Tetraphenylporphyrin Molecules Research Articles

A facile dual isolation and protection strategy for preparation of PtFe intermetallic compound in biomass-derived carbon with high activity and durability for pH-universal bifunctional electrocatalysts

A facile dual isolation and protection strategy is developed to prepare PtFe intermetallic electrocatalyst (PtFe–N–C@bioC) on porous biomass carbon (bioC) derived from peanut shell. In preparation, meso-tetraphenylporphyrine (H2TPP) together with platinum (II)-tetraphenylporphyrin (PtTPP) are in-situ fabricated on the porous peanut shell-derived bioC matrixes and then further absorbed Fe (III) tetraphenyl porphyrin (FeTPP) molecules through π−π interactions between PtTPP/H2TPP and FeTPP to form a mixed precursor of FeTPP/PtTPP/TPP-bioC. Upon pyrolysis of FeTPP/PtTPP/TPP-bioC, PtFe bimetallic-containing N-doped carbon formed on bioC (PtFe–N–C@bioC). The resultant PtFe–N–C@bioC showed excellent oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) activity across a wide pH range. In particular, under alkaline medium, PtFe–N–C@bioC shows the ORR performance with an onset potential (Eonset) of 0.989 V, a half-wave potential (E1/2) of 0.901 V and a limiting current density (JL) of −6.214 mA cm−2. Meanwhile, PtFe–N–C@bioC delivers an enhanced mass activity (1.197 A mg−1Pt), which is 13 times larger than commercial Pt/C. For HER, PtFe–N–C@bioC shows an impressive overpotential (η10) of 17 mV at a current density of 10 mA cm−2 under acidic medium. Further, it is applied to Zn-Air batteries with a power density performance of 98.7 mW cm−2 and good durability.

Construction of Cobalt Porphyrin-Modified Cu2O Nanowire Array as a Tandem Electrocatalyst for Enhanced CO2 Reduction to C2 Products.

Here, the molecule-modified Cu-based array is first constructed as the self-supporting tandem catalyst for electrocatalytic CO2 reduction reaction (CO2RR) to C2 products. The modification of cuprous oxide nanowire array on copper mesh (Cu2O@CM) with cobalt(II) tetraphenylporphyrin (CoTPP) molecules is achieved via a simple liquid phase method. The systematical characterizations confirm that the formation of axial coordinated Co-O-Cu bond between Cu2O and CoTPP can significantly promote the dispersion of CoTPP molecules on Cu2O and the electrical properties of CoTPP-Cu2O@CM heterojunction array. Consequently, as compared to Cu2O@CM array, the optimized CoTPP-Cu2O@CM sample as electrocatalyst can realize the 2.08-fold C2 Faraday efficiency (73.2%vs 35.2%) and the 2.54-fold current density (‒52.9vs ‒20.8mAcm-2) at ‒1.1V versus RHE in an H-cell. The comprehensive performance is superior to most of the reported Cu-based materials in the H-cell. Further study reveals that the CoTPP adsorption on Cu2O can restrain the hydrogen evolution reaction, improve the coverage of *CO intermediate, and maintain the existence of Cu(I) at low potential.

FRET‐Amplified Singlet Oxygen Generation by Nanocomposites Comprising Ternary AgInS2/ZnS Quantum Dots and Molecular Photosensitizers

AbstractAntibacterial photodynamic therapy (a‐PDT) has emerged as a promising non‐invasive therapeutic modality that utilizes the combination of a photosensitive agent, molecular oxygen, and excitation light to generate reactive oxygen species (ROS), demonstrating remarkable activity against multidrug‐resistant bacterial infections. However, the effective use of conventional photosensitizers is significantly limited by a number of their shortcomings, namely, poor water solubility and low selectivity. Herein, we present a novel biocompatible water‐soluble nanocomposite based on hydrophobic tetraphenylporphyrin (TPP) molecules and hydrophilic ternary AgInS2/ZnS quantum dots incorporated into a chitosan matrix as an improved photosensitizer for a‐PDT. We demonstrated that TPP molecules could be successfully transferred into chitosan solution while remaining primarily in the form of monomers, which are capable of singlet oxygen generation. We performed a detailed analysis of the Förster resonance energy transfer (FRET) between quantum dots and TPP molecules within the nanocomposite and proposed the mechanism of the singlet oxygen efficiency enhancement via FRET.

Light-responsive organic polaritons from first principles.

Controlling the optical properties of light-responsive organic molecules is essential for their application in photonics. We demonstrate how light-responsive organic polaritons formed inside an optical cavity can be used to modify these properties based on first principles. Specifically, we study the excited state properties of the trans-azobenzene molecule and the free base tetraphenyl porphyrin (H2TPP) molecule under weak to strong light-matter coupling. Our results show that the cavity can modulate the dispersion and absorption properties of organic molecules. Compared to the case outside the cavity, the anomalous dispersion of the trans-azobenzene molecule inside the cavity is suppressed and this suppression decreases with increasing coupling strength, showing the potential of strong light-matter coupling in manipulating the optical dipole trap of organic molecules. Moreover, by adjusting the cavity parameters to tune the strength of the light-matter coupling, we achieve free switching between symmetric Lorentz and asymmetric Fano line shapes for H2TPP polaritonic excitations. During the switching between these spectral features, we also find that the cavity can be used to control the spontaneous radiation of organic molecules via the Purcell effect. These findings provide a new pathway to manipulate the optical properties of light-responsive organic molecules.

Chemical Structure and Distribution in Nickel-Nitrogen-Carbon Catalysts for CO2 Electroreduction Identified by Scanning Transmission X-ray Microscopy.

Atomically dispersed metal-nitrogen-carbon (M-N-C) materials are a class of electrocatalysts for fuel cell and electrochemical CO2 reduction (CO2R) applications. However, it is challenging to characterize the identity and concentration of catalytically active species owing to the structural heterogeneity of M-N-C materials. We utilize scanning transmission X-ray microscopy (STXM) as a correlative spectromicroscopy approach for spatially resolved imaging, identification, and quantification of structures and chemical species in mesoscale regions of nickel-nitrogen-carbon (Ni-N-C) catalysts, thereby elucidating the relationship between Ni content/speciation and CO2R activity/selectivity. STXM results are correlated with conventional characterization approaches relying on either bulk average (X-ray absorption spectroscopy) or spatially localized (scanning transmission electron microscopy with electron energy loss spectroscopy) measurements. This comparison illustrates the advantages of soft X-ray STXM to provide spatially resolved identification and quantification of active structures in Ni-N-C catalysts. The active site structures in these catalysts are identified to be atomically dispersed NiN x /C sites distributed throughout entire catalyst particles. The NiN x /C sites were notably demonstrated by spectroscopy to possess a variety of chemical structures with a spectroscopic signature that most closely resembles nickel(II) tetraphenylporphyrin molecules. The quantification and spatial distribution mapping of atomically dispersed Ni active sites achieved by STXM address a target that was elusive to the scientific community despite its importance in guiding advanced material designs.

Proposal for All-Electrical Spin Manipulation and Detection for a Single Molecule on Boron-Substituted Graphene.

All-electrical writing and reading of spin states attract considerable attention for their promising applications in energy-efficient spintronics devices. Here we show, based on rigorous first-principles calculations, that the spin properties can be manipulated and detected in molecular spinterfaces, where an iron tetraphenyl porphyrin (FeTPP) molecule is deposited on boron-substituted graphene (BG). Notably, a reversible spin switching between the S=1 and S=3/2 states is achieved by a gate electrode. We can trace the origin to a strong hybridization between the Fe-d_{z^{2}} and B-p_{z} orbitals. Combining density functional theory with nonequilibrium Green's function formalism, we propose an experimentally feasible three-terminal setup to probe the spin state. Furthermore, we show how the in-plane quantum transport for the BG, which is non-spin polarized, can be modified by FeTPP, yielding a significant transport spin polarization near the Fermi energy (>10% for typical coverage). Our work paves the way to realize all-electrical spintronics devices using molecular spinterfaces.

Light Emission from Vibronic Polaritons in Coupled Metalloporphyrin-Multimode Cavity Systems.

In this study, we explore how one can use cavity polariton formation and a non-Condon vibronic coupling mechanism to form a type of hybrid light-matter state we denote as Herzberg-Teller (HT) vibronic polaritons. We use simple models to define the basic characteristics of these hybrid light-matter excitations including their dispersive energies. Experimentally, we find evidence of HT polaritons in the light emission spectra from copper(II) tetraphenylporphyrin (CuTPP) molecules strongly coupled to both single and multimode Fabry-Perot resonator structures. For specific resonator designs, we find evidence of significant enhancement of light emission from a short-lived sing-doublet state of CuTPP, which couples to a higher energy singlet state via a non-Condon vibronic mechanism. The results of a two-state model support the conclusion that this enhancement and the temperature-dependent dispersion of the light emission peak energy stem from radiative relaxation into cavity photon states dressed by collective vibrations of the molecules participating in polariton formation. These results show how researchers can leverage the complex interplay of electronic and nuclear degrees of freedom in light absorbing molecules to form a vaster array of coherent light-matter states and potentially transform platforms in optoelectronic and photocatalytic technologies.

Chitosan nanocomposites with CdSe/ZnS quantum dots and porphyrin.

Water-soluble nanocomposites based on CdSe/ZnS quantum dots (QDs) and hydrophobic tetraphenylporphyrin (TPP) molecules passivated by chitosan (CS) have been formed. Magnetic circular dichroism (MCD) spectra evidence TPP presence in both monomeric and agglomerated forms in the nanocomposites. The nanocomposites demonstrate more pronounced singlet oxygen generation compared to free TPP in CS at the same concentration due to the intracomplex Förster resonance energy transfer (FRET) with a 45% average efficiency.

Self-metalation of monophosphonic acid tetraphenylporphyrin on TiO2(110)-(1×1)

Fundamental studies on the interaction of porphyrin molecules with oxide surfaces are important due to the relevance of these systems in emerging technologies. In this work, we used X-ray photoelectron spectroscopy (XPS) to study the interaction of solution-deposited monophosphonic acid tetraphenylporphyrin (MPTPP) molecules with well-defined rutile TiO2(110)-(1×1) surfaces as a function of coverage and temperature. We found that molecules adsorb mainly in their free-base form with some molecules protonating on the surface at room temperature. In agreement with the behavior of carboxylic acid functionalized porphyrin molecules, raising the temperature results in porphyrin self-metalation and the temperature onset for self-metalation shifts to higher values as the coverage is increased. Furthermore, we found that self-metalation is accompanied by surface reduction, and we propose a mechanism based on the formation of oxygen vacancies driven by water desorption. Our findings contribute towards the understanding of the rich surface chemistry that porphyrin molecules have on oxide surfaces.

Local molecular probes of ultrafast relaxation channels in strongly coupled metalloporphyrin-cavity systems.

The quantum control of ultrafast excited state dynamics remains an unachieved goal within the chemical physics community. In this study, we assess how strongly coupling to cavity photons affects the excited state dynamics of strongly coupled zinc (II) tetraphenyl porphyrin (ZnTPP) and copper (II) tetraphenyl porphyrin (CuTPP) molecules. By varying the concentration of each chromophore within different Fabry-Pérot (FP) structures, we control the collective vacuum Rabi splitting between the energies of cavity polariton states formed through the strong coupling of molecular electrons and cavity photons. Using ultrafast transient reflectivity and transmission measurements probing optical transitions of individual ZnTPP and CuTPP molecules, we find that the polaritonic states localize into uncoupled excited states of these chromophores through different mechanisms. For ZnTPP, we build a simple kinetic model including a direct channel of relaxation between the polaritonic states. We find that our models necessitate a small contribution from this interpolaritonic relaxation channel to explain both our steady-state and transient optical spectroscopic measurements adequately. In contrast, we propose that strong cavity coupling slows the internal conversion between electronic states of CuTPP not directly interacting with the photons of FP structures. These results suggest that researchers must consider the vibrational structure and excited state properties of the strongly coupled chromophores when attempting to use polariton formation as a tool to control the dynamics of molecules central to photo-sensitizing and light harvesting applications.

Single-Molecule Vibrational Spectroscopy: Cobalt Tetraphenylporphyrin Deposited on a Cu2N Ultrathin Insulating Layer

The electronic and vibrational properties of cobalt tetraphenylporphyrin (CoTPP) molecules deposited onto a Cu2N–Cu(100) surface were studied by scanning tunneling microscopy. The Cu2N spacer layer...

Surface Reactions and Electronic Structure of Carboxylic Acid Porphyrins Adsorbed on TiO2(110)

We studied the coverage- and temperature-dependent proton transfer and self-metalation reactions of tetraphenylporphyrin molecules containing a carboxyl functional group (MCTPP) on rutile TiO2(110)...

Demetalation of Surface Porphyrins at the Solid-Liquid Interface.

Understanding the factors that control the demetalation of surface porphyrins at the solid-liquid interface is important as the molecular properties of porphyrins are largely determined by their metal centers. In this work, we used X-ray photoelectron spectroscopy (XPS) to follow the demetalation of Zn and Cd tetraphenylporphyrin molecules (ZnTPP and CdTPP) adsorbed as three-monolayer-thin multilayer films on Au(111), by exposing the molecular layers to acidic aqueous solutions. We found that porphyrin molecules at the solid-liquid interface are less prone to lose their metal center than molecules in solution. We propose that this behavior is due to either the incoming protons provided by the solution or the outgoing metal ion having to pass through the hydrophobic porphyrin multilayers where they cannot be solvated. Our results are relevant for the design of molecular devices based on porphyrin molecules adsorbed on solid surfaces.

Singlet oxygen generation by hybrid structures based on CdSe/ZnS quantum dots and tetraphenylporphyrin in organic medium

Photophysical properties of hybrid structures based on CdSe/ZnS quantum dots (QDs) and tetraphenylporphyrin (TPP) molecules have been studied. The hybrid structures are characterized by higher singlet oxygen (SO) generation compared to free TPP molecules due to high intracomplex Förster Resonance Energy Transfer (FRET) efficiency and saving TPP in the monomeric form in the hybrid structures. We show that all energy transferred from QDs to TPP is fully used to generate singlet oxygen since there are no new nonradiative channels in the structures. We believe that our result will stimulate renewed interest in QD based structures with photosensitizers as theranostics agents.

Revealing the morphology and the magnetic properties of single buried cobalt-ZnTPP hybrid interfaces by ferromagnetic nuclear resonance spectroscopy

The deeply buried, yet most important part of any spintronic device is the interface. This is even more interesting and much more complex when soft, light materials like organic molecules are in contact with an inorganic metallic electrode. Hence, exceptional care is required to better understand the phenomena driven by this type of organic/inorganic interfaces. To this end, ferromagnetic nuclear resonance (FNR) spectroscopy studies were performed to investigate the morphology and the magnetic properties of the hybrid organic-inorganic interfaces when zinc tetraphenyl porphyrin (ZnTPP) molecules are at the vicinity of ferromagnetic metallic cobalt (Co) layers. The FNR experimental results show that when ZnTPP is deposited on top of Co the resulting interface is smoother and sharper compared to the more extended interface obtained when Co is deposited on top of ZnTPP. The shape of the spectra suggests that no chemical bonds take place between the interfacial Co atoms and the ZnTPP molecules and that interactions at the interfaces are governed by weak van der Waals forces. Finally, FNR also showed that the magnetic anisotropy at the Co-ZnTPP hybrid interfaces is reduced compared to the magnetic anisotropy of the Co atoms inside the Co films.

Force Spectroscopy of Iron Tetraphenylporphyrin Molecules with Cl Tips

At low sample voltages, Cl ions may be bidirectionally transferred between a Fe tetraphenylporphyrin (FeTPP) molecule on Au(111) and the tip of a low-temperature scanning tunneling microscope that ...

Two-Dimensional Functionalized Ultrathin Semi-Insulating CaF2 Layer on the Si(100) Surface at a Low Temperature for Molecular Electronic Decoupling.

The ability to precisely control the electronic coupling/decoupling of adsorbates from surfaces is an essential goal. It is important for fundamental studies not only in surface science but also in several applied domains including, for example, miniaturized molecular electronic or for the development of various devices such as nanoscale biosensors or photovoltaic cells. Here, we provide atomic-scale experimental and theoretical investigations of a semi-insulating layer grown on a silicon surface via its epitaxy with CaF2. We show that, following the formation of a wetting layer, the ensuing organized unit cells are coupled to additional physisorbed CaF2 molecules, periodically located in their surroundings. This configuration shapes the formation of ribbons of stripes that functionalize the semiconductor surface. The obtained assembly, having a monolayer thickness, reveals a surface gap energy of ∼3.2 eV. The adsorption of iron tetraphenylporphyrin molecules on the ribbons of stripes is used to estimate the electronic insulating properties of this structure via differential conductance measurements. Density functional theory (DFT) including several levels of complexity (annealing, DFT + U, and nonlocal van der Waals functionals) is employed to reproduce our experimental observations. Our findings offer a unique and robust template that brings an alternative solution to electronic semi-insulating layers on metal surfaces such as NaCl. Hence, CaF2/Si(100) ribbon of stripe structures, whose lengths can reach more than 100 nm, can be used as a versatile surface platform for various atomic-scale studies of molecular devices.

Heavy Metal Ion Sensing Using Ultrathin Langmuir–Schaefer Film of Tetraphenylporphyrin Molecule

The exciting properties of porphyrin molecules can be employed for several applications like sensing, catalysis, photovoltaics and energy related fields. The assemblies of the molecules at interfaces can give rise to some unique physicochemical properties which can enhance the device performance. In this article, we report our studies on heavy metal ion sensing in aqueous medium using ultrathin film of tetraphenylporphyrin (TPP) molecules. The TPP molecules were synthesized and used for forming Langmuir monolayer at the air-water interface. The monolayer was transferred onto solid substrates by Langmuir-Schaefer (LS) method at different target surface pressure of deposition ( $\pi _{\text {T}}$ ). The morphological analysis of the films indicated supramolecular assembly of the molecules in the LS film deposited at $\pi _{\text {T}}={30}$ mN/m. The LS films of TPP molecules were employed for sensing heavy metal cations viz. Pb2+, Hg2+, Co2+ and Cd2+ from the aqueous medium by measuring piezoresponse from a quartz crystal microbalance. The sensing performance was found to be the best with LS film deposited at $\pi _{\text {T}}={30}$ mN/m. The sensitivity towards Pb2+ ion is found to be the highest. The sensing of the heavy metal cations using randomly oriented TPP molecules in spin coated thin film was found to be much inferior as compared to that of LS films of the molecule. The enhanced sensing performance by the LS film of TPP molecules may be attributed to the supramolecular assembly of the molecules. We report that the interference of the sensing measurement for the recognition of Cd2+ and Pb2+ ions is least and thus these species can be detected selectively with less errors. The cation species recognition features obtained from scanning electron microscope images and Raman spectroscopy were found to be remarkably different and therefore these cationic heavy metal species can be selectively detected using the LS film of TPP.

Quantum Control of Ultrafast Internal Conversion Using Nanoconfined Virtual Photons.

The rational control of nonradiative relaxation remains an unfulfilled goal of synthetic chemistry. In this study, we show how strongly coupling an ensemble of molecules to the virtual photons of an electromagnetic cavity provides a rational handle over ultrafast, nonradiative dynamics. Specifically, we control the concentration of zinc tetraphenyl porphyrin molecules within nanoscale Fabry-Perot cavity structures to show a variable collective vacuum Rabi splitting between cavity polaritons coincides with systematic changes in internal conversion rates. We find these changes deviate from the predictions of so-called gap laws. We also show that simple theories of structural changes caused by polariton formation cannot explain discrepancies between our results and established theoretical predictions. In light of these deficiencies, we explore other ways to explain the dependence of the internal conversion rate on polariton parameters. Our results demonstrate cavity polariton formation controls the photophysics of light harvesting and photocatalytic molecular moieties and the gap remaining in our fundamental understanding of mechanisms enabling this control.

Evaluation of molecular orbital symmetry via oxygen-induced charge transfer quenching at a metal-organic interface

Thin molecular films under model conditions are often exploited as benchmarks and case studies to investigate the electronic and structural changes occurring on the surface of metallic electrodes. Here we show that the modification of a metallic surface induced by oxygen adsorption allows the preservation of the geometry of a molecular adlayer, giving access to the determination of molecular orbital symmetries by means of near-edge X-ray absorption fine structure spectroscopy, NEXAFS. As a prototypical example, we exploited nickel tetraphenylporphyrin molecules deposited on a bare and on an oxygen pre-covered Cu(1 0 0) surface. We find that adsorbed atomic oxygen quenches the charge transfer at the metal-organic interface but, in contrast to a thin film sample, maintains the ordered adsorption geometry of the organic molecules. In this way, it is possible to disentangle π* and σ* symmetry orbitals, hence estimate the relative oscillator strength of core level transitions directly from the experimental data, as well as to evaluate and localize the degree of charge transfer in a coupled system. In particular, we neatly single out the σ* contribution associated with the N 1s transition to the mixed N 2px,y-Ni 3dx2-y2 orbital, which falls close to the leading π*-symmetry LUMO resonance.