bluuebunny/crossref_metadata_2025 huggingface dataset:
Modulating Conductivity in Paintable Films from Solvent-Exfoliated Inks of 2D MoS2 and Bi2te3
Authors: O'Dwyer Colm
Published: July 2021

Research on two-dimensional (2D) layered materials such as graphene,(1) transition metal dichalcogenides (TMDs), carbide and carbonitride relatives called MXenes,(2) has progressed beyond discovery to a wide range of uses. (3,4) In all applications where electronic transport is important, 2D materials, their assemblies, deposition, homo- and hetero-interfaces, layered networks, and composite with polymers, strongly influence the nature of conductivity and consequently the type of electrode or device. Photonics and optoelectronic investigations (5,6) are also sensitive to engineering of 2D materials and their composites, while energy storage and thermoelectric applications using 2D materials must take into account ion accessibility and thermal conductivity, respectively, in addition to electrical conductivity.

Exfoliation of parent bulk crystals to give 2D and few-layer MoS2 (7,8) and Bi2Te3 dispersions in solvents may also be promising functional inks. Whether thixotropic or dilatant, inks from particle dispersions are the basis of many printing and coating technologies.(9,10) Incorporating new functionality using 2D materials with standard processing has potential for interesting applications.

Here, we developed inks using high concentrations of exfoliated MoS2 and Bi2Te3 2D layer suspensions that can be painted as uniform films on substrates (11,12). Conductivity is controlled at material-level by high quality exfoliated 2D sheets, and in the case of Bi2Te3 we examined the influence of a PEG400 binder additive to the ink. We discuss the nature of in-plane electronic conductivity in painted films from both of these 2D material inks, and summarize measurements that show how conductivity is altered by the painting direction and aspect ratio of coated films.

References

(1) A. K. Geim, Science, 324, 1530 (2009).

(2) B. Anasori, M. R. Lukatskaya, and Y. Gogotsi, Nat. Rev. Mater., 2, 16098

(2017).

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Science, 340, 1226419 (2013).

(4) C. O’Dwyer, L. Walsh, F. Gity, S. Bhattacharjee, and P. K. Hurley, Electrochem.

Soc. Interface, 27, 53 (2018).

(5) L. Britnell et al., Science, 340, 1311 (2013).

(6) F. Xia, H. Wang, D. Xiao, M. Dubey, and A. Ramasubramaniam, Nat. Photon., 8,

899 (2014).

(7) E. Carroll, D. Buckley, D. Mc Nulty, and C. O’Dwyer, ECS J. Solid State Sci. Technol.
9 093015 (2020).

(8) V. Sánchez, E. Benavente, V. Lavayen, C. O’Dwyer, C. M. S. Torres, G. González, and M. A. S. Ana, Appl. Surf. Sci. 252, 7941 (2006).

(9) E. B. Secor, B. Y. Ahn, T. Z. Gao, J. A. Lewis, and M. C. Hersam, Adv. Mater., 27,

6683 (2015).

(10) D. McManus et al., Nat. Nanotechnol., 12, 343 (2017).

(11) E. Carroll, D. Buckley, V. Mogili, D. McNulty, M. S. Moreno, C. Glynn, G. Collins, J. D. Holmes, K. M. Razeeb, C. O’Dwyer, Chem. Mater.
29, 7390-7400 (2017).

(12) E. Carroll, D. P. Buckley, G. Collins, J. D. Holmes, K. M. Razeeb, and C. O'Dwyer, ECS Trans.
64, 1 (2015).
(Invited) Thickness-Modulated MoS2 for High-Frequency Electronic Applications
Authors: Adachi Michael M.
Published: July 2021

Two dimensional transition metal dichalcogenides (TMDs) (e.g. MoS2) are atomically thin semiconductors that have remarkable properties for electronic applications such as having a sizable electronic bandgap and relatively high carrier mobility. The atomically thin profile also facilitates the tuning of the electronic structure via surface effects such as charge traps and surface states. Two dimensional TMDs having two different thicknesses also have different electronic structures, forming heterojunctions. Here, we discuss the excellent rectification behavior of fabricated thickness-modulated (few layer - many layer) MoS2 diodes, including a large reverse breakdown voltage exceeding 10V. The IV characteristics of the diodes can be strongly tuned by application of a gate voltage facilitating the demonstration of gate-voltage controlled tuning of simple electronic circuits. The thickness modulated diodes are also characterized for high-frequency electronic application.
Exfoliated Silicate Nanosheets As Novel Near-Infrared Fluorophores for (Bio)Photonics
Authors: Selvaggio Gabriele , Weitzel Milan , Oleksiievets Nazar , Oswald Tabea Anne , Nissler Robert , Mey Ingo , Karius Volker , Enderlein Jörg , Tsukanov Roman , Kruss Sebastian
Published: July 2021

The near-infrared (NIR) region of the electromagnetic spectrum presents optimal characteristics for imaging of complex (biological) samples: this is mainly due to reduced light scattering, absorption, phototoxicity and autofluorescence. However, despite their clear potential over commonly employed visible fluorophores, only few NIR fluorescent materials are known so far, and even less are suitable for biomedical applications. For this reason, it is of great interest to search for novel materials that can enrich the so far poor library of NIR fluorophores.

We exfoliated a class of layered silicates: Egyptian Blue (CaCuSi4O10, EB), Han Blue (BaCuSi4O10, HB) and Han Purple (BaCuSi2O6, HP). These pigments fluoresce in the NIR (λ
emi ≈ 920-950 nm) with a long excited state lifetime (τ ≈ 10-100 µs). By milling, tip sonication and several centrifugation steps, small and monodisperse 2D nanosheets (NS) could be exfoliated. Most interestingly, the intense NIR fluorescence emission of the bulk counterparts is retained. In comparison to state-of-the-art fluorophores, EB-NS show no bleaching while displaying outstanding fluorescence intensity. Such qualities of EB-NS enabled us to inject them into systems of biological relevance such as developing Drosophila embryos, and perform in vivo single-particle tracking and microrheology measurements. Furthermore, it is possible to successfully detect EB-NS in plants. [1] In general, all the above mentioned three silicate NS prove bright enough to be imaged through several cm of tissue phantoms, which demonstrates the potential for (bio)photonics. Finally, we used the microsecond fluorescence lifetimes of EB-NS, HB-NS and HP-NS for micro- and macroscopic fluorescence lifetime imaging (FLIM). The results show that lifetime engineering of these silicate nanostructures is possible and can be used for lifetime-encoded imaging. [2]

In summary, we present a new exfoliation route that yields NIR fluorescent nanosheets of high promise as novel NIR fluorophores for bioimaging and photonics.

Literature:

[1] G. Selvaggio et al., Nat. Commun. 2020, 11, 1495.

[2] G. Selvaggio et al., in preparation.
Controlling One-Electron Vs Two-Electron Pathways in the Multi-Electron Redox Cycle of Nickel Diethyldithiocarbamate
Authors: Mazumder MD Motiur Rahaman , Burton Andricus , Richburg Chase S. , Saha Soumen , Cronin Bryan , Duin Evert , Farnum Byron H.
Published: July 2021

Energy storage is a vital aspect for the successful implementation of renewable energy resources on a global scale. Herein, we investigated the redox cycle of nickel dithiocarbamates for potential use as catholytes in non-aqueous redox flow batteries. The unique redox cycle of nickel dithiocarbamates (Ni(dtc)2) offers the ability to better understand these reactions by displaying 2e- chemistry upon oxidation from Ni(II) → Ni(IV) but 1e- chemistry upon reduction from Ni(IV) → Ni(III) → Ni(II). The underlying reasons for this cycle lie in the structural changes that occur between four-coordinate Ni(dtc)2 and six-coordinate [Ni(dtc)3]+. Cyclic voltammetry and spectroscopic experiments show that these 1e- and 2e- pathways can be controlled by the addition of ancillary ligands such as pyridine derivatives and Lewis acids such as Zn(II). Specifically, the addition of different pyridine based ancillary N-donor ligands (L) to the electrolyte solution results in 1e- oxidation producing a mixture of five-coordinate [Ni(dtc)2L]+ and six-coordinate [Ni(dtc)2(L)2]+ intermediate species which decay to [Ni(dtc)3]+ by parallel pathways. The equilibrium constants for L coordination were determined and found to increase with larger pKa values of the pyridine base. On the reduction side, the addition of Zn(II) to the electrolyte is shown to consolidate the two 1e- reduction peaks into a single 2e- reduction where [Ni(dtc)3]+ is reduced directly to Ni(dtc)2. This enhancement is believed to be due to chemical assistance in removing a dtc- ligand from a Ni(dtc)3 intermediate, allowing for easier reduction to Ni(dtc)2. Around 80% columbic efficiency obtained when Ni(dtc)2 was used as catholyte in the chrono potentiometric (CP) H cell experiment in presence of 24 mM Zn2+ ion.
Solvent Dependent Spectroscopic and Electrochemical Studies of Nickel (II) Diethyldithiocarbamate for Energy Storage
Authors: Islam Rezoanul , Mazumder MD Motiur Rahaman , Farnum Byron H.
Published: July 2021

In the field of electrochemical energy storage, multielectron molecular redox couples play significant roles. These redox couples have been used both as anolytes and catholytes in redox flow batteries (RFBs). The energy stored in an RFB is proportional to the number of electrons transferred per molecule. Thus, increasing the number of electrons transferred per molecule can enhance the amount of stored energy. Previous works in this field mostly looked for molecules containing multiple 1e- redox couples. The advantage of a single 2e- redox couple over multiple 1e- redox couples is that both electrons are stored and released at the same potential. In the case of multiple 1e- redox couples, two redox potentials are usually separated by more than 0.3 V. This can cause significant shifts in battery voltage and power during charging and discharging of an RFB. Nickel (II) diethyldithiocarbamate, NiII(Et2dtc)2 undergoes 2e- oxidation at a single potential to form [NiIV(Et2dtc)3]+. In different nonaqueous solvents NiII(Et2dtc)2 can offer divergent redox behavior based on their coordination properties. This divergent redox behavior means significant changes on the electrochemistry of the complex during oxidation and reduction. Pyridine, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), acetonitrile (MeCN), methanol (MeOH), acetone, and dichloromethane (DCM) have been studied in this work as they have dissimilar donor numbers with different coordination abilities towards the Ni center. Both cyclic voltammetry and spectroscopic data in the above-mentioned solvents show distinct behavior which is expected as solvent coordination ability varies. Due to its highest coordination ability among the solvents used in this study, pyridine hinders the Ni (II) to Ni (IV) oxidation by coordinating strongly to the Ni (III) center to form [NiIII(Et2dtc)2(Py)2]+. On the contrary, noncoordinating DCM allows oxidation to Ni (IV) albeit through two distinguishable 1e- oxidation processes. MeCN and acetone allow Ni (II)→(IV) oxidation at a single potential. DMSO, DMF, and MeOH show intermediate redox behavior between 1e- and 2e- transfer reactions. The presence of Ni (III) in the case of highly coordinating solvents was confirmed by low temperature EPR and UV-vis absorbance spectroscopy with the use of a chemical oxidant. These studies point to the ability of solvent to aid or hinder multielectron redox strategies which use Ligand Coupled Electron Transfer where changes in coordination environment are necessary.
Iodide Expulsion at Photoirradiated Mixed Halide Perovskite Interface
Authors: Mathew Preethi Susan , Samu Gergely F. , Janaky Csaba , Kamat Prashant V.
Published: July 2021

Visible light irradiation of a mixed halide perovskite (with bromide and iodide in the X-site) in contact with a solvent like dichloromethane (DCM) leads to selective expulsion of iodide from the film. This causes a concurrent blue-shift in band edge. We find that addition of Cs to A-site reduces the mobility of iodide ions under photoirradiation. In the absence of a solvent, these mixed halide perovskites undergo phase segregation, the rate of which decreases with the addition of Cs. Interestingly, the iodide expulsion rate in DCM is strongly dependent on the rate of photoinduced segregation. At Cs atomic concentrations greater than 50%, the films become stable as the iodide expulsion is largely suppressed. The role of the A-site cation in dictating the mobility of halide ions will be discussed in the talk.
(Invited) Nanopatterned Perovskite Films for High Performance Photo-Electronics
Authors: Park Cheolmin , Jeong Beomjin , Han Hyowon
Published: July 2021

Ordered nanostructured crystals of thin perovskites films are of great interest to researchers because of the dimensional-dependence of their photoelectronic properties for developing the perovskites with novel properties [1]. In this presentation, both top-down and bottom-up approaches for fabricating nanostructured perovskite films are demonstrated. First, a variety of micro/nanopatterns of a perovskite film are fabricated by either micro/nano-imprinting or transfer-printing a thin spin-coated precursor film in soft-gel state with a topographically pre-patterned polymer mold, followed by thermal treatment for complete conversion of the precursor film to a perovskite one [2]. Second, we also demonstrate a simple and robust route, involving the controlled crystallization of the perovskites templated with a self-assembled block copolymer (BCP), for fabricating nanopatterned perovskite films with various shapes and nanodomain sizes [3]. When the precursor ion solution of a perovskite and poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) was spin-coated on the substrate, a nanostructured BCP was developed by microphase separation. Spontaneous crystallization of the precursor ions preferentially coordinated with the P2VP domains yielded ordered nanocrystals with various nanostructures. The nanopatterned perovskites showed significantly enhanced photoluminescence (PL) with high resistance to both humidity and heat due to geometrically confining crystals in and passivation with the P2VP chains. Finally, we demonstrate that the perovskite crystals are more precisely controlled by the combination of the BCP self-assembly with top-down nanoimprinting.

References:

[1] B. Jeong, C. Park et al. Adv. Mater. 32, 2000597 (2020)

[2] B. Jeong, C. Park et al. ACS NANO 14, 2, 1645 (2020)

[3] H. Han, C. Park et al. Adv. Funct. Mater. 29, 1808193 (2019)
(Invited) Synthesis of Disilane-Bridged Aromatic Compounds for the Luminescent Materials
Authors: Yamanoi Yoshinori
Published: July 2021

π-Conjugated molecules with electron-donating (D) and -accepting (A) groups such as D-π-A compounds have been focused on strong photo/electro-luminescent materials by intermolecular charge transfer (ICT). However, π-conjugated molecules cause concentration quenching due to π-π stacking in the aggregated state, and these compounds display the low solubility in organic solvents. To develop functional organic luminophores, we synthesized the disilane-modified aromatic compounds. Conformational studies were investigated by X-ray diffraction and variable-temperature NMR experiments. These molecules display high solubility derived from the suppression of intermolecular interaction by large SiMe2 moieties and stimuli-responsive emission properties from σ-π conjugation, displaying blue-green ICT emission in the solid state with higher quantum yield.
(Invited) Novel Technique to Measure Thermal Diffusivity of Soft Crystal in Micro Scale
Authors: Ryu Meguya , Morikawa Junko
Published: July 2021

To control thermal properties in nano- and micro scale is one of the important topics with regards to the phonon engineering. Recently, the mechanical molecular crystals have been developed, which have the potential applications of actuators and soft robots. Most of the crystal motions are induced by photoisomerization or mechanical stress.

Thermal phase transition and the photothermal effect are considered as the underlying mechanism for the motions, such as bending, twisting, jumping, and rotating, etc., of the mechanical molecular crystals, called soft crystals. However, due to the lack of the measured data of heat transport properties such as thermal diffusivity or thermal conductivity of single crystals in micro volume size, the quantitative analysis of thermal phenomena in the molecular crystals has not yet been quantitatively analyzed. For example, the photo-thermally induced temperature rise produces the localized temperature distribution near the surface, and thermal diffusivity should be utilized to calculate the temperature distribution in the specimen.

To overcome such situation, we propose a micro scale temperature wave analysis (micro-TWA) method to measure the thermal diffusivity of soft crystals in micro scale. (Figure 1) This method enables to measure the axial orientation in single crystals. Furthermore, coupled with the photo-thermal stimulation, the kinetic measurement of thermal diffusivity under the stress induced and photo induced field has been realized. Demonstration of the super elastic phase transition of soft crystal, 3,5- difluorobenzoic acid (3,5−F2bza) and terephthalamide(TPA) will be presented.

This is a proposal of the new measurement method, because the experimental determination of the thermal diffusivity in micro scale of organic single crystals, under operating the deformation control, is still a challenge. The experimental validity is discussed with the theoretical analysis using the reference sample.

Figure 1
(Invited) Rotary Evaporation-Based Preparation of Metastable States
Authors: Ishii Kazuyuki
Published: July 2021

In soft crystals, macroscopic, weak stimulus-induced nanostructural changes often contain the dynamics from the metastable state to the stable state, and therefore, it is important to develop the preparation technologies for metastable states. In this study, I’ll introduce novel approaches for preparing the metastable states of chiral aggregates of phthalocyanines or polythiophenes, i.e., constituents of conducting materials, by using a rotary evaporator.

Macroscopic mechanical rotation-induced supramolecular c
hirality of
phthalocyanines: Fluid dynamics, resulting from the macroscopic mechanical rotation of a rotary evaporator or a magnetic stirrer, has been shown to selectively induce one of two enantiomers (mirror-image structures) in certain nanoscale supramolecules. We demonstrate a novel, highly reproducible, rotary evaporation-induced chiral aggregation of achiral phthalocyanines (Pcs), and proposed the mechanisms for preparing nanoscale chiral supramolecules by the use of macroscopic mechanical rotations. Here, the stable chiral thin films based on H-aggregates of MPcs (M = H2 or Pd) were prepared on the bottom of the flask by concentration of the monomeric solution with a rotary evaporator, and the chirality was shown to reproducibly depend on its rotational direction for the first time.

Evaporation rate-based selection of supramolecular chirality of polythiophene: Chirality of poly(3-((S)-3,7-dimethyloctyl)thiophene) (PT-1) aggregates was shown to depend on the rate of evaporation of its solution. In this system, the kinetically favoured, P-type aggregate is maintained in the fast evaporation process, while it transforms to the thermodynamically stable, M-type aggregate in the slow evaporation process. By selectively extracting the metastable P-type aggregate, spontaneous transformation to the M-type aggregate (i.e., molecular power springs) was experimentally demonstrated. This concept will be useful for designing soft crystals with metastable states.

References

M. Kuroha et al., Angew. Chem. Int. Ed., 2019,58, 18454-18459.

Hattori, et al., Chem. Commun., 2017, 53, 3066–3069.

Hattori, et al., J. Phys. Chem. B, 2019, 123, 2925–2929.
(Invited) Energy Transfer in Hybrid Plasmonic Nanostructures
Authors: Link Stephan
Published: July 2021

A surface plasmon in a metal nanoparticle is the coherent oscillation of the conduction band electrons leading to both strong absorption and scattering as well as large local electromagnetic fields. Plasmonic nanoparticles therefore have the potential to induce electronic transitions in nearby materials. However, but fast internal relaxation limits the efficiency of such plasmonic mediated processes. In this talk, I will discuss our recent results of a new type of nanomaterial: hybrid nanoantennas comprised of plasmonic nanorods with photoconductive polymer coatings that were grown by photo-electrochemistry. The formation of the conductive polymer shell is selective to the nanorods, while the polymerization is enhanced by photoexcitation. In situ single pareticle dark-field scattering spectroscopy and simulations support an energy transfer mechanism with up to 50% efficiency. These hybrid nanoantennas combine the unmatched light harvesting properties of a plasmonic nanoparticles with the similarly unmatched device processability of polymersl.
Visible Light Driven Hydrogen Evolution Reactions on Plasmonic Cathode
Authors: Minamimoto Hiro , Sato Daiki , Murakoshi Kei
Published: July 2021

The efficient light energy usage in the chemical reaction system is an important issue in the field of photoelectrochemical region. The visible light induced hydrogen evolution reaction can be recognized as the one of the promising challenges. For the realization of it, the wide-band semiconductor electrode could be the good candidate. However, semiconductor electrodes often have the limitation to the ultraviolet region because of their wide band gap energy. As the breakthrough for it, the introduction of the plasmonic metal nanostructures has been received much attention because the system which is recognized as the plasmonic photoconversion electrode shows the visible light response characters. Up to now, although various systems have been achieved both the cathodic and anodic reactions by the selection of the materials, the molecular process especially on the plasmonic cathode system has not been fully understood yet. In our previous study, we have established the plasmonic photocathode by using the plasmonic nanostructure and the p-type semiconductor electrode [1]. In this system, the holes excited in the metal structures injected into the valence band of the p-type semiconductor and the remained electron are consumed in the hydrogen evolution reaction. It was interesting that, in the pH dependence examination, the photocurrent generations under the neutral condition was comparable to the acidic condition which is the favorable to the hydrogen evolution. This unique property could derive from the unique molecular process influenced by the plasmonic field excitation. In this study, we have attempted to investigate the kinetic isotope effect on the plasmonic cathode system for the clarification of the molecular process on it. Through the various photoelectrochemical measurements, we have confirmed the unique inverse isotope effect on the plasmonic cathode system under the specific condition. Our current research would provide the novel insight for the accurate design of the high efficient light conversion device.

[1] H. Minamimoto et al., Chem. Lett., 2020, 49, 806.
(Invited) Side-Chain Engineering of Small-Molecular Organic Semiconductors for Organic Electronic Devices
Authors: Yamada Hiroko , Suzuki Mitsuharu
Published: July 2021

Molecular orientation and packing structure of small molecular organic semiconductors are very important for the charge carrier mobility of organic thin-film transistors (OTFT). Furthermore, the miscibility of p-and n-type materials and the grain size of each material in bulk heterojunction are critical for the performance of organic photovoltaics (OPVs). Benzoporphyrins (BPs) are one of the outstanding p-type organic semiconductors and have been studied for OTFT and OPV materials [1]. For practical use of organic electronic devices, solution process is desirable but BPs are not soluble in organic solvents.

To achieve the solution process of BPs, two strategies have been studied in the last two decades. One is a precursor approach: as-spun films of soluble precursors of BPs are in-situ converted into BP thin-films by retro-Diels–Alder reaction. With this method, the film of intact BP is available but the mixed film of edge-on and face-on grains are obtained because of the too-good crystallinity of BPs. The other is a substituent engineering: proper substituents induced to the BP framework can improve the solubility and processability of the film as well as the morphology and orientation of the molecules. Recently we were successful to obtain edge-on dominant film of BP derivatives by a simple dip-coating. 5,15-triisopropylsilyl-ethynyl(TIPS)-BP could make brickwork-type packing to achieve 1.1 cm2 V-1 s-1 FET charge carrier mobility (m
FET) [2].

This side-chain engineering was also effective for the control of packing structure of bulk-hetero junction OPV. The alkyl chain length drastically influenced the miscibility of p- and n-materials and the short-circuit current density [3]. We also found open-circuit-voltage shift of over 0.5 V in organic photovoltaic cells induced by a minor structural difference in alkyl substituents of acene-type p-materials [4]. In this presentation, the relation between control of packing structure and the OPV performance will be discussed.

References

[1] Yamada, H.;* D. Kuzuhara, Suzuki, M.; Hayashi, H.; Aratani, Bull. Chem. Soc. Jpn, 2020, 93, 1234.

[2] Takahashi, K.; Shan, B.; Xu, X.; Yang, S.; Koganezawa, T.; Kuzuhara, D.; Aratani, N.; Suzuki, M.;* Miao, Q.;* Yamada, H.* ACS Appl. Mater. Interfaces, 2017, 9, 8211.

[3] Takahashi, K.; Kumagai, D.; Yamada, N.; Kuzuhara, D.; Yamaguchi, Y.; Aratani, N.; Koganezawa, T.; Koshika, S.; Yoshimoto, N.; Masuo, S.; Suzuki, M.; Nakayama, K.; Yamada, H.* J. Mater. Chem. C., 2017, 5 14003.

[4] Suzuki, M.;* Terai, K.; Quinton, C.; Hayashi, H.; Aratani, N.; Yamada, H.* Chem. Sci.
2020, 11, 1825.
(Invited) Toward a Molecular Understanding of Photoinduced Charge Separation Process in Organic Solar Cells with Computational Approaches
Authors: Higashi Masahiro
Published: July 2021

Photoinduced charge separation (CS) process plays important roles in various fields such as natural and artificial photosynthesis, solar cell, and light-emitting diode. To investigate the photoinduced CS process theoretically, the CS state is often regarded as “static exciton” and described by several parameters such as free energy difference and electronic coupling between initial and final states according to Marcus theory. However, dynamical effects such as nuclear motions and spin-orbit coupling (SOC) are recently being recognized as important factors for controlling the CS efficiency. Therefore, the CS state should be considered as “dynamic exciton.” To analyze the dynamic exciton theoretically, we need to treat the photoexcited reaction dynamics quantum mechanically, where the locally excited and CS states, electronic coupling and SOC dynamically fluctuates. In addition, surrounding environment such as solvent are also important and required to be explicitly considered because the charge distribution of CS state is much different from that of initial state. It is impossible to treat all the systems including surroundings quantum mechanically. Therefore, combined quantum mechanical and molecular mechanical (QM/MM) method, in which an important subsystem is described quantum mechanically whereas the other surrounding is treated by molecular mechanics force field, is an essential tool. However, even the QM/MM method still requires large computational cost for the analysis of dynamic exciton because the calculation time of excited state is much longer than that of ground state. To overcome this difficulty, we have been developing several methods combining the QM/MM method and molecular dynamics simulation efficiently. In this presentation, we will show several applications toward a molecular understanding of photoinduced CS process in organic solar cells.
(Invited) In silico Material Design and Realization of Highly-Efficient Organic Light-Emitting Diodes
Authors: Kaji Hironori
Published: July 2021

Conversion of triplet excitons into light is very important to realize highly efficient organic light-emitting diodes (OLEDs). One solution is the use of transition-metal-based phosphorescent materials.1,2 Thermally activated delayed fluorescence (TADF)3 is another solution. Recently, we have developed various type of excellent TADF emitters using a simple high-throughput screening method. In this talk, I will present the method and the results we have obtained.4-8

The OLED performances are excellent, but further improvements are necessary to overcome efficiency roll-off problem etc. I will also show our recently proposed material design concept,9 named tilted Face-to-Face alignment with Optimal distance (tFFO), to further accelerate reverse intersystem crossing (RISC). Using this design concept, we developed a new material, TpAT-tFFO (Figure), which provided very fast RISC with a rate constant (k
RISC) over 107 s-1.

The results of multiscale charge transport simulations10-13 and dynamic nuclear polarization enhanced solid-state NMR14 will be also presented, if time permits.

We express sincere thanks to my group members, Prof. Adachi, and his group members. This work was supported by JSPS KAKENHI Grant Numbers JP20H05840 (Grant-in-Aid for Transformative Research Areas, “Dynamic Exciton”), JP17H01231, and JP17J09631, and FIRST Program. Computation time was provided by the Super Computer System, Institute for Chemical Research, Kyoto University. NMR measurements were supported by the international Joint Usage/Research Centre (iJURC) at the Institute for Chemical Research, Kyoto University, Japan.

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Figure 1
Achieving Consistent Diffusivity Measurement between GITT and EIS
Authors: Deng Changyu , Lu Wei
Published: July 2021

Accurate measurement of lithium diffusivity in electrode particles is essential for analyzing and predicting the performance of Li-ion batteries. There are two most widely used techniques: Galvanostatic Intermittent Titration Technique (GITT) and Electrochemical Impedance Spectroscopy (EIS). For GITT, a direct current (DC) pulse is applied to the cell. For EIS, the cell is connected to an alternating current (AC) source. The responses of the batteries are used to calculate diffusivity. GITT and EIS, despite different techniques, measure the same material property and are supposed to yield identical results. However, what has puzzled the community for a long time is that these two techniques often give an order of magnitude difference in the results.

Our research aims to resolve this large discrepancy between these two techniques. By analyzing the diffusion profile and approximation error for various particle geometries, we show that these two techniques are consistent only when the current excitation does not impact deep inside the particles, which corresponds to the condition of short pulse time for GITT or high frequency for EIS. GITT does not depend on particle size by its assumption while EIS does. Thus, we propose an innovative approach to use EIS to determine diffusivity accurately independent of particle size or geometry. We further demonstrate experimentally that the two techniques yield identical results under the right measurement conditions. This work may provide insight on the scattering of measured diffusivity data in literature.

Figure 1
Electrochemistry of Innocent Cyanocobalt Corroles
Authors: Kadish Karl , Osterloh William Ryan , Desbois Nicolas , Quesneau Valentin , Brandès Stéphane , Fleurat-Lessard Paul , Fang Yuanyuan , Blondeau-Patissier Virginie , Paolesse Roberto , Gros Claude
Published: July 2021

The electrochemical and spectroscopic properties of numerous transition metal corroles have been examined under a wide variety of solution conditions with particular interest being placed on the innocent or non-innocent nature of the corrole macrocycle and oxidation state of the central metal ion. The innocence of the redox active corrole ligand, as well as the half-wave potentials and sites of electron transfer are known to be strongly influenced by the type of central metal ion, degree of axial coordination (i.e. four-, five- or six-coordinate) and type of peripheral substituents at the meso or β-pyrrole positions of the corrole ligand. Our laboratories have previously investigated five- and six-coordinate cobalt corroles with P, N or O donor ligands and a wide variety of peripheral corrole substituents. In this work, we describe the intriguing electrochemical and spectroscopic properties of several innocent cobalt(III) corroles which are axially ligated by two pyridine molecules, one or two cyanide ions or one pyridine and one cyanide ion. Examples of the investigated corroles are shown in Chart 1 and represented as [(R)3CorCo(Py)2], [(R)3CorCo(Py)(CN)]-, [(R)3CorCo(CN)]- and [(R)3CorCo(CN)2]2- where (R)3Cor is the corrole macrocycle and R is one of several meso-substituents.

Figure 1
Engineering Cells, Membranes and Light Harvesting/Photosystem II Super-Complexes in Bio-Photoelectrochemical Cells
Authors: Adir Noam
Published: July 2021

Photosynthetic organisms, membranes and complexes are attractive starting materials for solar energy conversion (SEC). Our overall goal is to develop methods to perform SEC using these materials in simple, inexpensive and a fashion that will be non-polluting and will not compete with the growth of food materials. I will describe here how the remarkable photocatalytic activity of the photosynthetic apparatus can provide overall water splitting with oxygen and hydrogen production in Bio-Photo-Electro-Chemical (BPEC) cells via the simplest and cleanest of processes wither in the absence or presence of added electron transport molecules. With plant thylakoids, electrons are shuttled by FeCN to a transparent FTO electrode, yielding a photocurrent density of 0.5 mA·cm-2. Hydrogen evolution occurs at the cathode at a bias as low as 0.8 V. A tandem cell comprising the BPEC cell with the thylakoid membranes and a Si photovoltaic module achieves overall water splitting with solar to hydrogen conversion efficiency of 0.3% (Pinhassi et al. Nature Communications 2016). With cyanobacterial cells, electrons from the respiratory system are energized by the photosynthetic system and transferred directly to a graphite electrode, utilizing endogenous electron carriers, especially NADPH (Saper et al. Nature Communications 2018 and Shlosberg et al.
iScience 2020). The current produced can be used for hydrogen production at low additional bias for significantly longer durations than the plant thylakoids.

Another route is to use isolated photosynthetic complexes and chemically connect them to the electrochemical cell. One of the issues with this strategy is the small number of light absorbing chromophores connected to the complex, lowering the photochemical efficiency. Connection of isolated light harvesting (LH) complexes can help to overcome this deficiency. Photosystem II (PSII) is the only enzyme that catalyzes light-induced water oxidation being the basis for its application as a biophotoanode in various bio-photovoltaics and photo-bioelectrochemical cells. However, the absorption spectrum of PSII limits the quantum efficiency in the range of visible light, due to a gap in the green absorption region of chlorophylls (500 - 600 nm). To overcome this limitation, we have used two strategies: stabilizing the interaction between PSII and Phycobilisomes (PBSs) –LH complex or direct connection to modified gold-nanoparticles (Au-NPs) that serve both as LH and electron conduit. Integration of the PBS-PSII super-complexes within an Os-complex-modified hydrogel on macro-porous indium tin oxide electrodes (MP-ITO) resulted in notably improved, wavelength dependent, incident photon-to-electron conversion efficiencies (Hartmann et al. J. Mat. Chem. A. 2020). With the Au-NPs, record currents were obtained, with strong improvement in the SPR range of wavelengths that are not absorbed by chlorophylls.
Exploring Unusual Electrochemistry and Nlo Properties of Highly Electron-Deficient β-Functionalized Porphyrins
Authors: Rohal Renu Kumari , Sankar Muniappan
Published: July 2021

A series of β-tetracyanobutadiene(TCBD) appended porphyrins, M-TCBDP (M = 2H (2), Cu(II) (3), Ni(II) (4), Co(II) (5), Zn(II) (6)) were synthesized and characterized by various spectroscopic and electrochemical techniques. These porphyrins exhibit mutiredox process. Particularly, the unusual reduction potential in the range of -0.06 to -0.10 V is the consequence of TCBD group present at the β-position. The existence of enhanced polarization and intramolecular charge transfer in the absorption spectra are held responsible for nonlinear optical responses exhibited by the M-TCBD series as compared to the precursor (H2-PE2 (1)). Femtosecond Z-Scan experiments were performed to elucidate the third-order nonlinear optical properties and the temporal response of these porphyrin molecules are investigated using pump-probe spectroscopy to study the excited state transient absorption dynamics. Z-scan measurement reveals that Co-TCBD (5) exhibits better nonlinear optical response as compared to free base porphyrins. Two-photon absorption coefficient (β) and the imaginary part of third-order NLO susceptibility (χ(3)
) were procured from open aperture experiment whereas close aperture experiment delivers magnitude and sign of nonlinear optical refractive index (η2) and the real part of χ(3)
. The excellent optical limiting threshold of synthesized porphyrins makes them adorable material for laser protection.
Design, Synthesis and Characterization of Molecular Components for Light Induced Molecular Machines
Authors: Bayard Brandon
Published: July 2021

Molecular machines are systems of molecules that convert chemical energy into mechanical forces. They have a range of potential applications such as transportation of chemicals or use as an arity signal for computation. In literature, most molecular machines are activated through some form of chemical signal. This has a range of drawbacks from limiting the range of environments the machine can function in to the buildup of byproducts of the chemical reaction. The solution to these limitations was found in the synthesis and characterization of various light induced molecular machines. Like the name implies, this subset of molecular machines uses light as the signal that activates the mechanism. The model of molecular machine being worked on in this research is a porphyrin-based molecular shuttle shown in scheme 1.

Upon photoexcitation of the porphyrin acceptor, represented by the symbol A, an electron transfer from naphthyl group to the porphyrin occurs. Following this photoinduced electron transfer, a radical pair is formed between the porphyrin and naphthyl group. The newly generated naphthyl cation is expected to drive the macrocycle situated around the naphthalene towards the aryl group due to the more favourable interactions. Upon relaxation of the radical pair through back electron transfer, the macrocycle is expected to return to the naphthalene group due to the regeneration of the electron density on the naphthyl group. In this context, novel molecular machine components have been synthesized and characterized using various spectroscopic and electrochemical techniques. The goal of which, is to fine tune the chemical, physical and synthetical properties such that they are suitable for future use in a complete molecular machine as described in scheme 1.

Figure 1
Functionalized Corroles for Sensor Applications
Authors: Paolesse Roberto , Nardis Sara , Caroleo Fabrizio , Di Zazzo Lorena , Mandoj Federica , Magna Gabriele
Published: July 2021

Corrole continues to attract the interest of different research groups, since this macrocycle shows peculiar and intriguing characteristics, which open its application in different fields.

In the last few years, we have been interested to exploit corrole derivatives as receptors in chemical sensors, because the peculiar coordination chemistry of this contracted macrocycle can allow the preparation of optimized cross sensitive sensor arrays.

For this reason, the functionalization of the corrole is a fundamental step for the optimization of the macrocycle features for the target application.

We have been interested in the introduction at the peripheral positions of the corrole ring of different substituents, because they can allow the preparation of hybrid materials. These hybrid materials have been successfully exploited to develop chemical sensors.

The characterization of these species, together the applications of the functionalized corroles will be presented and discussed.
Solar Energy Conversion Schemes: Photon- and Charge-Management
Authors: Guldi Dirk
Published: July 2021

In Nature, energy and electron transfer processes in the photosynthetic machinery following light absorption have been perfectionated. To mimic the aforementioned, that is, efficiently utilizing light to separate charges and, in turn, to generate solar fuels, a great variety of multicomponent artificial photosynthetic systems have been designed and synthesized. Incentives for the design build around molecules have been taken from Nature: For example, implementing suitable electrochemical gradients across arrays of several molecular building blocks have enabled the unidirectional transformation of solar energy into electrical energy. A key parameter is the right balance between the reduction / oxidation strengths of the individual building blocks and their spatial arrangements. Both affect the thermodynamic driving forces for each step and, in turn, the overall efficiency. Notably, acceptor-donor1-donor2 or acceptor-donor1-donor2-donor3 types of artificial photosynthetic systems have been reported. Besides an initial charge transfer, charge shifts take place via oxidative electron transfers from donor1 to donor2 and, eventually, to donor3.

Considering the effectiveness of multicomponent systems, in which photoexcitation triggers a cascade of short range electron transfers, we report on two sets of novel multicomponent DA1A2s – Figure 2. These DA1A2 types feature electron transport chains with C60 and C70 of different electron acceptor strengths to create an electrochemical gradient. As a complement to electron accepting C60 / C70 either zinc porphyrins (ZnP) and zinc phthalocyanines (ZnPc) were employed. The motivation for our pump-probe investigations was to establish the role of ZnPc or ZnP as light harvester and electron donor to power unidirectional (reductive) charge shift reactions along a variety of electron transport chains.

In summary, we will demonstrate the control over unidirectional charge shift along electron transport chains en route towards highly energetic, long-lived charge separated states. Key is, however, a charge shift mediating state, whose relative energy determines the overall efficiency. If the energy of the mediating state, on one hand, is higher than the charge separated state, resonance conditions enable efficiencies as high as 50%. If the energy, on the other hand, is lower than the charge separated state, deactivation to the ground state limits the efficiency to 10%.
Development of Efficient Sensitizers Based on Porphyrin Dimers and Fused Porphyrins for Dye-Sensitized Solar Cells
Authors: Higashino Tomohiro , Imahori Hiroshi
Published: July 2021

In recent years, dye-sensitized solar cells (DSSCs) have attracted much attention as an alternative to silicon-based solar cells owing to their low-cost production and high power-conversion efficiency. Porphyrin sensitizers have made remarkable contribution to performance improvement in DSSCs. The push–pull type porphyrin sensitizers have displayed excellent light-harvesting ability and demonstrated high power conversion efficiencies more than 10% in DSSCs.

We have designed and synthesized various porphyrin sensitizers and evaluated their photovoltaic performances of the dye-sensitized solar cells. Recently, we reported a general synthetic strategy for ABC-ABC-type meso-meso linked porphyrin dimers. A meso-meso directly linked donor-π-acceptor (D-π-A) type porphyrin dimer was prepared and exhibited the high power conversion efficiency. Furthermore, we succeeded in design and synthesis of substituted methylene-bridged thiophene-fused porphyrins. The DSSC with the thiophene-fused porphyrin sensitizer achieved the highest power conversion efficiency ever reported for DSSCs with fused porphyrin sensitizers, which is comparable to that of DSSC with GY50, a representative high-performance push-pull type porphyrin sensitizer.
Investigation By NMR Spectroscopy of the Structural Characteristics of Modified Oligo-Nucleotides with Pendant Porphyrins
Authors: Solladie Nathalie
Published: July 2021

Exerting control over the position and distance of the porphyrins along a specifically designed oligonucleotidic scaffold was our main goal over the past years. Indeed, in naturally occurring light-harvesting complexes, biopolymer scaffolds hold pigments at intermolecular distances that optimize photon capture, electronic coupling, and energy transfer. We thus focused on the synthesis of four uridine-porphyrin conjugates (a monomer, dimer, tetramer and octamer) dedicated to adopt a pre-organized conformation with face-to-face porphyrins, and capable to self-organize in a stable sandwich type complexe with bidentate base such as DABCO. Using a similar strategy as the one used in antisense research, an artificial nucleotidic backbone was built from modified deoxy-uridine units linked with a more rigid linker than the phosphodiester moieties found in natural oligonucleotides. Antisense research uses modified oligonucleotides, less flexible than natural strands, to pre-organize the system toward the obtaining of stable double helices between synthesized and natural oligonucleotides. A modified oligonucleotidic backbone was here used to target a parallel conformation of the porphyrins appended to each deoxy-uridine moiety. To provide a rigid environment for the porphyrins, the uridine units were coupled in 3’-5’ stepwise fashion using ether-ester type of spacer of suitable length, and porphyrins were anchored to the uridine by means of robust carbon-carbon bonds.

To investigate the conformation of our four uridine-porphyrin conjugates, they were subjected to a comprehensive conformational analysis by using NMR spectroscopy. The collected NOE NMR data highlighted characteristic and strong interactions indicating that the glycosidic angle between the ribose and uracil base is anti. In order to further invastigate the conformation of this family of molecules, NMR experiments were carried out at variable temperature. At low temperature, the signals of the porphyrinic protons decoalesce showing two sets of b-pyrrolic protons. Similar observations are made for the signals corresponding to the sugar moieties and especially the H1’ protons, indicating molecular motions within our porphyrin-uridin arrays. These results testify in favor of the existence of a dynamic process between C3’-endo and C2’-endo conformations.

We thus document the fact that the choice of rigid spacers is not the only way to pre-organize bis-porphyrins, and that some well-chosen nucleosidic linkers offer an interesting option for the synthesis of such devices. Furthermore, the chirality and enantio-purity of the nucleosidic linkers paves the way toward the selective complexation of enantio-pure bidentate guests and the resolution of racemates.

Acknowledgements

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

References

Merkas, M. Zinic, R. Rein, N. Solladié, J. Porphyrins Phthalocyanines
2019, 23, 797-812.

Figure 1