Platinum Porphyrin Research Articles

Gold Corroles as Near-IR Phosphors for Oxygen Sensing.

The triplet state of gold(III) corroles is exploited for optical oxygen sensing. We report intense phosphorescence for gold(III) corroles in the near-IR, an optical window that is ideal for tissue transparency. Moreover, the triplet excited-state emission exhibits significant changes in intensity and lifetime over the 0-160 Torr O2 pressure range. This renders these compounds sensitive at biologically relevant pressures and overcomes the spectral limitations of palladium and platinum porphyrins for oxygen sensing in biology.

Low‐Temperature Plasma Processing of Platinum Porphyrins for the Development of Metal Nanostructured Layers

This article establishes the bases for a vacuum and plasma supported methodology for the fabrication at mild temperatures of nanostructured platinum in the form of porous layers and nanocolumns using platinum octaethylporphyrin as precursor. In addition, the application of these materials as tunable optical filters and nano‐counterelectrodes is proved. On one hand, the transparency in the ultraviolet–visible–near infrared range can be adjusted precisely between 70% and 1% by tuning the deposition and processing conditions, obtaining a high spectral planarity. Deviations of the spectra from an ideal flat filter are below 4%, paving the way to the fabrication of neutral density filters. The transparency limit values yield a sheet resistivity of ≈1350 and 120 Ω □−1, respectively. On the other hand, the catalytic properties of the nanostructures are further demonstrated by their implementation as counterelectrodes of excitonic solar cells surpassing the performance of commercial platinum as counterelectrode in a 20% of the overall cell efficiency due to simultaneous enhancement of short‐circuit photocurrent and open‐circuit photovoltage. One of the most interesting features of the developed methodology is its straightforward application to other metal porphyrins and phthalocyanines readily sublimable under mild vacuum and temperature conditions.

Photo and electroluminescence of a platinum porphyrin doping of complexes with two metal cores

In this paper, four new complexes with two metal cores [2Sm, 2Sn, 2Zn and 2Pb] were prepared and utilized as host material in in the electroluminescence (EL) devices. Devices with two metal cores and with the structure of ITO/PEDOT: PSS (60 nm)/PVK (55 nm)/[2Sm, 2Sn, 2Zn and 2Pb]: %8 [2,5PtTPP] (45 nm)/Al (200 nm) were fabricated, A blue–green photoluminescence (PL) emission with a blue shift compared to the 2,5PtTPP was observed. 2,5PtTPP doped in 2Sm and 2Sn showed more pure red color compared to 2Zn and 2Pb based devices. We believe that energy transfer occurring at 2,5PtTPP/[2Sm, 2Sn] molecules is responsible for the red color in the EL of the device. The electronic effect of two metal cores of complexes influenced the maximum current density, brightness, and luminous efficiency of the devices. Finally, we have demonstrated the samarium complex of 8-hydroxyquinoline is a promising host material for red OLEDs with high efficiency and has a simple device structure.

A platinum porphyrin modified TiO2 electrode for photoelectrochemical hydrogen production from neutral water driven by the conduction band edge potential of TiO2.

The onset potential for H2 production from neutral water (pH 7) catalyzed by a platinum(ii) porphyrin (PtP-py) modified TiO2 electrode positions very close to the standard water reduction potential (less than 50 mV). H2 production is driven by the conduction band edge potential of TiO2 at the PtP-py-modified TiO2 cathode.

High-performance dissolved oxygen sensors based on platinum(ii) porphyrin embedded in polystyrene beads

A ratiometric dissolved oxygen sensor synthesized via a swelling method exhibits high sensitivity, good reversibility and photo-stability.

Photoactive meso-tetra(4-pyridyl)porphyrin-tetrakis-[chloro(2,2'bipyridine)platinum(ii) derivatives recognize and cleave DNA upon irradiation.

In this work, we evaluate the interaction of the peripheral Pt(bpy)Cl+ substituted porphyrins, H2PtPor and ZnPtPor with DNA using UV-vis, emission fluorescence, CD spectroscopy, and DNA melting properties altered by the Pt(ii)-porphyrinoid compounds. Additionally, we observe the ability of these porphyrin derivatives to generate 1O2 and to efficiently photocleave plasmid DNA upon visible light irradiation based on a mixed (oxidative/hydrolytic) mechanism.

Synthesis, characterization and reactivity of trans-dihydroxy platinum(IV) porphyrins

Synthesis of two trans-dihydroxy platinum(IV) porphyrins (TPP, tetraphenylporphyrin and F[Formula: see text]TPP, tetrakispentafluorophenylporphyrin) by dimethyl dioxirane (DMD) oxidation of their Pt[Formula: see text] porphyrin precursors have been described. The oxidation state of Pt cation in such complexes was assessed by X-ray photoelectron spectroscopy and shown to be [Formula: see text]4. More importantly, proton was found to promote the formation and stabilization of the trans-dihydroxy platinum(IV) porphyrins, as revealed by UV-vis spectroscopic results and single crystal structures. In addition, these trans-dihydroxy Pt[Formula: see text] porphyrins were much easier to be reduced than their Pt(II) counterparts and capable to transfer oxygen atom to triphenylphosphine and thioanisol, which is important for further application of Pt(IV) complexes in catalytic reactions.

(Invited) Long-Lived Charge Separated States Exclusively from the Triplet Excited States in Palladium Porphyrin-Fullerene Conjugates

Molecular engineering of donor-acceptor conjugates to control their photoinduced processes to yield the much desired long-lived charge separated states has been one of the major goals in artificial photosynthesis. The charge separated states of sufficient lifetime and stored energy are key in ultimately driving the photocatalytic processes of either light-to-electricity conversion or light-to-fuel production. In simple donor-acceptor dyads, charge separation from the singlet excited donor or acceptor due to rapid charge recombination process results in a short-lived charge separated state of singlet spin character. Utilization of high energy triplet sensitizers instead of the traditionally employed singlet sensitizers could be an elegant approach to generate long-lived charge separated states. The radical ion-pairs of triplet spin character charge recombine to the ground state slowly due to spin forbidden nature of the process. However, witnessing such a process purely from the triplet excited state without the interference of the singlet excited state and other competing photochemical events such as excitation energy transfer has been challenging to establish. Here, we report our strategy to observe electron transfer exclusively from the triplet excited state of the donor in PdP-C60 dyads (see figure below). Using transient absorption spectral studies operating at different timescales and time-resolved electron paramagnetic resonance (TR-EPR) studies, photoinduced electron transfer from 1PdP* to C60 leading to the formation of PdP•+-C60 •- charge separated state of singlet spin character has been witnessed in 2 (instead of triplet-triplet energy transfer observed in 1 1) due to the close proximity of the donor and acceptor entities. In contrast, by lowering the energy of the [(TPA)3PdP]•+-C60 •- state owing to the presence of electron rich TPA entities (facile oxidation) compared to that of 3C60*, electron transfer from 3(TPA)3PdP* to C60 leading to [(TPA)3PdP]•+-C60 •- charge separated state of triplet spin character with lifetime in the microsecond range has been observed in 3 in polar solvents. Results of these findings and its significance will be highlighted. C. Obondi, G. N. Lim, F. D’Souza, Triplet-Triplet Excitation Transfer in Palladium Porphyrin – Fullerene and Platinum Porphyrin – Fullerene Dyads’ J. Phys. Chem. C 2015, 119, 176-185. Figure 1

Stable Optical Oxygen Sensing Material Based on Perfluorinated Polymer and Fluorinated Platinum(II) and Palladium(II) Porphyrins

Commercially available dissolved oxygen analyzer with an optical detection method based on phosphorescence quenching was created. The sensitive element of the sensor contains a metal complex of fluorine-substituted porphyrin (platinum(II) or palladium(II) 5,10,15,20-mesotetrakis-(2,3,4,5,6-pentafluorophenyl)-porphyrin) dissolved in poly(hexafluoropropylene) (PHFP) matrix. Perfluorinated polymer was applied to avoid interaction of singlet oxygen with polymer matrix. The measurement of oxygen concentration is based on the change of the lifetime of the phosphorescent state due to luminescence quenching by molecular oxygen, which is more precise than the intensity detection method. A series of test were performed to estimate metrological characteristics of the analyzer. The presented sensor system exhibits lower noise, higher resolution and higher sensitivity than electrochemical sensors previously used.

Highly selective and efficient oxidation of sulfide to sulfoxide catalyzed by platinum porphyrins

Two platinum porphyrins, meso-tetramesitylporphyrinatoplatinum and meso-tetrakis(pentaflourophenyl) porphyrinatoplatinum, are explored for catalytic application in the selective oxidation of sulfide to sulfoxide by iodosylbenzene. The obtained overall turnover number of 90,000 in the oxidation of thioanisole in the presence of meso-tetrakis(pentaflourophenyl) porphyrinatoplatinum indicates the pronounced catalytic activity of the platinum porphyrins. Perfect selectivity toward sulfoxide or sulfone also was achieved via stoichiometric control of reactants.

Synthesis of π-extended platinum porphyrins

We report the efficient synthesis of tetrabicycloporphyrin platinum under mild conditions (60°C). The platinum complexes were heated under vacuum to give π-extended platinum porphyrins in 100% yield. The porphyrins are expected to have interesting properties such as high-quantum-efficiency near-IR phosphorescence and large absorptivity in the near-IR region.

In-Situ Measurement of Oxygen Particial Pressure on the Surface of a Cathode GDL with Automotive Compatible Operating Conditions

Cathode oxygen concentration is vital for fuel cell performance. In-situ measurement of oxygen partial pressure provides a method to determine the local oxygen concentration in the cathode. A novel method that uses oxygen sensitive fluorophore materials has been developed to directly measure the oxygen partial pressure in the cathode flow field during fuel cell operation. Fluorescent luminescence is sensitive to oxygen quenching as described by the Stern-Volmer equation. The oxygen quenching rate was modified to meet a desired range of oxygen partial pressure measurement. In a previous study, a fluorophore ink material with a platinum porphyrin based fluorophore dispersed in the FIB polymer was developed. This fluorophore ink material showed a sufficient level of intensity of fluorescent luminescence to cover the typical operating condition of an automotive proton exchange membrane fuel cell (PEMFC). However, this fluorophore ink material was too viscous for the surface of the gas diffusion layer (GDL) where ink material clogged the pores of the GLD and lowered the fuel cell performance. In this study, the fluorophore ink material was modified. A newly developed less viscous fluorophore ink material was confirmed that the fuel cell performance was not affected by the sprayed ink materials. Concurrently, it was confirmed that the oxygen quenching rate of this fluorophore materials were retained. The Stern-Volmer calibration enabled accurate in-situ oxygen partial pressure measurements on the surface of the cathode GDL to cover the typical operating conditions of an automotive PEMFC.

In-Situ Measurement of Oxygen Particial Pressure on the Surface of a Cathode GDL with Automotive Compatible Operating Conditions

Improvement of the area specific power density of a proton exchange membrane fuel cell (PEMFC) can reduce the total active area of the membrane electrode assembly (MEA). Reducing the total active area of the MEA is a significant opportunity to reduce the cost of a fuel cell because it can reduce the amount of the expensive materials in the MEA, including platinum based electrocatalysts, polymer electrolyte membranes, and gas diffusion media. Mass transport overpotential at high current densities is the major barrier to achieving high area specific power density. Oxygen partial pressure in the cathode is highly linked to the mass transport performance. Therefore, direct measurement of the oxygen partial pressure at the cathode is required for mass transport studies. A novel method has been developed to directly measure the oxygen partial pressure in the cathode flow field during fuel cell operation. This method uses fluorophore materials with fluorescent luminescence that is sensitive to oxygen quenching as described by the Stern-Volmer equation. The measurement range of oxygen partial pressure is dependent on the sensitivity of oxygen quenching of the fluorophore materials. Oxygen quenching rate should be modified to meet a desired range of oxygen partial pressure measurement. In the previous study, the fluorophore material with a platinum porphyrin based fluorophore, which is highly sensitive to oxygen quenching, dispersed in the polymer binder of poly-heptafluoro-n-butly, methacrylate-co-hexafluroisoporopyl, and methacrylate, a.k.a. FIB polymer, was developed. This material showed a sufficient level of intensity of fluorescent luminescence for 7 kPa to 53 kPa oxygen partial pressure. The detected oxygen partial pressure was calibrated within the acceptable temperature sensitivity, between 40°C to 90°C. This range covers the typical operating condition of an automotive PEMFC. The ink of this fluorophore material was sprayed on the surface of the cathode flow field. An in-situ measurement of the oxygen partial pressure at the cathode flow field was demonstrated to investigate the effectiveness of water management in the cathode flow field. However, this fluorophore ink material was too thick to use on the surface of the cathode GDL, because the ink materials clogged the pores of the GDL and lowered the fuel cell performance. In this study, this fluorophore ink material, platinum porphyrin based fluorophore in FIB polymer, was modified. A newly developed thinner fluorophore ink material was sprayed on the surface of the cathode GDL and it was confirmed that the fuel cell performance was not affected by the sprayed ink materials. Concurrently, it was confirmed that the oxygen quenching rate of this fluorophore materials were retained. The Stern-Volmer calibration indicates a small deviation of calibration curves between the fluorophore materials sprayed on the flat glass surface and the porous GDL surface. Numbers of bright spots were observed on the Stern-Volmer calibrated image of the GDL surface. These bright spots were considered to be corresponding to the shadow of the excitation light on the rough GDL surface. When two excitation light sources were used from different angles, the deviation was significantly mitigated. The fluorophore ink modification in this study enabled accurate in-situ oxygen partial pressure measurements on the surface of the cathode GDL to cover the typical operating conditions of an automotive PEMFC. Combined with the previously developed method of oxygen partial pressure on the flow field wall, further analysis was enabled. A significant oxygen partial pressure difference is observed between on the top ceiling of the flow field channel and on the surface of GDL. It was considered that the oxygen concentration in the cathode flow field exhibits a clear gradient from the top wall of the channel towards the GDL surface. This suggests that oxygen was drawn to the GDL surface in a laminar flow scenario in the fuel cell cathode. Detailed analysis will be discussed at the ECS meeting.

Aromatically π-Extended Porphyrins with Large Two-Photon Absorption Cross-Sections and Bright Phosphorescence

The ability to form triplet excited states upon two-photon excitation is important for several applications of metalloporphyrins. Here we present two-photon absorption (2PA) properties of several platinum (II) porphyrins, focusing on the effect of aromatic π-extension and peripheral substitution on 2PA cross-sections. p-Extension of the tetrapyrrolic macrocycle by way of syn-fusion with two external aromatic fragments, such as in syn-dibenzo- (DBP) and syn-dinaphthoporphyrins (DNP), removes the center-of-inversion symmetry in the porphyrins macrocycle. As a result, DBPs and DNPs exhibit stronger 2PA into their one-photon-allowed states (e.g. Soret state) than fully-symmetrical non-extended Pt(II) porphyrins (D4h symmetry). However, much stronger absorbing 2PA-allowed states still lie above the Soret state and cannot be accessed directly due to the interfering linear absorption. 2PA near the Soret state increases dramatically (up to 50 fold) upon introduction of alkoxycarbonyl groups (CO2R) into the benzo rings in DBP. TDDFT/sum-over-states calculations reveal that in these porphyrins low-lying molecular orbitals spanning over CO2R groups via configuration form new 2PA-allowed states located just above the Soret state. Furthermore, computations predicted major stabilization of gerade-states in fully-symmetrical D4h Pt alkoxycarbonyltetrabenzoporphyrins. Measurements confirmed that e.g. in PtTBP(CO2Bu)8 2PA cross-section near 810 nm is ~900 GM. Combined with ultrafast intersystem crossing and exceptionally bright phosphorescence 2PA makes alkoxycarbonyl-substituted p-extended porphyrins very promising candidates for several 2P applications.

Facile and Practical Synthesis of Platinum(II) Porphyrins under Mild Conditions

Abstract A facile and mild method for the preparation of platinum(II) porphyrin complexes is reported. A simple treatment of free-base porphyrins with 1.5 equiv of [PtCl2(PhCN)2] in the presence of sodium propionate in refluxing chlorobenzene (bp: 131 °C) affords the corresponding Pt(II) complexes in good yields within a few hours. Furthermore, the work-up processes for our methods are less complex than those for the reported ones because chlorobenzene can be easily removed by simple evaporation.

Fluorescent/phosphorescent dual-emissive conjugated polymer dots for hypoxia bioimaging.

A kind of fluorescent/phosphorescent dual-emissive conjugated polyelectrolyte has been prepared by introducing phosphorescent platinum(ii) porphyrin (O2-sensitive) into a fluorene-based conjugated polyelectrolyte (O2-insensitive), which can form ultrasmall conjugated polymer dots (FP-Pdots) in the phosphate buffer solution (PBS) via self-assembly caused by their amphiphilic structures with hydrophobic backbones and hydrophilic side chains. These FP-Pdots can exhibit an excellent ratiometric luminescence response to O2 content with high reliability and full reversibility for measuring oxygen levels, and the excellent intracellular ratiometric O2 sensing properties of the FP-Pdots nanoprobe have also been confirmed by the evident change in the Ired/Iblue ratio values in living cells cultured at different O2 concentrations. To confirm the reliability of the O2 sensing measurements of the FP-Pdots nanoprobe, O2 quenching experiments based on lifetime measurements of phosphorescence from Pt(ii) porphyrin moieties have also been carried out. Utilizing the sensitivity of the long phosphorescence lifetime from Pt(ii) porphyrins to oxygen, the FP-Pdots have been successfully applied in time-resolved luminescence imaging of intracellular O2 levels, including photoluminescence lifetime imaging and time-gated luminescence imaging, which will evidently improve the sensing sensitivity and reliability. Finally, in vivo oxygen sensing experiments were successfully performed by luminescence imaging of tumor hypoxia in nude mice.

Photoinduced triplet-state electron transfer of platinum porphyrin: a one-step direct method for sensing iodide with an unprecedented detection limit

Herein, we report for the first time the photoinduced triplet-state electron transfer of Pt(ii)TMPyP as an easy, rapid, environmentally friendly, ultra-sensitive and economical method for the determination of iodide in the aqueous phase.

Triplet–Triplet Excitation Transfer in Palladium Porphyrin–Fullerene and Platinum Porphyrin–Fullerene Dyads

Covalently linked donor–acceptor dyads involving palladium(II) and platinum(II) porphyrins as triplet sensitizers and fullerene as an acceptor have been newly synthesized. These dyads were characterized by optical absorbance, emission, and electrochemical methods. In contrast to the earlier reported zinc(II) porphyrin and free-base porphyrin-based dyads of similar structures, photoinduced electron transfer from the short-lived singlet and long-lived triplet excited metalloporphyrin to the fullerene was not observed, although these processes are energetically possible according to the energy level diagrams. That is, diagnostic transient bands corresponding to MP•+ [M = Pd(II) or Pt(II)] in the 600–650-nm range and C60•– in the 1000-nm range were absent in the femtosecond and nanosecond transient absorption spectra. Interestingly, excited energy transfer from the triplet excited metalloporphyrin to the fullerene was witnessed in both palladium and platinum porphyrin-derived dyads by nanosecond transient absorption studies. Three solvents with different polarities were employed to visualize the medium effects. The determined rate of energy transfer, kEnT, was found to be higher for the PdP-based dyad than the PtP-based dyad in a given solvent and that the rates were higher for polar solvents than for nonpolar solvent. The present investigation demonstrates how the heavy-metal ion in the porphyrin cavity modulates photoinduced processes and the solvent-dependent kinetics of these events.

Synthesis of phosphorescent asymmetrically π-extended porphyrins for two-photon applications.

Significant effort has been directed in recent years toward porphyrins with enhanced two-photon absorption (2PA). However, the properties of their triplet states, which are central to many applications, have rarely been examined in parallel. Here we report the synthesis of asymmetrically π-extended platinum(II) and palladium(II) porphyrins, whose 2PA into single-photon-absorbing states is enhanced as a result of the broken center-of-inversion symmetry and whose triplet states can be monitored by room-temperature phosphorescence. 5,15-Diaryl-syn-dibenzoporphyrins (DBPs) and syn-dinaphthoporphyrins (DNPs) were synthesized by [2 + 2] condensation of the corresponding dipyrromethanes and subsequent oxidative aromatization. Butoxycarbonyl groups on the meso-aryl rings render these porphyrins well-soluble in a range of organic solvents, while 5,15-meso-aryl substitution causes minimal nonplanar distortion of the macrocycle, ensuring high triplet emissivity. A syn-DBP bearing four alkoxycarbonyl groups in the benzo rings and possessing a large static dipole moment was also synthesized. Photophysical properties (2PA brightness and phosphorescence quantum yields and lifetimes) of the new porphyrins were measured, and their ground-state structures were determined by DFT calculations and/or X-ray analysis. The developed synthetic methods should facilitate the construction of π-extended porphyrins for applications requiring high two-photon triplet action cross sections.

Visible‐Light‐Induced Annihilation of Tumor Cells with Platinum–Porphyrin Conjugates

AbstractDespite the extensive use of porphyrins in photodynamic therapy (PDT), tetraplatinated porphyrins have so far not been studied for their anticancer properties. Herein, we report the synthesis of such novel platinum–porphyrin conjugates as well as their photophysical characterization and in vitro light‐induced anticancer properties. These conjugates showed only minor cytotoxicity in the dark, but IC50 values down to 19 nM upon irradiation with light at 420 nm.These values correspond to an excellent phototoxic index (PI=IC50 in the dark/IC50 in light), which reached 5000 in a cisplatin‐resistant cell line. After incubation with HeLa cells, nuclear Pt concentrations were 30 times higher than with cisplatin. All of these favorable characteristics imply that tetraplatinated porphyrin complexes are worthy of exploration as novel PDT anticancer agents in vivo.