Platinum Porphyrin Research Articles

Tunable Fluorescent/Phosphorescent Platinum(II) Porphyrin–Fluorene Copolymers for Ratiometric Dual Emissive Oxygen Sensing

A series of new platinum(II) 5,15-bis(pentafluorophenyl)-10,20-bis(phenyl)porphyrin-9,9-dioctylfluorene copolymers, in which the relative intensities of the blue fluorescence and red phosphorescence can be easily tuned by the initial feed ratio of the two monomers or energy transfer between the fluorescent and phosphorescent units, have been designed and prepared for the application in ratiometric dual emissive oxygen sensing. To the best of our knowledge, this is the first example of a ratiometric oxygen sensor based on dual fluorescent/phosphorescent polymers or copolymers containing transition-metal complexes. It also provides an alternative and easy way to achieve dual emissive oxygen sensing.

Highly efficient conversion of aldehydes to carboxylic acid in the presence of platinum porphyrin sensitizers, air and sunlight

A variety of aromatic and aliphatic aldehydes were oxidized to the corresponding carboxylic acids in the presence of platinum porphyrin, sunlight and air in acetonitrile solvent under mild conditions. Nitrobenzaldehydes were found to be very efficient 1O2 scavengers that quench the formation of acids from any aldehyde in the presence of free-base porphyrin sensitizers. However, nitrobenzaldehydes were converted to the corresponding acids in the presence of platinum porphyrins. The platinum porphyrins are very good and efficient catalysts for a wide range of applications in the aerobic conversion of aldehydes to acids.

Extended Conjugation Platinum(II) Porphyrins for use in Near-Infrared Emitting Organic Light Emitting Diodes

A family of π-extended platinum(II) porphyrins has been synthesized and incorporated into solution processed polymer light emitting diodes (PLEDs) and vapor deposited multilayer organic light emitting diodes (OLEDs), giving rise to devices with peak emission ranging from 771 to 1005 nm. The longest wavelength emitter, platinum(II)-5,10,15,20-(3,5-di-tert-butylphenyl)tetraanthroporphyrin (Pt-Ar4TAP), shows an emission maximum at 1005 nm, an external quantum efficiency (EQE) of 0.12%, and a maximum radiant emittance (Rmax) of 0.23 mW/cm2 in single layer PLED architectures, which is enhanced to an EQE of 0.20% with an Rmax of 0.57 mW/cm2 upon vapor deposition of an electron transport layer. In an effort to understand substituent effects and enhance the performance of π-extended Pt-porphyrins in PLEDs and OLEDs, a family of Pt-tetrabenzoporphyrins (Pt-TBPs) with varying functionality was investigated. The luminescent lifetimes of the Pt-TBPs in solution and in films were measured, and a strong correlation was demonstrated between the film lifetimes and the PLED and OLED efficiencies. An improvement in external quantum efficiency (EQE) from 2.07 to 2.49% for PLEDs and from 8.0 to 9.2% for OLEDs was observed between the less substituted Pt-tetraphenyltetrabenzoporphyrin and the more substituted Pt-5,10,15,20-(3,5-di-tert-butylphenyl)tetrabenzoporphyrin. The PLED EQEs were further enhanced to 3.02% with the disubstituted Pt-5,15-(3,5-di-tert-butylphenyl)tetrabenzoporphyrin; however, this increase was not observed for the OLEDs where an EQE of 7.8% was measured.

Photophysical Properties of Near-Infrared Phosphorescent π-Extended Platinum Porphyrins

A comprehensive photophysical study is reported on a family of π-extended platinum(II) porphyrin complexes. The platinum(II) complexes are synthesized from the corresponding free base porphyrins by treatment with platinum(II) acetate in hot benzonitrile, affording the complexes in considerably higher yield than by reaction with platinum(II) chloride. A quantitative study of the absorption and luminescence properties of the metalloporphyrins is presented. A series including tetraarylbenzo-, tetraarylnaphtho-, and tetraarylanthroporphyrin exhibits efficient phosphorescence at 773, 890, and 1020 nm in the near-infrared region, with quantum yields of 0.35, 0.15, and 0.08, respectively. The triplet lifetimes and phosphorescence yields decrease with increasing emission wavelength, consistent with energy gap law behavior. A set of six Pt-tetrabenzoporphyrins (TBPs) with different meso-substituents were examined. The Pt-TBPs exhibit efficient phosphorescence with λmax ∼ 770 nm and with a quantum yield ranging from 0.26–0.49, depending on the substitution pattern. The results show that the 5,15-diarylbenzoporphyrins feature 50–60% higher phosphorescence emission yield compared to the 5,10,15,20-tetraarylbenzoporphyrins. The highest phosphorescence quantum efficiency is observed for a platinum(II) 5,15-diarylbenzoporphyin which emits at 770 nm with a quantum yield of 49%.

Saturated red polymer electrophosphorescent devices with meso-tetrakis (4-n-decanoyl-phenyl) porphyrin platinum (Ⅱ) complex as emitters

在聚2,7-（9,9-二辛基）芴（PFO）和30%的2-（对联苯基）-5-（对叔丁基苯基）-1,3,4-二唑（PBD）主体材料中掺杂短磷光寿命的meso-四（对正葵酰氧基苯基）卟啉铂（TDPPPt）,制成聚合物基发光器件。器件结构为：ITO/PEDOT∶PSS/PVK/PFO＋30%PBD∶TDPPPt/Ca/Al（ITO：氧化铟锡;PEDOT：聚3,4-乙撑二氧噻吩;PSS：聚苯乙烯磺酸盐;PVK：聚乙烯基咔唑）。当客体掺杂浓度≥3%时,器件给出饱和的红色发射。当驱动电压从7 V升高至14 V时,器件发光色度保持不变,CIE（国际发光照明委员会）色坐标稳定在（0.66,0.28）左右。器件的最大亮度和电流效率分别为1 390 cd/m2和1.34 cd/A。在电流密度100×10-3和150×10-3 A/cm2时,电流效率分别为1.18和0.99 cd/A,器件在高电流密度下具有良好的稳定性。

Synthesis and aggregation behavior of a novel water-soluble porphyrin platinum(II) terpyridine complex

A new water soluble tetranuclear platinum(II) porphyrin complex cation has been synthesized through the coordination of four [ Pt (2,2′:6′,2″-terpyridine)] moieties to the pyridyl groups of 5,10,15,20-tetrakis(4-pyridyl)-21H,23H-porphine (TPyP). The porphyrin derivative has been fully characterized by a combination of spectroscopic techniques. The high positive charge of the complex cation (8+) inhibits the aggregation in aqueous solution at low concentrations. By increasing the ionic strength, the electrostatic repulsion is screened leading to the formation of large unstable aggregates. The formation of microsized globular objects still emissive on the solid state is easily achieved by simple evaporation from diluted solutions. The solubilization of the complex in anionic aqueous surfactant solutions (sodium dodecyl sulfate, SDS) has revealed the inclusion of the complex ion in the hydrophobic region of the micelles as a monomeric species. Kinetics of Cu(II) insertion into the free-base tetranuclear Pt(II) porphyrin complex have been carried out in micellar media and the rate constants have been determinated.

Platinum (II) porphyrin-containing thermoresponsive poly( N-isopropylacrylamide) copolymer as fluorescence dual oxygen and temperature sensor

A random copolymer, poly(NIPAAm- co-PtPorphyrin), consisting of N-isopropylacrylamide (NIPAAm) and platinum (II) porphyrin units, behaves as an optical dual sensor for oxygen and temperature. The dual sensor is designed by incorporating an oxygen-sensitive platinum (II) porphyrin ( M1) into a temperature-sensitive polymer (PNIPAAm). The polymer exhibited low critical solution temperature (LCST) property at 31.5 °C. This LCST affected the polymer's aggregation status, which in turn affected the nanostructures, fluorescence intensities, and responses to dissolved oxygen. This enables the polymer to functionalize as a dual temperature and dissolved oxygen sensor. Oxygen response of the platinum (II) porphyrin probes in the polymer followed a two-site Stern–Volmer model, indicating the nonuniform distribution of the probes. The copolymer was used to preliminarily monitor the oxygen consumption of Escherichia coli ( E. coli) bacteria. The results indicate a potential application of the polymer in biological fields.

Circularly polarized photoluminescence from platinum porphyrins in organic hosts: Magnetic field and temperature dependence

We study the temperature and magnetic field-dependent photoluminescence from the metalorganic molecules octaethyl-porphine platinum (PtOEP) and porphine platinum (PtP) that are doped into organic hosts. We first consider PtOEP in the polymer host poly-dioctylfluorene (PFO), which is characteristic of the phosphorescent dopants and polymers used in organic light-emitting diodes. We observe that the intensity of the PtOEP zero-phonon emission band, which is strongly suppressed at low temperatures to 1.6 K, increases dramatically with applied magnetic field and is accompanied by a marked circular polarization. This “magnetic brightening” effect, similar to that observed in other organic systems such as carbon nanotubes, highlights the interplay between low-energy optically active and optically forbidden excited states of PtOEP, which become mixed in applied magnetic fields. To elucidate these findings, we also investigate (i) dilute PtOEP in n-octane hosts (where emission lines are much sharper), and (ii) dilute PtP in n-octane hosts, for which the emission spectra are simpler and can be directly compared with theory. Detailed electronic structure calculations of PtP were performed, and a model for the magnetic field and temperature dependence of the zero phonon emission lines is developed, which agrees quantitatively with the data for PtP and with the circular polarization of the PtOEP emission.

Multiparametric luminescence method for quantitative cell surface protein expression analysis and imaging

A luminometric method for quantitative cell surface protein expression analysis has been developed in a microtiter plate format. The method is based on immunocytochemistry, the use of long-lived europium(III) and terbium(III) chelates and platinum(II) porphyrin luminescence labels in addition to short-lived syto13 DNA stain, and detection of photoluminescence emission from adhered cells by both time-resolved luminescence and conventional fluorescence. After the immunoreactions, the wells were evaporated to dryness, allowing repeated and postponed luminescence analysis even after months and cellular protein localization studies by microscopy imaging. The multiparametric method assayed the cell surface expression of ß1-integrin, E-selectin and intercellular adhesion molecule 1 (ICAM-1) in HUVE cells (human umbilical vein endothelial cells). The expression of E-selectin and ICAM-1 was enhanced by treating HUVECs with tumor necrosis factor α (TNF-α), while the expression level of ß1-integrin remained unchanged. The sensitivity limit of TNF-α detection by the method was ca. 1pg/ml and the Z′-factors for the quantification of E-selectin and ICAM-1 were >0.7 suggesting a highly robust method. The novel approach proposed in this paper can be potentially applied to cell surface protein expression analysis in screening applications combined with localization studies of the target proteins by fluorescence microscopy imaging.

Ultrabright planar optodes for luminescence life-time based microscopic imaging of O 2 dynamics in biofilms

New transparent optodes for life-time based microscopic imaging of O 2 were developed by spin-coating a μm-thin layer of a highly luminescent cyclometalated iridium(III) coumarin complex in polystyrene onto glass cover slips. Compared to similar thin-film O 2 optodes based on a ruthenium(II) polypyridyl complex or a platinum(II) porphyrin, the new planar sensors have i) higher brightness allowing for much shorter exposure times and thus higher time resolution, ii) more homogeneous and smaller pixel to pixel variation over the sensor area resulting in less noisy O 2 images, and iii) a lower temperature dependency simplifying calibration procedures. We used the new optodes for microscopic imaging of the spatio-temporal O 2 dynamics at the base of heterotrophic biofilms in combination with confocal imaging of bacterial biomass and biofilm structure. This allowed us to directly link biomass distribution to O 2 distribution under both steady state and non-steady state conditions. We demonstrate that the O 2 dynamics in biofilms is governed by a complex interaction between biomass distribution, mass transfer and flow that cannot be directly inferred from structural information on biomass distribution alone.

Microparticle ratiometric oxygen sensors utilizing near-infrared emitting quantum dots

Luminescent sensors incorporating two luminophores, an indicator and a reference, offer many advantages over intensity measurements from sensors made with one indicator dye. Quantum dots have yet to be widely employed as insensitive reference luminophores in such systems. This work describes the use of near-infrared emitting quantum dots in conjunction with a long-lifetime platinum(II) porphyrin phosphor in a microsphere-based, ratiometric oxygen sensor. The process for self-assembly of the nanocomposite system was developed, and the response and photostability of the prototypes were investigated. Results indicate the sensors possess excellent sensitivity (K(SV) = 0.00826 µM(-1)) at oxygen concentrations below 300 µM and were resistant to photobleaching. The sensor luminophores displayed minimal spectral overlap and little interference from excitation light, preventing the need for optical filters. A reversible photoenhancement of the quantum dot signal was also observed when exposed for extended periods of time. This work demonstrates the advantages of incorporating long-wavelength quantum dots into ratiometric intensity sensing schemes and highlights some key limitations that must be considered in their use.

Platinum porphyrins as ionophores in polymeric membrane electrodes

A comparative study of Pt(II)- and Pt(IV)-porphyrins as novel ionophores for anion-selective polymeric membrane electrodes is performed. Polymeric membranes of different compositions, prepared by varying plasticizers, cationic and anionic additives and Pt porphyrins, have been examined by potentiometric and optical techniques. Pt porphyrin-based devices were found to exhibit enhanced potentiometric selectivity toward iodide ion compared to electrodes based on a typical anion-exchanger (e.g. tridodecylmethylammonium chloride). It is shown that Pt(II)-porphyrins function as neutral anion carriers within the electrode membranes, while those based on Pt(IV)TPPCl(2) operate via a mixed mode carrier mechanism, evidencing also a partial reduction of the starting ionophore to Pt(II)TPP. Spectrophotometric measurements of thin polymeric films indicate that no spontaneous formation of hydroxide ion bridged porphyrin dimers occurs in the membrane plasticized both with high or low dielectric constant plasticizer, due to a low oxophilicity of central Pt. The computational study of various anion-Pt(IV)TPPCl(2) complex formation by means of semi-empirical and density functional theory (DFT) methods revealed a good correlation between calculated and measured ionophore selectivity.

A dissolved oxygen sensor based on composite fluorinated xerogel doped with platinum porphyrin dye

A new functional fluorinated material taking n-propyltrimethoxysilicane (n-propyl-TriMOS) and 3,3,3-trifluoropropyltrimethoxysilicane (TFP-TriMOS) as precursors was applied to construct a novel dissolved oxygen sensing film. The sensing film was fabricated by dip-coating the functional fluorinated material-doped [meso-tetrakis(pentafluorophenyl) porphyinato] platinum(II) (PtF(20) TPP) onto a glass slide. The oxygen sensing film exhibited a good linear relationship, fast response time, long stability and high sensitivity to dissolved oxygen. In the developed optical oxygen sensor, an LED and a photodiode were composed to construct a back-detection optical system not needing an optical fiber based on fluorescence intensity detection. The smart optical oxygen sensor based on the PtF(20) TPP fluorescence quenching possesses the advantages of portability and low cost and can be applied to the dissolved oxygen in situ monitoring in seawater.

Platinum and palladium complexes of fluorenyl porphyrins as red phosphors for light-emitting devices

Platinum(II) and palladium(II) complexes of a porphyrin with fluorenyl groups linked directly at the meso-positions (TFP) have been synthesized and characterized. Their luminescence properties in solution have been studied under ambient conditions and at 77 K. Compared to the corresponding complexes of tetraphenylporphyrin TPP, the emission is red-shifted in both cases. Radiative rate constants are found to be enhanced by the fluorenyl substituents, although non-radiative decay rates are also increased in solution. Short-wavelength UV excitation leads to no detectable fluorenyl-based fluorescence, indicating that a very efficient transfer of energy to the porphyrin occurs. An OLED in which PtTFP is used as a red phosphor has been prepared and its electroluminescence performance assessed. High current “roll-off” is significantly delayed to higher currents compared to previously described OLEDs that make use of standard platinum porphyrins as emitters, an effect which can be attributed to the shorter radiative lifetime of PtTFP.

Photoinduced Electron Transfer in Zn(II)porphyrin−Bridge−Pt(II)acetylide Complexes: Variation in Rate with Anchoring Group and Position of the Bridge

The synthesis and photophysical characterization of two sets of zinc porphyrin platinum acetylide complexes are reported. The two sets of molecules differ in the way the bridging phenyl-ethynyl unit is attached to the porphyrin ring. One set is attached via an ethynyl unit on the β position, while the other set is attached via a phenyl unit on the meso position of the porphyrin. These were compared with previously studied complexes where attachment was made via an ethynyl unit on the meso position. Femtosecond transient absorption measurements showed in all systems a rapid quenching of the porphyrin singlet state. Electron transfer is suggested as the quenching mechanism, followed by an even faster recombination to form both the porphyrin ground and triplet excited states. This is supported by the variation in quenching rate and porphyrin triplet yield with solvent polarity, and the observation of an intermediate state in the meso-phenyl linked systems. The different linking motifs between the dyads resulted in significant variations in electron transfer rates.

Tunable Phosphorescent NIR Oxygen Indicators Based on Mixed Benzo- and Naphthoporphyrin Complexes

A series of π-extended phosphorescent palladium(II) and platinum(II) porphyrin complexes were synthesized, in which additional benzene rings are fused radially onto at least one of the four peripheral benzo groups. The photophysical properties of the metalloporphyrins palladium(II)-meso-tetra-(4-fluorophenyl)mononaphthotribenzoporphyrin (Pd1NF), cis-palladium(II)-meso-tetra-(4-fluorophenyl)dibenzodinaphthoporphyrin (Pd2NF), and palladium(II)-meso-tetra-(4-fluorophenyl)monobenzotrinaphthoporphyrin (Pd3NF) and the corresponding platinum(II) compounds (Pt1NF, cis-Pt2NF, Pt3NF) were investigated. The compounds under investigation absorb intensively in the near-infrared region (628−691 nm) and emit at room temperature at 815−882 nm. Phosphorescence quantum yields of the platinum(II) porphyrins range from 25 to 53% with luminescence decay times of 21 to 44 μs in deoxygenated toluene solutions at room temperature. The corresponding palladium(II) complexes exhibit quantum yields in the range of 7 to 18% with lifetimes of 106 to 206 μs. Density functional theory (DFT) calculations revealed nonplanar geometries for all complexes and corroborate the absorption characteristics. The subsequent π extension of the porphyrin system leads to near-infrared absorbing oxygen indicators with tailor-made luminescence properties as well as tunable oxygen sensitivity.

Influence of matrices on oxygen sensing of three sensing films with chemically conjugated platinum porphyrin probes and preliminary application for monitoring of oxygen consumption of Escherichia coli ( E. coli)

Oxygen sensing films were synthesized by a chemical conjugation of functional platinum porphyrin probes in silica gel, polystyrene (PS), and poly(2-hydroxyethyl methacrylate) (PHEMA) matrices. Responses of the sensing films to gaseous oxygen and dissolved oxygen were studied and the influence of the matrices on the sensing behaviors was investigated. Silica gel films had the highest fluorescence intensity ratio from deoxygenated to oxygenated environments and the fastest response time to oxygen. PHEMA films had no response to gaseous oxygen, but had greater sensitivity and a faster response time for dissolved oxygen than those of PS films. The influence of matrices on oxygen response, sensitivity and response time was discussed. The influence is most likely attributed to the oxygen diffusion abilities of the matrices. Since the probes were chemically immobilized in the matrices, no leaching of the probes was observed from the sensing films when applied in aqueous environment. One sensing film made from the PHEMA matrix was used to preliminarily monitor the oxygen consumption of Escherichia coli ( E. coli) bacteria. E. coli cell density and antibiotics ampicillin concentration dependent oxygen consumption was observed, indicating the potential application of the oxygen sensing film for biological application.

Platinum(II) and Platinum(IV) Porphyrin Pincer Complexes: Synthesis, Structures, and Reactivity

Pt(II) and Pt(IV) porphyrin pincer complexes were synthesized and characterized. Their structures and electronic properties were influenced by the valence state of platinum at the outer coordination site. The considerable distortion in the porphyrin core of the Pt(II) complex was relieved in the Pt(IV) complex, due to the change of the coordination geometry of platinum. Oxidation of the phenylplatinum(II) pincer complex with iodine induced a facile carbon−carbon bond formation reaction at the meso position via reductive elimination.

Optical oxygen sensors based on platinum porphyrin dyes encapsulated in ORMOSILS

A strategic approach to develop an “ideal” sensor platform is addressed. Novel quenchometric O 2 sensing materials with 100-fold adjustable sensitivity ( I N 2 / I O 2 from 3 to over 300), reverse and fast response (1 s), linear calibration, and long-term stability are developed. These materials are spin-casted composite ORMOSILs (organically modified silicates) xerogel films sequestered with luminophore Pt(II) octaethylporphine (PtOEP) and Pt(II) meso-tetra(N-methyl-4-pyridyl)porphyrin tetrachloride (PtTMP). The composite xerogels studied are pentafluorophenylpropyltrimethoxysilane (PFTMOS)/ n-octyltrimethoxysilane (C 8TMOS)/tetramethoxysilane (TMOS) and 3,3,3-trifluoropropyltrimethoxysilane (TFTMOS)/ n-propyltrimethoxysilane (C3TMOS). Luminescence spectroscopy (steady state and time resolved) have been used to investigate their analytical figures of merit for gaseous O 2 sensing and to determine the underlying reasons for the observed performance. Results show that, except for PtTMP-doped PFTMOS/C8TMOS/TMOS, all other xerogel composites show linear Stern–Volmer relationship and the single exponential time-resolved intensity decay, which indicate the homogeneous environment of the luminophore. For PtTMP-doped PFTMOS/C8TMOS/TMOS xerogels, the Stern–Volmer plots are non-linear and the time-resolved intensity decay profiles are best fitted by double exponential decay model, which are resulted from the heterogeneous environment of the luminophore. The sensitivity of the sensing materials can be tuned by adjusting the xerogel composition and luminophore. For PtOEP-doped PFTMOS/C8TMOS/TMOS, while keeping C8TMOS and TMOS at the same mol ratio, sensitivity ( I N 2 / I O 2 ) decreases from 333 to 246 with increased PFTMOS% from 0 to 30%, which is due to the decreased bimolecular quenching constant ( k q ). However, I N 2 / I O 2 = 3 was observed from PtTMP-doped PFTMOS/C8TMOS/TMOS. For PtTMP-doped TFTMOS/C3TMOS, sensitivity increases with increased TFTMOS% from 0 to 50% and decreases with further increased TFTMOS% from 50 to 100%, which is mainly due to corresponding increase and decrease of k q . An optimized composition with high sensitivity is observed at 10 PFTMOS/45C8TMOS/45 C8TMOS with I N 2 / I O 2 = 330 .

First electrogeneration of a platinum(iv) porphyrin: elucidation of the PtII/IV and PtIV/II oxidation-reduction processes in nonaqueous media

The first example for electrogeneration of a Pt(IV) porphyrin from its Pt(II) form is presented and the Pt(II/IV) and reverse Pt(IV/II) oxidation-reduction processes are elucidated by electrochemistry and thin-layer UV-visible spectroelectrochemistry. Three products, [(TPP˙(+))Pt(II)](+), [(TPP)Pt(IV)](2+) and [(TPP˙(+))Pt(IV)](3+), produced by electrooxidation of the Pt(II) porphyrin have been characterized by in situ spectroelectrochemistry and ESR measurements after controlled potential bulk electrolysis. The first definitive evidence for the electrochemical conversion of a Pt(iv) porphyrin to its Pt(II) form is also presented. The potential for this electroreduction is highly dependent upon the nature of the anion, ClO(4)(-) or Cl(-). A mechanism for the reversible conversion between Pt(II) and Pt(IV) tetraphenylporphyrins is proposed.