Zinc Tetraphenylporphyrin Research Articles

Growth of a highly ordered inhomogeneous kinetically trapped molecular monolayer

It is often assumed that the self-assembly of organic molecules on a noble-metal surface results in a structure that is in thermodynamic equilibrium. Here, using scanning tunnel microscopy, we observe instead a highly ordered metastable striped monolayer phase of zinc tetraphenylporphyrin, self-assembled at 300 K on Ag(100). The usually reported stable square phase is found only after higher-temperature annealing. We use a statistical mechanical model to reveal a possible molecular mechanism for this process, in which the competition of molecule and substrate interactions at the growth front leads to the growth of a kinetically trapped inhomogeneous ordered structure. Our proposed mechanism rests only on simple features of molecular geometry and interactions, and the resulting principles could be used to promote particular outcomes of growth in other examples of molecular assembly at surfaces.

A Reversible Spectrophotometric Method Based on a Coupled Microfluidic Chip for Highly Selective Ammonium Detection

A coupled chip aiming at economical and highly selective ammonium detection was fabricated. It consisted of a reaction chip, a gas-diffusion chip, and a detection chip. Zinc tetraphenylporphyrin dyed on the cation-exchange resin microbeads was used as the indicating material to avoid excess consumption for its reversibility. PDMS was selected as the material of the gas-diffusion membrane. A portable spectrometer was applied for spectrum analysis. By analysis of spectrum change, the high selectivity was confirmed because no component had interference on detection effect. Good performance was shown for all the tested concentrations (0.2–50 mg·L−1). The stability and reversibility were also judged by the spectrum data obtained from the indicating process and the recovering process. Finally, real samples containing ammonium were tested and the results were compared to those came from a standard method to confirm the accuracy of our method.

Interrogating the Structure of Molecular Cavity Polaritons with Resonance Raman Scattering: An Experimentally Motivated Theoretical Description

The formation of exciton polaritons by strongly coupling molecular electronic transitions to spatially confined photons may change photochemical processes. However, the fundamental physical drivers of these proposed changes remain unclear. To understand the role of changes to molecular structure caused by polariton formation in these photochemical processes we develop an experimentally motivated theoretical description of resonance Raman scattering from exciton polaritons. By modeling the structural parameters of light absorption in zinc tetraphenyl porphyrin and exciton polaritons formed from this molecule in nano-structured Fabry-Perot cavities, we simulate resonance Raman scattering excitation spectra from exciton polaritons and assess how these spectra depend on the polariton characteristics. We find the detuning of the cavity mode energy from that of the molecular transition can affect the structure of the resulting polaritonic states, as inferred from our simulated spectra. We also find previously u...

Synthesis, Spectral, Electrochemical and Photovoltaic Studies of A3 B Porphyrinic Dyes having Peripheral Donors.

Three new 'push-pull' A3 B Zn(II)porphyrin dyes having meso-pyrenyl, carbazolyl and phenothiazine as electron donors (A) and phenylcarboxylic acid as acceptor/anchor (B) were synthesized and utilized for DSSC application. The spectral and electrochemical redox properties of these new dyes were studied and compared with trans-A2 BC Zn(II) porphyrin dyes under similar experimental conditions. Red-shifted, broadened absorption peaks, lower fluorescence quantum yields, and shortened lifetimes were observed for the A3 B dyes as compared to zinc tetraphenylporphyrin control, ZnTPP. DFT optimized structures suggested effective charge separation related to enhanced charge injection efficiency. Driving force for electron injection (ΔGinj ) and dye regeneration (ΔGreg ) calculated from the spectral and electrochemical studies predicted facile electron injection from excited dye into semiconductor TiO2 in the constructed solar cells. Phenothiazine appended dye (KP-TriPTZ-Zn) showed the highest η value of 7.3 % for PCE with greater Jsc and Voc values due to its better light harvesting ability and reduced dye aggregation as compared to other dyes. Our studies demonstrate that the dyes having multiple electron-donating groups exhibit higher photon-to-current conversion efficiency.

Assembly, charge-transfer and solar cell performance with porphyrin-C60 on NiO for p-type dye-sensitized solar cells.

A series of zinc tetraphenylporphyrin photosensitizers furnished with three different anchoring groups, benzoic acid, phenylphosphonate and coumarin-3-carboxylic acid, were prepared using 'click' methodology. All three gave modest performances in liquid junction devices with I3-/I- as the electrolyte. The distinct spectroscopic properties of the porphyrins allowed a detailed investigation of the adsorption behaviour and kinetics for charge transfer at the NiO|porphyrin interface. The adsorption behaviour was modelled using the Langmuir isotherm model and the phosphonate anchoring group was found to have the highest affinity for NiO (6.65 × 104 M-1) and the fastest rate of adsorption (2.46 × 107 cm2 mol-1 min-1). The photocurrent of the p-type dye-sensitized solar cells increased with increasing dye loading and corresponding light harvesting efficiency of the electrodes. Coordinating the zinc to a pyridyl-functionalized fullerene (C60PPy) extended the charge-separated state lifetime from ca 200 ps to 4 ns and a positive improvement in the absorbed photon to current conversion efficiency was observed. Finally, we confirmed the viability of electron transfer from the appended C60PPy to phenyl-C61-butyric acid methyl ester, a typical electron transporting layer in organic photovoltaics. This has implications for assembling efficient solid-state tandem solar cells in the future. This article is part of a discussion meeting issue 'Energy materials for a low carbon future'.

Ultrafine Fibers of Poly-(3-Hydroxybutyrate) with Zinc–Tetraphenylporphyrin Obtained by Electrospinning

Ultrathin fibers of poly(3-hydroxybutyrate) (PHB) with a zinc–tetraphenylporphyrin complex (0-5%) were obtained by electrospinning. Optical microscopy, differential scanning calorimetry, electron paramagnetic resonance, and x-ray structural analysis were used to study the structure of the fibers. It was shown that addition of the ZnTPP complex to the PHB fiber increases the crystallinity and lowers the molecular mobility in the amorphous regions of the polymer. The action of heat on the fiber (annealing at 140°C) leads to significant increase of crystallinity and molecular mobility in the amorphous regions of fibers of PHB and of PHB with 1% of ZnTPP. With 3-5% content of the complexes the crystallinity of the fiber is substantially reduced. The results of the work make it possible to recommend the investigated materials for biomedical application as matrices with antibacterial activity

Two-Dimensional Film Growth of Zinc Tetraphenylporphyrin with the Aid of Solvent Coordination

Abstract Since the performance of an organic film device largely depends on the molecular arrangement in the film, control of the arrangement is crucial. Low molecular-weight organic semiconductor compounds, however, tend to have the edge-on orientation spontaneously due to crystallization on an inert surface. In fact, orientation control of a high-crystallinity compound is often difficult especially on an inert surface. In the present study, a face-on crystalline thin film of zinc tetraphenylporphyrin (ZnTPP) has readily been obtained on an inert surface by using solvent annealing (SA) with an appropriate solvent, formamide (FA). The prepared film is carefully analyzed by using the infrared (IR) p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) and grazing incidence X-ray diffraction (GIXD) techniques. The measurements show that an FA molecule coordinated on a zinc atom blocks the stacking interaction sites of the porphyrin ring, and instead the side to side interaction between the C–H group of the porphyrin rings and π orbital of the phenyl rings forms a two-dimensional sheet-like structure realizing face-on orientation.

Intrinsic and Catalyzed Photochemistry of Phenylvinylketone for Wavelength‐Sensitive Controlled Polymerization

AbstractReversible addition‐fragmentation chain transfer (RAFT) photopolymerization of phenylvinylketone (PVK) is investigated. The polymerization is investigated both in the presence of two photocatalysts (iridium tris(phenylpyridine (Ir(ppy)3) and zinc tetraphenylporphyrin (ZnTPP)). The polymerization was efficient in the absence of photocatalyst, and accelerated by Ir(ppy)3, whereas ZnTPP was found to lead to retardation of polymerization. In all cases, well‐controlled polymers were synthesized with linear growth in Mn with conversion and narrow molecular weight distributions. The observed photopolymerization kinetics were consistent with a Norrish Type 1 reaction of PVK to give two radicals. The polymerization kinetics were investigated as a function of wavelength, with the reaction rate being fastest with blue irradiation (440 nm), which is surprisingly far from the absorption maximum of PVK and Ir(ppy)3. Photodegradation of PVK was observed under UV irradiation, but the polymers were stable against visible light.

Oriented Self-Assembled Monolayer of Zn(II)-Tetraphenylporphyrin on TiO2 Electrode for Photoelectrochemical Analysis.

The photoelectrochemical performance of a zinc porphyrin sensitized TiO2 photoelectrode fabricated through the axial-coordination strategy has been studied. Zinc(II) tetraphenylporphyrin (TPPZn) was immobilized on the TiO2 electrode through the axial coordination reaction with surface premodified methyl 4-(1 H-imidazol-1-yl)benzoate (PhImMe). Spectral characterizations were carried out to confirm the robust interaction between TPPZn and PhImMe, while the chemical bonding of PhImMe on TiO2 surface has been evidenced by XPS measurement. The modified TiO2 electrode produces a stable and enhanced photocurrent signal under 410 nm irradiation at a bias of 0.2 V in phosphate buffer solution, compared with pristine TiO2. A sensitive increment of the photocurrent is observed with the addition of l-glutathione. A possible mechanism for this photoelectrochemical process includes the photoexcitation of the porphyrin, electron injection from porphyrin toward the TiO2, and the hole-scavenging process by the reductants. The "lying-low" surface conformation of the porphyrin plane might facilitate the PEC process owing to the enhanced electronic coupling between the porphyrin plane and the TiO2 substrate. A PEC analysis on l-glutathione has been carried out to evaluate the photoelectrochemical performance of the modified TiO2 electrode, which presents the wide linear ranges of 5-80 μM and 80-5000 μM, with a lower detection limit of 3.21 μM at an S/N ratio of 3. This work reports for the first time on the PEC performance of metalloporphyrin axially coordinated on a semiconductor surface and could lead to the designing of more efficient photoelectrochemical sensors and devices based on similar electrode structures.

Hydrophobic Functionalization of ZnO Nanosheets by In Situ Center‐Substituted Synthesis for Selective Photocatalysis under Visible Irradiation

AbstractThe selective degradation of specific substances in mixed contaminants is quite challenging. And a general approach for sensitized oxide semiconductor relies on dip‐coating method with sensitizer. Here, hydrophilic 2D, nest‐like architecture ZnO (ZnO NA) was hydrophobicly functioned by monomolecular–layer tetraphenylporphyrin zinc (ZnTPP), where ZnTPP was synthesized by means of an in situ center‐substituted (ISCS) process., i.e., the hydrogen atoms in the core of metal‐free tetraphenylporphyrin (H2TPP) are substituted by the unsaturated zinc ions in ZnO NAs. ZnTPP/ZnO NA was exhibited with significant hydrophobicity, benefitting to absorb hydrophobic phenol (PL). Further, it is realized to selectively photodegradate PL in the mixture by ZnTPP/ZnO NAs under visible irradiation. Note that the rate of degradation to hydrophobic PL by ZnTPP/ZnO NA is 9.17 times of that for ZnO NA within 150 min; on the contrary, the degradation rate of hydrophilic rhodamine B (RhB) by ZnTPP/ZnO is reduced by 40%. Radiative lifetime of photogenerated charges is obviously increased by ZnTPP/ZnO NA compared with that of ZnTPP, indicating the effective charge separation for ZnTPP/ZnO NAs. In addition, ZnTPP/ZnO NA produced more superoxide radicals (·O2−) in comparison to ZnO NA. With surface functionalization, the feasibility of selective photocatalysis under visible irradiation is demonstrated.

Parameters dependent synthesis of zinc stannate nanowires using CVD and its porphyrin dye loaded optical studies

Polycrystalline zinc stannate (Zn2SnO4) nanowires have been studied for its synthesis optimization using novel carbothermal catalytic method, wherein binary oxide precursors were used under inert atmosphere at variable CVD synthesis parameters. X-ray diffraction, FESEM, EDS, HRTEM, Raman and CL measurements are used to understand the typical behaviour of ternary metal oxide nanowires i.e. Zn2SnO4 growth. The optimization of Zn2SnO4 nanowires has been discussed via synthesis parameters followed with reaction equations corresponding to its optical and room temperature electrical properties. Further, its visible range sensitization has been demonstrated for suitable sample using zinc tetra phenyl porphyrin (ZnTPP) dye via dye adsorption method. Corresponding optical and IPCE studies of photo-electrodes shows broadened visible range absorption in 300–600 nm range and conversion efficiency of 28% (at ∼447 nm) for the nanowires having indirect band gap of ∼3.4 eV. This study opens up the potential application in photovoltaic, sensors and photo catalytic devices.

Specific Features of the Electron Structure of ZnTPP Aggregated Forms: Data of Optical Measurements and Quantum-Chemical Calculations

Zinc tetraphenylporphyrin (ZnTPP) films and ZnTPP-based composites are promising materials of organic photonics. Porphyrins are inclined towards self-assembly and the formation of molecular ensembles or differently structured aggregates. The energies of the formation of aggregates and ordered structures and modifications of their electron structures compared to that of a free ZnTPP molecule have not been adequately explored. In the study, the first comprehensive investigation of the structure, absorption and luminescence spectra, and photoluminescence kinetics of structurally perfect ZnTPP thin films produced under quasi-equilibrium conditions in vacuum is conducted. It is shown that changes in the absorption spectra and the red shift of the luminescence spectra of films by 0.15 eV from the spectra observed for ZnTPP solutions in toluene can be interpreted as a result of the formation of an ordered thin-film structure through the dimerization of porphyrin planar molecules under nearly equilibrium conditions. The optimal geometric structure, the energy of the ground state, and the electronic spectrum of excitations of the dimerized (ZnTPP)2 state are calculated in the context of density functional theory and time-dependent density functional theory. The energy gain on the formation of a dimer of symmetry Ci compared to two separate molecules is 0.23 eV per dimer; the HOMO–LUMO gap for the dimer is decreased by 70 meV. The radiative emission time in the ordered solid phase is an order of magnitude shorter than that in the solution in toluene and corresponds to 277 ps, which is typical of J aggregates of porphyrins.

Exciton Dynamics of Photoexcited Pendant Porphyrin Polymers in Solution and in Thin Films.

Several new polymers with rotatable zinc porphyrin pendants have been synthesized and their optical spectroscopic and photophysical properties, including upconversion efficiencies, determined in both fluid solution and thin films. Comparisons made with the β-substituted zinc tetraphenylporphyrin monomers and ZnTPP itself reveal that the yield of triplets resulting from either Q-band or Soret-band excitation of the polymers is surprisingly small. A detailed kinetic analysis of the fluorescence decays and transient triplet absorptions of the substituted monomers and their corresponding polymers reveals that this phenomenon is due to two parallel internal singlet quenching processes assigned to transient intrachain excimer formation. Consequently, the yields of upconverted S2 fluorescence resulting from Q-band excitation in the degassed polymers are significantly diminished in both fluid solution and thin films. Implications of these results for the design of polymer upconverting systems are discussed.

Structure control of a zinc tetraphenylporphyrin thin film by vapor annealing using fluorine containing solvent

The solvent vapor annealing (SVA) technique is one of the useful post processing techniques of a thin film, which is an alternative technique of the thermal annealing one. SVA has a great advantage that the molecular rearrangement in the film is made moderately by employing an appropriate solvent without the sample heating. The moderate processing is expected to yield a benefit that the molecular coalescence would be suppressed, which would readily keep the continuous surface topography of the film during the annealing, and another benefit that a metastable structure would be obtained. To make the best use of the SVA-specific characteristics, in the present study, a material having a metastable structure is chosen. The sample is zinc tetraphenylporphyrin (ZnTPP) that yields a metastable triclinic crystal structure, which can easily be converted to a monoclinic crystal structure by thermal annealing. A triclinic-structure film of ZnTPP by the combination of a wet process and the thermal annealing has thus never been reported. By choosing a fluorine-containing solvent, which has a low affinity to ZnTPP, a triclinic-structure film has first been obtained by a wet process while the surface continuity is protected.

Fully Atomistic Real-Time Simulations of Transient Absorption Spectroscopy.

We have implemented an electron-nuclear real-time propagation scheme for the calculation of transient absorption spectra. When this technique is applied to the study of ultrafast dynamics of Soret-excited zinc(II) tetraphenylporphyrin in the subpicosecond time scale, quantum beats in the transient absorption caused by impulsively excited molecular vibrations are observed. The launching mechanism of such vibrations can be regarded as a displacive excitation of the zinc-pyrrole and pyrrole C-C bonds.

Acrylamide polymers with covalently linked zinc(ii)tetraphenylporphyrin groups: synthesis and complexation with amino acids

New copolymers of acrylamide with zinc 5,10,15,20-tetrakis-(4-allyloxyphenyl)porphyrinate were synthesized and tested as cysteine and histidine sensors.

Efficient Upper-Excited State Fluorescence in an Organic Hyperbolic Metamaterial.

Upper-excited state emission is not usually observed from molecules owing to competition with much faster nonradiative relaxation pathways; however, it can be made more efficient by modifying the photonic density of states to enhance the radiative decay rate. Here, we show that embedding the small molecule zinc tetraphenylporphyrin (ZnTPP) in a hyperbolic metamaterial enables an ∼18-fold increase in fluorescence intensity from the second singlet excited state ( S2) relative to that from the lowest singlet excited state ( S1). By varying the number of periods in the HMM stack, we are able to systematically tune the ZnTPP fluorescence spectrum from red (dominated by emission from S1) to blue (dominated by emission from S2) with an instrument-limited decay lifetime <10 ps. Our results are consistent with a broadband Purcell enhancement in the radiative rate of both transitions predicted via transfer matrix modeling and point to a general opportunity to harness upper-excited states for spectrally tunable, ultrafast fluorescence via radiative decay engineering.

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...

Preparation and Properties of Hybrid Nanostructures of Zinc Tetraphenylporphyrinate and an Amphiphilic Copolymer of N-Vinylpyrrolidone in a Neutral Aqueous Buffer Solution

Water-soluble forms of a hydrophobic dye, zinc tetraphenylporphyrinate, are obtained via its solubilization by polymer particles of the micellar type formed by a copolymer of N-vinylpyrrolidone with triethylene glycol dimethacrylate. Hydrodynamic radii Rh and the size distribution of such particles in neutral aqueous buffer solutions are determined via dynamic light scattering. The electrochemical activity of the encapsulated dye is found, and its photochemical properties (absorption and fluorescence) are studied.

Dual functionality of metal-tetraphenylporphyrin in ZnO-based hybrid thin film transistors

Complementary hybridization of ZnO thin films with aluminum tetraphenylporphyrin (Al(III)TPP), zinc tetraphenylporphyrin (Zn(II)TPP) and H2TPP (tetraphenylporphyrin) was adopted for tuning the hybrid thin film transistor (TFT) performance and improving their flexibility. After the hybridization with the organic layers, the chemical and structural features of ZnO thin films were well-preserved as compared with those of solely ZnO thin films. The existence of organic layers was monitored by X-ray photoelectron spectroscopy depth profiling. We fabricated the TFT based on ZnO/organic layers, resulting in the on-off ratio and threshold voltage of the devices manipulated by selecting the organic layers. These results can be understood by the performance tuning mechanisms related with the electron charge transfer induced by a work function difference. Remarkably, a significant improvement of the flexibility in the hybrid films was achieved without any significant loss in optical transmittance, which will be high demand in transparent and flexible electronics.