bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Significant Effect of Electronic Coupling on Electron Transfer between Surface-Bound Porphyrins and Co2+/3+ Complex Electrolytes
Authors: Cho Inseong , Mozer Attila Janos , Wagner Pawel , Mori Shogo , Gordon Keith , Innis Peter , Mapley Joseph , Shahshahan Sayedmohsen 
Published: May 2020

The coordination of metal ions such as Zn2+ with the π-conjugated porphyrin ring is one of the simplest and the most often used structural modification to alter the electronic nature of a molecule without significantly affecting its size or geometry. The question answered in this work is to what extent electron transfer rates between a surface bound Zn2+porphyrin and a cationic electron donor (Co2+ polypyridyl complexes) is affected by the altered electrostatic interaction between the two molecules at the same electrochemical driving force (DG°). To date, very few studies addressed the effect of electrostatic intermolecular interactions on electron transfers explicitly.
We measured electron transfer rates between 4 porphyrin (2 freebase and 2 Zn porphyrin) molecules attached to TiO2 electrodes and 5 Co2+/3+ complexes dissolved in electrolytes covering a DG° range of close to 1 V. The porphyrin molecules were photo-excited at 532 nm leading to an oxidized porphyrin and an electron injected into the conduction band of the TiO2 electrode. The rate of electron transfer was been determined using transient absorption spectroscopy (TAS) by monitoring the absorption change of the oxidized porphyrin molecules in the presence of the redox mediators in various concentrations. The measured rate constants were fitted to Marcus theory. We have found that even the simplest dimethyl substitution on the bipyridine ligands of the Co2+/3+ complexes resulted in a significant decrease in electron coupling. To account for the variation in electron coupling among the Co2+/3+ complexes, the electron rate constants were normalized by the square of the ratio of the electronic coupling factors. The normalized rate constants showed a 30% increase in electron coupling of the free base porphyrins with Co2+/3+ compared to the electronic coupling between Zn porphyrins and Co2+/3+. Increased coupling suggests shorter donor – acceptor distance or better wavefunction overlap, which could be due to electrostatic interaction of the Co2+ with the lone pairs of the free base porphyrin, which interaction is blocked by Zn2+ coordination. The measurements were also performed in 1,2-dimethoxyethane instead of acetonitrile with a five times lower dielectric constant, resulting in even larger difference in electron transfer rates between free base and Zn porphyrins. This suggests that the origin of the different coupling is indeed electrostatic in nature.
The key finding of this work is that electronic coupling can be as significant contributor to electron transfer rates as the driving force even between similar molecular structures, hence redox active molecules should not be selected based on their free energy difference alone.
Exciton Coherence in Phthalocyanine Crystalline Thin Films
Authors: Hua Kim Ngan , Liang Libin , Furis Madalina 
Published: May 2020

Intermolecular interactions in small molecule crystals play an important role in the exciton delocalization process and can lead to robust exciton coherence. The spatial extension of this delocalization, and the exciton coherence length, significantly influence practical applications that rely on excitonic radiative recombination, dissociation or electron transport. The porphyrins and phthalocyanines derivatives family represent the ideal system for a comprehensive study of excitonic coherence because they represent an iconic example of a one-dimensional
J
-like aggregate system.
At the University of Vermont, the Furis group focuses on exploring excitonic states in solution-processed phthalocyanine thin films using a dual Linear Dichroism/Photoluminescence Laser Scanning Microscope developed in -house. These studies are among the first to directly probe the supramolecular structure-property relationships in these electronic materials. The experiments reported here investigate the effect of alkyl substitutions and dynamic disorder (i.e. exciton-phonon coupling) on exciton coherence in solution-processed crystalline thin films of porphyrin and phthalocyanine derivatives.
Specifically, the largest exciton coherence length (approx.15 nm) was measured for an octabutoxy derivative, where the saddle shape of the molecules and the crystalline packing result in weaker coupling to the acoustic phonons (low energy) modes. Enhancing the size of the macrocycle ring to a naphthalocyanine also results in long coherence lengths despite larger intermolecular nearest-neighbor (NN) distances. Most importantly, this study brings evidence that excitonic coherence can engineered in a systematic manner through chemical and physical routes. For example, applying uniaxial strain to the same thin films deposited on Kapton substrates results in continuous bandgap energy tuning, in analogy to inorganic semiconductors.
Engineering Cells, Membranes and Light Harvesting/Photosystem II Super-Complexes in Bio-Photoelectrochemical Cells
Authors: Adir Noam 
Published: May 2020

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, following a brief treatment that does not induce loss of cell viability, electrons from both the respiratory and photosynthetic systems are transferred directly to a graphite electrode, utilizing endogenous electron carriers (Saper et al. Nature Communications 2018). 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 isolate the 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 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 - 650 nm). To overcome this limitation, we have stabilized the interaction between PSII and Phycobilisomes (PBSs) – the cyanobacterial light harvesting complex, in vitro. The PBS of different cyanobacteria were analyzed for their ability to transfer energy to Thermosynechococcus elongatus (Te) PSII by fluorescence spill-over and photocurrent action spectra. 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 (IPCE). IPCE values in the green gap were doubled from 3 % to 6 % compared to PSII electrodes without PBS and a maximum IPCE up to 10.9 % at 670 nm was achieved.

Figure 1
Peptide Targeting of Photosensitisers for Photodynamic Therapy and Drug Delivery
Authors: Eggleston Ian M , Yaghini Elnaz , Dondi Ruggero , Tewari Kunal , Edler Karen J , Loizidou Marilena , MacRobert Alexander J 
Published: May 2020

The conjugation of tetrapyrroles and related photosensitisers with proteins or targeting peptides is now a well-established approach for enhancing the solubility and tissue selectivity of such molecules in the photodynamic therapy (PDT) of cancer. We are interested in developing chemical strategies for the generation of novel porphyrin-related molecules for targeted PDT, and also porphyrin-based systems whose structures are tailored for use in the light-triggered delivery of therapeutic agents by photochemical internalisation (PCI) [1]. PCI is a light-based approach that exploits the technique of PDT to enhance the delivery of nano-sized biotherapeutics that would normally be prevented from reaching their intended intracellular targets due to sequestration in certain sub-units or organelles within the cell. Effective PCI requires the use of photosensitisers that have the appropriate physical properties to localize in the membranes of the organelles (endosomes or lysosomes) where a therapeutic agent may be trapped. Upon irradiation, reactive oxygen species that are generated may then induce a highly selective damaging effect and cause partial rupture of the organelles, allowing entrapped molecules to escape to their targets within the cell. In this communication, we will describe some of our studies on the synthesis and biological evaluation of porphyrin and chlorin derivatives that are targeted with cationic cell-penetrating peptides (CPPs) via biorthogonal ligation chemistries [1, 2], and the application of these conjugates for PCI of saporin, a nano-sized protein toxin. We will also describe the extension of this principle to the CPP-targeting of liposomal nanocarriers [3] to produce molecular assemblies that allow the codelivery of a porphyrin photosensitizer and a macromolecular therapeutic in order to produce an optimal PCI effect.
[1] R. Dondi, E. Yaghini, K. M. Tewari, L. Wang, F. Giuntini, M. Loizidou, A. J. MacRobert and I. M. Eggleston, Org. Biomol. Chem. 2016, 14, 11488-11501.
[2] E. Yaghini, R. Dondi, K. M. Tewari, M. Loizidou, I. M. Eggleston and A. J. MacRobert, Sci. Rep. 2017, 7, 6059.
[3] E. Yaghini, R. Dondi, K. J. Edler, M. Loizidou, A. J. MacRobert and I. M. Eggleston, Nanoscale 2108, 10, 20366-20376.
Polypeptides with Pendant Porphyrins: From the Recognition of Bidentate Bases to Inter-Digitated Photo-Active Strands
Authors: Rein Regis , Solladie Nathalie , Aziat Farid 
Published: May 2020

In natural photosynthetic systems, the solar energy is collected by pigment molecules attached to the light harvesting complexes. In these units, the chlorophylls are held in a favored spacing and orientation by fairly short a-helical polypeptides. In this way, the energy contained in a single photon is conducted in a very short time and with minimal loss of energy from the point where it is absorbed to where it is needed. The extraordinary efficiency of the energy migration over long distances with minimal loss of energy is ascribed to the favored spacing and orientation of the chlorophylls which are held in an appropriate parallel conformation. Beyond the control of the structure of multi-chromophoric arrays, monitoring the spatial orientation of the chromophores in artificial light harvesting devices is a challenge of growing interest. Indeed, multi-porphyrinic arrays attract more and more attention for the elaboration of photonic and electronic wires.
An octapeptide and a hexadecapeptide derived from the L-lysine and functionalized with porphyrins have been prepared. Beyond a certain degree of oligomerisation, we observed the development of a secondary structure such as a 310 helix which forces the porphyrins to arrange in a defined spatial arrangement. Due to the overlap of the porphyrins in such a conformation, the chromophores undergo a sufficient electronic coupling to favor a good exciton migration.
The ability of these peptides to accomodate guests was investigated through ligand binding studies carried out in dichloromethane with DABCO as bidentate base. The complexation of DABCO by these peptides was monitored by UV-visible spectrophotometric titration in CH2Cl2. We showed that the enhanced stability of the complexe octapeptide/DABCO can be ascribed to a pre-organization of the octapeptide forming cavities, and provides convincing evidence that the bidentate base is inserted into the cavities of the octapeptide via host/guest interactions.

Acknowledgements

This work was supported by the CNRS and the French Ministry of Research.
(Invited) Vanadium Based Phosphate, Phosphite, Oxalate Cathode Materials for Lithium Batteries
Authors: VenkatashamyReddy MogalahalliVenkatesh 
Published: May 2020

Commercial lithium ion batteries (LIBs) use layer-type compounds, lithium cobalt oxide (LiCoO2) or LiFePO4 as the cathode (positive electrode) and graphite (C) as the anode (negative electrode) material, and a non-aqueous Li- ion conducting electrolyte. The liquid electrolyte in the form of a solution or immobilized in a gel-polymer. LIBs with an operating voltage of 3.6 V are extensively used in the present-day portable electronic devices like, cell phones and other low power operated devices. For high-power applications like, electric/hybrid electric vehicles and back-up power supplies and, the LIBs need to satisfy several criteria, namely, cost-reduction, improvement in the energy density, safety-in-operation at high current charge/discharge rates and improvement in the low-temperature-operation. To satisfy the above criteria, researches are being carried out worldwide to find alternative cathode materials.
In my presentation, I will discuss our group studies on V-based Flouro phosphates cathode materials. Specifically, I will focus bare and Fe doped-LiVPO4F, αI-LiVOPO4 and V-based metal organic framework materials, MX[(VO)2N2(C2O4)], where M= K, Li, Na , N= HPO4, HPO3. and LiSiV2O6. Materials were prepared variety of chemical methods carbothermal/Graphenothermal reduction, hot plate and hydrothermal methods. Materials were characterized by Rietveld refinement X-ray diffraction, X-ray photoelectron spectroscopy, Raman, XPS, Microscopy (SEM &TEM) and BET surface area methods. Electro analytical studies like cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy techniques. Interestingly V-based cathodes showed around 4 V redox couple (except LiSiV2O6) which is higher than that of LiFePO4 (3.5V vs. Li) and observed reversible capacity is order 80-140 mAh/g. Discuss in detail long term cycling studies and rate capabilities and reaction mechanisms.

Keywords: Materials synthesis; Batteries; Cathodes; Electrochemical Properties; Energy storage

References

1. M.V. Reddy, M. V.; G.V. Subba Rao, B.V.R. Chowdari, Chem. Rev. 113 (2013) 5364
2. A.S. Hameed, M.V. Reddy*, M. Nagarathinam, T. Runčevski, R.E. Dinnebier, S. Adams, B.V.R. Chowdari, J.J. Vittal, Scientific Reports, 5 (2015) 16270
3. M. Shahul, M. V. Reddy*, N.Sarakar, B. V. R. Chowdari,J. J. Vittal RSC Adv., 5(2015), 60630
4. M. Shahul, M. Nagarathinam, M. V. Reddy*, B. V. R. Chowdari,J. J. Vittal Journal of Materials Chemistry 22(2012)7206-7213.
5. M. Nagarathinam, K. Saravanan, E. J. Han Phua, M. V. Reddy*, B. V. R. Chowdari,J. J. Vittal Angewandte Chemie Intl. 51(24)(2012)5866-5870.
6. M .V. Reddy, G.V. Subba Rao and B. V. R. Chowdari Journal of Power Sources 195(2010)5768-5774.
Optimization of Micro-Scale Organic Energy Storage Devices
Authors: Herrera Jose Ramon 
Published: May 2020

In pseudo-capacitors the energy storage process is due to fast, reversible faradic processes. For their higher specific capacitance with respect to conventional electrical double-layer capacitors that make use of high surface area carbons, these devices are among the most promising to provide high energy density and power necessary for modern and future applications. But the era of searching only for the best performance leaving environmental concerns is in the past: and now we have the moral obligation and responsibility of making every new technology evolving into sustainable and eco-friendly alternatives.
Our group has achieved binder-free eco-friendly organic supercapacitors on different substrates such as carbon paper and polyethylene terephthalate (PET), using drop casting and microfabrication techniques, obtaining a specific capacitance of 167 Fg-1 on carbon paper, and 10.8 Fg-1 on flexible PET [1].
In this work we optimize the microfabricated structure of flexible melanin-based electrodes by modifying the geometric architecture, maximizing the electrode/electrolyte interaction. Specifically, we report about the energy storage of flexible melanin-based micro-capacitors in aqueous electrolytes (NH4CH3COO(aq)).
References
[1] Prajwal Kumar, Eduardo Di Mauro, Shiming Zhang, Alessandro Pezzella, Francesca Soavi, Clara Santato, Fabio Cicoira."Melanin-based flexible supercapacitors". J. Mater. Chem. C, 2016, 4, 9516.
Does DUAL Layer Cathode Increase the POWER Density of Lithium-ION Batteries ?
Authors: Asselah Islam Samah 
Published: May 2020

Lithium-ion batteries is one of the most popular technological innovations for storing electrical energy also in the automotive field. They have many advantages due to lithium’s high storage capacity to weight ratio. Lithium also has the highest voltage and thus practical best energy density of all metals. One of the problems encountered with lithium-ion batteries in the automotive field is the poor power capability. Optimizing the lithium-ion battery performances is a trade-off between energy and power density. To increase the energy density, we need to increase the electrode density, the thickness and minimize redox inactive components. However, to improve power performance we must increase the electrolyte transport in the electrode, which entails lowering the active material fraction as well as the thickness. Moreover, combining several different active materials individually optimized for high power or high capacity may assist in attaining the optimal performance for a given application.
In this project, the main goal is to have an analytical handle on the performance of a cathode which is composed of a double layer LiFePO4 and LiNi1/3 Mn1/3 Co1/3 O2 and compare them to their respective single layer (figure1). We study their behavior separately within the double layer structure using a specific current density and their unique potential windows. For the characterization, we are using galvanostatic cycling, chronoamperometry and scanning electron microscopy to relate the electrode performance to their morphology. We also compared the dual layer performance with that of blended electrodes, i.e. a blended mixture of both materials rather than separate layers (figure1).

Figure 1
(Keynote) Nanomaterials for Printable Electronics
Authors: Malenfant Patrick R. L. 
Published: May 2020

The National Research Council (NRC) is Canada’s premier organization for research and technology development. NRC’s Printable Electronics (PE) program develops materials and inks for additive manufacturing in order to enable a sustainable PE sector in Canada. Progress has been made over the last 20 years, yet many challenges remain at the materials, fabrication and integration level, limiting performance and commercialization. This presentation covers our progress in high purity semiconducting single-walled carbon nanotube (sc-SWCNT) enrichment and transistor fabrication via solution based processes as well as conductive molecular ink development [1-11]. I will highlight our recent progress in understanding sc-SWCNT enrichment using conjugated polymers (isolation of high purity sc-SWCNT), with special consideration given to the effects of solvent parameters and doping on the mechanism and yield/purity of the final product [2-4]. Removal of the wrapping polymer using a dry process on-wafer will also be described [5]. Challenges and advances associated with using polymer-based dielectrics and encapsulants will be discussed as well [6-7]. Such transistor packages have enabled the realization of fully inkjet-printed transistors as a result of the excellent electrical properties of sc-SWCNTs [8]. A demonstration of a fully additive process to make TFT backplanes via R2R printing will also be highlighted. Developments in conductive molecular inks and progress towards the commercialization of new applications such as in-mold electronicswill also be described [9-11]. The development of new functional nanomaterials and their successful integration into devices will enable additive manufacturing of TFT arrays and in-mold electronics.
[1] J. Lefebvre et al. Acc. Chem. Res. 50, 2479 (2017).
[2] J. Ouyang et al. ACS Nano 12, 1910 (2018).
[3] J. Ding et al. J. Phys. Chem. C 120, 21946 (2016).
[4] Z. Li et al. ACS Omega 3, 3413 (2018).
[5] Z. Li et al. Adv. Funct. Mater. 28, 1705568 (2018).
[6] J. Lefebvre et al. Appl. Phys. Lett. 107, 243301 (2015).
[7] F. Lapointe et al. Appl. Mater. Interfaces 11, 36027 (2019).
[8] C. Homenick et al. ACS Appl. Mater. Interfaces 8, 27900, (2016)
[9] A. J. Kell et al. ACS Appl. Mater. Interfaces 9, 17226 (2017).
[10] C. Paquet et al. Nanoscale 10, 17226 (2018).
[11] B. Deore et al. ACS Appl. Mater. Interfaces 11, 38880 (2019).
Corrosion Mitigation By Photocatalytic Effect of TiO2 Coating on Low Carbon Steel
Authors: Kao Wei-Sheng , Yeh Tsung-Kuang , Wang Mei-Ya 
Published: May 2020

Titanium dioxide (TiO2) is one of the most commonly used photocatalyst at the field of environmental remediation and energy applications. TiO2 is an n-type semiconductor that can be excited by photon irradiation to generate electron-hole pairs in its space charge layer under UV illumination. The excited electrons in the conduction band are then transferred to the metal surface, leading to decrease in both the corrosion potential and the oxidation reaction rate of the metal.
In this study, the photoelectrochemical behavior of the carbon steel with TiO2 coating by sol-gel method were investigated to preventing or minimizing the atmospheric corrosion. Various oxide structure of carbon steel and the TiO2 annealing process were also investigated in this study.
The crystallinity of TiO2 was analyzed with grazing incident X-ray diffraction (GIXRD) and the interfacial oxide layer composition and thickness were analyzed via the Raman spectroscopy and SEM, respectively. Potential dynamic analyses and open circuit potential (OCP) measurement were carried out under a designated solution to evaluate the corrosion mitigation of the TiO2 coated carbon steel with or without UV illumination. These results indicated that the TiO2 treatment with UV illumination would effectively reduce the carbon steel corrosion rate in atmospheric environments.