Tetraphenylporphyrin Thin Films Research Articles

Качественный и количественный анализ морфологии поверхности порфириновых пленок

The surface morphology of tetraphenylporphyrin thin polycrystalline films – H2TPP and ZnTPP obtained by vacuum condensation under quasi-equilibrium conditions is analyzed by sc. The use of analytical methods for processing images of the organic films surface obtained by standard methods, allows to identify not only qualitative, but also quantitative characteristics of the polycrystalline films structure: the average grain size, grain size distribution, the presence of texture and characteristic of crystallites orientations. It is shown that free based H2TPP tetraphenylporphyrin films have a more pronounced texture and a larger crystallite size than ZnTPP, which is due to the peculiarities of self-organization of molecules, if condensation occurs under the same conditions. The applicability of this method of image analysis for obtaining information about the structure and morphology of the surface of thin organic films during vacuum condensation is shown.

Interfacial electronic properties of FeTPP-Cl on HOPG

Conjugated tetrapyrrole complexes have potential for novel spintronic and optoelectronic devices. Detailed understanding of electronic properties at molecule–substrate interface is essential for their potential applications. In this report, electronic properties of iron (III) chloride tetraphenylporphyrin (FeTPP-Cl, C44H28ClFeN4) thin films on highly oriented pyrolytic graphite (HOPG) have been investigated using photoemission and X-ray absorption spectroscopy. Photoemission analysis shows that no significant charge transfer takes between FeTPP-Cl and HOPG. Fe 2P3/2 core level analysis indicates towards dechlorination of FeTPP-Cl on HOPG in the monolayer regime. Fe L2,3 edge X-ray absorption spectroscopy reveal that iron oxidation state changes from +2 to +3 due to adsorption on to HOPG, suggesting a substrate driven dechlorination of FeTPP-Cl. Curve fitting analysis of XPS Fe 2p3/2 spectrum for the deposition of FeTPP-Cl on HOPG in the monolayer regime confirms +2 oxidation state of central metal atom. An interface dipole of 0.2 eV has been found at FeTPP-Cl/HOPG interface suggesting weaker molecule–substrate interactions.

Substrate-Independent Control of Polymorphs in Tetraphenylporphyrin Thin Films by Varying the Solvent Evaporation Time Using a Simple Spin-Coating Technique

Porphyrin derivatives are promising materials for various thin-film-based devices such as solar cells, field-effect transistors, and gas sensors. Since the molecular aggregation structure in a thin film significantly influences the device performance, controlling the aggregation structure is of crucial importance. In this study, we show that three different crystalline polymorphs of free-base tetraphenylporphyrin (H2TPP) can be made to form in spin-coated thin films depending on the evaporation time of the solvent. The results show that the aggregation structure in the as-spun films is controlled by the solvent evaporation time, and the initial film structure determines the polymorphs obtained after thermal annealing.

Spectroscopic characterization of thermally evaporated oxovanadium(IV) tetraphenylporphyrin thin films

Thin films of oxovanadium(IV) tetraphenylporphyrin (VOTPP) were prepared on quartz substrates by using thermal evaporation technique. The surface morphology and x-ray diffraction analysis of the VOTPP thin films were investigated. The micrographs of atomic force microscope of the films reveled nanostructure formation. The spectroscopic measurements of the transmittance and reflectance for VOTPP films were recorded in the spectrum range 190 –2000 nm, and from which many optical constants such as refractive index, extinction index and dielectric constant were determined. The absorption spectrum of VOTPP film showed an intense Soret band, two electronic quasi-states (Q-band) and two other bands (N and L) extended over the UV–Vis spectral region. The type of electronic transition bands of VOTPP films showed indirect allowed. The values of optical energies band-gaps were determined to be 1.89, 2.15 and 2.61 eV, in addition to Urbach tail energy was 0.044 eV. Furthermore, Wemple-DiDomenico model was applied to a normal dispersion region of the refractive index spectrum in order to extract many dispersion parameters such single oscillator energy, dispersion energy, infinite dielectric constant and lattice dielectric constant. The present spectroscopic results reveals that the thin films of VOTPP could be utilized as promising absorbing layers in energy conversion devices.

Raman spectroscopy and optical constants of nanostructured oxovanadium(IV) tetraphenylporphyrin thin films

Oxovanadium(IV) tetraphenylporphyrin (VOTP) thin films were prepared by thermal evaporation technique. The structural investigation and surface morphology of the VOTPP films were characterized by X-ray diffraction (XRD) and atomic force microscopy techniques (AFM). The XRD patterns used to extract lattice parameters, Miller indices, crystallite sizes and dislocation densities for VOTPP films are computed. While the micrographs of AFM of the films showed nanoparticles of cones-shaped structures turned to the agglomerations of nanostructures with the annealing temperature up to 250 °C. Raman spectroscopy of the as-deposited and annealed VOTPP films was recorded to identify their vibrational modes and functional groups and revealed thermal stability for these films. Moreover, UV–Vis absorption spectroscopy of the VOTPP films showed highly intense Soret band, two quasi-electronic Q-bands and two other L and N bands. The spectroscopic measurements of transmittance and reflectance of VOTPP thin films were recorded under different annealing temperatures, and from which, many optical constants and dispersive parameters were determined such as refractive index, absorption index, absorption coefficient, dielectric constant, oscillator energy and dispersion energy. The optical band gaps for as-deposited and annealed VOTPP films were calculated to be 1.9 and 1.69 eV, respectively. The annealing temperature induced changes significantly in the structural properties and spectroscopic characterizations and optical constants of VOTPP films. The present results revealed that VOTPP films could be utilized as promising absorbing layers in photovoltaics.

Temperature-dependent photoluminescence of H2TPP and ZnTPP thin films on Si substrates

Temperature-dependent photoluminescence (PL) properties of tetraphenyl porphyrin (H2TPP) and Zinc-tetraphenyl porphyrin (ZnTPP) thin films on the silicon substrates has been investigated. The photoluminescence (PL) properties are observed within the temperature range of 163–543 °K. The 405 nm diode laser beam is used to excite the molecule during the photoluminescence measurement. The integrated PL intensity exhibits abnormal behaviour, the intensity decreases with temperature in the temperature range of 163-273 °K, and then followed by the increase in the further temperature range of 273-543 °K. This anomaly reflects the competition between the radiative recombination process and the non-radiative recombination processes, i.e. carrier capture, thermalization, and carrier relaxation processes. The peak energy of 0-0 and 0-1 transitions show a red-shift with temperature, while their full width at half maximum increases.

Amino acid adsorption on tetraphenyl porphyrin films

In this work, metal free, zinc and copper tetraphenyl porphyrin thin films were employed as substrates to study their interaction with glycine, serine, glutamate, lysine and argynine amino acids in order to investigate the effect of the metallic center and the amino acid characteristics in the adsorption phenomena. The amount of amino acid adsorbed on the films was quantified by using the Ruhemann method. Adsorption isotherms were obtained and analyzed in order to predict the adsorption mechanism for each case. In addition, the morphology of the films was investigated before and after the amino acid immersion by using scanning electron and atomic force microscopies. On the other hand, dynamic contact angle measurements were performed to monitor the spreading phenomena and changes in the hydrophobic nature of the surfaces after the amino acid interaction. From the results, it was observed that the largest deposited amino acid on all three surfaces corresponded to the positively charged compounds, while serine was the lowest adsorbed amino acid in all cases. These results can be attributed to electronic interactions between the amino acids’ lateral chains and the electronic [Formula: see text] distribution of the porphyrin macrocycle ring, and they provide important information regarding the amino acid selectivity of adsorption on tetraphenyl porphyrin films.

Morphological, Optical and Electrical Characterization of the Interfaces in Fullerene-Porphyrin Thin Films.

The role of the interfaces on the optoelectronical properties of porphyrin-fullerene composites has been studied by means of ultraviolet-visible (UV-Vis) and Raman spectroscopy, atomic force microscopy (AFM) and electric conductivity measurements. A simple method of synthesis of donor- acceptor complexes has been performed by subsequent deposition of C60 fullerene and tetraphenylporphyrin (H₂TPP) thin films, using physical vapor deposition (PVD) on a (100) silicon substrate. UV-Vis spectra showed that the interaction of π-orbitals leads to a more ordering for the dipole moments arrangement and the π-orbitals overlapping between C60 and H₂TPP molecules. Besides, Raman spectra presented intensity changes at 960 and 1000 cm-1, both related to the vibration of the pyrrole ring and the rocking of the H on the C atoms within the macrocycle. Therefore, it can be expected that the interface C60-H₂TPP should have a main role in the electric response of the multilayer films. The measurements of surface conductivity indicated that interface has specific contribution, and the value of surface conductivity is enhanced by charge delocalization mechanisms occur by π-π stacking interactions. It was found that the transversal conductivity of 3-layer films was enhanced by a factor of 4 in comparison to 2-layer film, due to charge transfer mechanisms occur in the junctions that could extend the diffusion length of the charge carriers. Finally, the interface generated between C60 and H₂TPP films, without any linking molecule, enhance charge transport mechanism through the films.

Scanning tunneling microscopy of the tetraphenylporphyrin thin films on a graphite single-crystal substrate

Features of the surface topography of a tetraphenylporphyrin film on a graphite single crystal (HOPG) substrate and the local current-voltage characteristics were studied using a scanning tunneling microscope under ambient conditions. STM images of surface were acquired on a scale from a few nanometers to 4 micrometers. Local tunnelling current-voltage characteristics in different ranges of bias voltage and in different directions of voltage scanning can have hysteresis due to the hopping electron conductivity in porphyrin.

Optical and electrochemical gas sensing applications of Cu Tetraphenylporphyrin thin films

A Cu tetraphenylporphyrin (CuTPP) gas sensor has been designed and fabricated for detection of volatile organic compounds (VOCs). The synthesized CuTPP was characterized by X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance spectroscopy (1H NMR), then deposited onto a single mode potassium (K+) ion-exchanged glass optical waveguide (OWG) surface by spin coating and dip-coating of a CuTPP thin film on the surface of an alumina ceramic tube, where they acted as a sensing layer. The surface topography of the CuTPP thin film/K+-exchanged layer was investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM), where it showed a root-mean-square (RMS) roughness of about 3.4 nm with cross-section of nanoparticles exhibit rectangular pyramid morphology. CuTPP film sensors used to detect styrene gas as a typical example of VOCs. The experimental results showed that, at room temperature, CuTPP thin film/K+-exchanged OWG sensing device revealed higher response to styrene and xylene in the range of 10 ppb-1000 ppm; the response to CuTPP electro-chemical sensor response to styrene and xylene were 3.6 and 2.3, respectively.

The Effect of Crystallization Conditions on the Spectral Characteristics of Tetraphenylporphyrin Thin Films

The goal of this work is to study the processes of self-organization in tetraphenylporphyrin (H2TPP) films made by condensation under various conditions. Experimental studies of the spectral characteristics of H2TPP thin films obtained by the liquid method from a H2TPP toluene solution and by vacuum deposition on different substrates are carried out. It is shown that the structure of the H2TPP samples changes depending on the technique of synthesis on different substrates, which shows itself in changes (“red” shift) in the photoluminescence and absorption spectra. The changes are caused by a different degree of crystallinity depending on the homogeneity of the surface of the substrates and their temperature.

Impact of Kinetically Restricted Structure on Thermal Conversion of Zinc Tetraphenylporphyrin Thin Films to the Triclinic and Monoclinic Phases

The powerful combination of p-polarized multiple-angle incidence resolution spectroscopy (pMAIRS) and grazing incidence X-ray diffraction (GIXD) is applied to the structural characterization of zinc tetraphenylporphyrin (ZnTPP) in vapor-deposited films as a function of the deposition rate. The deposition rate is revealed to have an impact on the initial film structure and its conversion by thermal annealing. The pMAIRS spectra reveal that a fast deposition rate yields a kinetically restricted amorphous film of ZnTPP having a “face-on orientation”, which is readily discriminated from another “randomly oriented” amorphous film generated at a slow deposition rate. In addition, the GIXD patterns reveal that the film grown at a slow deposition rate involves a minor component of triclinic crystallites. The different initial film structure significantly influences the thermal conversion of ZnTPP films. The randomly oriented amorphous aggregates with the triclinic crystallite seeds are converted to the thermodyna...

Effect of γ- irradiation on structural, optical and electrical properties of thermally evaporated iron (III) chloride tetraphenylporphyrin thin films

Influence of γ-irradiation on structural, optical and electrical properties of thermally evaporated iron (III) chloride tetraphenylporphyrin (FeTPPCl) thin films have been reported. The structural features are investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. The optical constants of as-deposited and γ-irradiated FeTPPCl thin films have been determined in the wavelength range 200–2500nm using spectrophotometric measurements at nearly normal incidence of light. The calculated values of the absorption coefficient,α, are used to estimate the type of transitions for as-deposited and γ-irradiated FeTPPCl thin films. The real part of the refractive index in the transparent region is discussed by using a single-oscillator and Drude models. According to Millerʼs rule, the single oscillator model is used to deduce the third-order nonlinear susceptibility, χ(3). The temperature dependence of DC electrical conductivity, σDC, confirms the semiconducting behaviour of FeTPPCl thin films. A free band type in the higher temperature region and hopping type in the low-temperature region have been used to explain the DC conduction mechanisms of FeTPPCl thin films.

Growth of tetraphenyl-porphyrin thin films on Ag(111)

The growth of tetraphenyl-porphyrin (2H-TPP) thin films on Ag(111) has been investigated in situ using differential reflectance spectroscopy (DRS) and low energy electron diffraction (LEED). Based on the evolution of the optical properties during deposition, the growth of 2H-TPP on Ag(111) can be assigned to follow the Stranski–Krastanov mode with a three monolayer (ML) thick wetting layer. The optical properties of the first three monolayers differ substantially from each other and from those of 3D crystallites grown on top of the wetting layer. This observation is assigned to the formation of two dimensional J-aggregates in the 2H-TPP wetting layer. The results illustrate how self assembly of organic molecules on surfaces can introduce novel optical properties.

Effect of illumination on thermally evaporated iron (III) chloride tetraphenylporphyrin thin organic films

Influence of illumination by a white light of incandescent lamp (150 W) on the optical properties of thermally evaporated iron (III) chloride tetraphenylporphyrin (FeTPPCl) thin films have been performed. The optical constants of As-deposited and illuminated FeTPPCl thin films have been determined in the wavelength range 400–2500 nm using spectrophotometric measurements at nearly normal incidence of light. The type of optical transitions for As-deposited and illuminated FeTPPCl thin films is ascertained from the spectral behavior of their absorption coefficient, α. The real part of the refractive index of As-deposited and illuminated FeTPPCl thin films in the region of optical transparency is analyzed basing on single-oscillator and Drude models. The third order nonlinear susceptibility, χ(3), of As-deposited and illuminated FeTPPCl thin films is obtained from the single-oscillator model and the Miller’s rule.

Probing Two-Dimensional vs Three-Dimensional Molecular Aggregation in Metal-Free Tetraphenylporphyrin Thin Films by Optical Anisotropy

Porphyrins represent molecular building blocks for the development of a large variety of functional materials. The control of subtle intramolecular and intermolecular processes in solid porphyrin aggregates is promising for the establishment of organic nanotechnology, which requires the knowledge of the properties of nanometric aggregates down to single atoms. Within this framework, the optical anisotropy in thin and ultrathin metal-free tetraphenylporphyrin (H2TPP) films deposited on graphite carries interesting information related to their molecular aggregation. In this work, we compare the surface morphology and the optical anisotropy of H2TPP 2D layers, obtained following a recently developed experimental strategy, with thin films where both 2D and 3D aggregates are present. After reaching a fine control of the relative amount of the two phases present in films of different thicknesses, we propose a precise physical model for the optical response of the pure 2D phase, therefore correlating its optical anisotropy with the electronic properties of single H2TPP molecules, the occurrence of intramolecular chemical reactions, and the molecular arrangement. The response of thicker films, characterized by the coexistence of the 2D and 3D phases, is described by a phenomenological model that considers the main spectroscopic features.

Structural, absorption and dispersion characteristics of nanocrystalline copper tetraphenyl porphyrin thin films

Thin films of tetraphenyl porphyrin (CuTPP) were prepared by thermal evaporation technique under vacuum. The surface morphology and crystalline structural characteristics of CuTPP were achieved by atomic force microscopy (AFM). The crystalline structure of CuTPP thin films was investigated by using X-ray diffraction. The average crystallite size, D, was calculated using the modified Scherrer's equation. Optical constants (refractive index, n, and absorption index, k) of CuTPP films were estimated by using spectrophotometric measurements of transmittance and reflectance in the spectral range from 200 to 2500nm.The optical constants of CuTPP are independent of film thickness in the thickness range 400–1270nm. The dependence of absorption coefficient on the photon energy was determined and the analysis of the result showed that the optical transition in CuTPP films is allowed and indirect. The onset and optical energy gap for are 1.80 and 2.30eV, respectively. The UV–vis absorption spectrum was analyzed in terms of both molecular orbital and band theories. The optical dispersion parameters of CuTPP thin films such as oscillator energy, Eo, dispersion energy, Ed, the lattice dielectric constant, ɛL, the high frequency dielectric constant, ɛ∞, and the ratio of the free charge carrier concentration to the effective mass, N/m* were investigated. Moreover, third order nonlinear susceptibility, χ(3) of CuTPP films was also considered.

Effect of annealing on structural and optical properties of copper tetraphenylporphyrin (CuTPP) thin films

Thin films of CuTPP were prepared by thermal evaporation techniques. X-ray diffraction technique, Infrared spectra and scanning electron microscope were used to investigate the crystalline structure and morphologies of CuTPP thin films before and after annealing. The optical properties of the as-deposited and annealed CuTPP thin films were investigated by using spectrometric measurements at nearly normal incidence of light in the wavelength range 200–2500 nm. The type of electronic transition and the optical energy gap were estimated by using the obtained data of the absorption index, k, for the as-deposited and annealed CuTPP films. The third order nonlinear susceptibility was estimated for as-deposited and annealed CuTPP thin films. The dispersion parameters and the real and imaginary parts of dielectric constant were also calculated.

Effect of illumination on the structural and optical properties of Cu (II) tetraphenyl porphyrin (CuTPP) thin films

CuTPP thin films were prepared by thermal evaporation technique, on glass and quartz substrates. Illumination by a white light of incandescent lamp (150W) was found to be accompanied by structural effects, which, in turn, lead to changes in the optical properties of CuTPP thin films. An optical characterization method based on spectrophotometeric measurements of transmittance and reflectance at normal incidence of light in the wavelength range 200–2500nm was used to analyze the optical properties of CuTPP thin films. The obtained optical constants were used to estimate the type of optical transitions for the as-deposited and illuminated CuTPP thin films. The optical parameters such as oscillator energy, Eo, dispersion energy, Ed, lattice dielectric constant, εL, high frequency dielectric constant, ε∞, and the ratio of the free charge carrier concentration to the effective mass, N/m⁎ were estimated.

Optical and magneto-optical properties of metal phthalocyanine and metal porphyrin thin films

The optical constants together with the magneto-optical Voigt constants of several phthalocyanine (Pc) and methoxy functionalized tetraphenylporphyrin (TMPP) thin films prepared on silicon substrates are presented. The materials investigated are MePc with Me = Fe, Co, Ni, Cu, Zn and MeTMPP with Me = Cu, Ni. We also compared our results to the metal-free H2Pc, H2TPP and H2TMPP. The experimental results will be supported by electronic structure calculations based on density functional theory (DFT) and interpreted using the perimeter model initially proposed by Platt. The model allows for qualitative understanding of the forbidden character of transitions in planar, aromatic molecules, and is able to qualify differences between Pc and TMPP type materials.