platinum(II) Octaethylporphyrin Research Articles

Triplet–triplet annihilation-based photon-upconversion to broaden the wavelength spectrum for photobiocatalysis

Photobiocatalysis is a growing field of biocatalysis. Especially light-driven enzyme catalysis has contributed significantly to expanding the scope of synthetic organic chemistry. However, photoenzymes usually utilise a rather narrow wavelength range of visible (sun)light. Triplet–triplet annihilation-based upconversion (TTA-UC) of long wavelength light to shorter wavelength light may broaden the wavelength range. To demonstrate the feasibility of light upconversion we prepared TTA-UC poly(styrene) (PS) nanoparticles doped with platinum(II) octaethylporphyrin (PtOEP) photosensitizer and 9,10-diphenylanthracene (DPA) annihilator (PtOEP:DPA@PS) for application in aqueous solutions. Photoexcitation of PtOEP:DPA@PS nanoparticles with 550 nm light led to upconverted emission of DPA 418 nm. The TTA-UC emission could photoactivate flavin-dependent photodecarboxylases with a high energy transfer efficiency. This allowed the photodecarboxylase from Chlorella variabilis NC64A to catalyse the decarboxylation of fatty acids into long chain secondary alcohols under green light (λ = 550 nm).

Triplet‐Triplet Annihilation Up‐Conversion Luminescent Assisted Free‐Radical Reactions of Polymers Using Visible Light

AbstractDue to low penetration ability of ultraviolet (UV) light, UV‐induced free radical reactions of polymers are limited to the preparation of thin‐layer materials such as coatings and inks. Although upconversion (UC) nanomaterials that can be excited by near‐infrared (NIR) light and emit UV light which is used to achieve polymerization or curing of monomers or prepolymers, low quantum efficiency and high excitation threshold limit their applications. Here, triplet‐triplet annihilation up‐conversion luminescent (TTA‐UCL) chromophores of platinum (II) octaethylporphyrin (PtOEP) and 9,10‐diphenylanthracene (DPA) are used to realize TTA‐UCL‐assisted photoinitiated polymerization of butyl acrylate (BA) and ethoxylated trimethylolpropane triacrylate (ETPTA) as well as photo curing of polyurethane acrylates (PUA) using visible light at 520 nm. The effects of chromophores concentrations and incident light power density on double‐bond conversion rate are investigated. The results show that a mediate TTA‐UCL chromophore concentration of 0.02% is beneficial for polymerization of ETPTA‐co‐BA with thickness of 25 mm within 15 min. Satisfied adhesion of colored plastic substrates using PUA prepolymers can be achieved after irradiation for 30 s when chromophore concentration of 0.1% is used. TTA‐UCL assisted photoinitiated reactions show great potential in engineering aspects including quick repair of leaking tubes and photocuring of adhesives underwater.

A highly sensitive and flexible photonic crystal oxygen sensor

Oxygen sensing attracts high research interest because it is applicable to early diagnosis and health monitoring. Herein, based on photonic crystals (PCs), a novel fluorescence enhancement effect (FEE) was explored to achieve highly sensitive and accurate oxygen detection. A flexible oxygen sensor was fabricated from heterogeneous polydimethylsiloxane (PDMS) and polystyrene (PS) PCs embedded with platinum(II) octaethylporphyrin (PtOEP) oxygen-sensitive dye. Two different fluorophore incorporation (PtOEP-in and PtOEP-out) PCs were compared in terms of their FEE and oxygen-sensing performance. Simultaneously, photoluminescence enhancement was experimentally and theoretically examined and was determined to be the main factor in improving the performance of the oxygen sensor. In particular, the optimized PC oxygen sensor showed a 12-fold higher PL intensity than PS microspheres (control group). Moreover, the optimized sensor demonstrated high sensitivity to oxygen, with excellent accuracy, photostability and flexibility. This work is expected to provide a universal route to design flexible PC sensors for health monitoring through fluorescent ultratrace detection.

Active-Targeting Polymeric Dual Nanosensor for Ratiometrically Measuring Proton and Oxygen Concentrations in Mitochondria

Dysfunction of mitochondria is closely related to neurodegenerative diseases, heart diseases, cancers, and so on. Because both proton and oxygen participate in vital biochemical reactions occurring in mitochondria such as adenosine triphosphate (ATP) generation, measuring proton and oxygen concentrations in mitochondria is therefore crucial for monitoring mitochondria activities and understanding cellular behavior. For this purpose, we developed a ratiometric fluorescent nanosensor for simultaneously sensing and imaging O2 and pH in mitochondria. The steps are as follows: (1) Styrene was copolymerized with 2-aminoethyl methacrylate hydrochloride to produce amino-functionalized polymer nanoparticles. (2) The reference dye rhodamine B isothiocyanate (RBITC) and oxygen-sensitive dye platinum(II) octaethylporphyrin (PtOEP) were encapsulated into a polymer sphere during polymerization, while the pH indicator fluorescein isothiocyanate (FITC) and mitochondrial-targeting molecule (3-carboxypropyl)triphenylphosphonium bromide (TPP) were further modified on the surface of the nanoparticles. The developed nanosensor shows a narrow distribution of particle size, high sensitivity toward O2 and pH, excellent stability, and low cytotoxicity. These remarkable features of the dual nanosensor render them capable of real-time sensing and imaging of O2 and pH in mitochondria with high spatial resolution. Applying the mitochondrial-targeted dual nanosensor in HeLa cells, we quantitatively measured and imaged mitochondrial proton and oxygen concentration variations after carbonyl cyanide m-chlorophenylhydrazone (CCCP) treatment.

Synergetic effect of silver nanoplate and magnetic field on photon upconversion based on sensitized triplet–triplet annihilation in polymer system

Effects of silver nanoplate (AgPL) and magnetic field on photon upconversion based on sensitized triplet–triplet annihilation (PUC-TTA) were examined in the system of platinum(II) octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA), when AgPLs were incorporated into polymer thin films containing PtOEP and DPA. In the presence of AgPL, the PUC emission intensity increased as compared with that in the absence of AgPL. The result is most likely attributable to the localized surface plasmon resonance of AgPL. On the other hand, in the absence of AgPL, the PUC emission intensity decreased in the presence of magnetic field, while in the presence of AgPL, the PUC emission intensity increased drastically in the presence of magnetic field. The synergetic effect of AgPL and magnetic field on the PUC emission intensity in PUC-TTA was observed for the first time.

Europium-based luminescent sensors for mapping pressure distribution on surfaces

An apparatus for measuring the effect of pressure on luminescence characteristics of molecular sensors was designed and constructed. Next, the apparatus was applied for studies of the effect of pressure on luminescence of a series of europium(III) complexes. The following Eu(III) complexes were evaluated as potential pressure sensors for pressure sensitive paints: tris[4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dionyl]europium(III), [2-(2-pyridyl)imidazo[1,2-a]pyridine]tris[4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dionyl]europium(III), (2,2′-bipyridine)tris[4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dionyl]-europium(III), [4-phenyl-2,6-bis(2-pyridyl)pyridine]tris[4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dionyl]europium(III), tris[4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dionyl]bis(trioctylphosphine oxide)europium(III) and tris[4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dionyl]bis(tributylphosphine oxide)europium(III). These complexes were incorporated into polyacrylic or silicone polymer matrices and their sensitivity to pressure in the presence or absence of an inert solvent was measured. It was found that the luminescence intensity of the compositions studied decreased with increase of pressure. The complexes containing pyridine derivatives as auxiliary ligands showed highest sensitivity to pressure, when incorporated into the silicone polymer matrix containing toluene absorbed within the polymer structure. That sensitivity was of the order 50%/bar at atmospheric pressure, which was comparable to the sensitivity of platinum(II) octaethylporphyrin (PtOEP) sensor in a similar silicone polymer. However, the PtOEP was usually used for preparation of pressure-sensitive paints, which worked by oxygen-quenching mechanism, while the Eu(III) complexes do not require presence of oxygen to work.

Absolute Method to Certify Quantum Yields of Photon Upconversion via Triplet-Triplet Annihilation.

For the consistent development of the field of photon upconversion via triplet-triplet annihilation (TTA-UC), it is pivotal to know the true quantum yield of TTA-UC emission. Although TTA-UC quantum yields have been determined by common relative measurements using quantum yield standards, there is still a discrepancy between the reported values even for the benchmark sensitizer-emitter pair of platinum(II) octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA). Here, to resolve this situation, we show a method to obtain the absolute quantum yield of TTA-UC photoluminescence. The difficulty in obtaining absolute TTA-UC quantum yield by the integrating sphere measurement is to accurately calibrate the contribution of reabsorbed upconverted emission by triplet sensitizers. The reabsorption correction is successfully carried out by comparing sensitizer phosphorescence with and without the integrating sphere. An absolute TTA-UC quantum yield of the PtOEP-DPA pair is obtained as 36%, which shows a good agreement with the relative TTA-UC quantum yield. An absolute TTA-UC quantum yield of another red-to-blue TTA-UC pair, platinum(II) meso-tetraphenyltetrabenzoporphyrin (PtTPBP) and 2,5,8,11-tetra-tert-butylperylene (TTBP), is obtained as 27%. These absolute TTA-UC quantum yields can be used as certified values to check the measurement setup and sample condition for determining relative TTA-UC quantum yields in each laboratory.

Kinetically controlled crystal growth approach to enhance triplet energy migration-based photon upconversion

Improving efficiency of triplet–triplet annihilation-based photon upconversion (TTA-UC) in crystalline media is challenging because it usually suffers from the severe aggregation of the donor (sensitizer) molecules in acceptor (emitter) crystals. We show a kinetically controlled crystal growth approach to improve donor dispersibility in acceptor crystals. As the donor–acceptor combination, a benchmark pair of platinum(II) octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA) is employed. A surfactant-assisted reprecipitation technique is employed, where the concentration of the injected PtOEP–DPA solution holds the key to control dispersibility; at a higher PtOEP–DPA concentration, a rapid crystal growth results in better dispersibility of PtOEP molecules in DPA crystals. The improvement of donor dispersibility significantly enhances the TTA-UC quantum yield. Thus, the inherent function of donor-doped acceptor crystals can be maximized by controlling the crystallization kinetics.

Effect of gold nanoparticle on photon upconversion based on sensitized triplet–triplet annihilation in polymer films

ABSTRACTEffect of gold nanoparticle (AuNP) on photon upconversion based on sensitized triplet-triplet annihilation (PUC-TTA) were examined in the system of platinum(II) octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA), when AuNPs were incorporated into polymer thin films containing PtOEP and DPA. The enhancements of the upconversion fluorescence from DPA and the phosphorescence of PtOEP were observed in the presence of AuNP. The enhancements were varied with AuNP loading and the maximum of enhancements was obtained at the AuNP loading (3.0%). The enhancements of PUC-TTA are most likely attributable to large electric fields due to localized surface plasmon resonance of AuNP.

CdS/Pt photocatalytic activity boosted by high-energetic photons based on efficient triplet–triplet annihilation upconversion

We herein report the triplet–triplet annihilation upconversion luminescence (TTA-UCL) clusters achieved by loading the platinum(II)-octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA) into silica shells. This aqueous-based system possesses a core–shell structure which is of crucial importance for enhancing the mobility of core liquid. The encapsulated clusters with efficient green-to-blue upconversion without deoxygenation are conjoined with cadmium sulfide (CdS) as the photocatalyst. Platinum (Pt) is used to improve the separation of electron−hole pairs on the photocatalytic system. Given the band gap of photocatalysts, tetracycline (TC) degradation and photoinduced hydrogen evolution are used to perform the photocatalytic activity. CdS loaded with Pt has higher Pseudo-first-order rate constant (kpfo) in decomposing tetracycline than pure CdS. Moreover, the excellent hydrogen evolution property appears when the converted high energy photons from TTA-UCL-based clusters are introduced to the photocatalytic system. The quantum efficiency of hydrogen evolution increases further after the cocatalyst Pt deposition. This work not only fabricates an encapsulated structure for TTA-UCL clusters, but also provides an effective TTA-supported upconversion-photocatalysis system.

Luminescent oxygen sensors with highly improved sensitivity based on a porous sensing film with increased oxygen accessibility and photoluminescence

In this study, we present the effects of the morphological modification of an oxygen-sensing film on improving the sensitivity of luminescent oxygen sensors. Pores were made inside the volume and on the external surface of the oxygen-sensing film consisting of platinum(II) octaethylporphyrin (PtOEP) oxygen-sensitive dye embedded in a polystyrene (PS) polymer matrix. The size of the pores with diameters from 300nm to 1μm was controlled through the phase separation of the ternary system of PS, polyethylene glycol (PEG), and chloroform. Photoluminescence (PL) intensity and oxygen accessibility of the oxygen-sensing film were considered the main factors affecting the sensitivity of the sensors. PL intensity was analyzed through the diffused reflectance and absorbance of the oxygen-sensing film. Oxygen accessibility was analyzed based on the Langmuir-Hill absorption theory by considering the sensitivity saturation behaviors of the oxygen-sensing film above the excitation light source intensity of 1000cd/m2. The optimized porous-structured oxygen-sensing film showed 61% higher sensitivity than the solid oxygen-sensing film. According to the measurement results, the sensitivity enhancement in the porous sensing film was significantly more driven by the increase in oxygen accessible sites than the increase in PL intensity. Furthermore, the sensing film with pores only on its external surface and not inside its volume showed 72% enhanced sensitivity relative to the solid sensing film. Therefore, the external surface area of the sensing film affects the sensitivity of the oxygen-sensing film significantly more than the pores inside the volume of the sensing film because the external surface acts as an oxygen diffusion barrier that limits the amount of oxygen that can access the oxygen-sensitive dye embedded in the polymer matrix.

Photochemical Upconversion in Silicone Core/Silica Shell Nanoparticles

We report a thorough investigation of triplet–triplet annihilation upconversion (TTA-UC) in the silicone core/silica shell hollow nanoparticles (SSNPs). The results demonstrate that Platinum(II) octaethylporphyrin (PtOEP) and 9, 10-diphenylanthracene (DPA) were successfully captured in the hollow particles. It was also observed that TTA upconversion intensity from SSNPs increases with the concentration of DPA increasing. The mobility of chromophores was improved by the liquid core of the SSNPs, leading to the increasing of TTA-UC intensity. These results shed light onto the strategies to construct TTA-UC systems in solid substrates.

Effect of the Formation of Highly Ordered Platinum(II) Octaethylporphyrin Adlayer on the Surface Reconstruction of Gold and Supramolecular Assembly of Fullerenes

The structures of 2D molecular assemblies of platinum(II) octaethylporphyrin (PtOEP) on Au(111) and Au(100) surfaces were examined using in situ scanning tunneling microscopy (STM) in 0.05 M HClO4 solutions. The in situ STM observations revealed that the reconstructed rows of Au(111) and Au(100) were stabilized through the formation of highly ordered arrays by adsorption of PtOEP in a wide potential range of the electric double-layer region and that the PtOEP overlayer expanded the stable potential range for the reconstructed phase. Furthermore, the supramolecular assembly of C60 and C84 on a highly ordered PtOEP adlayer formed on Au(111) surfaces was investigated. STM images revealed site-selective supramolecular assembly of fullerenes, especially C84, which exhibited a low coverage on the PtOEP adlayer. C60 molecules exhibited a full coverage and formed highly ordered adlayers on PtOEP, whereas C84 exhibited disordered arrays. The results of this study showed that the strong π-electron donation by the PtOEP molecules stabilized the reconstructed rows of single-crystal Au planes and that the PtOEP adlayer acted as a strong electron-donating layer, aiding the formation of supramolecularly assembled C60 molecules.

Regulation of responsiveness of phosphorescence toward dissolved oxygen concentration by modulating polymer contents in organic–inorganic hybrid materials

Platinum(II) octaethylporphyrin (PtOEP)-loaded organic–inorganic hybrids were obtained via the microwave-assisted sol–gel condensation with methyltrimethoxysilane and poly(vinylpyrrolidone). From transparent and homogeneous hybrid films, the strong phosphorescence from PtOEP was observed. Next, the resulting hybrids were immersed in the aqueous buffer, and the emission intensity was monitored by changing the dissolved oxygen level in the buffer. When the hybrid with relatively-higher amount of the silica element, the strong phosphorescence was observed even under the aerobic conditions. In contrast, the emission from the hybrids with lower amounts of the silica element was quenched under the hypoxic conditions. This is, to the best of our knowledge, the first example to demonstrate that the responsiveness of the phosphorescence intensity of PtOEP in hybrid films to the dissolved oxygen concentration in water can be modulated by changing the percentage of the contents in the material.

RGB color ratiomatric planar optode로 측정한 표층 퇴적물의 2차원 산소 분포

We measured two-dimensional (2-D) oxygen distribution in the surface sediment layer of intertidal sediment using a simple and inexpensive planar oxygen optode, which is based on a color ratiometric image approach. The recorded emission intensity of red color luminophore light significantly changed with oxygen concentration by O₂ quenching of platinum(II)octaethylporphyrin (PtOEP). The ratios between the intensity of red and green emissions with oxygen concentration variation demonstrated the Stern-Volmer relationship. The 2-D oxygen distribution image showed microtopographic structure, diffusivity boundary layer and burrow in surface sediment layer. The oxygen penetration depth (OPD) was about 2 mm and the one-dimensional vertical diffusive oxygen uptake (DOU) was 12.6 mmol m -2 d -1 in the undisturbed surface sediment layer. However, those were enhanced near burrow by benthic fauna, and the OPD was two times deeper and DOU was increased by 34%. The simple and inexpensive oxygen planar optode has great application potential in the study of oxygen dynamics with high spatiotemporal resolution, in benthic boundary layers.

Anchoring Energy Acceptors to Nanostructured ZrO2 Enhances Photon Upconversion by Sensitized Triplet–Triplet Annihilation Under Simulated Solar Flux

Photon upconversion by sensitized triplet–triplet annihilation (UC-STTA) is a promising strategy for boosting the theoretical maximum efficiency of single threshold solar cells, in particular, dye-sensitized solar cells (DSSCs). Here, we report a substantial increase in the efficiency of UC-STTA on a nanostructured surface, using noncoherent excitation light with intensities as low as 0.5 mW cm–2, easily achieved under sun illumination. The studied surface was a mesoporous ZrO2 film working as a proxy system for the study of photophysics relevant to DSSCs. A well-known UC-STTA “emitter” dye, 9,10-diphenylanthracene (DPA), was chemically modified to yield methyl 4-(10-p-tolylanthracen-9-yl)benzoate (MTAB), which was chemisorbed onto ZrO2. The “sensitizer” dye, platinum(II) octaethylporphyrin (PtOEP), was free in butyronitrile (BuN) solution surrounding the ZrO2 nanostructure. A rigorous oxygen removal minimized photodegradation of the dyes and enhanced triplet–triplet annihilation efficiency. The system already approaches the so-called “strong annihilation limit” at light intensities below 8 mW cm–2. Highly efficient triplet–triplet annihilation is a requisite for the use of UC-STTA in DSSCs. Time-resolved data show that the limiting process in the UC-STTA mechanism of the present system is the dynamic triplet energy transfer step from PtOEP in solution to MTAB on the surface of ZrO2. This result can guide the way toward a better understanding and further efficiency improvement of UC-STTA on nanocrystalline metal oxides.

A simple and inexpensive high resolution color ratiometric planar optode imaging approach: application to oxygen and pH sensing.

A simple, high resolution colormetric planar optode imaging approach is presented. The approach is simple and inexpensive yet versatile, and can be used to study the two‐dimensional distribution and dynamics of a range of analytes. The imaging approach utilizes the inbuilt color filter of standard commercial digital single lens reflex cameras to simultaneously record different colors (red, green, and blue) of luminophore emission light using only one excitation light source. Using the ratio between the intensity of the different colors recorded in a single image analyte concentrations can be calculated. The robustness of the approach is documented by obtaining high resolution data of O2 and pH distributions in marine sediments using easy synthesizable sensors. The sensors rely on the platinum(II)octaethylporphyrin (PtOEP) and lipophilic 8‐Hydroxy‐1,3,6‐pyrenetrisulfonic acid trisodium (HPTS) salt derivate for O2 and pH measurements, respectively. The brightness of both indicators is dramatically enhanced by making use of energy transfer from a donor molecule (Macrolex yellow coumarin). Furthermore, the emission from the donor serves as an internal reference for the O2 sensor. The approach relies on semitransparent sensors, facilitating visual inspection of the sediment behind the sensors during measurements. Software for data acquisition and calibration will be available from the authors, whereas all hardware is available from a range of commercial sources. The total cost of the complete measuring system is approximately $3000 US.

Electron-Exchange-Assisted Photon Energy Up-Conversion in Thin Films of π-Conjugated Polymeric Composites

The mechanism of triplet–triplet annihilation (TTA)-induced up-converted (UC) delayed luminescence is studied in two different binary organic systems consisting of platinum(II) octaethyl porphyrin (PtOEP) mixed with either poly(fluorene) (PF26) or ladder-type pentaphenylene (L5Ph). Cyclic voltammetry and differential pulse voltammetry are employed for estimating the ionization potentials of PtOEP and L5Ph. Delayed luminescence spectroscopy sets the energy of the lowest excited triplet state of L5Ph 0.20 eV higher than the triplet state of PtOEP (1.90 eV). The different phosphorescence PtOEP lifetime indicates differences in PtOEP aggregation in the polymer matrices. The presented results propose that the difference in the relative intensities of the delayed UC luminescence is determined by the difference between the ionization potentials of PtOEP and the polymer matrix. In the solid state, the electric-field-induced quenching of the delayed L5Ph UC luminescence suggests the formation of an intermediate charge-transfer state after the TTA within the PtOEP domains.

Theoretical study of phosphorescence in dye doped light emitting diodes

Phosphorescence of platinum(II) octaethyl porphyrin (PtOEP), which has been used in organic light emitting diodes to overcome the efficiency limit imposed by the formation of triplet excitons, is studied by time-dependent (TD) density functional theory (DFT). The spin-orbit coupling (SOC) effects and the phosphorescence radiative lifetime (tau(p) (r)), calculated by the TD DFT method with the quadratic response technique, are analyzed for a series of porphyrins in order to elucidate the internal heavy atom effect on tau(p) (r). While the significance of the d(pi) orbital admixture into the lowest unoccupied molecular orbital e(g)(pi(*)), proposed by Gouterman et al. [J. Chem. Phys. 56, 4073 (1972)], is supported by our SOC calculations, we find that the charge-transfer (CT) mechanism is more important; the CT state of the (3)A(2g) symmetry provides effective SOC mixing with the ground state, and a large (3)A(2g)-(3)E(u) transition dipole moment gives the main contribution to the radiative phosphorescence rate constant. The IR and Raman spectra in the ground state and first excited triplet state (T(1)) are studied for proper assignment of vibronic patterns. An orbital angular momentum of the T(1) state is not quenched completely by the Jahn-Teller effect. A large zero-field splitting is predicted for PtP and PtOEP which results from a competition between the SOC and Jahn-Teller effects. A strong vibronic activity is found for the e(g) mode at 230 cm(-1) in PtP phosphorescence which is shifted to 260 cm(-1) in PtOEP. This out-of-plane vibration of the Pt atom produces considerable change of the SOC mixing. The role of charge-transfer state of d(pi)pi(*) type is stressed for the explanation of the electroluminescent properties of the dye doped light emitting diode.

Electrogenerated chemiluminescence of the platinum (II) octaethylporphyrin/tri- n-propylamine system

The electrogenerated chemiluminescence (ECL) of platinum (II) octaethyl-porphyrin (PtOEP) in acetonitrile:methylene chloride (CH 3CN:CH 2Cl 2, 50:50 v/v) and CH 2Cl 2 is reported. ECL was generated upon sweep to positive potentials using tri- n-propylamine (TPrA) as an oxidative–reductive coreactant. ECL efficiencies ( ϕ ecl) of 0.18 in CH 3CN:CH 2Cl 2 (50:50 v/v) and 3.90 in methylene chloride were obtained using Ru(bpy) 3(PF 6) 2 (bpy = 2,2′-bipyridine) as a relative standard ( ϕ ecl = 1). The ECL intensity peaks at a potential corresponding to oxidation of PtOEP and TPrA, and ECL emission spectra are nearly identical to photoluminescence emission spectra, indicating that emission is from the PtOEP triplet state.