Tetraphenylporphyrin Molecules Research Articles

Crystal structure of chlorido-(5,10,15,20-tetra-phenyl-porphyrinato-κ(4) N)manganese(III) 2-amino-pyridine disolvate.

In the title compound, [Mn(C44H28N4)Cl]·2C5H6N2, the Mn(III) centre is coordinated by four pyrrole N atoms [averaged Mn-N = 2.012 (4) Å] of the tetra-phenyl-porphyrin mol-ecule and one chloride axial ligand [Mn-Cl = 2.4315 (7) Å] in a square-pyramidal geometry. The porphyrin macrocycle exhibits a non-planar conformation with major ruffling and saddling distortions. In the crystal, two independent solvent mol-ecules form dimers through N-H⋯N hydrogen bonding. In these dimers, one amino N atom has a short Mn⋯N contact of 2.642 (1) Å thus completing the Mn environment in the form of a distorted octa-hedron, and another amino atom generates weak N-H⋯Cl hydrogen bonds, which link further all mol-ecules into chains along the a axis.

Scrutinizing individual CoTPP molecule adsorbed on coinage metal surfaces from the interplay of STM experiment and theory

The cobalt tetraphenyl porphyrin (CoTPP) molecule and its adsorption on clean Cu and Ag surfaces are comparatively analyzed within the Density Functional Theory (DFT) framework. Different sets of exchange-correlation functionals — the Local Density Approximation (LDA) and the Gradient Generalized Approximation (along with the PBE functional and the semi-empirical Grimme's corrections of dispersion) — are compared. Two prominent structural adsorption properties are disclosed in all sets of calculations: an asymmetric saddle deformation of CoTPP with an enhanced tilting of the upwards bent pyrroles and a single adsorption site where the Co center occupies a bridge position and one molecular axis (along the direction of the lowered pair of opposite pyrroles) is aligned with the dense-packed 〈11¯0〉 substrate direction. The similarities between Cu(111) and Ag(111) surfaces extend to the interfacial electronic structure with similar electronic redistribution and molecular charging. However subtle differences between the two substrates are revealed with bias-dependent STM simulations, especially in the low-bias imaging range. The STM calculations underline the difficulty for the commonly used GGA + D2 DFT framework to quantitatively predict the energy positions of the frontier molecular orbitals (MOs).

Influence of Tetraphenylporphyrin on the Supra Molecular Structure of Cellulose Diacetate

The degrees of crystallinity of powdered CTA and CDA that were calculated from x-ray crystal structure analysis (XSA) data were 27.9% and 6.7%, respectively. It was found that anisotropic placement of structural elements in cellulose acetate membranes destroyed the spherical scattering symmetry and hindered determination of the degree of crystallinity of the films. Tetraphenylporphyrin molecules in CDA films formed from a solution were proved to be dispersed using XSA and spectrophotometry. It was shown that the added porphyrin lowered the CDA film anisotropy by preventing the polymer layers from ordering.

Antiferromagnetic coupling of Cr-porphyrin to a bare Co substrate

We report the discovery of an antiferromagnetic coupling of the magnetic moment of chromium(II) tetraphenyl-porphyrin (CrTPP) molecules to the magnetization of the clean ferromagnetic Co(001) substrate. We assign this unusual molecule-substrate exchange coupling to the less than half-filled chromium $3d$ orbitals interacting with Co valence band electrons via porphyrin-ligand molecular orbitals. X-ray magnetic circular dichroism, x-ray photoelectron spectroscopy, and scanning tunneling microscopy are combined with $\mathrm{DFT}+U$ calculations and provide evidence for a surprising type of antiferromagnetic ${90}^{\ensuremath{\circ}}$ indirect magnetic exchange coupling.

Noncovalent functionalization of carbon nanotubes and graphene with tetraphenylporphyrins: stability and optical properties from ab initio calculations

The stability, electronic, and optical properties of single-walled carbon nanotubes (CNTs) and graphene non-covalently functionalized with free-base tetraphenylporphyrin (TPP) molecules is addressed by density functional theory calculations. We study the TPP physisorption on 42 CNT species, particularly those with chiral indices $$(n,m)$$ , where $$5 \le n \le 12$$ and $$0\le m\le n$$ . Our results show a quite strong $$\pi $$ – $$\pi $$ interaction between TPP and the CNT surface, with binding energies ranging from 1.1 to 1.8 eV, where higher energies can be associated with increasing CNT diameters. We also find that the TPP optical absorptions would not be affected by the CNT diameter or chirality. Results for the TPP physisorption on graphene show a remarkable stability with binding energy of 3.2 eV, inducing a small redshift on the $$\pi $$ -stacked TPP absorption bands. The strong graphene–TPP interaction also induces a charge transfer from TPP to graphene, indicating a n-type doping mechanism without compromising the graphene structure.

Electronic interaction between nitrogen-doped graphene and porphyrin molecules.

The chemical doping of graphene is a promising route to improve the performances of graphene-based devices through enhanced chemical reactivity, catalytic activity, or transport characteristics. Understanding the interaction of molecules with doped graphene at the atomic scale is therefore a leading challenge to be overcome for the development of graphene-based electronics and sensors. Here, we use scanning tunneling microscopy and spectroscopy to study the electronic interaction of pristine and nitrogen-doped graphene with self-assembled tetraphenylporphyrin molecules. We provide an extensive measurement of the electronic structure of single porphyrins on Au(111), thus revealing an electronic decoupling effect of the porphyrins adsorbed on graphene. A tip-induced switching of the inner hydrogen atoms of porphyrins, first identified on Au(111), is observed on graphene, allowing the identification of the molecular conformation of porphyrins in the self-assembled molecular layer. On nitrogen-doped graphene, a local modification of the charge transfer around the nitrogen sites is evidenced via a downshift of the energies of the molecular elecronic states. These data show how the presence of nitrogen atoms in the graphene network modifies the electronic interaction of organic molecules with graphene. These results provide a basic understanding for the exploitation of doped graphene in molecular sensors or nanoelectronics.

Strong π-π interaction of porphyrins on (6,5) carbon nanotubes with full surface coverage: Ab-initio calculations

The stability, electronic, and optical properties of (6,5) single-walled carbon nanotubes (CNTs) functionalized with free-base tetraphenylporphyrin (TPP) molecules through π-stacking interactions are studied by ab-initio calculations. The stability and optical response of the CNT-TPP compounds for increasing CNT-surface coverage are investigated. Our results show that four TPP molecules forming a ring around the CNT is the most stable configuration, showing strong binding energies of about 2.5 eV/TPP. However, this binding energy can increase even more after additional molecules assemble side by side along the CNT, favoring the formation of a full single layer of TPP, as experimentally suggested. The strong π-π attractive forces induce molecular distortions that move the TPP higher-occupied molecular orbital levels inside the CNT bandgap, changing the optical response of the TPP molecules stacked on the CNT.

Interaction and local magnetic moments of metal phthalocyanine and tetraphenylporphyrin molecules on noble metal surfaces

In order to understand the Kondo effect observed in molecular systems, first-principles calculations have been widely used to predict the ground state properties of molecules on metal substrates. In this work, the interaction and the local magnetic moments of magnetic molecules (3d-metal phthalocyanine and tetraphenylporphyrin molecules) on noble metal surfaces are investigated based on the density functional theory. The calculation results show that the dz2 orbital of the transition metal atom of the molecule plays a dominant role in the molecule—surface interaction and the adsorption energy exhibits a simple declining trend as the adsorption distance increases. In addition, the Au(111) surface generally has a weak interaction with the adsorbed molecule compared with the Cu(111) surface and thus serves as a better candidate substrate for studying the Kondo effect. The relation between the local magnetic moment and the Coulomb interaction U is examined by carrying out the GGA+U calculation according to Dudarev's scheme. We find that the Coulomb interaction is essential for estimating the local magnetic moment in molecule—surface systems, and we suggest that the reference values of parameter U are 2 eV for Fe and 2–3 eV for Co.

Modulation of porphyrin photoluminescence by nanoscale spacers on silicon substrates

We investigate photoluminescence (PL) properties of quasi-monolayered tetraphenyl porphyrin (TPP) molecules on silicon substrates modulated by three different nanoscale spacers: native oxide layer (NOL), hydrogen (H)-passivated layer, and Ag nanoparticle (AgNP) thin film, respectively. In comparison with the PL intensity from the TPP molecules on the NOL-covered silicon, the fluorescence intensity from the molecules on the AgNP-covered surface was greatly enhanced while that for the H-passivated surface was found dramatically suppressed. Time-resolved fluorescence spectra indicated shortened lifetimes for TPP molecules in both cases, but the decay kinetics is believed to be different. The suppressed emission for the H-passivated sample was attributed to the weaker decoupling effect of the monolayer of hydrogen atoms as compared to the NOL, leading to increased nonradiative decay rate; whereas the enhanced fluorescence with shortened lifetime for the AgNP-covered sample is attributed not only to the resonant excitation by local surface plasmons, but also to the increased radiative decay rate originating from the emission enhancement in plasmonic “hot-spots”.

Coupling of Cobalt–Tetraphenylporphyrin Molecules to a Copper Nitride Layer

For applications such as molecular electronics and spintronics, it is very important to accurately describe the interface between molecular species and the underlying surfaces. In this work, we have used low temperature scanning tunneling microscopy to study the physical and chemical interaction between individual cobalt−tetraphenylporphyrin molecules and a copper nitride monolayer. We have demonstrated that the Cu3N−Cu(110) system promotes a selective decoupling of the porphyrin macrocycle from the local environment, allowing visualization of the molecular orbitals and vibronic states of the molecule, while maintaining a strong coupling between the Co-dz 2 orbital and the substrate. The reverse behavior was observed for adsorption of the same molecule onto a metallic Cu(110) surface. First-principles calculations confirm both the molecular adsorption site and the electronic decoupling of the molecular states from the substrate.

Significant sensitivity and stability enhancement of tetraphenylporphyrin-based optical oxygen sensing material in presence of perfluorochemicals

Emission-based oxygen sensing properties of highly luminescent tetraphenylporphyrin molecules were investigated in polystyrene, ethyl cellulose, poly(1-trimethylsilyl-1-propyne) and poly(isobutylmethacrylate) matrices. The effect of perfluorochemicals (PFCs) on oxygen sensitivity and stability of the sensor materials was also examined. Fluorescence intensity and lifetime measurements of meso-tetraphenylporphyrinato Zn ( II ) (ZnTPP) and meso-tetraphenylporphyrin (H2TPP) materials were performed in the concentration range of 0–100% pO 2. The fluorescence intensity variation of H2TPPvs. oxygen was 86%. H2TPP-based composite also yielded higher Stern–Volmer constant, faster response and regeneration time, excellent long term photostability and larger linear response range with respect to ZnTPP. The detection limit of oxygen for H2TPP was less than 0.5%. When stored in sealed bags protected from sunlight, no decrease in oxygen sensitivity was observed during approximately five months. As far as we know, the gathered utilization of PFCs and H2TPP embedded in polymer matrices was not previously described in literature, and has present amelioration compared to materials already existing.

Theoretical investigation of fluorescence properties of EDTA and DTPA substituted tetraphenylporphyrin molecules

The matrix elements of spin–orbit coupling operator (HSO) and non-adiabatic coupling operator (Ω) for the H2ATPP–EDTA and H2ATPP–DTPA molecules were calculated using INDO method. Rate constants of internal conversion and of intersystem crossing were calculated using the values of matrix elements of HSO and Ω operators and excitation energies both calculated with the ADC(2) and TDDFT methods and obtained from experimental data. Results of calculations show that the probability of radiationless deactivation in internal conversion channel is greater than the probability of radiationless transition in intersystem crossing channel for considered molecules. Obtained theoretical values of fluorescence quantum yield have good agreement with their experimental values.

Electronic absorption spectrum of monoaminosubstituted tetraphenylporphyrin with diethylenetriaminepenetaacetic acid for the substitute

The equilibrium geometry of the ground electronic state of amine derivative of the tetraphenylporphyrin molecule comprising diethylenetriaminepentaacetic acid for the substitute is obtained by the functional density method using the B3LYP functional in the 6-31G (d, p) basis. The electronic absorption spectrum of the molecule in ethanol solution is measured in the wavelength range 400–650 nm and interpreted by the PCM/TDDFT method (with B3LYP and CAMB3LYP functionals) in the 6-31G (d, p) basis.

A study of vibrational spectra of metallotetraphenyl porphryins: an algebraic approach

Using Lie algebraic method, we report a study of the vibrational frequencies of various metallotetraphenyl porphyrins and its cation radicals, i.e. Cu[TPP], Cu[TPP]+, Ni(TPP), Ni(TPP)+, ClFe(TPP) and ClFe(TPP)+ for 60 vibrational bands each using U(2) algebraic model Hamiltonian. Intermode couplings in algebraic models have been included to achieve improved RMS deviations as well as to get deep insight into detailed spectroscopy for these tetraphenyl porphyrin molecules.

Transfer of Cl Ligands between Adsorbed Iron Tetraphenylporphyrin Molecules

Iron tetraphenylporphyrin chloride (FeTPPCl) adsorbed on a Au(111) substrate is investigated using low-temperature scanning tunneling microscopy. Cl is controllably transferred between the Fe center of a selected molecule and the tip of the microscope without disrupting the surrounding molecular pattern. Cl abstraction from FeTPPCl is triggered by removing an electron from the highest occupied molecular orbital. Density functional calculations suggest that the reaction involves a change in the oxidation state of the Fe ion.

Band alignment and charge transport characteristics of TPP/ZnO hybrid for photovoltaic cell potential

Growth of ZnO nanocrystals has been carried out by a two-electrode electrochemical cell arrangement. The nanocrystals serve as substrates onto which tetraphenylporphyrin (TPP) is evaporated under integrated UHV conditions for the development of TPP/ZnO hybrid specimen. The quality of the hybrid specimen is investigated by XPS measurement. Direct interaction between the valence electrons of the adsorbed TPP molecules and ZnO electronic levels is revealed by Ultraviolet Photoemission Spectroscopy (UPS). Absorption spectroscopic studies are used to examine the ground state electronic structure and polarization dependence (excitation to π* and σ* vacant orbitals) of the hybrid specimen. The studies further show efficient charge transfer from donor (TPP) to proximate acceptor (ZnO). Thus, porphyrin molecules act as an active layer for generation of electron and as an enhancement for subsequent sudden transfer of the charge to the ZnO at a timescale faster than that of core hole.

Gold–sulfur bond breaking in Zn(II) tetraphenylporphyrin molecular junctions

Quantized conductance measured from single tetraphenylporphyrin molecules with and without a central zinc(II) [Zn(II)] atom was measured using a molecular break junction (MBJ) method. From the conductance histograms we observed an additional 1.7Å stretch for two-state conductance in a single Zn(II) tetraphenylporphyrin (ZnTPP) molecule as compared to single state conductance in a free tetraphenylporphyrin (TPP) molecule, i.e., no central Zn(II) atom. First-principles density functional calculations, using an electrode–molecule–electrode model, are completed to provide insight into the mechanisms attributed to bond stretching, and eventual bond breaking, to better understand the additional 1.7Å of stretching observed with ZnTPP.

Theoretical investigation of fluorescence properties of EDTA and DTPA substituted tetraphenylporphyrin molecules

Theoretical investigation of fluorescence properties of EDTA and DTPA substituted tetraphenylporphyrin molecules

A surface-anchored molecular four-level conductance switch based on single proton transfer

The development of a variety of nanoscale applications requires the fabrication and control of atomic or molecular switches that can be reversibly operated by light, a short-range force, electric current or other external stimuli. For such molecules to be used as electronic components, they should be directly coupled to a metallic support and the switching unit should be easily connected to other molecular species without suppressing switching performance. Here, we show that a free-base tetraphenyl-porphyrin molecule, which is anchored to a silver surface, can function as a molecular conductance switch. The saddle-shaped molecule has two hydrogen atoms in its inner cavity that can be flipped between two states with different local conductance levels using the electron current through the tip of a scanning tunnelling microscope. Moreover, by deliberately removing one of the hydrogens, a four-level conductance switch can be created. The resulting device, which could be controllably integrated into the surrounding nanoscale environment, relies on the transfer of a single proton and therefore contains the smallest possible atomistic switching unit.

Self-Assembly of Insoluble Porphyrins on Au(111) under Aqueous Electrochemical Control

Self-assembled monolayers of a water-insoluble porphyrin, tetraphenyl porphyrin (TPP), in the presence of an aqueous electrolyte were characterized in situ with electrochemical scanning tunneling microscopy (EC-STM) at working electrode potentials of between 0.5 and -0.2 V. Isolated domains of TPP monolayers with differing orientation were observed on Au(111) in 0.1 M HClO(4) over this entire potential window. Individual TPP molecules could be resolved over a range of 700 mV, from open circuit potential (OCP) to near the hydrogen evolution potential. The unit cell is square, and the distance between neighboring molecules is about 1.4 ± 0.1 nm. High-resolution images allow the internal molecular structure to be discerned. No changes in the STM contrast of individual molecules were observed as the potential was changed. In a neutral electrolyte (0.1 M KClO(4), pH ~6), the potential range of stability of ordered structures is reduced. On HOPG, TPP forms ordered hexagonal structures with a lattice constant of about 2.6 nm in the double-layer potential region in 0.1 M HClO(4).