bluuebunny/crossref_metadata_2025 huggingface dataset:
Thin Film Electrodes and Electrochemical Reactions at Three-Phase Boundary in Alkaline Media: A DFT Approach
Authors: Kubal Joseph , Zeng Zhenhua , Greeley Jeff
Published: February 2020

With increased energy demands, fuel cells offer a viable solution due to their efficient conversion of energy from various fuels. Switching to a basic electrolyte, many metals that would be susceptible to corrosion in an acidic environment become stable in an alkaline one. This allows for the inclusion of non-precious metals in the electrodes. However, the kinetics in an alkaline environment tend to be sluggish; this must be overcome for alkaline fuel cells to become commercially realizable. While many model electrodes have been investigated for possibility to improve the kinetics in alkaline fuel cells, this work focuses on thin film electrodes and reactions happening at the interphase between the substrate and the film. The introduction of three-phase boundaries can allow the various reaction intermediates to preferentially bind to different locations, thus possibly allowing one to break away from scaling relationships. This could ideally enable the catalyst to reach higher catalytic activity [1].

To determine the effectiveness of these electrodes, density functional theory (DFT) is employed. Before work was done to model the interphases, extensive work was done examining various moiré patterns for various oxidation states of transition metal films, with a focus on FeOxHy films. In this work, the stability of a variety of transition metal (hydr)oxide thin films on Pt and Au are first examined for stability for their future prospects of viable catalysts for fuel cell applications. In addition, phase diagrams are constructed to determine the state of the film at a given voltage, something crucial for designing optimal catalysts. A DFT + U scheme is employed to model the thin films, where U values are fitted by correcting the formation energies.

While the oxidation state and strain of the film are predicted from the full film phase diagrams, the nature of the interphase needed to be determined. The focus , hydrogen evolution and CO oxidation at these interphases with each reaction occurring at a different equilibrium potentials. This knowledge necessitated the creation of phase diagrams for the interfaces, to identify the most stable oxidation state the edge may take. With these phase diagrams, the thermodynamics and kinetics for the two reactions could be calculated with DFT along with nudged elastic band (NEB) calculations to calculate the activation barriers. These results are then compared with those on a clean Pt surface.

 [1] R. Subbaraman, D. Tripkovic, K. Chang, D. Strmcnik, A. P. Paulikas, P. Hirunsit, M. Chan, J. Greeley, V. Stamenkovic, N. M. Markovic. Nature Materials. 11, 550 (2012)
Synthesis, Pore and PTFE Distribution Studies of Monolithic Gas Diffusion Media for PEMFC By Varying Solvent
Authors: Kattamanchi Sruthi , Prathap Haridoss
Published: February 2020

Proton Exchange Membrane Fuel cells (PEMFC) are the focus of research internationally, due to their potential in solving energy problems by enabling energy conversion in a clean manner.  Gas Diffusion Medium (GDM) is a vital component of a PEMFC which controls the transport of gas and water molecules. The performance of a fuel cell is impacted by mass transport losses. Existing GDMs are based on carbon paper and carbon cloth structures that are commercially available and have specific structures. These commercially available starting materials therefore restrict the overall design of the GDM to work within the constraints of their structure.

In the present work the focus is to make a combined porous self standing GDM constituting meso and macro pores using Carbon black (CB) and PTFE. PTFE content as well as its distribution play a prominent role in wicking out water from the reaction site.  Method for preparation of the self standing GDM is tailored with starting materials such as CB, Graphite, and Teflon. Factors affecting the uniform distribution of PTFE are identified. Pore size, uniformity and pore distribution obtained through the use of four different solvents – IsoPropylAlcohol (IPA), Glycerol, Ethanol, and Water, are studied. The GDMs prepared are characterized using SEM and Mercury Intrusion Porosimetry.  Pore distribution, sizes and composition are examined using SEM images and composition maps on a comparative basis. Optimization of conductivity, hydrophobicity and water transport is carried out. The results obtained are presented and discussed and compared. The advantages a particular solvent and factor contributing an uniform PTFE distribution is recognized as a part of this approach.
Controlling Polysulfide Shuttling in Lithium-Sulfur Batteries
Authors: Pathak Manan , Suthar Bharatkumar , Subramanian Venkat
Published: February 2020

Most electric cars run on rechargeable lithium-ion batteries, a pricey technology that accounts for more than half of the vehicle's total cost [1]. The development of renewable, low cost, high performance energy technologies is a key scientific challenge. Active research is being pursued to develop a new technology that can replace Li-ion batteries. One promising alternative is the lithium-sulfur battery, which can theoretically store five times more energy at a much lower cost [2].

The major drawback of a lithium-sulfur battery is the polysulfide shuttling [3, 4] between anode and cathode, which induces low Coulombic efficiency, low utilization of the sulfur cathode, and severe degradation of cycle life. In this work, an electrochemical engineering model [2, 5, 8, 9] is used to understand the shuttling mechanism. In particular, the electrochemical engineering model will be reformulated for improved computational efficiency to enable real-time simulation and model based control [6, 7]. The control of polysulfide shuttle across the electrodes will be explored by obtaining optimal charging profiles. Controlling the polysulfide shuttling would ensure a longer battery life for the lithium-sulfur battery [10].

Acknowledgements

The work presented herein was funded in part by the Clean Energy Institute at the University of Washington, Seattle.

References

X. B. Cheng, J. Q. Huang, H. J. Peng, J. Q. Nie, X. Y. Liu, Q. Zhang and F. Wei, Journal of Power Sources, 253, 263-268, 2014.

K. Kumaresan, Y. Mikhaylik and R. E. White, J. Electrochem. Soc., 155 (8), A576-A582, 2008.

A. Manthiram, Y. Fu, S. H. Chung, C. Zu, and Y. S. Su, Chemical Reviews, 2014

A. Manthiram, Y. Fu, and Y. S. Su, Acc. Chem. Res., 46, 1125–1134,  2012.

J. Newman, Electrochemical Systems, 2nd ed. Prentice Hall, 1991.    

V. R. Subramanian, V. Boovaragavan, V. Ramadesigan, and M. Arabandi, J. Electrochem. Soc., 156 (4), A260-A271, 2009.

 P. W. C. Northrop, V. Ramadesigan, S. De, and V. R. Subramanian, J. Electrochem. Soc., 158 (12), A1461-A1477, 2011.

M. R. Busche, P. Adelhelm, H. Sommer, H. Schneider, K. Leitner and J. Janek, Journal of Power Sources, 259, 289-299, 2014.

A. F. Hofmann, D. N. Fronczek and W. G. Bessler, Journal of Power Sources, 259, 300-310, 2014.

D. N. Fronczek and W. G. Bessler, Journal of Power Sources, 244, 183-188, 2014.
Increased Conductivity of Li2xMg1-Xo/Nanostructured Carbon Composites
Authors: Chayed Nor Fadilah , Kamarulzaman Norlida , Rusdi Roshidah , Abdul Aziz Nor Diyana
Published: February 2020

Lithium conducting ceramics are important for applications in thin film batteries.  In this work, novel Li2xMg1-xO materials were synthesized by the sol-gel method. Optimization of the synthesis method showed that annealing at 950 oC gave pure, single phase materials of cubic crystal structure. Conductivity studies, using a.c. impedance showed that incorporating nanostructured carbon enhances the conductivities of the composite materials. The nanostructured carbon acted like a bridge connecting the voids between the crystals and improved the electronic and Li+ ionic diffusion through the materials.
Extreme Long Life Battery Via Atomic Layer Deposition of Solid Electrolyte on CFx Electrodes
Authors: Xing Weibing
Published: February 2020

Modern defense and commercial applications, such as environmental sensors or implantable medical devices, require battery power sources with a wide operating temperature range, excellent reliability, an ability to resist abuse including mechanical vibrations and shock, high energy density and extreme long battery life (20 years). Unfortunately, state-of-the-art (SOA) battery power sources cannot adequately meet the combined energy density and long life requirements.

Here we present a promising method to prepare extreme long life batteries via atomic layer deposition (ALD) of solid electrolyte onto inherently high energy density and stable CFxelectrodes.             

Figure 1 shows discharge voltage profiles of cells containing ALD solid electrolyte coated electrodes, overlaid with a control cell without oxide coating. The anode was metallic lithium and a conventional Li-ion electrolyte was used. The cells were discharged with a constant, one-year current rate, a relatively fast rate for 20 year service life. The ALD solid electrolyte coated cell showed no voltage delay at the initial discharge which is shown in the control cell, a phenomenon characteristic of CFx chemistry which is believed to result from the low conductivity of fresh CFx materials [1]. The elimination of the voltage delay presents significant performance advantages at start-ups. The ALD solid electrolyte coated CFxcells demonstrated more than 60mV higher discharge running voltage than that of the control cell, resulting in higher energy density and, potentially, longer battery service life. 

Figure 2 shows Nyquist plots of electrochemical impedance spectroscopy (EIS) carried out for ALD solid electrolyte coated and the control cells.  The ALD solid electrolyte coated cell showed a much smaller semi-circle representing a 66% smaller charge transfer resistance (leading to faster charge transfer kinetics) than the control cell. The EIS data strongly support the improved discharge performance presented above.   

We will show that ALD enabled solid electrolyte coatings on CFx lead to significantly improved storage stability at extreme temperatures (e.g. 85°C) and superior after-storage discharge performance, compared with CFxwithout coating.  

Our results in this study suggest solid electrolyte coating via ALD on CFx is a promising material processing methodology for extreme long life battery power sources with a complete elimination of CFx voltage delay and significantly enhanced charge transfer kinetics, energy density and electrochemical stability at extreme temperatures. Such methodology is potentially scalable economically when high throughput and high volume ALD processes are implemented.

Reference

Sheng S. Zhang, Donald Foster, Jeff Wolfenstine, Jeffrey Read, Journal of Power Sources
187, 233 (2009).

Figure 1
(Invited) Singlet Exciton Fission in Molecular Solids
Authors: Wasielewski Michael R , Eaton Samuel W. , Margulies Eric A
Published: February 2020

Singlet fission (SF) is the process by which a singlet exciton in a molecular material is energetically down-converted into two independent triplet excitons. Thermodynamic modeling predicts that using a SF material can theoretically increase the Shockley-Queisser limit for power conversion efficiency in solar cells from 32% to 44%, assuming that SF results in the formation of two triplet excitons, each of which produce an electron-hole pair quantitatively. We are examining new dye molecules, which undergo SF, using guidance from electronic structure calculations to assure the requisite relationships between molecular singlet and triplet energy levels. We are preparing hierarchical assemblies from these chromophores, starting from covalent dimers and trimers, then developing supramolecular assemblies, and engineered crystalline materials to investigate SF in bulk, ordered materials. We are using femtosecond transient spectroscopy as well as time-resolved electron paramagnetic resonance spectroscopy to characterize the SF mechanism and the factors that determine its efficiency at time scales down to 100 fs. We are also using X-ray diffraction to investigate the single crystal structures of these materials and X-ray scattering on their thin polycrystalline solid films to determine how their structures correlate with their ability to carry out SF. Our results suggest that a p-p slip-stacked geometry is important for maximizing SF efficiency.
(Invited) Deprotonation of a Multi-Nuclear Copper Complex for High Oxygen Reduction Reaction Activity Investigated By in Situ X-Ray Absorption Fine Structure Spectroscopy
Authors: Kato Masaru , Kimijima Ken'ichi , Shibata Mari , Notsu Hideo , Ogino Kazuya , Inokuma Kiyoshi , Ohta Narumi , Oyaizu Nobuhisa , Uehara Hiromitsu , Ohba Tadashi , Uemura Yohei , Takakusagi Satoru , Asakura Kiyotaka , Yagi Ichizo
Published: February 2020

The oxygen reduction reaction (ORR) occurs at the cathode in polymer electrolyte fuel cells (PEFCs) and its sluggish kinetics is one of the limiting factors for widespread applications of PEFCs. Although ORR catalysts have been extensively studied, platinum-based ORR catalysts with a high overpotential (>200 mV) are used even in the present state-of-the-art PEFCs.

In nature enzymatic oxygen reduction is known to occur at low overpotentials: multi-copper oxidases such as laccase catalyze ORR with an overpotential of ca. 20 mV on electrode surfaces and have been employed in enzymatic fuel cells [1-2]. These enzymes, however, are fragile and their footnotes are large, making them unsuitable for use in practical PEFCs. It is highly desirable to design and develop artificial ORR catalysts with electrocatalytic properties similar to those of the enzymes [3].

Here, we present our resent studies on in situ X-ray absorption fine structure (XAFS) spectroscopy of a dinuclear copper complex of 3,5-diamiono-1,2,4-triazole, Cu-Hdatrz [4,5], supported on a carbon black under catalytic and non-catalytic conditions to gain insights into designing highly active copper-based catalysts. It is known that the Cu-Hdatrz catalyst shows high ORR activity in basic solution [5]. Our in situ XAFS measurements in neutral and basic solutions revealed that the electron transfer from a CuI species to O2 was faster under basic conditions than that under the neutral condition and deprotonation from the triazole ligand might cause the coordination geometrical changes under a basic condition, suggesting that the deprotonated structure of the CuIactive species may be a key to understand the high ORR activity of Cu-Hdatrz or to design multinuclear copper-triazole catalysts with low overpotentials. 

Acknowledgements

This work was supported by New Energy, Industrial Technology Development Organization (NEDO). XAFS experiments were performed under the approval of the Photon Factory Program Advisory Committee (Proposal No. 2010G200 and 2013G173)

 
References

[1] N. Mano, V. Soukharev, A. Heller, J. Phys. Chem. B, 110, 11180 (2006)

[2] M.S. Thorum, C.A. Anderson, J.J. Hatch, A.S. Campbell, N.M. Marshall, S.C. Zimmerman, Y. Liu, A.A. Gewirth, J. Phys. Chem. Lett, 1, 2251 (2010)

[3] C.H. Kjargaard, J. Rossmeisi, J.K. Norskov, Inorg. Chem.,
49, 3567 (2010)

[4] E. Aznar, S. Ferrer, J. Borras, F. Lloret, M. Liu-Gonzalez, H. Rodriguez-Prieto, S. Garcia-Granda, Eur. J. Inorg. Chem.,
2006, 5115 (2006)

[5] M.S. Thorum, J. Yadav, A.A. Gewirth, Ang. Chem. Int. Ed.,
48, 165 (2008)
How Biphthalocyanine Molecules Do Arrange on Single Crystalline Surfaces
Authors: Witkowski Nadine , Lüder Johann , Brena Barbara , Puglia Carla , Bidermane Ieva
Published: February 2020

Phthalocyanine molecules have been the subject of a large number of investigations due to their versatile applications in the area of gas-sensing devices, photovoltaic

materials, light-emitting diodes, solar and fuel cells and molecular magnets. There is an evident need to characterize the molecular arrangement and the electronic properties of such organic molecules on the substrates, for getting a better understanding of the molecule-molecule as well as molecule-surface interactions.To achieve this goal, it is crucial to characterize the molecular arrangement of the molecules and link their physical properties to the structure of the film. In this study, we focus on the double decker biphthalocyanine of lutetium (LuPc2), which interest relies in its particular electronic properties. We have studied the growth and structure of LuPc2 molecules on clean and passivated Si(100)-2x1 and also on Au(111) surface, by molecular vapor deposition under vacuum [1, 2, 3].

We have used various surface experimental techniques such as surface differential optical spectroscopies, local probe microscopies and electron spectroscopies. We identified the growth mode and found that on the passivated silicon surface favors the self-organization of the molecules and we evidenced a strong influence of the flux during the formation of the molecular films. We could then propose the scenario for the growth of LuPc2 molecules on the two silicon surfaces, clean and passivated ones from few molecules up to about 40 nm.

On  Au(111) surface, molecules are found to absorb flat on the surface forming a bilayer [5] at initial coverages whereas clusters develop for larger coverages influencing their electronic structure.

References                                                                                                                                                              

1.   I. Bidermane et al., J. Chem. Phys. 138, 234701 (2013)

2.   S. Boudet et al., Phys. Rev. B 86, 115413 (2012)

3.  S. Boudet et al.,submitted to J. Phys. Chem. C

4.  Z. H. Cheng et al., J. Phys. Chem. C, 111,  2007

5.  I. Bidermane et al, in manuscript
Taming C60 Fullerene: Tuning Intramolecular Photoinduced Electron Transfer Process with Subphthalocyanines
Authors: Guldi Dirk M.
Published: February 2020

Two subphthalocyanine-C60 conjugates have been prepared by means of the 1,3-dipolar cycloaddition reaction of (perfluoro) or hexa(pentylsulfonyl) electron deficient subphthalocyanines to C60.  Comprehensive assays regarding the electronic features – in the ground and excited state – of the resulting conjugates revealed energy and electron transfer processes upon photoexcitation.  Most important is the unambiguous evidence – in terms of time-resolved spectroscopy – of an ultrafast oxidative electron transfer evolving from C60 to the photoexcited subphthalocyanines.  This is, to the best of our knowledge, the first case of an intramolecular oxidation of C60 within electron donor-acceptor conjugates by means of only photoexcitation.
All-Solid-State Dye-Sensitized Solar Cells Based on Push-Pull Zinc Porphyrin and Metal-Free Organic Sensitizers
Authors: Diau Eric Wei-Guang
Published: February 2020

Porphyrins have been designed and synthesized based on the molecular structure of YD2-oC8 for applications of dye-sensitized solar cell (DSSC) to reach PCE 13 % using cobalt-based liquid-type electrolyte. However, traditional liquid-type devices suffered from leaking of electrolyte and the best solution is to replace it with solid hole transporting materials like spiro-OMeTAD. In this lecture, I will present our recent results of all-solid-state DSSC based on a series of novel porphyrin sensitizers together with co-sensitization of porphyrins with organic dyes and/or porphyrin dimers. Extension of p-conjugation can be achieved by attaching various cyclic aromatic hydrocarbon substituents, such as anthracene, tetracene, pyrene, fluorene, and amino-substituted electron-donating groups opposite to the anchoring group of the target porphyrin. The reference porphyrin is the LD14 dye, which makes a traditional DSSC attaining PCE 9.2 % using iodine-based electrolyte. When the functional group has been inserted into the position between porphyrin core and the donor group, the efficiency of the device made of spiro-OMeTAD HTM attained PCE 4.1 %. The solid state device has the configuration FTO/TiO2 (1.8 mm)/porphyrin/spiro (180 nm)/Ag. Another new push-pull porphyrin was designed to insert the functional group Benzothiadiazole (BTD) in the position between the porphyrin core and the anchoring group. By co-sensitization of this porphyrin with a newly designed organic dye on a TiO2 film of 1.8 mm, the solid-state device showed a promising performance with PCE 5.5 %. Both time-resolved (TAS) and frequency-domain (EIS) techniques were applied to understand charge transport and recombination kinetics with respect to their photovoltaic performances.
Using Porphyrins in Solar Cells
Authors: Lin Ching-Yao
Published: February 2020

In this report, we demonstrate that porphyrins with suitable chemical structures can be efficiently used in dye-sensitized solar cells (DSSC) as well as in polymer solar cells.

For DSSC in the near-IR region, a series of new porphyrins (LWP1 - 4) were prepared by attaching pyrene or 4-dimethylaminophenyl group in combination with anthracene to modify the porphyrin core.1 Significantly, DSSCs adopting the LWP1 dye exhibit energy conversion up to 800 nm without compromising the high overall efficiency. This achievement is attributed to the collective effects of the broadened and red-shifted IPCE spectra, elevated energy level at the excited states of the dyes, proper dye soaking processes, and suitable electron-donating substituent. To further this achievement, we prepared LD31 porphyrin based on LWP3.2 The device made of LD31 exhibited panchromatic spectral feature covering the whole visible region and further extending over 800 nm. When combined with an organic dye (AN-4), the performance of the LD31/AN-4 co-sensitized device attained Jsc
/mA

cm-2 = 20.3, Voc
/mV = 704, FF = 0.72, and the overall efficiency of power conversion η = 10.3 %.

For porphyrin-incorporated polymer (PPor) solar cells, a pyrene-modified porphyrin was used as a complementary light-harvesting unit (LHU). It was found that adding proper amount of the LHU increased light absorption in the 400-500 nm region, rendering the porphyrin-incorporated D-A copolymers (PPor) panchromatic light absorbers. Voc
-Jsc
trade-offs commonly seen in many D-A polymers were not found in the PPors reported in this work. This is attributed to the presence of the LHU increasing the J
sc without sacrificing the Voc
and FF of the polymer solar cells (PSCs). Thus, 8.0% PCE was observed for the PPor-2:PC71BM single-junction PSCs. Significantly, 8.6% PCE was achieved when a C-PCBSD cathodic interlayer was introduced to suppress linkage current.3

References:

1. C.-H. Wu, M.-C. Chen, P.-C. Su, H.-H. Kuo, C.-L. Wang, C.-Y. Lu, C.-H. Tsai, C.-C. Wu,* C.-Y. Lin,* J. Mater. Chem. A, 2014, 2, 991-999.

2. C.-L. Wang, J.-Y. Hu, C.-H. Wu, H.-H. Kuo, Y.-C. Chang, Z.-J. Lan, H.-P. Wu, E. W.-G. Diau,* C.-Y. Lin,* Energy Environ. Sci., 2014, 7, 1392–1396.

3. Y.-H. Chao, J.-F. Jheng, J.-S. Wu, K.-Y. Wu, M.-Ch. Tsai, C.-L. Wang, Y.-N. Hsiao, C.-L. Wang,* C.-Y. Lin,* C.-S. Hsu,* Adv.
Mater., 2014, 26, 5205-5210.

Acknowledgment: This work is supported by the Ministry of Science and Technology, Taiwan.
Structure and Electrical Properties of the Selected Crown Ether-Derivatized Bis(2,2'-bithienyl)Methanes in Langmuir-Blodgett Films
Authors: Gawecka Karolina , Noworyta Krzysztof R. , Chitta Raghu , D'Souza Francis
Published: February 2020

Physical properties of thin films of thiophene derivatives and their polymers are greatly affected by the structure and orientation of their molecules, as well as the local environment.1  In order to obtain thin films of such compounds for practical applications, from electronic devices to chemo- and biosensors.2-3, it is important to control orientation and order of the molecules in the formed functional materials.  Interesting and efficient way to allow for such a control is Langmuir and Langmuir-Blodgett technique.

  In the presented contribution formation and properties of ultrathin films of the series of bis(2,2’-bithienyl)methane derivatives appended with crown ethers of varying size are presented.  Uniform Langmuir films of liquid-expanded type were obtained at water-air interface for all of the used compounds.  The influence of metal ions on the orientation of the molecules in the films was relatively small.  Obtained Langmuir films were subsequently transferred onto the solid substrates by using Langmuir-Blodgett technique forming mono- and multilayers.  In order to further elucidate structure of the formed layers AFM and STM techniques have been applied.  The morphology of the multilayer films depended both on the size and orientation of the crown ether moiety in the molecules.  However, in all cases formed multilayers were porous (Fig. 1).  In case of monolayers, the STM studies helped to ascertain organization of the molecules in the Langmuir-Blodgett film.  On the other hand the scanning tunnelling spectroscopy (STS) allowed acquisition of information about the electrical properties of the studied thiophene derivatives.

Bibliography

1.   D. Hu, J. Yu, K. Wong, B. Bagchi, P. J. Rossky, P. F. Barbara, Nature,
405, (2000), 1030.

2.   A. G. MacDiarmid, Angew. Chem., Int. Ed., 40, (2001),2581.

3.   R. Singhal, A. Chaubey, K. Kaneto, W. Takashima, B. D. Malhotra, Biotechnol. Bioeng.,
85 (2004), 277.

Figure 1
Post-Assembly Transformations of Porphyrin-Containing Metal-Organic Framework (MOF) Films Fabricated Via Automated Layer-By-Layer Coordination
Authors: So Monica C. , Beyzavi M. Hassan , Sawhney Rohan , Shekhah Osama , Eddaoudi Mohamed , Al-Juaid Salih S. , Hupp Joseph T. , Farha Omar K.
Published: February 2020

Metal–organic frameworks (MOFs) are hybrid materials composed of inorganic vertices connected to organic linkers. Due to the plethora of available linkers and vertices, MOFs can be easily tuned towards specific applications such as electrochromics1 and catalysis2. For some of these applications, it is desirable that MOFs be deposited as thin films. Among the most versatile and useful approaches to MOF film synthesis is layer-by-layer (LbL) coordination also called liquid-phase epitaxy.3 This approach successively and repetitively introduces solutions of each framework building block into contact with functionalized substrate and subsequently the growing MOF film. The advantage of LbL over other techniques is that MOF layer thicknesses can be controlled with molecular-scale precision. Thus, complex, multifunctional crystalline MOF structures are obtainable.  The presentation will demonstrate the robustness of LbL-assembled pillared-paddlewheel-type MOF films by utilizing solvent-assisted linker exchange (SALE) or post-assembly linker metalation towards the conversion of one LbL film (L2-MOF) to another LbL film (SALEF-1 and Mg-L2-MOF).4 Notably, Mg-L2-MOF cannot be formed through other de novo strategies. While beyond the scope of our initial investigation, we believe that the ability of the known metal lability of magnesiated porphyrins should facilitate incorporation of other metal ions, including weakly bound ions, displaying interesting redox and photophysical behaviors. The findings effectively diversify the arsenal of techniques that can be deployed to obtain desired MOF films for energy conversion applications.

References

Hod, I.; Bury, W.; Karlin, D. M.; Deria, P.; Kung, C. W.; Katz, M. J.; So, M. C.; Klahr, B.; Jin, D.; Chung, Y. W.; Odom, T. W.; Farha, O. K.; Hupp, J. T. Adv. Mater., 
2014, 26, 6295.

Nguyen, H. G. T.; Schweitzer, N. M.; Chang, C., Drake, T. L.; So, M. C.; Stair, P. C.; Farha, Omar K.; Hupp, J. T., Nguyen, S. T., ACS Catal., 2014, 4, 2496.

So, M. C.; Jin, S.; Son, H.-J.; Farha, O. K.; Wiederrecht, G. P.; Hupp, J. T., J. Am. Chem. Soc., 2013, 135, 15698.

So, M. C.; Beyzavi, M. H.; Sawhney, R.; Shekah, O.; Eddaoudi, M.; Al-Juaid, S. S.; Hupp, J. T.; Farha, O. K., Chem. Commun., 2014, DOI: 10.1002/adma.201401940.

Figure 1
The Dehaloperoxidase Paradox: How Nature Juggles Oxygen Transport, Peroxidase, and Peroxygenase Activities at a Single Heme Active Site
Authors: Ghiladi Reza Arman
Published: February 2020

Dehaloperoxidase (DHP) from the terebellid polychaete Amphitrite ornata is the first oxygen-binding globin that possesses a biologically relevant peroxidase activity. The two known isoforms of DHP, A and B, have been shown to oxidize trihalophenols to dihaloquinones in a dehalogenation reaction that utilizes hydrogen peroxide as the oxidant. More recently, however, we have shown that DHP possesses both peroxygenase and oxidase activities using a new class of substrate, haloindoles, in addition to its previously identified O2-binding and peroxidase functions. Using 5-Br-indole as a representative substrate, the major monooxygenated products were found to be 5-Br-2-oxindole and 5-Br-3-oxindolenine. Isotope 18O-labeling studies confirmed that the oxygen atom incorporated was derived exclusively from H2
18O2, indicative of a previously unreported peroxygenase activity for DHP. Peroxygenase activity could be initiated from either the ferric or oxyferrous states with equivalent substrate conversion and product distribution. It was found that 5-Br-3-oxindole, a precursor of the product 5-Br-3-oxindolenine, readily reduced the ferric enzyme to the oxyferrous state, demonstrating an unusual product-driven reduction of the enzyme. As such, DHP returns to the globin-active oxyferrous form after peroxygenase activity ceases. Reactivity with 5-Br-3-oxindole in the absence of H2O2 also yielded 5,5’-Br2-indigo above the expected reaction stoichiometry under aerobic conditions, and O2-concentration studies demonstrated dioxygen consumption. Non-enzymatic and anaerobic controls both confirmed the requirements for DHP and molecular oxygen in the catalytic generation of 5,5’-Br2-indigo, and together suggest a newly identified oxidase activity for DHP. Preliminary data also suggest that DHP is able to catalyze the oxidation of 2,3-dimethylindole by a previously unreported oxygenase activity. The two major products were identified by HPLC and LC-MS analysis to be the dioxygenated product o-acetamidoacetophenone and the monooxygenated product 3-hydroxy-2,3-dimethylindole. Isotope labeling studies verified that the oxygen atom incorporation into the products were derived exclusively from molecular oxygen. Consistent with these results, the reaction did not proceed under anaerobic conditions, and was also decreased in the presence of radical scavengers. Our initial studies suggest that the observed radical-based oxygenase activity of DHP is reminiscent of lipoxygenase, a non-heme dioxygenase. The breadth of chemical reactivity demonstrated by DHP not only expands our current understanding of this multifunctional enzyme, but also highlights the plasticity of a single heme active site within a globin-fold to function as an oxygen-transport center, as a peroxidase for phenolic substrate oxidation, and as a peroxygenase for indolic substrate oxygenation.

Figure 1
Probing Molecular Chirality Using Metallo-Bisporphyrin Hosts
Authors: Rath Sankar Prasad
Published: February 2020

Supramolecular chirogenesis is one of the most important interdisciplinary field to be looked into, because of its occurrences in many natural (DNA double helix, heme proteins, secondary α-helix structure of proteins etc.) and artificial systems. Although, chiroptical spectroscopy such as Circular Dichroism (CD) is inherently sensitive to chirality, it has not enjoyed tremendous use as a method for stereochemical determinations, mainly because the results of CD analysis are empirical. Exciton Coupled Circular Dichroism (ECCD) is a nonempirical spectroscopic method that is based on detecting the through-space exciton interaction between helically orientated independently conjugated chromophores. The relative orientation of the two chromophores in space results in a predicted sign of the couplet; i.e., a clockwise orientation of two interacting chromophores yields a positive couplet and vice versa. Therefore, the challenge lies in orienting two or more chromophoric receptor groups in a chiral fashion as a direct result of the binding of a chiral compound and extrapolating the chirality of the bound compound from the ECCD spectra. This presentation will showcase some of our recent research activity along the line.

Representative referances:

S. A. Ikbal, S. Brahma, S. P. Rath Chem. Commun.
2014, 50, 14037-14040.

S. A. Ikbal, S. Brahma, S. P. Rath Chem. Commun.
2014, 50, ASAP. (DOI: 10.1039/c4cc07955h)

S. Brahma, S. A. Ikbal, S P Rath Inorg. Chem.
2014, 53, 2381-2395.

S. Brahma, S. A. Ikbal, S P Rath Inorg. Chem.
2014, 53, 49-62.

S. Brahma, S. A. Ikbal, S. P. Rath Chem. Commun.
2012, 48, 4070-4072.

Figure 1
Photo-Assisted Chemical Sensors Based on Porphyrins Coated ZnO
Authors: Sivalingam Yuvaraj , Magna Gabriele , Catini Alexandro , Pomarico Giuseppe , Martinelli Eugenio , Paolesse Roberto , Di Natale Corrado
Published: February 2020

Hybrid materials formed by a layer of dye molecules over a wide-band gap semiconductor are endowed by a number of properties making them appealing for optoelectronics and photovoltaic applications. However besides the conversion of visible photons into an excess of carriers, the combination of organic-inorganic materials offer other additional properties such as gas sensing.

ZnO and porphyrins are good examples of a metal oxide semiconductor and a dye molecule that give rise to a hybrid material with interesting properties. ZnO has been studied for gas sensors, optoelectronics, electronic devices, photo-anodes for dye-sensitized solar cells, and for mechanical energy harvesting. Porphyrins play fundamental roles in living systems such as the oxygen transport and charge transfer for catylitic processes in animals and the photosynthesis in plants. The rich chemistry makes them interesting for chemical sensing, indeed porphyrins are among the most versatile ligand platforms that can interact with airborne molecules by a wide spectrum of different mechanisms. The sensing properties of porphyrins are exploited for the development of artificial sensorial systems. In our group we have been interested to study the interplay of light and gas sensitivity in porphyrins-ZnO materials. We found that the conductivity of porphyrins-ZnO is both sensitive to the visible light and to donor-acceptor gases such as amines and alcohols. Furthermore, under visible light the sensitivity increases and, most interestingly, the selectivity towards electron donor species (e.g. amines) strongly increases.

In further studies we measured the surface photovoltage. This quantity that can be easily measured in the laboratory with a Kelvin probe is exploited in organic functionalized Field Effect Transistors sensors and it is also of great importance in the characterization of materials for photovoltaic applications. Kelvin probe studies, illustrates the interplay between the photosensitivity and the gas sensitivity in organic molecule functionalized semiconductor metal oxide nanostructure suggesting that volatile compounds may act as a doping to improve the photovoltaic properties of the dye-semiconductor hybrid.

The sensing properties of layers of porphyrins onto ZnO nanostructures offer a further degree of freedom for the design of sensor arrays extending the properties and the capabilities of porphyrins based sensor array in particular for medical diagnosis, the quality and control of foods and the detection of compounds signalling harmful or dangerous substances.
Host-Guest Driven Self-Assembly of Non-Pi Aggregated Multi-Porphyrin Nanoarchitectures
Authors: Jayawickramarajah Janarthanan , Zhang Hong , Aryal Gyan H , Zhu Mengyuan
Published: February 2020

The central focus of this talk will be on the molecular recognition, supramolecular chemistry, and photonic properties associated with non-pi aggregated multi-porphyrinic nanoarchitectures in water. The initial segment of the seminar will discuss the self-assembly and photophysical evaluation of porphyrin nanowires, nanowire networks, and nanospheres, assembled through hydrophobically-driven, β-cyclodextrin (β-CD)-based, host-guest interactions. In the second portion of the talk, we will detail the construction of multi-layer thin films of porphyrin and perylene diimide chromophores via a straightforward layer-by-layer host-guest driven deposition strategy. As a result of the inter-disciplinary nature of this research, a variety of studies will be presented, ranging from organic synthesis to spectroscopic experiments as well as microscopic studies.
Advances in the Applications of Boron Tetrapyrrole and Dipyrrin Complexes
Authors: Brothers Penelope Jane
Published: February 2020

Over the years we have developed the chemistry of boron complexes of porphyrins and corroles, and have recently made the first examples of boron calixphyrin and porphyrazine complexes.  The unifying motifs are the coordination of two borons per tetrapyrrole macrocycle, with both the structural stereochemistry and the chemical reactivity dictated by the steric demands of incorporating two boron atoms within a tightly defined cavity.  We are now exploring the physical properties of these classes of complexes with a view to developing applications, for example in PDT.  We have also explored new chemistry of the well-known boron dipyrrins (or BODIPYs) and have developed new chemistry for directly attaching BODIPY groups to substrates that are useful in biology and materials science.

Figure 1
Solvent-Free Reactions of p-Extended Pyrroles with Aromatic Aldehydes Leading to New Organic Chromophores
Authors: Swavey Shawn
Published: February 2020

Solvent-free reactions of pyrroles with extended p-systems and substituted aromatic aldehydes have led to a series of new organic chromophores. These compounds display electronic transitions in the visible region of the spectrum with relatively high molar absorptivities along with intense emission spectra.
Nonplanr Meso-Trifluoromethyl Substituted β-Octaalkylporphyrins
Authors: Suzuki Masaaki , Hoshino Tyuji , Neya Saburo
Published: February 2020

A trifluoromethyl (CF3) group gives a drastic perturbation to an aromatic compound owing to not only the three-dimensional steric bulkiness but also the strong electron-withdrawing characters.  When introduced at sterically crowded meso-positions of β–alkyl substituted porphyrins, it is expected to cause major update of both the structural and electronic properties of the molecule.  However, introduction of CF3 groups required preparation of CF3-embedded precursors such as dipyrromethanes, resulting in tedious synthetic strategies.  This time, we performed the serendipitous but reproducible formation of meso-trifluoromethylated 2,3,7,8,12,13,17,18-octaalkylporphyrins by reactions of 5,5’-dicarboxy-3,3’,4,4’-tetraalkyl-2,2’-dipyrromethanes and large excess amount of trifluoroacetic acid without any additional sources of meso-carbons like aldehyde.  The numbers of CF3 groups increased up to two by elongation of the reaction time and the positions of second CF3 groups varied depending on the β-substituents.  The structural characterizations by X-ray diffraction analyses revealed their distorted conformations reflecting the steric repulsions around the CF3 groups.  In the UV-visible absorption spectra, the lowest energy bands were red-shifted stepwise by introduction of each CF3group.

Metallation behavior was also investigated.  In the cases of zinc complexes, the CF3 groups gradually changed into methoxycarbonyl (CO2Me) groups probably due to methanol in the mixture.  The influence of CO2Me groups were smaller than CF3groups according to the relatively flat X-ray structures and the less-shifted absorption bands.

Reference

M. Suzuki, S. Ishii, T. Hoshino, S. Neya Chem. Lett.
2014, 43, 1563–1565.

Figure 1
Core-Modified Porphyrins Containing Novel Heterocyclic Moieties
Authors: Shen Zhen
Published: February 2020

Aromaticity is a fundamental concept of chemical structure and bonding, which describes the enhanced stability that is derived from the delocalization of π-electrons in cyclic conjugated macrocycles.  In recent years there has been a growing focus on the synthesis and characterization of ring-expanded porphyrinoids with both heteroaromatic and nonaromatic π-systems. The aromatic character can be fine-tuned through protonation, by modifying the solvent polarity and coordination environment, and by incorporating novel heterocyclic moieties as building blocks.  Herein we report that the aromaticity of ring-expanded core-modified porphyrins can be tuned using dithienylethene as a building block[1].  Two stable core-modified rubyrins bearing one and two dithienylethene (DTE) units (C-1 and O-1) have been synthesized (Figure 1). With one “closed-form” DTE unit, C-1 shows aromaticity associated with its conjugated circuit of 26 pelectrons.  In contrast, rubyrin O-1 containing one “open-form” DTE unit has nonaromatic properties. An analysis of the MCD spectral data and the TD-DFT and ACID calculations clearly demonstrated that the p-systems of C-1 and O-1 are aromatic and nonaromatic, respectively. The use of a dithienylethene moiety as a building block, therefore,  offers a new vista of opportunities for tuning the aromaticity of ring-expanded core-modified porphyrins.

Figure 1
Comparative Electrochemical Properties of Phthalocyanines Bearing Fc(CH2)n- and/or Alkyl Substituents in Non-Peripheral and/or Peripheral Positions.
Authors: Swarts Jannie C
Published: February 2020

Phthalocyanines and their metal complexes1have been studied for their interesting chemical, electrochemical, thermal and photochemical properties as well as for the numerous applications they may be used for.   These include the vast domain of catalysis, as photosensitizers for photodynamic therapy of cancer, ink-jet printing components and in memory devices. The phthalocyanine macrocycle may be modified by introduction of redox-active moieties (here ferrocene) in peripheral or non-peripheral positions to append the existing macrocycle redox centers (usually four are observable in DCM as solvent).  Non-peripherally substituted long alkyl chains also influence the redox and other physical properties such as mesophase behaviour. 

It is well known that the redox properties of phthalocyanine macrocycles change depending on the type of metal that is coordinated in the macrocyclic cavity.   The tendency of cadmium macrocycles to oligomerise even to heptamers is less known.  Further changes in the redox properties of this macrocycle may be induced by systematically changing the “meso” or “outer” nitrogen atoms to CH ultimately to liberate a benzoporphyrin.  

In this presentation, the synthesis of the above compounds will be presented very shortly.  Thereafter, the influence that alkyl chain length (expressed as R = C10H21 – C18H37 above),2 linker atom X = S or O, metallocenyl chain length ( n = 1 – 4), coordinated metal species, M, and the effect of axial dimerisartion and trimerisation of Cd complexes on especially the redox properties  of these  unique macrocycles will be highlighted and brief mention will be made of the mesophase behaviour these changes induce.   Electrochemical results obtained for the systematical conversion from phthalocyanine to benzoporphyrin will also be presented.   

References

1.   E. Fourie, J. C. Swarts, I. Chambrier, M. J. Cook, Dalton Trans., 1145-1154 (2009).

2.   J. C. Swarts, E. H. G. Langner, N. Krokeide-Hove, M. J. Cook, J. Mater. Chem., 11, 434-443 (2001).

Figure 1
Synthesis and Property of Novel Phthalocyanine Having Pentafluorosulfanyl (SF5) Group on the Peripheral Positions
Authors: Shibata Norio
Published: February 2020

The pentafluorosulfanyl (SF5) group is probably one of the most obscure, but attractive fluorinated functional groups in future materials. The SF5 moiety is thermally, hydrolytically and chemically stable and is considered to be a “super-trifluoromethyl (CF3) group”. Besides, the SF5 group is larger than the CF3 group with higher lipophilicity and electronegativity. In addition, the geometry of these two functional groups is completely different: the SF5 group presents a pyramidal electron density while the CF3 displays an inverted cone of density. Although applications of SF5 compounds in material science and medicinal chemistry have been reported, there is no example of the synthesis of phtalocyanineshaving an SF5 moiety in their structures. In this paper, we disclose the synthesis and properties of SF5-substituted phtalocyanines.
Intermolecular Communication in a Supramolecular Assembly of Porphyrins and Phthalocyanines
Authors: Tanaka Kentaro
Published: February 2020

Programmable construction of a multiple molecular system is the best measure for bringing out the integrated properties evolved from the intermolecular communications in the molecular assemblies. Especially, controlling sequential and spatial arrangements of building components in the molecular array is crucial for developing novel functions of the designer nanoarchitecture. Since organized assemblies of porphyrins and phthalocyanines are promising for generating higher functionalized systems, we have recently reported the supramolecular arrays in which a porphyrin and a phthalocyanine are connected by four-fold rotaxanes [1-4] and sequential and spatial organization of metalloporphyrins inside a peptide duplex [5].

In this paper, we will present construction of the suplamolecular arrays of a metallo-porphyrin and a metallo-phthalocyanine through four-fold rotaxane formation between a tetradactyl porphyrin with alkylammmonium moieties and a phthalocyanine bearing four crown ethers (Figure 1a) and significant electronic communications between the metal complexes (Figure 1b). Since synthetic strategy for the rotaxane is applicable to pre- and post-metallation of both porphyrin and phthalocyanine centers, the four-fold rotaxane framework is suitable for homo- and hetero-assemblage of metal ions. In a homo-dinuclear Cu2+ complex of the four-fold rotaxane, the Cu2+-porphyrin and the Cu2+-phthalocyanine showed a switching behavior in the spin–spin interaction through change of the spatial distance between the two metal centers induced by protonation and deprotonation.

1) Y. Yamada, M. Okamoto, K. Furukawa, T. Kato, and K. Tanaka, Angew. Chem. Int. Ed.,
51, 709–713 (2012). 2) Y. Yamada, N. Mihara, and K. Tanaka, Dalton Trans., 42, 15873-15876 (2013). 3) Y. Yamada, N. Mihara, S. Shibano, K. Sugimoto, and K. Tanaka, J. Am. Chem. Soc., 135, 11505-11508 (2013). 4) Y. Yamada, M. Okada, and K. Tanaka, Chem. Commun., 49, 11053-11055 (2013). 5) Y. Yamada, T. Kubota, M. Nishio, and K. Tanaka, J. Am. Chem. Soc., 136, 6505-6509 (2014).

Figure 1
Factors Affecting the Rate of Electrocatalytic O2 Reduction By Iron Porphyrin Complexes
Authors: Dey Abhishek
Published: February 2020

Electrochemical O2 reduction reaction (ORR) catalyzed by iron porphyrin complexes are investigated using surface enhanced resonance Raman spectroscopy coupled to rotating disc electrochemistry. The data suggests that the cleavage of O-O bond is the rate determining step (rds). Further the competitive hydrolysis of this rate determining FeIII-OOH species results in 2e/2H+ reduction of O2. Additional functionalities are included in the design of these iron porphyrin complexes to enhance the O-O cleavage rate and thus increase the rate of ORR. While inclusion of residues that allow facile PCET to the active site helps deter the 2e/2H+ pathway, introduction of the push effect of a thiolate axial ligand or the pull effect of protonated residues in the distal side is found to enhance the rate of ORR by 100-1000 times relative to an unfunctionalized porphyrin.