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At least 127 records · Page 7

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NASA NTRS2012

Detection of Carbon Monoxide Using Polymer-Composite Films with a Porphyrin-Functionalized Polypyrrole

Post-fire air constituents that are of interest to NASA include CO and some acid gases (HCl and HCN). CO is an important analyte to be able to sense in human habitats since it is a marker for both prefire detection and post-fire cleanup. The need exists for a sensor that can be incorporated into an existing sensing array architecture. The CO sensor needs to be a low-power chemiresistor that operates at room temperature; the sensor fabrication techniques must be compatible with ceramic substrates. Early work on the JPL ElectronicNose indicated that some of the existing polymer-carbon black sensors might be suitable. In addition, the CO sensor based on polypyrrole functionalized with iron porphyrin was demonstrated to be a promising sensor that could meet the requirements. First, pyrrole was polymerized in a ferric chloride/iron porphyrin solution in methanol. The iron porphyrin is 5, 10, 15, 20-tetraphenyl-21H, 23Hporphine iron (III) chloride. This creates a polypyrrole that is functionalized with the porphyrin. After synthesis, the polymer is dried in an oven. Sensors were made from the functionalized polypyrrole by binding it with a small amount of polyethylene oxide (600 MW). This composite made films that were too resistive to be measured in the device. Subsequently, carbon black was added to the composite to bring the sensing film resistivity within a measurable range. A suspension was created in methanol using the functionalized polypyrrole (90% by weight), polyethylene oxide (600,000 MW, 5% by weight), and carbon black (5% by weight). The sensing films were then deposited, like the polymer-carbon black sensors. After deposition, the substrates were dried in a vacuum oven for four hours at 60 C. These sensors showed good response to CO at concentrations over 100 ppm. While the sensor is based on a functionalized pyrrole, the actual composite is more robust and flexible. A polymer binder was added to help keep the sensor material from delaminating from the electrodes, and carbon was added to improve the conductivity of the material.

Homer, Margie L.↗

DOE OSTI2012

Porphyrin coordination polymer nanospheres and nanorods

A porphyrin coordination polymer nanostructure comprising a network of pyridyl porphyrin molecules and coordinating metal ions coordinatively bound through the pyridyl groups. In some embodiments, the porphyrins are metalloporphyrins. A variety of nanostructures are formed by the network polymer, including nanospheres, polygonal nanostructures, nanorods, and nanofibers, depending on a variety of factors including coordination metal ion, porphyrin type, metal of the metalloporphyrin, and degree of agitation during nanostructure formation. Reduction of coordinating metal ions may be used to form metal nanoparticles on the coordination polymer nanostructure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2013

Porphyrin coordination polymer nanospheres and nanorods

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2022

Peptide-assisted supramolecular polymerization of the anionic porphyrin meso-tetra(4-sulfonatophenyl)porphine

Electronics made from biological materials are desirable for use in medical devices, biosensors, and soft robotics because they have properties inaccessible to current inorganic technologies. Here, a series of cationic peptides were developed to self-assemble with the anionic porphyrin meso-tetra(4-sulfonatophenyl)porphine (TPPS4) into supramolecular light-harvesting wires known as J-aggregates were developed. In addition to quantifying the binding events between each peptide and TPPS 4 , we found co-incubation with mixed peptides allowed TPPS 4 to bridge two different peptides at their terminal porphyrin-binding regions. The J-aggregates formed on macroscopic scale in near quantitative yield within similar to 3 h and readily interconverted with the soluble monomers upon cycling the pH; to our knowledge, this is the first report of a peptide-porphyrin system with such properties. This work has practical and conceptual relevance to the development of new bioelectronic materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Synthesis, Photophysical Properties and Application of New Porphyrin Derivatives for Use in Photodynamic Therapy and Cell Imaging

New derivatives of tetrakis(4-carboxyphenyl) porphyrin were designed, synthesized and characterized by IR, proton NMR and mass spectroscopy. The ground and excited state nature of new derivatives were examined using UV-Vis. absorption and fluorescence spectroscopy, fluorescence quantum yield and fluorescence lifetime studies. The singlet oxygen quantum yield of each synthesized derivative of porphyrin was estimated for their further efficacy as potential photosensitizer in biological studies. The significant photophysical data of all synthesized derivatives was supplementary accessed to examine the cell imaging and cytotoxicity against two cancer cell lines viz. MBA-MD-231 and A375. The fluorescence lifetime, fluorescence quantum yield and efficiency of singlet oxygen generation suggests alkyl amine and alkyl hydrazide linked new porphyrin photosensitizers can be useful for PDT agent in cancer treatment.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2018

Perturbations in carotenoid and porphyrin status result in differential photooxidative stress signaling and antioxidant responses

Highlights: • Two modes of photooxidation by inhibition of carotenoid and porphyrin biosynthesis. • We examine differential photooxidative stress signaling and antioxidant responses. • OF results in greater oxidative damage with respect to membrane integrity than NF. • Free SA and redox state of Asc and GSH have roles in protection from photooxidation. • Differential regulation of ROS-scavenging enzymes between NF and OF plants. We examined differential photooxidative stress signaling and antioxidant responses in rice plants treated with norflurazon (NF) and oxyfluorfen (OF), which are inhibitors of carotenoid and porphyrin biosynthesis, respectively. Plants treated with OF markedly increased levels of cellular leakage and malondialdehyde, compared with NF-treated plants, showing that OF plants suffered greater oxidative damage with respect to membrane integrity. The enhanced production of H{sub 2}O{sub 2} in response to OF, but not NF, indicates the important role of H{sub 2}O{sub 2} in activation of photooxidative stress signaling in OF plants. In response to NF and OF, the increased levels of free salicylic acid as well as maintenance of the redox ratio of ascorbate and glutathione pools to a certain level are considered to be crucial factors in the protection against photooxidation. Plants treated with OF greatly up-regulated catalase (CAT) activity and Cat transcript levels, compared with NF-treated plants. Interestingly, NF plants showed no noticeable increase in oxidative metabolism, although they did show considerable increases in ascorbate peroxidase (APX) and peroxidase activities and transcript levels of APX, as in OF plants. Our results suggest that perturbations in carotenoid and porphyrin status by NF and OF can be sensed by differential photooxidative stress signaling, such as that involving H{sub 2}O{sub 2}, redox state of ascorbate and glutathione, and salicylic acid, which may be responsible for at least part of the induction of ROS-scavenging enzymes.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2014

The visible light degradation activity and the photocatalytic mechanism of tetra(4-carboxyphenyl) porphyrin sensitized TiO{sub 2}

Highlights: • Tetra(4-carboxyphenyl) porphyrin were chemically sensitized on TiO{sub 2}. • S2–S0 fluorescence intensity is enhanced and lifetime prolonged noticeably by TiO{sub 2}. • The TCPP-TiO{sub 2} exhibits better photoactivity under visible light than that of TiO{sub 2}. • The electronic relaxation dynamics is presented, catalytic mechanism is discussed. • Adsorption and photo degradation of MB were systematically investigated. - Abstract: Tetra(4-carboxyphenyl) porphyrin(TCPP) were chemically sensitized on TiO{sub 2} to act as visible light antenna and to modify the photoresponse properties of TiO{sub 2} particles, their properties of photo-generated holes and electrons were studied by transient absorption spectroscopes. The time-correlated single-photon counting (TCSPC) technique revealed that the S2–S0 fluorescence intensity of TCPP is enhanced noticeably by TiO{sub 2}, and the lifetime prolonged. Adsorption and photo degradation of methylene blue (MB) over TCPP-TiO{sub 2} were systematically investigated. Moreover the overall picture of electronic relaxation dynamics for TCPP-TiO{sub 2} is presented, and the detailed short-time dynamics for visible-light induced catalytic mechanism was discussed. The development of the porphyrin-based photocatalyst provides an alternative approach in harnessing solar visible light and show promising prospect for the treatment of dye pollutants from wastewaters in future industrial application.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Phosphonate-Derivatized Porphyrins for Photoelectrochemical Applications

A series of phosphonate-derivatized, high redox potential porphyrins with mesityl, pentafluorophenyl, and heptafluoropropyl meso-substituents were synthesized by acid-catalyzed condensation reactions. Ground and excited state redox potentials in the series were varied systematically with the electron-donating or electron-accepting nature of the meso-substitutents. Here, the extent of excitation and injection by porphyrin singlet excited states surface-bound to SnO 2 /TiO 2 core/shell metal oxide nanoparticle films varies with the excited state reduction potential, E°'(P+/P*). Furthermore, with the mesityl-substituted porphyrin, high current density and sustained photocurrents are observed at pH 7 with the addition of the electron transfer donor hydroquinone.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Nanoscopic Titanium Dioxide Overlayers Improve the Durability of Porphyrin Molecular Electrocatalysts while Maintaining Molecular Structure and Redox Activity

Molecular catalysts, such as metalated porphyrins, are attractive cocatalysts for photocatalytic water splitting owing to their potential to simultaneously catalyze target reactions at their metal center, extend charge-separated-state lifetimes, and accumulate the requisite charge for product formation. However, porphyrin catalysts, like most molecular catalysts, are often limited by poor stability associated with demetalation, inactivation by undesired bonding (e.g., O2 coordination/redox/dimerization), and detachment from electrode supports or semiconducting photoabsorbers. In this study, nanoscopic titanium dioxide (TiO2) overlayers, deposited by atomic layer deposition (ALD), are demonstrated to encapsulate cobalt(III) meso-tetra(4-carboxyphenyl) porphyrin chloride (CoTCPP) molecular catalysts and thereby improve their adhesion to electrode surfaces over a wide range of electrode potentials spanning from -1.0 V vs RHE to +1.8 V vs RHE. Through analysis of Raman and ultraviolet-visible spectroscopy, it was confirmed that the metalloporphyrin structure was maintained when the surface-bound CoTCPP was encapsulated by 10 - 250 ALD cycles (~2 - 18 nm thick) of TiO2. Additional characterization of CoTCPP catalysts before and after electrochemical measurements reveals that up to 97% of the encapsulated CoTCPP remains tethered to the electrode surface after chronoamperometry tests under hydrogen evolution reaction (HER) conditions, compared to <36% for unencapsulated CoTCPP. This study also shows that encapsulated CoTCPP molecules remain partially redox active for overlayers up to 8 nm, which can also attenuate undesired redox mediator back reactions like ferricyanide reduction.

08 HYDROGEN↗

DOE OSTI2016

New Terthiophene-Conjugated Porphyrin Donors for Highly Efficient Organic Solar Cells

To mimic the natural photosynthetic systems utilizing chlorophylls to absorb light and store light energy, two new porphyrin-based small molecules of PTTR and PTTCNR have been developed for photovoltaic applications. The highest power conversion efficiency of 8.21% is achieved, corresponding to a short-circuit current of 14.30 mA cm –2 , open-circuit voltage of 0.82 V, and fill factor of 70.01%. The excellent device performances can be ascribed to the engineering of molecule structure and film morphology. We report the horizontal conjugation of 3,3"-dihexyl-terthiophene to porphyrin-core with the vertical aliphatic 2-octylundecyl peripheral substitutions, can not only effectively increase the solar flux coverage between the conventional Soret and Q bands of porphyrin unit, but also optimize molecular packing through polymorphism associated with side-chains and the linear π-conjugated backbones. And the additive of 1,8-diiodooctane and subsequent chloroform solvent vapor annealing facilitate the formation of the blend films with [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) characteristics of bicontinuous, interpenetrating networks required for efficient charge separation and transportation.

36 MATERIALS SCIENCE↗

DOE OSTI2014

The effect of structural changes on charge transfer states in a light-harvesting carotenoid-diaryl-porphyrin-C{sub 60} molecular triad

We present a detailed study of charge transfer (CT) excited states for a large number of configurations in a light-harvesting Carotenoid-diaryl-Porphyrin-C{sub 60} (CPC{sub 60}) molecular triad. The chain-like molecular triad undergoes photoinduced charge transfer process exhibiting a large excited state dipole moment, making it suitable for application to molecular-scale opto-electronic devices. An important consideration is that the structural flexibility of the CPC{sub 60} triad impacts its dynamics in solvents. Since experimentally measured dipole moments for the triad of ∼110 D and ∼160 D strongly indicate a range in structural variability in the excited state, studying the effect of structural changes on the CT excited state energetics furthers the understanding of its charge transfer states. We have calculated the variation in the lowest CT excited state energies by performing a scan of possible variation in the structure of the triad. Some of these configurations were generated by incrementally scanning a 360° torsional (dihedral) twist at the C{sub 60}-porhyrin linkage and the porphyrin-carotenoid linkage. Additionally, five different CPC{sub 60} conformations were studied to determine the effect of pi-conjugation and particle-hole Coulombic attraction on the CT excitation energies. Our calculations show that configurational changes in the triad induces a variation of ∼0.6 eV in CT excited state energies in the gas-phase. The corresponding calculated excited state dipoles show a range of 47 D–188 D. The absorption spectra and density of states of these structures show little variation except for the structures where the porphyrin and aryl conjugation is changed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

Synthesis, optical and electrochemical properties of Zn-porphyrin for dye sensitized solar cell applications

Zn-Porphyrin dye has been synthesized by the reaction between aldehydes and pyrrole. The dye structure was confirmed by {sup 1}H NMR, {sup 13}C NMR spectrum. The functional group of the dye molecule was confirmed by FTIR spectrum. The UV-Vis-NIR absorption spectrum of Zn-Porphyrin in DMF solution was recorded in spectrophotometer. The UV-Vis NIR spectrum of dye exhibits a strong Soret band and Q-band. Cyclic Voltammograms were obtained with three electrode systems: Pt as counter electrode, saturated calomel used as a reference electrode and glassy carbon as working electrode at a scan rate of 100 mV/s. The curves recorded the oxidation of 0.5 mM compound Zn-Porphyrin in a dichloromethane solution containing 0.1M TBAP as supporting electrolyte, reveal two successive quasi reversible redox couples with the first anodic and cathodic peak potentials of -0.2 V and -1 V. The second anodic and cathodic peak potentials are 0.82 V and 0.01 V respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

The many-body electronic interactions of Fe(II)–porphyrin

Fe(II)–porphyrin complexes exhibit a diverse range of electronic interactions between the metal and macrocycle. Herein, the incremental full configuration interaction method is applied to the entire space of valence orbitals of a Fe(II)–porphyrin model using a modest basis set. A novel visualization framework is proposed to analyze individual many-body contributions to the correlation energy, providing detailed maps of this complex’s highly correlated electronic structure. Furthermore, this technique is used to parse the numerous interactions of two low-lying triplet states ( 3 A 2 g and 3 E g ) and to show that strong metal d–d and macrocycle π–π orbital interactions preferentially stabilize the 3 A 2 g state. d–π interactions, on the other hand, preferentially stabilize the 3 E g state and primarily appear when correlating six electrons at a time. Ultimately, the Fe(II)–porphyrin model’s full set of 88 valence electrons are correlated in 275 orbitals, showing the interactions up to the 4-body level, which covers the great majority of correlations in this system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Covalent-Organic Frameworks Composed of Rhenium Bipyridine and Metal Porphyrins: Designing Heterobimetallic Frameworks with Two Distinct Metal Sites

The incorporation of homogeneous catalysts for CO 2 reduction into extended frameworks has been a successful strategy for increasing catalyst lifetime and activity, but the effects of the linkers on catalysis are underexplored. In this work, a novel rhenium bipyridine complex was synthesized for the purpose of designing a covalent-organic framework (COF) with both metalloporphyrin and metal bipyridine moieties. Investigation of the rhenium complex as a homogeneous catalyst shows a faradaic efficiency of 81(8)% for the electrocatalytic conversion of CO 2 to CO upon the addition of methanol as the proton source. Treatment of the rhenium complex with tetra(4-aminophenyl)porphyrin under Schiff base conditions produces the desired COF, as indicated by powder X-ray diffraction (PXRD) studies. Metalation of the porphyrins was accomplished through postsynthetic modification with CoCl 2 and FeCl 3 metal precursors. The retention of the PXRD peaks and appearance of new Co and Fe peaks in the corresponding X-ray photoelectron spectroscopy spectra suggest the successful incorporation of a secondary metal site into the framework. Cyclic voltammetry measurements display increases in current densities when the atmosphere is changed from N 2 to CO 2 . Finally, controlled potential electrolyses show that the cobalt-postmetalated COF has the highest activity toward CO 2 reduction, reaching a faradaic efficiency of 18(2)%.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Photophysical Properties and Electronic Structure of Zinc(II) Porphyrins Bearing 0–4 meso -Phenyl Substituents: Zinc Porphine to Zinc Tetraphenylporphyrin (ZnTPP)

Six zinc(II) porphyrins bearing 0–4 meso-phenyl substituents have been examined spectroscopically and theoretically. Comparisons with previously examined free base analogues afford a deep understanding of the electronic and photophysical effects of systematic addition of phenyl groups in porphyrins containing a central zinc(II) ion versus two hydrogen atoms. Trends in the wavelengths and relative intensities of the absorption bands are generally consistent with predictions from time-dependent density functional theory calculations and simulations from Gouterman’s four-orbital model. These trends derive from a preferential effect of the meso-phenyl groups to raise the energy of the highest occupied molecular orbital. The calculations reveal additional insights, such as a progressive increase in oscillator strength in the violet-red (B-Q) absorption manifold with increasing number of phenyls. Progressive addition of 0–4 phenyl substituents to the zinc porphyrins in O 2 -free toluene engenders a reduction in the measured lifetime of the lowest singlet excited state (2.5–2.1 ns), an increase in the S 1 → S o fluorescence yield (0.022–0.030), a decrease in the yield of S 1 → T 1 intersystem crossing (0.93–0.88), and an increase in the yield of S 1 → S o internal conversion (0.048–0.090). The derived rate constants for S 1 decay reveal significant differences in the photophysical properties of the zinc chelates versus free base forms. Here, the unexpected finding of a larger rate constant for internal conversion for zinc chelates versus free bases is particularly exemplary. Collectively, the findings afford fundamental insights into the photophysical properties and electronic structure of meso-phenylporphyrins, which are widely used as benchmarks for tetrapyrrole-based architectures in solar energy and life sciences research.

14 SOLAR ENERGY↗

DOE OSTI2018

Synthesis and Photophysical Properties of a Covalently Linked Porphyrin Chromophore–Ru(II) Water Oxidation Catalyst Assembly on SnO 2 Electrodes

In this work, we describe the preparation and surface photophysical properties of a covalently linked, chromophore-catalyst assembly between a phenyl phosphonate-derivatized pentafluorophenyl-substituted porphyrin and the water oxidation catalyst, [Ru II (terpyridine)(2-benzimidazolylpyridine)(OH 2 )] 2+ , in a derivatized assembly of porph-Ru II –OH 2 2+ . The findings of nanosecond transient absorption measurements on nanoparticle SnO 2 electrodes in aqueous acetate buffer at pH 4.7 are consistent with rapid electron injection into SnO 2 with transfer of oxidative equivalents to the assembly. Electron transfer from the singlet excited state of the porphyrin to the conduction band of the electrode, SnO 2 (e – )|-porph + -Ru II –OH 2 2+ , is favored as the porphyrin singlet excited state lies 0.44 eV above the SnO 2 conduction band edge. Electron injection is rapid ($\langle$τ inj $\rangle$ < 10 –8 s), and occurs with high efficiency. Based on measured redox potentials, following excitation and injection, intra-assembly oxidation of the catalyst, -porph+-Ru II –OH 2 2+ → -porph-Ru III –OH 2+ + H + , is favored in the transient equilibrium state by 0.62 eV at pH 4.7. However, immediately after the flash, a distribution exists at the surface between isomers with SnO 2 (e – )|-porph+-Ru II –OH 2 2+ undergoing back electron transfer to the surface with an average lifetime of $\langle$τ 1 $\rangle$ ~ 10 –7 s and a slower component for back electron transfer from SnO 2 (e – )|-porph-Ru III –OH 2+ with $\langle$τ 2 $\rangle$ ~ 4 × 10 –5 s.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

High-Energy Charge-Separated States by Reductive Electron Transfer Followed by Electron Shift in the Tetraphenylethylene–Aluminum(III) Porphyrin–Fullerene Triad

A high-potential supramolecular triad (TPE-AlPor ← Im-C 60 ) composed of aluminum(III) porphyrin (AlPor), fullerene (C 60 ), and tetraphenylethylene (TPE) has been constructed. The fullerene and tetraphenylethylene units are bound axially to opposite faces of the porphyrin plane via coordination and covalent bonds, respectively. The ground and excited-state properties of the triad and reference dyads are studied using steady-state and time-resolved spectroscopic techniques. The transient data show that photoexcitation results in charge separation from tetraphenylethylene to the excited singlet state of the porphyrin ( 1 AlPor*), generating a high-energy (2.14 eV) charge-separated state, (TPE) •+ -(AlPor) •– , in toluene. A subsequent electron migration from the AlPor –• to fullerene generates a second high-energy (1.78 eV) charge-separated state (TPE) •+ -AlPor ← Im-(C60) •– . The lifetime of the charge separation is about 25 ns. Here, the high energy stored in the form of charge-separated states along with their reasonable lifetimes makes these donor–acceptor systems potential electron-transporting catalysts to carry out energy-demanding photochemical reactions, especially in artificial photosynthesis for conversion of solar energy into chemical energy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Selective Excited-State Dynamics in a Unique Set of Rationally Designed Ni Porphyrins

In this work, we report the design and photophysical properties of a unique class of Ni porphyrins, in which the tert-butyl benzene substituents at the meso positions of the macrocycle were tethered by ethers with alkyl linkers. This not only results in the permanently locked ruf distortion of the macrocycle but also enables the engineering of the degree of distortion through varying the length of alkyl linkers, which addressed the complication of uncertainty in the specific structural distortions that has long plagued the porphyrin photophysical community. Using advanced time-resolved optical and X-ray absorption spectroscopy, we observed tunability in the excited-state relaxation pathway depending on the degree of distortion and characterized the associated transient intermediate structure. Furthermore, these findings provide a new avenue to afford accessibility to a wide range of excited-state properties in nonplanar porphyrins.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗