Platinum Porphyrin Research Articles

Room-Temperature Near-Infrared Phosphorescence from C64 Nanographene Tetraimide by π-Stacking Complexation with Platinum Porphyrin.

Near-Infrared (NIR) phosphorescence at room temperature is challenging to achieve for organic molecules due to negligible spin-orbit coupling and a low energy gap leading to fast non-radiative transitions. Here, we show a supramolecular host-guest strategy to harvest the energy from the low-lying triplet state of C64 nanographene tetraimide 1. 1H NMR and X-ray analysis confirmed the 1 : 2 stoichiometric binding of a Pt(II) porphyrin on the two π-surfaces of 1. While the free 1 does not show emission in the NIR, the host-guest complex solution shows NIR phosphorescence at 77 K. Further, between 860-1100 nm, room temperature NIR phosphorescence (λmax=900 nm, τavg=142 μs) was observed for a solid-state sample drop-casted from a preformed complex in solution. Theoretical calculations reveal a non-zero spin-orbit coupling between isoenergetic S1 and T3 of π-stacked [1 ⋅ Pt(II) porphyrin] complex. External heavy-atom-induced spin-orbit coupling along with rigidification and protection from oxygen in the solid-state promotes both the intersystem crossing from the first excited singlet state into the triplet manifold and the NIR phosphorescence from the lowest triplet state of 1.

Room‐Temperature Near‐Infrared Phosphorescence from C64 Nanographene Tetraimide by π‐Stacking Complexation with Platinum Porphyrin

AbstractNear‐Infrared (NIR) phosphorescence at room temperature is challenging to achieve for organic molecules due to negligible spin–orbit coupling and a low energy gap leading to fast non‐radiative transitions. Here, we show a supramolecular host–guest strategy to harvest the energy from the low‐lying triplet state of C64 nanographene tetraimide 1. 1H NMR and X‐ray analysis confirmed the 1 : 2 stoichiometric binding of a Pt(II) porphyrin on the two π‐surfaces of 1. While the free 1 does not show emission in the NIR, the host–guest complex solution shows NIR phosphorescence at 77 K. Further, between 860–1100 nm, room temperature NIR phosphorescence (λmax=900 nm, τavg=142 μs) was observed for a solid‐state sample drop‐casted from a preformed complex in solution. Theoretical calculations reveal a non‐zero spin–orbit coupling between isoenergetic S1 and T3 of π‐stacked [1 ⋅ Pt(II) porphyrin] complex. External heavy‐atom‐induced spin–orbit coupling along with rigidification and protection from oxygen in the solid‐state promotes both the intersystem crossing from the first excited singlet state into the triplet manifold and the NIR phosphorescence from the lowest triplet state of 1.

Singlet oxygen generation proportion from triplet state of porphyrin in water

The proportion of singlet oxygen (R) produced from the triplet state of porphyrin in aqueous solutions was investigated by substituting porphyrin molecules with the metalloporphyrin Platinum(II) meso-tetraphenylporphyrin (Pt-TPP). The feasibility of using platinum porphyrin as a substitute for porphyrin to study the photophysical properties in photodynamic therapy (PDT) was confirmed. The model of first-order decay in a water-methanol mixed solution encompasses potential deactivation processes of the excited triplet states and was built, which was confirmed by monitoring the change in the total transition rate of the T1 state (A0) value at different water contents under anoxic environments, obtained through measuring the phosphorescence lifetime (τp) of Pt-TPP. Combined with A0 and the quenching rate constant of T1 by O2 (kq), the formula for R in relation to changes in oxygen can be deduced in pure water.

Fast, efficient, narrowband room-temperature phosphorescence from metal-free 1,2-diketones: rational design and the mechanism.

We report metal-free organic 1,2-diketones that exhibit fast and highly efficient room-temperature phosphorescence (RTP) with high colour purity under various conditions, including solutions. RTP quantum yields reached 38.2% in solution under Ar, 54% in a polymer matrix in air, and 50% in crystalline solids in air. Moreover, the narrowband RTP consistently dominated the steady-state emission, regardless of the molecular environment. Detailed mechanistic studies using ultrafast spectroscopy, single-crystal X-ray structure analysis, and theoretical calculations revealed picosecond intersystem crossing (ISC) followed by RTP from a planar conformation. Notably, the phosphorescence rate constant k p was unambiguously established as ∼5000 s-1, which is comparable to that of platinum porphyrins (representative heavy-metal phosphor). This inherently large k p enabled the high-efficiency RTP across diverse molecular environments, thus complementing the streamlined persistent RTP approach. The mechanism behind the photofunction has been elucidated as follows: (1) the large k p is due to efficient intensity borrowing of the T1 state from the bright S3 state, (2) the rapid ISC occurs from the S1 to the T3 state because these states are nearly isoenergetic and have a considerable spin-orbit coupling, and (3) the narrowband emission results from the minimal geometry change between the T1 and S0 states. Such mechanistic understanding based on molecular orbitals, as well as the structure-RTP property relationship study, highlighted design principles embodied by the diketone planar conformer. The fast RTP strategy enables development of organic phosphors with emissions independent of environmental conditions, thereby offering alternatives to precious-metal based phosphors.

Application of pressure-sensitive paint for explosive blast measurements

This study demonstrates the application of fast response pressure-sensitive paint (PSP) to explosively driven blast wave testing. A sprayable polymer ceramic fast response PSP was applied to an aluminium disc before being coated with platinum porphyrin compound as the active luminophore. The disc was then exposed to a blast wave and the response was measured using a high-speed video camera. The PSP measured the transit of the incident shock wave clearly, albeit with a slight response delay following the instantaneous change in pressure. A time domain-based method for improving temporal response, whilst considering both spatial and temporal effects, is described. This study clearly demonstrates that the spatial distribution of a blast wave on a surface may be captured by PSP technology. Integrated parameters such as impulse can correctly be characterised using this method. This technology offers an enhanced and more efficient way of characterising blast.

Optimizing Transcutaneous Oxygen Measurement Sites on Humans.

This study utilizes an optical method of transcutaneous oxygen sensing that has the potential to revolutionize at-home care. This technique is based on quenching the luminescence of a platinum porphyrin film. Since oxygen quenches luminescence, its lifetime is further measured to assess the partial pressure of transcutaneous oxygen diffusing through the skin. Unlike conventional transcutaneous oxygen monitors that use electrochemical sensors, the luminescence-based sensor allows the use of dry electrodes that do not require heating and reduce the risk of accidental skin irritations or burns. These properties not only improve patient safety but also allow the creation of miniature wearable transcutaneous oxygen sensors for continuous and accurate remote respiratory monitoring. To this end, it is critical to assess the efficiency of the wearable sensor by determining the optimal location for its placement on the body. Depending on the location on the body, physiological factors such as blood flow rate and skin thickness affect dermal perfusion of transcutaneous oxygen. In this work, four healthy volunteers participated in subject testing. We assessed each participant at the following locations: thumb, top of the wrist, forearm, thigh, and shin. All locations consistently reported accurate and reliable data. Among them, the thumb demonstrated shorter settling times and the most uniform luminescence lifetime values.

Regulating WORM/Flash electrical memory behavior of metallopolymers through varying metal centers

To study the influence of metal atoms on the performance of organic polymer memory devices, four new metallopolymers P0, P1, P2 and P3 were designed and synthesized for organic resistive random-access memory (RRAM) applications. Among them, the device based on P1 shows nonvolatile binary write-once-read-many-times (WORM) memory behavior, while the devices based on P2 and P3 show vastly different nonvolatile binary Flash-type memory behavior. The charge transfer (CT) effect between the platinum (Pt) ligand and porphyrin moieties of metallopolymers is determined to be the origin of the electrical switching behavior of P1, which is proved by the electrochemical and DFT calculations. While the reason of the Flash type memory characteristic of P2 and P3 is ascribed to the formation of metal filaments because of the introduction of metal ions (Co and Ni) into the porphyrin ring. It is suggested that the metal ions can form an internal electrode and act as a bridge during the CT process, which contributes to both the CT and back CT, consequently regulating the WORM/Flash conversion. The results indicate the feasibility of modulating the memory behavior of metallopolymers by varying the central metal ions, manifesting the significance of metal complexes in the application of organic memory devices and will attract wide research interest of scientists. The as-fabricated device based on P3 was also successfully applied to memory logic gates and display function, which offers great application prospect as smart sensor in artificial intelligence (AI) network.

Visualization of flow boiling heat transfer using temperature sensitive paint with high spatial and temporal resolution

Boiling heat transfer plays an important role in a wide range of industrial applications. Recent advances in optical measurement technology have made possible the visualization of the heat transfer distribution on the heating surfaces. We designed a multilayer structure of temperature sensitive paint (TSP) and transparent heating layer on a heat transfer surface to measure boiling heat transfer with high-speed visualization. A TSP layer containing a fluorescent material, platinum porphyrin (PtTFPP), was formed on a heat transfer surface, and a forced flow boiling experiment was conducted using HFE-7000 as the test fluid. The temperature of the heat transfer surface was visualized with a spatial resolution of 64 µm and measurement speed of 2 kHz under a mass velocity of 104 kg/(m2·s) and average heat flux of 96 kW/m2. We observed a high temperature area underneath the nucleated vapor bubbles on the heat transfer surface possibly due to heat transfer degradation caused by expansion of dry patches and a low temperature area around the vapor bubbles due to convective heat transfer in the liquid layer. We found that the temperature distribution at the bottom of the bubbles followed the growth and movement of the bubbles. In addition, we demonstrated that it is possible to quantitatively evaluate the unsteady heat transfer coefficient distribution when a dry zone is created at the bottom of large slug bubbles.

NIR-II J-Aggregated Pt(II)-Porphyrin-Based Phosphorescent Probe for Tumor-Hypoxia Imaging.

The luminescence of traditional phosphorescence-based hypoxia probes is limited to the visible and first near-infrared wavelength regions (<1000nm), which has defects of higher light scattering and lower penetration depth in contrast with the second near-infrared wavelength window (NIR-II, 1000-1700nm) for optical bioimaging. Herein, 5,15-bis(2,6-bis(dodecyloxy)phenyl)-porphyrin platinum(II) (PpyPt) with J-aggregation induced NIR-II phosphorescence is reported. J-aggregates of PpyPt are confirmed by the X-ray diffraction data in the crystalline state. Moreover, the emission and excitation spectra of PpyPt in the solid states reveal NIR-II luminescence feature of PpyPt in J-aggregates. More importantly, by preparation of water-soluble PpyPt nanoparticles (PpyPt NPs4.76 ) with J-aggregates, it has NIR-II phosphorescent lifetime of microseconds and good oxygen-sensitivity in water. Moreover, the good biological hypoxia-sensing potential of PpyPt NPs4.76 is demonstrated in cells and 4T1-tumor-bearing mice. This study provides an efficient strategy to design NIR-II phosphorescent probe for sensitive tumor-hypoxia detection through the construction of J-aggregates.

Optically Coupled PtOEP and DPA Molecules Encapsulated into PLGA-Nanoparticles for Cancer Bioimaging

Triplet-triplet annihilation upconversion (TTA-UC) nanoparticles (NPs) have emerged as imaging probes and therapeutic probes in recent years due to their excellent optical properties. In contrast to lanthanide ion-doped inorganic materials, highly efficient TTA-UC can be generated by low excitation power density, which makes it suitable for clinical applications. In the present study, we used biodegradable poly(lactic-co-glycolic acid) (PLGA)-NPs as a delivery vehicle for TTA-UC based on the heavy metal porphyrin Platinum(II) octaethylporphyrin (PtOEP) and the polycyclic aromatic hydrocarbon 9,10-diphenylanthracene (DPA) as a photosensitizer/emitter pair. TTA-UC-PLGA-NPs were successfully synthesized according to an oil-in-water emulsion and solvent evaporation method. After physicochemical characterization, UC-efficacy of TTA-UC-PLGA-NPs was assessed in vitro and ex vivo. TTA-UC could be detected in the tumour area 96 h after in vivo administration of TTA-UC-PLGA-NPs, confirming the integrity and suitability of PLGA-NPs as a TTA-UC in vivo delivery system. Thus, this study provides proof-of-concept that the advantageous properties of PLGA can be combined with the unique optical properties of TTA-UC for the development of advanced nanocarriers for simultaneous in vivo molecular imaging and drug delivery.

Optical and photophysical properties of platinum benzoporphyrins with C2v and D2h symmetry

Platinum(II) mono- and di-benzoporphyrins carrying either ester or imide peripheral groups have been successfully synthesized. These benzoporphyrins possessing C[Formula: see text] and D[Formula: see text] symmetry were investigated using a range of techniques including UV-Vis and phosphorescence spectroscopy, differential pulse voltammetry, and transient absorption spectroscopy covering wide spatial and temporal ranges. Up to three oxidation and three reductions within the accessible potential window of dichlorobenzene were observed. Facile reductions for both mono- and dibenzoporphyrin derivatives, more so with imide peripheral substituents were witnessed. Computational studies were supportive of push-pull type interactions within these molecular systems. The formation of triplet excited states within 5 ps after laser excitation was confirmed by femtosecond transient absorption studies. Nanosecond transient absorption studies coupled with phosphorescence lifetime studies revealed relatively rapid relaxation of the triplet excited states as compared to a controlled platinum porphyrin suggesting push-pull type interactions on a slower time scale.

Palladium(II) and Platinum(II) Porphyrin Donors for Organic Photovoltaics

Three new A-π-D-π-A structural porphyrin-based donors, C19-H2P, C19-PdP, and C19-PtP, are designed and synthesized, with porphyrin (D) moieties equipped with no metal, palladium (Pd), and platinum (Pt) as the core, respectively, and end-capped with electron-deficient 3-ethylrhodanine (A) via a π-bridge of phenylene ethynylene linker. C19-PdP and C19-PtP exhibit low-lying highest occupied molecular orbital levels than C19-H2P. The three porphyrin donors show highly intensified and broad absorptions at ca. 400–530 nm (Soret bands) and at ca. 550–800 nm (Q-bands) with an absorption valley at ca. 540 nm. Using PC71BM as an electron acceptor, the devices based on C19-PdP and C19-PtP donors achieve power conversion efficiencies (PCEs) of 8.09 and 7.31% under 1 Sun, respectively, whereas the C19-H2P device, that has no metal, has a very low PCE of 2.51%. Furthermore, at 300 lux LED source, the C19-PdP and C19-PtP devices deliver promising PCEs of 16.54 and 16.74%, respectively. The improved performance of C19-PdP- and C19-PtP-based devices is mainly due to more efficient charge collection, faster charge transport, more suppressed recombination behavior, and smoother surface morphology. These findings pave the way for the development of new metalloporphyrin-based donors for organic solar cells using simple structural engineering.

Singlet Oxygen Generation in Peripherally Modified Platinum and Palladium Porphyrins: Effect of Triplet Excited State Lifetimes and meso-Substituents on 1 O2 Quantum Yields.

A series of meso-substituted with aromatic (=tolyl, pyrenyl, fluorenyl, naphthyl, and triphenylamine) substituents, platinum (Pt), and palladium (Pd) porphyrins have been synthesized and characterized by spectroscopic and single-crystal X-ray diffraction studies to probe structure-reactivity aspects on the electrochemical redox potentials, and phosphorescence quantum yields and lifetimes. In the X-ray structures, the aromatic meso-substituents were rotated to some extent from the planarity of the porphyrin ring to minimize steric hindrance. Both Pt and Pd porphyrins revealed higher electrochemical redox gaps as compared to their free-base porphyrin analogs as a result of the harder oxidation and reduction processes. The ability of both Pt and Pd porphyrins to generate singlet oxygen was probed by monitoring the photoluminescence of 1 O2 at 1270 nm. Higher quantum yields for both triplet sensitizers compared to their free-base analogs were witnessed. Singlet oxygen quantum yields close to unity were possible to achieve in the case of Pt and Pd porphyrins bearing triphenylamine substituents at the meso-position. The present study brings out the importance of different meso-substituents on the triplet porphyrin sensitizers in governing singlet oxygen quantum yields; a key property of photosensitizers needed for photodynamic therapy, chemical synthesis, and other pertinent applications.

Response to the comment on: “Dissolved oxygen sensing characteristics of plastic optical fiber coated with hydrogel film” – The wider context of fibre optic oxygen sensing

In, F. Formenti (2021) proposed that ruthenium complexes, as an unsafe and toxic material, are not suitable for clinical applications and indicated that platinum porphyrin has been clinically applied to optical fiber oxygen sensors with short response time. This article will answer the questions raised by F. Formenti from the following aspects: 1.The toxicity of ruthenium complexes was overestimated. This article will briefly outline some biomedical applications based on ruthenium. 2. Hydrogels have been used in different biomedicine purpose, the ruthenium indicator in this article [2] will not leak from the polymer network structure hydrogel. 3. The response time in this article [2] is shorter than reported and the sensing system [2] has other excellent properties.

Comment on: “Dissolved oxygen sensing characteristics of plastic optical fiber coated with hydrogel film” – The wider context of fibre optic oxygen sensing

A recently published article by Bian et al. (2021) presents a novel plastic optical fibre coated with hydrogel film to measure dissolved oxygen via luminescence quenching. The article concludes that “The sensor with biocompatible material is expected to be applied to the monitor of dissolved oxygen in the domain of biomedicine”. However, the oxygen sensor presented contains ruthenium, a toxic material that is considered unsafe for clinical applications. It is unclear whether the hydrogel film coating may be sufficient to prevent direct contact between ruthenium and human tissue in clinical applications. However, platinum porphyrin has been used in fibre optic oxygen sensors in pre-clinical applications. This Comment article provides a brief overview of some platinum porphyrin-based fibre optic oxygen sensors that, despite an advanced degree of maturity and biocompatibility, were overlooked in the recently published article.

A stable platinum porphyrin based photocatalyst for hydrogen production under visible light in water

A stable system containing a Pt metalated porphyrin as a molecular solid photocatalyst in acidic aqueous solution is able to produce hydrogen efficiently, under visible light irradiation.

Investigation of powerful fungicidal activity of tetra-cationic platinum(II) and palladium(II) porphyrins by antimicrobial photodynamic therapy assays

This manuscript reports enhanced antimicrobial photoinactivation using tetra-cationic porphyrins with peripheral platinum(II) and palladium(II) complexes against fungal dermatophyte strains. Six different positively charged porphyrins were used and applied in antimicrobial photodynamic therapy experiments (aPDT) against dermatophyte fungi colonies. The microbiological tests were conducted with an adequate concentration of photosensitizer (PS) under white-light irradiation for 120 min and the most effective PS meta isomer 3PtP significantly reduced the concentration of viable fungal colony. In this way, tetra-cationic porphyrins containing platinum(II)-bipyridyl complexes may be promising fungicidal aPDT agents with potential applications in future clinical cases.

Synthesis, Structure, Photophysics, and Singlet Oxygen Sensitization by a Platinum(II) Complex of Meso‐Tetra‐Acenaphthyl Porphyrin

AbstractA new platinum(II) porphyrin complex has been synthesized and characterized via various spectroscopic techniques. Single‐crystal XRD analysis reveals that the geometry around the Pt(II) center is near the perfect square planar geometry. The Pt(II)−N bond distances are in the ranges of 2.005 Å–2.020 Å. The platinum(II) porphyrin derivative exhibited one reversible oxidative couple at +1.10 V and a reversible reductive couple at −1.47 V versus Ag/AgCl. In deaerated dichloromethane solution at 298 K, a strong phosphorescence is observed at 660 nm, with emission quantum yield of 35 % and lifetime of 75 μs. Upon excitation of the acenaphthene chromophores at 300 nm, sensitised phosphorescence of the Pt(II) porphyrin is observed with a unitary efficient energy transfer, demonstrating that this system behaves as a light harvesting antenna. The red phosphorescence is strongly quenched by oxygen, resulting in singlet oxygen production with a very high quantum yield of 88 %. This result indicates that this Pt(II) porphyrin is an excellent photosensitizer for the production of singlet oxygen and will have potential applications in the field of photodynamic therapy as well as oxygen sensors.

An Exemplary Gay Scientist and Mentor: Martin Gouterman (1931-2020).

Martin Gouterman (1931-2020) was one of the foundational figures of modern porphyrin science. After completing his Ph.D. at The University of Chicago in 1958, he joined Harvard, where he developed his eponymous four-orbital model. In 1966, he moved to the University of Washington Seattle (UW). Here he came out as gay and helped set up Seattle's first gay rights group, the Dorian Society. At UW, Gouterman accomplished an "optical taxonomy" of the major classes of porphyrin derivatives and pioneered pressure-sensitive paints based on phosphorescent platinum porphyrins to map the partial pressure of oxygen on airplane wings. Revered by his students and co-workers for his brilliant yet gentle advising, Gouterman remains a beacon for a more humane and inclusive scientific enterprise.

An Exemplary Gay Scientist and Mentor: Martin Gouterman (1931–2020)

AbstractMartin Gouterman (1931–2020) was one of the foundational figures of modern porphyrin science. After completing his Ph.D. at The University of Chicago in 1958, he joined Harvard, where he developed his eponymous four‐orbital model. In 1966, he moved to the University of Washington Seattle (UW). Here he came out as gay and helped set up Seattle's first gay rights group, the Dorian Society. At UW, Gouterman accomplished an “optical taxonomy” of the major classes of porphyrin derivatives and pioneered pressure‐sensitive paints based on phosphorescent platinum porphyrins to map the partial pressure of oxygen on airplane wings. Revered by his students and co‐workers for his brilliant yet gentle advising, Gouterman remains a beacon for a more humane and inclusive scientific enterprise.