Zinc Meso-tetraphenylporphyrin Research Articles

Anchoring porphyrin self-assembled dye sensitized solar cells: synthesis and photovoltaic application

Anchoring porphyrin, ZnPAc, featuring cyanoacetic acid group has been synthesized for application in a dye-sensitized solar cell. Capping layer dyes zinc meso-tetraphenyl porphyrin (ZnTPP) with anchoring porphyrin ZnPAc through axial coordination bonds of Zn-to-ligand self-assembles solar cell devices. With the introduction of cyanoacetic acid anchor, the higher electrons are effectively injected into the TiO2 semiconductor surface. Thus, the ZnTPP-ZnPAc-based device has more short-circuit current (JSC ) compared with our previously reported ZnTPP-ZnPA-based solar cell. The ZnPA and ZnPAc porphyrin anchoring dyes maintain a broad absorption spectrum and also improve electron injection and lower charge recombination compared to our previous reports on organic molecule anchored dye W3. Hence, the ZnTPP-ZnPAc self-assembled dye has higher power conversion efficiency. The assembled modes were also verified by transmission electron microscopy (TEM). To understand ZnTPP-ZnPAc for photovoltaic performance trends, we have carried out charge extraction, transient photovoltage decay and electrochemical impedance spectroscopy analysis.

Photoinduced electron transfer in metalloporphyrins

As a macromolecular heterocyclic compound, metalloporphyrin has proven to be very important for energy, environment, catalysis, and especially biological processes and biomedical applications. Herein, we synthesized a series of butterfly-shaped and distorted tetrahedral geometry tetracobalt complexes with different monophosphine ligands and coordinated them to zinc meso‑tetraphenylporphyrin (ZnTPP). The supra-molecular systems have been studied by fluorescence spectra, electrochemistry, and density functional theory (DFT), confirming that the electron transfer from the photo-excited ZnTPP to cobalt atoms relied on the zinc-nitrogen coordination bond, thereby quenching the fluorescence intensity from 4495.3 to 266.0 (Stern-Volmer constant). These characteristics have important potential in inhibiting photodynamic therapy (PDT) side effects and can be further researched and developed for photonics, imaging, acoustics, photocatalysis, and related biomedicine, energy, and environment applications.

Zinc porphyrin-anthraquinonylimidazole supramolecular dyads

In this work, the synthesis and spectroscopic characterization of new zinc porphyrin-anthraquinone dyads is proposed. In particular, electron donor units based on zinc meso-tetraphenylporphyrin (ZnTPP) and zinc octaethylporphyrin (ZnOEP) have been coupled with differently substituted anthraquinones as acceptors. The quinone moiety was properly functionalized with imidazole, thus ensuring porphyrin complexation through zinc ion coordination. Accordingly, absorption and emission measurements demonstrated that the coordination occurred, and calculated binding constants were in the range 6.6 [Formula: see text] 10[Formula: see text]–3.9 [Formula: see text] 10[Formula: see text] M[Formula: see text]. Transient absorption spectroscopy for ZnTPP and ZnOEP dyads demonstrated that the electron transfer occurred, with the formation of the corresponding charge separated state, ZnTPP[Formula: see text]-AQ. Moreover, in ZnOEP complexes, a strong correlation between the chain length and flexibility with the charge separated state lifetime was observed.

Photoinduced electron transfer from zinc meso-tetraphenylporphyrin to a one-dimensional perylenediimide aggregate: Probing anion delocalization effects

Organic photovoltaics incorporating non-fullerene acceptors based on perylenediimide (PDI) now rival fullerene acceptor-based devices in performance, although the mechanisms of charge generation in PDI-based devices are not yet fully understood. Fullerene-based systems are proposed to undergo electron transfer directly from the photoexcited donor into a band of delocalized acceptor states, thus increasing charge generation efficiency. Similarly, anion delocalization has been shown to enhance the rate of electron transfer from a photoexcited donor to two electronically coupled PDI acceptors. Here we investigate how additional electron acceptors may further increase the rate of electron transfer from the donor zinc meso-tetraphenylporphyrin (ZnTPP) to an aggregate of PDI acceptors (PDI[Formula: see text]. Femtosecond transient visible and mid-infrared absorption spectroscopies show that the rate of electron transfer from 1*ZnTPP to the PDI assembly ZnTPP2-PDI3 is statistically identical to that of the previously examined ZnTPP-PDI2. A Marcus theory analysis indicates that the parameters governing electron transfer are nearly identical for the two molecules, suggesting that the maximum electron transfer rate enhancement has been achieved in a cofacial PDI dimer because the ZnTPP directly couples to the first two PDI acceptors whereas the coupling to the third PDI is too weak.

Chitosan Nanoparticles as a Potential Drug Delivery System for Photodynamic Therapy of Cancer

Objective: Chitosan nanoparticles (CS-NP) can imbibe water insoluble anticancer agents into its hydrophobic multicores. In the present study, chitosan nanoparticles, a nanoscale drug carrier system is investigated for its potential as a drug delivery system for porphyrin based photodynamic therapy. Methods: Zinc meso tetra phenyl porphyrin (ZnmTPP) encapsulated CS-NP was prepared by ionic gelation method. The synthesized nanoparticles were characterized using dynamic light scattering studies, zeta potential analysis and AFM analysis. Results: Freshly prepared chitosan nanoparticles had an average hydrodynamic diameter of 175 nm and are nearly spherical in shape as per light scattering measurements and atomic force imaging respectively. As nanoscale drug carriers, (ZnmTPP) encapsulated chitosan nanoparticles exhibited high encapsulation efficiency and controlled release pattern. The encapsulated photosensitizer exhibited efficient singlet oxygen generation upon photo irradiation, retaining the photosensitization capacity of encapsulated hydrophobic ZnmTPP. The in vitro phototoxicities of free and nano-encapsulated ZnmTPP, studied using MTT assay in DLA cell lines demonstrate a concentration dependent response of photosensitizer in free and CS-nano formulations.

Cobaltocenium substituents as electron acceptors in photosynthetic model dyads

Cobaltocenium carboxylic acid hexafluorophosphate has been attached to a zinc(II) meso-tetraphenyl porphyrin chromophore via an amide linkage. Optical and electrochemical studies reveal that the metallocene and the porphyrin interact only negligibly in the ground state of the dyad. Photoinduced charge-shift from the zinc porphyrin to the cobaltocenium substituent to give the zinc porphyrin radical cation and the cobaltocene occurs upon exciting the porphyrin with light. Steady state emission, time-resolved fluorescence and transient absorption pump–probe spectroscopy in addition to density functional theory calculations suggest that the charge shift to the cobaltocenium substituent can occur from several excited states of the porphyrin, namely from the S2, S1 and T1 states. The triplet states of the cobaltocenium substituent (3E1g) and the triplet state of the zinc porphyrin (T1) are higher in energy than the charge-shifted state. This energy sequence of states of the dyad is beneficial for photoinduced charge-shift reactions.

Influence of Anion Delocalization on Electron Transfer in a Covalent Porphyrin Donor-Perylenediimide Dimer Acceptor System.

Photodriven electron transfer from a donor excited state to an assembly of electronically coupled acceptors has been proposed to enhance charge transfer efficiency in functional organic electronic materials. However, the circumstances under which this may occur are difficult to investigate in a controlled manner in disordered donor-acceptor materials. Here we investigate the effects of anion delocalization on electron transfer using zinc meso-tetraphenylporphyrin (ZnTPP) as a donor and a perylene-3,4:9,10-bis(dicarboximide) dimer as the acceptor (PDI2). The PDI units of the dimer are positioned in a cofacial orientation relative to one another by attachment of the imide group of each PDI to the 4- and 5-positions of a xanthene spacer. Furthermore, the distal imide group of one PDI is linked to the para-position of one ZnTPP phenyl group to yield ZnTPP-PDI2. The data for the dimer are compared to two different ZnTPP-PDI monomer reference systems designed to probe electron transfer to each of the individual PDI molecules comprising PDI2. The electron transfer rate from the ZnTPP lowest excited singlet state to PDI2 is increased by 50% relative to that in ZnTPP-PDI, when the data are corrected for the statistics of having two electron acceptors. Femtosecond transient IR absorption spectroscopy provides evidence that the observed enhancement in charge separation results from electron transfer producing a delocalized PDI2 anion.

Self-assembled dimethyldihydropyrene-pyridyl substituted ligands with zinc(ii) meso-tetraphenylporphyrin via axial coordination.

A series of dimethyldihydropyrene (DHP)-pyridyl photochromic derivatives has been synthesized and its photochemical behaviour characterized by spectroscopic and electrochemical methods. The corresponding noncovalently-linked electron donor-acceptor complexes have been isolated. They combine the DHP-pyridyl ligand as a donor and the zinc(ii) tetraphenylporphyrin as acceptor. Such association allowed to explore the efficiency of dative bonds to monitor the interactions between the two units.

Pyridine-Functionalized Luminescent Organoboron Quinolate Block Copolymers as Versatile Building Blocks for Assembled Nanostructures

Novel luminescent boron quinolate block copolymers with pyridine functionalities were prepared via RAFT polymerization and employed as building blocks for assembled nanostructures. In selective solvents, the block copolymers self-assembled into vesicles, spherical and extended branched aggregates. Quaternization reactions were performed to modify the solubility of the block copolymers and to prepare a cross-linked polymeric gel. As polymeric Lewis bases, the pyridine-functionalized block copolymers are able to form supramolecular complexes with metal ions and Lewis acids. Coordination to ZnCl2 in chloroform led to spherical micelles or larger aggregates. The supramolecular coassembly of PS-b-PBQPy-1 and zinc meso-tetraphenylporphyrin (ZnTPP) in cyclohexane as a selective solvent for PS resulted in extended branched structures with controllable emission properties. Energy transfer from the boron chromophores to the ZnTPP moieties was observed in these supramolecular complexes.

Determination of Stability of Molecular Complexes of Zinc(II) meso-Tetraphenylporphyrin with Heterocyclic N-Oxide and Pyridine by Different Methods

Determination of Stability of Molecular Complexes of Zinc(II) meso-Tetraphenylporphyrin with Heterocyclic N-Oxide and Pyridine by Different Methods

Colloidal silica beads modified with quantum dots and zinc (II) tetraphenylporphyrin for colorimetric sensing of ammonia

Colloidal crystal beads (CCBs) were fabricated by assembling monodisperse silica nanoparticles via a microfluidic device. The pore size of the CCBs was tuned by using different nanoparticles. The CCBs were then coated with cadmium telluride quantum dots and zinc(II) meso-tetraphenylporphyrin for the purpose of optical sensing. Ammonia causes the color of the sensor to change from green to red. The method has a dynamic range of 0–2500 ppm, good reversibility, and is not sensitive to humidity. The limit of detection is 7 ppm. The sensor has the advantage of a porous microcarrier structure and that pore sizes can be well controlled and thus can fulfill various demands in gas detection.

Ultrafast Intersystem Crossing and Spin Dynamics of Zincmeso-Tetraphenylporphyrin Covalently Bound to Stable Radicals

tert-Butylphenylnitroxide (BPNO(•)) and α,γ-bisdiphenylene-β-phenylallyl (BDPA(•)) stable radicals are each attached to zinc meso-tetraphenylporphyrin (ZnTPP) at a fixed distance using one of the ZnTPP phenyl groups. BPNO(•) and BDPA(•) are oriented para (1 and 3, respectively) or meta (2 and 4, respectively) relative to the porphyrin macrocycle. Following photoexcitation of 1-4, transient optical absorption spectroscopy is used to observe excited state quenching of (1)*ZnTPP by the radicals and time-resolved electron paramagnetic resonance (TREPR) spectroscopy is used to monitor the spin dynamics of the paramagnetic product states. The presence of BPNO(•) or BDPA(•) accelerates the intersystem crossing rate of (1)*ZnTPP about 10- to 500-fold in 1-4 depending on the structure compared to that of (1)*ZnTPP itself. In addition, the lifetime of (3)*ZnTPP in 1 is shorter than that of (3)*ZnTPP itself as a result of enhanced intersystem crossing (EISC) from (3)*ZnTPP to the ground state. The TREPR spectra of the three unpaired spins produced within 1 and 2 show spin-polarized excited doublet (D(1)) and quartet (Q) states and subsequent formation of a spin-polarized ground state radical (D(0)). All three signals are absorptive for 1 and emissive for 2. Polarization inversion of the Q state is observed on a tens of nanoseconds time scale in 2, while no polarization inversion is observed for 1. The lack of polarization inversion in 1 is attributed to the short lifetime of the doublet-quartet manifold as a result of the very large exchange interaction. The TREPR spectra of 3 and 4 show ground state radical polarization at X-band (9.5 GHz) at room temperature, but not at 85 K, and similarly no polarization is observed at W-band (94 GHz). No evidence of excited doublet or quartet states is observed, indicating that the exchange interaction is both weak and temperature dependent. These results show that although ultrafast EISC produces (3)*ZnTPP within 1-4, the magnitude of the exchange interactions between the three relevant spins in the resulting (3)*ZnTPP-BPNO(•) and (3)*ZnTPP-BDPA(•) systems dramatically alters their spin dynamics.

Photoinitiated multistep charge separation in ferrocene–zinc porphyrin–diiron hydrogenase model complex triads

Two covalently linked linear electron donor–acceptor triads Fc-ZnTPP-[NMI-FeI-FeI-S2(CO)6] (1) and Fc-Ph-ZnTPP-[NMI-FeI-FeI-S2(CO)6] (2) consisting of a zinc meso-tetraphenylporphyrin (ZnTPP) chromophore, a naphthalene monoimide diiron hydrogenase active site model [NMI-FeI-FeI-S2(CO)6], and a ferrocene (Fc) secondary electron donor have been synthesized along with their corresponding dyad reference molecules ZnTPP-[NMI-FeI-FeI-S2(CO)6] (3), Fc-ZnTPP (4), and Fc-Ph-ZnTPP (5). Time-resolved transient absorption and emission studies in CH2Cl2 show that selective photoexcitation of ZnTPP in triads 1 and 2 results in two competing quenching pathways for 1*ZnTPP: electron transfer from 1*ZnTPP to [NMI-FeI-FeI-S2(CO)6] and energy transfer from 1*ZnTPP to low-lying Fc excited states. Our studies on reference dyads 4 and 5 show that the majority of 1*ZnTPP produced by the laser pulse decays rapidly by energy transfer to Fc in triad 1 (τ < 10 ps), while electron transfer to [NMI-FeI-FeI-S2(CO)6] dominates in triad 2, allowing the second rapid electron transfer step from Fc to ZnTPP+˙ to proceed. Quantum yields of the fully charge separated states Fc+-ZnTPP-[NMI-Fe0-FeI-S2(CO)6] and Fc+-Ph-ZnTPP-[NMI-Fe0-FeI-S2(CO)6] are 0.13 and 0.71, respectively. Charge recombination in Fc+-ZnTPP-[NMI-Fe0-FeI-S2(CO)6] occurs with τCR = 9 ± 1 ns and τCR = 67 ± 2 ns for Fc+-Ph-ZnTPP-[NMI-Fe0-FeI-S2(CO)6]. By incorporating a secondary electron donor, the lifetime of the reduced diironhydrogenase mimic was extended by a factor of >450. Studies of photochemical hydrogen evolution using 1 and 2 reveal that the hydrogen generation efficiency depends on the lifetime of the final charge separated state. The ability to execute a multi-electron proton-coupled electron transfer mechanism in a stepwise manner will allow us to investigate the structural and electronic requirements for each step aiding in overall system optimization. Thus, it is possible to use the same multi-step electron transfer strategy that has been employed to extend the lifetime of charge-separated states in photodriven donor–acceptor systems to extend the lifetime of the reduced states of metal complexes of potential use in catalytic proton reduction.

Oxidative Degradation of Zinc Porphyrin in Comparison with Its Iron Analogue

Zinc hydroxyisoporphyrin (2), under sunlight and argon, is reduced back to zinc meso-tetraphenylporphyrin (1), but stays stable in oxygen in the absence of light. This behavior is in contrast to its iron analogue and stresses the redox role of iron in heme degradation. Compound 2 also responds to chlorophyll-type degradation (3) under sunlight and oxygen.

Tuning the optical properties of ZnTPP using carbonyl ring fusion

Zinc meso-tetraphenylporphyrin ( ZnTPP) was modified in such a way to allow the effect of an asymmetric structural distortion on its optical properties to be investigated. This involved the fusion of a phenyl group to an adjacent pyrrole ring via a carbonyl bridge. With the aid of Density Functional Theory (DFT) and time-dependent DFT (TD-DFT) calculations it was found that the asymmetric distortion away from planarity induced by the carbonyl fusion resulted in a loss of degeneracy in the two lowest unoccupied molecular orbitals (LUMOs). The effect was a red shift of the electronic absorbance bands, an increased Q:B ratio from 0.046 in ZnTPP to 0.096 in the fused derivative, and the appearance of additional UV–vis peaks. This study therefore suggests that structural distortions, as well as electronic substituents may be used to alter absorbance spectra, a technique which is of interest in the design of light-harvesting dyes.

An investigation on electron transfer quenching of zinc(II) meso-tetraphenylporphyrin (ZnTPP) by colloidal TiO 2

The interaction of zinc(II) meso-tetraphenylporphyrin (ZnTPP) with colloidal TiO 2 was studied by absorption, steady state and time-resolved fluorescence spectroscopy. The quenching was found to obey the Stern–Volmer equation and the corresponding Stern–Volmer plots were linear in the range of quencher concentration used 0–5 × 10 −4 M. The bimolecular quenching rate constants ( k q) were 20.5 × 10 10 M −1 s −1 (steady-state) and 2.85 × 10 10 M −1 s −1 (time resolved). The quenching process is suggested to involve electron transfer from the ZnTPP to TiO 2 considering the experimental evidences obtained.

Copper Ion-Selective Fluorescent Sensor Based on the Inner Filter Effect Using a Spiropyran Derivative

A highly selective copper(II) ion fluorescent sensor has been designed based on the UV-visible absorption of a spiropyran derivative coupled with the use of a metal porphyrin operative on the fluorescence inner filter effect. Spiropyrans, which combine the characteristics of metal binding and signal transduction, have been widely utilized in cationic ion recognition by UV-visible spectroscopy. In the present work, the viability of converting the absorption signal of the spiropyran molecule into a fluorescence signal was explored. On account of overlap of the absorption band of the spiropyran (lambda(abs) = 547 nm) in the presence of copper ion with the Q-band of an added fluorophore, zinc meso-tetraphenylporphyrin (lambda(abs) = 556 nm), the effective light absorbed by the porphyrin and concomitantly the emitted light intensity vary as a result of varying absorption of the spiropyran via fluorescence inner filter effect. The metal binding characteristic of the spiropyran presents an excellent selectivity for copper ion in comparison with several other heavy or transition metal ions. Since the changes in the absorbance of the absorber translate into exponential changes in fluorescence of the fluorophore, the novelty of the present device is that the analytical signal is more sensitive over that of the absorptiometry or that of the fluorometry using one single dye. To realize a practical fluorescent sensor, both the absorber and fluorophore were immobilized in a plasticized poly(vinyl chloride) membrane, and the sensing characteristics of the membrane for copper ion were investigated. The sensor is useful for measuring Cu2+ at concentrations ranging from 7.5 x 10(-7) to 3.6 x 10(-5) M with a detection limit of 1.5 x 10(-7) M. The sensor is chemically reversible, the fluorescence was switched off by immersing the membrane in copper ion solution and switched on by washing it with EDTA solution.

Novel spectral and electrochemical characteristics of triphenylamine-bound zinc porphyrins and their intramolecular energy and electron transfer

Porphine bearing triphenylamine (TPA) pendant groups and their zinc complexes, zinc meso-tetra-p-(di-p-phenylamino)phenylporphyrin (ZnTDPAPP) and zinc meso-tetra-p-(di-p-tolylamino)phenylporphyrin (ZnTDTAPP) are synthesized and their spectral and electrochemical characteristics are studied. Zinc meso-tetraphenylporphyrin (ZnTPP) and zinc meso-tetra-p-aminophenylporphyrin (ZnTAPP) are also used as reference complexes. The B and Q bands of ZnTDPAPP and ZnTDTAPP are located at higher wavelengths and the bandwidths become broader compared with those of ZnTPP and ZnTAPP, indicating the peripheral TPA affects the electronic configuration of zinc porphyrins. Upon excitation in CH2Cl2 at room temperature, the compounds exhibit intramolecular singlet energy transfer from the TPA to the porphyrin core, and emission from the porphyrins are observed. Both ZnTDPAPP and ZnTDTAPP are easier to be oxidized and harder to be reduced than ZnTPP, in agreement with the strong electron-donating effect of the TPA groups. Extra waves corresponding to the oxidation of TPA substituents are also observed. The cation radical ZnTDTAPP+* exhibits an absorption spectrum very different from the typical spectra for porphyrin cation radicals. The NIR absorption band at 1296 nm indicates the electron transfer occurs intramolecularly. The above results evince the ability of TPA to modulate the electronic structure of zinc porphyrins.

Light absorption efficiencies of photoactive multilayered films: a realistic approach for porous materials

In the present work the authors report a methodology to obtain an accurate calculation of the light absorption efficiency of hybrid photoactive layers. The photoactive layer (PAL) is a semiconductor matrix doped with a molecular species. The chosen matrix was TiO 2 prepared either by sputtering or by sol–gel techniques. Zinc meso-tetraphenylporphyrin and Nile red were selected as light absorbing dopants due to their absorption spectra for solar light. The proposed methodology takes into account a detailed optical characterization of each PAL where the morphology and the porosity of the semiconductor matrix are considered. The role of direct excitation of the semiconductor could also be discriminated. Moreover, the method allows an accurate estimate of the effective light absorption efficiency of complex multilayered materials from the optical characterization of each layer separately.

Competitive Electron Transfer from the S2 and S1 Excited States of Zinc meso-Tetraphenylporphyrin to a Covalently Bound Pyromellitimide: Dependence on Donor−Acceptor Structure and Solvent

Zinc meso-tetraphenylporphyrin (ZnTPP) is known to have a relatively slow S2 → S1 internal conversion rate, (1−3 ps)-1, so that electron transfer from S2 to a nearby acceptor is possible. We have synthesized two zinc porphyrins in which a pyromellitimide (PI) acceptor is attached to the para position of a meso-phenyl group of the porphyrin (ZnTPP−PI) or to that of a β-phenyl group of the porphyrin (ZnTPP−β-PhPI). We report here on competitive electron transfer from the S2 (excitation at 420 nm) and S1 states (excitation at 550 nm) of these zinc porphyrins to PI in 2-methyltetrahydrofuran (MTHF) and toluene. Our transient absorption studies show that efficient electron transfer occurs from S2 of ZnTPP to PI in these porphyrins despite the presence of the intervening phenyl between the zinc porphyrin macrocycle and the PI acceptor. Moreover, the results show that while charge separation from S1 is about 6 times faster for PI attached to the meso-phenyl than for PI attached to the β-phenyl, the opposite is observed for charge separation from S2. Subsequent charge recombination is 2.6−2.8 times faster for PI attached to the meso-phenyl relative to that of the β-phenyl. Comparisons of rates between MTHF and toluene show that the ordering of rates is the same for both solvents, although the rate ratios are larger in MTHF than in toluene.