing the cell voltage realized3. These have been addressed and mitigated through both materials4 and engineering solutions5. In this talk, we will traverse the three decades of scientific and development journey and along the way we will cover the key contributions by S.R. Narayanan to this important technological pathway for achieving net zero CO2 emission.

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Suppressing Shuttle Effect in Lithium-Sulfur Batteries Using Perovksite Lead Zirconate Titanante Nanofibers
Authors: Joshi Aashish , Gupta Amit , Joshi Aashish
Published: August 2024

Rapid capacity fade and untimely failure caused by the infamous “shuttle effect” prevents the commercialization of Lithium-sulfur batteries (LSB). In this work, Lead Zirconate Titanate (PZT) nanofibers have been employed as polysulfide immobilizer in LSB. Ferroelectric materials possess a unique domain structure where each individual domain carries a dipole moment. The dipole-dipole interaction between the domains of the ferroelectric PZT nanofibers and polysulfides inhibits the diffusion of polysulfides from the cathode. In addition to electrostatic interactions, the 1-dimensional nanofibers with large specific surface area are accompanied by lithiophilic and sulfiphilic heteroatoms which act as anchoring points for chemically binding the polysulfides. Moreover, the enhanced wettability of the electrode arising from the favorable affinity of PZT nanofibers towards the electrolyte along with lithiophilic heteroatoms aids the diffusion of Lithium-ions. This enhanced wettability and the presence of lithiophilic surface promotes the diffusion of lithium ions which boosts the reaction kinetics. Briefly, the synergy of physical and chemical interaction of PZT nanofibers towards the polysulfide species is found to mitigate the shuttle effect and improve electrochemical performance of LSB. Further, a promising long-term cycling over 200 cycles for LSB cell with PZT interlayer is observed with 98 % Coulombic efficiency and slow fade rate of 0.08 % per cycle. Moreover, cells with higher sulfur loading and lower electrolyte to sulfur ratio reveal superior electrochemical performance with 80.8 % capacity retention over 100 cycles.

Figure 1
Ultrasensitive Electrochemical Sensor for Catecholamine Detection Using Stable Covalent pH Sensitive Thin Films
Authors: Mashazi Philani
Published: August 2024

Electrochemical detection of catecholamine neurotransmitters has been widely studied and possess lots of potential for the onsite analysis. Electrochemical sensors, however, have limitations that are due to strong interfering species that exist in the same sample matrix as the analyte of interest. In addition, the stability of the fabricated electrochemical sensor is important for reusability and reproducibility. Our research group activities have focused on fabricating stable thin films of electrocatalysts (phthalocyanines) and their graphene conjugates using covalent coupling reactions and electrografting method. The formed thin films exhibited excellent stability, electroanalytical and electrocatalytic properties. The flexible structural modification of phthalocyanines allowed for the incorporation of pH sensitive functional group and different metal ions for electrocatalysis. The use of pH sensitive electrocatalysts is a step away from using insulating and negatively charged polymers for screening interferents. The evaluation of modified electrodes were conducted in the negative and positively charged redox systems, such as [Fe(CN)6]3-/4- and [Ru(NH3)6]2+/3+. Excellent electrocatalytic properties were obtained and the electrodes could detect the neurotransmitters selectively and screen-off ascorbic acid, uric acid using the solution pH.
Cooperativity in Molecular Recognition of Porphyrin Clefts
Authors: Haino Takeharu , Hisano Naoyuki
Published: August 2024

The electron-rich cleft cavities of porphyrin-based molecular tweezers encapsulate various electron-deficient guest molecules via π-π stacking and donor-acceptor interactions. In this presentation, we will describe negative cooperativity in the molecular recognition of a trisporphyrin host molecule possessing two cleft cavities. A 1:2 host-guest complexation of the trisporphyrin host with various electron-deficient guest molecules showed strong negative cooperativity. The quantitative discussion of the negative cooperativity was provided by a detailed analysis using isothermal titration calorimetry.

1) Hisano, N.; Kodama, T.; Haino, T., Chem. Eur. J. 2023, 29, e202300107

2) Hisano, N.; Haino, T., J. Org. Chem. 2022, 87, 4001-4009.

Figure 1