Porphyrin Nanostructures Research Articles

Porphyrin oriented self-assembled nanostructures for efficient exciton dissociation in high-performing organic photovoltaics

Herein we report on enhanced organic solar cell performance through the incorporation of cathode interfacial layers consisting of self-organized porphyrin nanostructures with a face-on configuration. In particular, a water/methanol-soluble porphyrin molecule, the free base meso-tetrakis(1-methylpyridinium-4-yl)porphyrin chloride, is employed as a novel cathode interlayer in bulk heterojunction organic photovoltaics. It is demonstrated that the self-organization of this porphyrin compound into aggregates in which molecules adopt a face-to-face orientation parallel to the organic semiconducting substrate induces a large local interfacial electric field that results in a significant enhancement of exciton dissociation. Consequently, enhanced photocurrent and open circuit voltage were obtained resulting in overall device efficiency improvement in organic photovoltaics based on bulk heterojunction mixtures of different polymeric donors and fullerene acceptors, regardless of the specific combination of donor–acceptor employed. To highlight the impact of molecular orientation a second porphyrin compound, the Zn-metallated meso-tetrakis(1-methylpyridinium-4-yl)porphyrin chloride, was also studied and it was found that it forms aggregates with an edge-to-edge molecular configuration inducing a smaller increase in the device performance.

Effects of different light irradiations on structure and optical properties of methoxy-substituted tetraphenylporphyrins

UV lamp, filtered halogen lamp (at 425 nm) and Green laser (532 nm) experiments on a series of meso-substituted tetra phenyl porphyrin, TPP, bearing methoxy peripheral groups together with a metal derivate of 3,4 dimethoxy TPP were lead to different protonation and aggregation structures. Properties of irradiated porphyrins were investigated using their absorption and emission spectra in dichloromethane solution. The results show that the optical properties of the TPP derivates depend on light irradiation source, which shows the tuning of the absorption and emission spectra of the TPP derivates. From the dynamic light scattering measurements, the size distribution of samples was estimated about 5–15 nm in solvent after irradiation. Atomic force microscopy images of deposited porphyrins on the glass surface were shown average particle size between 10 and 30 nm. Particularly, self-assembly of the porphyrin derivates was also observed when green laser was used. We suggest that the irradiation source plays an important role in the controlling of size and morphology of products, and we propose a self-organization model to explain the formation of the porphyrin nanostructures.

Self-assembly into temperature dependent micro-/nano-aggregates of 5,10,15,20-tetrakis(4-carboxyl phenyl)-porphyrin

Various nanostructures of 5,10,15,20-tetrakis(4-carboxyl phenyl)-porphyrin (H2TCPP) can be easily synthesized by a surfactant-assisted self-assembly (SAS) method at different temperatures. When the DMF solution of porphyrin monomer was injected into cetyltimethylammonium bromide (CTAB) aqueous solution by a syringe, diverse H2TCPP nanostructures dependent on the different temperatures, including hollow nanospheres, solid nanospheres and nanospheres with holes, were successfully obtained. As a result, the suitable concentration of the CTAB aqueous solution used to form nanostructues of porphyrin ranges from 0.15 to 0.2mM. The various morphologies of porphyrin nanostructures were characterized by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). UV–vis adsorption spectra showed that the micro-/nano-aggregate properties of porphyrin transformed from H-aggretates to J-aggregates during the process of self-assembly of porphyrin at different temperatures. Fluorescence spectra revealed a greater fluorescence quenching of various micro-/nano-aggregatess of porphyrin formed at different temperatures in aqueous solution, compared to the DMF solution of porphyrin monomer.

Morphology Controlled Nanostructure of Zinc Porphyrin

We have shown that various Zinc porphyrin-based nanostructures can be easily synthesized by a surfactant-assisted self-assembly method, where nonionic, anionic and cationic surfactants are employed. It was found that tuning the type of surfactant offered an alternative to promote the formation of Zinc porphyrin nanostructure with different morphologies in aqueous solutions. As-prepared nano-scale self-assemblies, including disc-shaped, ellipsoid, square and quadrangular pyramidal nanoparticles, were investigated in solution via UV/vis, fluorescence spectroscopy and SEM microscopy. The different UV/vis as well as fluorescent spectra between nano-porphyrin and its monomer further conformed that the nano-crystallization of porphyrin would result in novel optical properties differing from the single subunits.

(Invited) Chemical Synthesis in Solution and Porphyrin Nanostructures on Surfaces - Similar Concepts, Different Results

The chemistry of porphyrins is reaching out to more complex and ever larger polyporphyrin arrays. In solution the synthesis of porphyrin arrays is greatly aided by recent advances in organometallic chemistry which now allows the rational construction of selected tetrapyrrole scaffolds. Examples for these are unsymmetrical porphyrin arrays with conjugating and nonconjugating linker groups and the use of presenting scaffolds such as triptycenes. In order to circumvent a laborious and step-wise organic synthesis of porphyrin arrays efforts are underway to utilize principles of self-aggregation and organization for the construction of ordered nanostructural arrays on metal surfaces. Here, even rather simple systems are able to form highly ordered structures. On the other hand, thermal activation can be used to form covalent bonds between individual porphyrin molecules to yield highly ordered, large, and stable arrays. The type of structures formed depends on the porphyrinoid material, the metal surface, and the deposition methods.

Long range order in Si(100) surfaces engineered with porphyrin nanostructures

Engineering of Si(100) with ordered organic nanostructures represents an advanced method to manufacture hybrid organic/inorganic systems useful for different applications. Well-ordered and densely packed molecules can be obtained by a self-assembly process that depends on directional inter-molecular interactions such as π–π stacking, electrostatic, dipole–dipole or van der Waals interactions, and other more complex forces. Macrocycles are well known to aggregate both in solution and in thin films as a result of some of the above-mentioned interactions. In our study, Si(100) substrates were functionalized with a covalent 4-ClCH2C6H4SiCl3 monolayer that binds to the surface using the –SiCl3 group and leaves a –CH2Cl group unreacted. The remaining alkyl chloride functionality at the top of the Si(100) substrate allowed additional covalent functionalization with a porphyrin monolayer that resulted in ordered, surface-confined porphyrin assemblies. X-ray photoelectron spectroscopy gave indication of the porphyrin grafting mode. Atomic force microscopy showed a long range order of these nanostructures. Emission measurements confirmed the porphyrin luminescence.

(Invited) Chemical Synthesis in Solution and Porphyrin Nanostructures on Surfaces - Similar Concepts, Different Results

not Available.

(Invited) Molecular Organization and Conductivity in Self-Assembled Binary Porphyrin Nanostructures

not Available.

Porphyrin Nanorods Modified Glassy Carbon Electrode for the Electrocatalysis of Dioxygen, Methanol and Hydrazine

AbstractPorphyrin nanorods (PNR) were prepared by ionic self‐assembly of two oppositely charged porphyrin molecules consisting of free base meso‐tetraphenylsulfonate porphyrin (H4TPPS42−) and meso‐tetra(N‐methyl‐4‐pyridyl) porphyrin (MTMePyP4+M=Sn, Mn, In, Co). These consist of H4TPPS42−SnTMePyP4+, H4TPPS42−CoTMePyP4+, H4TPPS42−InTMePyP4+ and H4TPPS42−MnTMePyP4+ porphyrin nanorods. The absorption spectra and transmission electron microscopic (TEM) images of these structures were obtained. These porphyrin nanostructures were used to modify a glassy carbon electrode for the electrocatalytic reduction of oxygen, and the oxidation of hydrazine and methanol at low pH. The cyclic voltammogram of PNR‐modified GCE in pH 2 buffer solution has five irreversible processes, two distinct reduction processes and three oxidation processes. The porphyrin nanorods modified GCE produce good responses especially towards oxygen reduction at −0.50 V vs. Ag|AgCl (3 M KCl). The process of electrocatalytic oxidation of methanol using PNR‐modified GCE begins at 0.71 V vs. Ag|AgCl (3 M KCl). The electrochemical oxidation of hydrazine began at around 0.36 V on H4TPPS42−SnTMePyP4+ modified GCE. The GCE modified with H4TPPS42−CoTMePyP4+ H4TPPS42−InTMePyP4+ and H4TPPS42−MnTMePyP4+ porphyrin nanorods began oxidizing hydrazine at 0.54 V, 0.59 V and 0.56 V, respectively.

Morphology and chirality controlled self-assembled nanostructures of porphyrin–pentapeptide conjugate: effect of the peptide secondary conformation

An optically active porphyrin–pentapeptide conjugate 1, actually a porphyrinato zinc complex covalently linked with a glycinyl–alanyl–glycinyl–alanyl–glycine (GAGAG) peptide chain, was designed and synthesized. The self-assembly properties of this novel porphyrin–pentapeptide conjugate in THF/n-hexane and THF/water were comparatively investigated by electronic absorption, circular dichroism (CD), IR spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) technique. Associated with the different secondary conformation of the pentapeptide chain covalently linked to the porphyrin ring in different solvent systems, self-assembly of conjugate 1 leads to the formation of nanofibers with right-handed helical arrangement and nanotubes with left-handed helical arrangement in a stack of porphyrin chromophores according to the CD spectroscopic result in apolar THF/n-hexane (1 : 3) and polar THF/water (1 : 3) system depending on the cooperation between intramolecular or intermolecular hydrogen bonding interaction with chiral discrimination between pentapeptide chains and porphyrin–porphyrin interactions in the direction parallel to the tetrapyrrole ring of neighboring conjugate molecules. IR spectroscopic result clearly reveals the α-helix and β-sheet secondary conformation, respectively, employed by the pentapeptide chain attached at the porphyrin core in the nanostructures formed in THF/n-hexane (1 : 3) and THF/water (1 : 3). The X-ray diffraction (XRD) result confirms that in the nanotubes, a dimeric supramolecular bilayer structure was formed through an intermolecular hydrogen bonding interaction between two conjugate molecules which, as the building block, self-assembles into the target nanostructures. These results clearly reveal the effect of a secondary conformation of pentapeptide chain in the conjugate molecule on the packing mode of porphyrin chromophore, supramolecular chirality, and morphology of the self-assembled nanostructure. The present result represents not only the first example of organic nanostructures self-assembled from a covalently linked porphyrin–pentapeptide conjugate, but more importantly the first effort towards controlling and tuning the morphology and in particular the supramolecular chirality of porphyrin nanostructures via tuning the secondary conformation of peptides in different solvent systems, which is helpful towards understanding, designing, preparing, and mimicking the structure and role of naturally occurring porphyrin–peptide conjugates. In addition, both nanofibers and nanotubes were revealed to show good semiconducting properties.

In Situ Fabrication of meso-Tetrakis(4-sulfonatophenyl)porphyrin Nanostructures with Excitonic Absorption on Glass Substrate

In this article, we report in situ fabrication of meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) nanostructures with excitonic absorption on glass substrate. The exposure of TPPS thin film coated on a glass plate to HCl vapor resulted in the formation of nanostructures of TPPS. The formed TPPS nanostructures on glass plate were characterized by UV-vis, steady state emission spectral techniques, atomic force microscopy, and high resolution transmission electron microscopy (HR-TEM). A new sharp and intense absorption band (excitonic band) at 490 nm was observed for TPPS nanostructures on glass plate. Protonation of tertiary nitrogen atoms of TPPS ring by HCl molecules leads to the formation of nanostructures of J-aggregates of TPPS on glass surface. The height of the TPPS nanostructures was found to be 50-170 nm with an average width of 100 nm. HR-TEM images showed that the formed TPPS J-aggregates consist of tiny nanorods. The size of the nanostructures was tuned successfully by varying the concentration of TPPS used for thin film preparation.

Evolution of Various Porphyrin Nanostructures via an Oil/Aqueous Medium: Controlled Self-Assembly, Further Organization, and Supramolecular Chirality

We have shown that various porphyrin-containing nanostructures can be easily synthesized by a surfactant-assisted self-assembly (SAS) method, where an oil/aqueous medium is employed. When a chloroform solution of zinc 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (ZnTPyP) was added dropwise into cetyltrimethylammonium bromide (CTAB) aqueous solution, diverse ZnTPyP-based nanostructures, including hollow nanospheres, solid nanospheres, nanotubes, nanorods, and nanofibers, were successfully assembled. Depending on the aging time, when a low-concentration CTAB aqueous solution was employed, hollow nanospheres or nanotubes were produced. In contrast, either solid nanospheres or nanorods were obtained by using a CTAB aqueous solution in moderate concentration. Moreover, solid nanospheres or nanofibers were produced, when a high-concentration CTAB aqueous solution was used. We have further shown that the nanorods can be hierarchically organized into a regular nanoarray on silicon substrates over a large area, while the other nanostructures cannot. Interestingly, the nanorods displayed distinct supramolecular chirality although the employed ZnTPyP is achiral. On the basis of the information obtained from scanning electron microscopy, high-resolution transmission electron microscopy, fast Fourier transformation, energy-dispersive X-ray spectroscopy, X-ray diffraction, and UV-vis and circular dichroism spectra, a tentative explanation has been proposed. Our investigation suggests that the SAS method via an oil/aqueous medium is an efficient way to synthesize organic nanostructures in a controlled manner, and that such nanostructures can show different chiroptical and assembly properties.

Differing HOMO and LUMO Mediated Conduction in a Porphyrin Nanorod

In this communication we provide the first UHV-STM images and STM-based current-voltage (I-V) and orbital mediated tunneling spectroscopy (OMTS) data on a self-assembled porphyrin nanostructure at the single structure level. We will show that transverse conductivity over distances less than 10 nm can occur by barrier type tunneling but that long distance conduction solely occurs through the LUMO band. These nanorods are very highly rectifying.

Ionic self-assembly of porphyrin nanostructures on the surface of charge-altered track-etched membranes

Track-etched polymer membranes are typically used as templates in the synthesis of various nanowires or nanotubes arrays. The unique advantages of track-etched membranes, such as uniform pore structure, excellent porosity, easily tailored pore sizes, and a well characterized surface chemistry, may find use in self-assembly strategies where colloidal nanostructures can be tethered to a suitable substrate to produce devices of interest. Meso-tetrakis(4-phenylsulfonicacid)porphyrin dihydrochloride and Sn(IV) tetrakis(4-pyridyl)porphyrin were used to synthesize ionic self-assembled porphyrin nanorods. The track-etched membranes surface charge was changed from negative to positive using polyethyleneimine. The porphyrin nanorods were either filtered through or self-assembled onto the surface of track-etched membranes. Comparisons were made with track-etched membranes modified with, and without, polyethyleneimine. Assembly of the porphyrin nanotubes only occurred on the surface of positively charged track-etched membranes, and filtration of the porphyrin nanorods produced a mesh-like structure on the surface of the membrane irrespective of the track-etched membrane pore diameter. In each case the characteristic absorbance profiles of the porphyrin nanorods was maintained. Transmission electron microscopy, scanning electron microscopy, atomic force microscopy, and UV-vis spectroscopy were used to characterize the various systems.

Fullerene–Porphyrin Nanostructures in Photodynamic Therapy

Photodynamic therapy represents an alternative treatment with great potential in some types of cancer and premalignant conditions. In the quest to improve this therapy, potential new nontetrapyrrole photosensitizers are currently under research. Hence, in the last few years fullerenes attracted an increased interest because they prove characteristics for nanotechnology's biomedical applications. Fullerenes derivatization for biology application in general and in particular for photodynamic therapy, led to the idea of their association with porphyrins. Porphyrins, well-known players in this domain, could form in association with fullerenes, new compounds with unique properties, namely new photosensitizers with enhanced efficiency in terms of singlet oxygen generation and tumor cell penetration. This article is an attempt to underscore the enormous effort currently dedicated to an emerging field represented by these new nanostructures for biomedicine and in particular for photodynamic therapy.

Metal Octaethylporphyrin Nanowire Array and Network toward Electric/Photoelectric Devices

A vapor transfer deposition method was developed to fabricate metal (metal = Co, Ni, Cu, Zn, Mg) octaethylporphyrin (MOEP) nanowire arrays in large area on a variety of substrates. The formation process of MOEP nanowire arrays was investigated by time-dependently terminating deposition at various stages, based on which, a vaporization−condensation−recrystallization (VCR) mechanism was proposed to understand the formation of nanowires and thus guide the synthesis of three-dimensional (3D) sea urchin-like nanowire assemblies and two-dimensional (2D) nanowire networks. As application examples of these porphyrin nanostructures, the porphyrin nanowires demonstrated a good field emission property and the photoelectric device based on the 2D MOEP nanowire network was fabricated, showing a good light-induced signal amplification behavior.

Self-assembly of discotic liquid crystal porphyrin into more controllable ordered nanostructure mediated by fluorophobic effect

The novel nanoscale discotic liquid crystal porphyrin with partial chain perfluorination, which has the same basic structure as the best photoreceptor in nature (chlorophyll), shows an exceptionally enhanced tendency to self-assemble into ordered nanostructure. Defect-free homeotropically aligned fluorinated porphyrin thin films were, for the first time, fabricated and characterised. The ability to self-assemble large π-conjugated discotic molecules into highly ordered nanostructure via partial chain perfluorination provides new insight for the bottom-up nanofabrication of molecular devices. The controllable ordered porphyrin nanostructure with directed molecular arrangement holds great promise for use in high-performance electronic devices.

Self-assembled porphyrin nanostructures

Porphyrins and related tetrapyrroles have been extensively studied because of their importance in biological processes and they are often used in the development of artificial photosynthesis, catalysis, and sensor systems. Challenges in the development of functional nanoscale porphyrin systems are many, including the need to organize the porphyrins (e.g., to facilitate processes such as energy- and electron transfer) and to couple the porphyrin nanostructures to other nanoscale components (e.g., catalytic elements and conductors) to produce multifunctional nanoscale systems. This article summarizes recent advances in the synthesis of discrete self-assembled porphyrin nanostructures with well-defined shapes and sizes. A novel method for growing metal on the porphyrin nanostructures to produce nanocomposites with metal catalysts or interconnects is also described. Current and potential applications of these nanostructures and porphyrin-metal nanocomposites are discussed.

Effect of Heat on the Morphology and Optical Properties of Porphyrin Nanostructures

Porphyrin nanostructures of well-defined shapes were prepared by ionic self-assembly of two oppositely charged porphyrins. These nanostructures were prepared using meso-tetra(4-phenylsulfonic acid) porphyrin, tin (IV) meso-tetra(4-pyridyl)porphyrin dichloride and vanadium (IV) oxide meso-tetra (4-pyridyl)porphyrin. The effect of heat resulted in intense agglomeration and production of porphyrin nanotubes of larger sizes and a greater population. These features of nanoporphyrins structures were observed using transmission electron microscope (TEM) and scanning electron microscope (SEM). UV-VIS absorption spectra of the samples show that those prepared at 70°C have intense soret bands, with broadening of J-aggregate bands, when compared with those prepared at room temperature.

Subsecond-response SAW humidity sensor with porphyrin nanostructure deposited on bare and metallised piezoelectric substrate

The surface acoustic wave (SAW) humidity sensor based on the Meso-tetra (4 sulfonatophenyl) porphyrin (TPPS4) nanostrip structure deposited on a bare or metallised surface of the piezoelectric YZ LiNbO3 substrate has been investigated. The SAW attenuation, which greatly increases with humidity in sensors with TPPS4 layers on bare substrates, is almost humidity-independent in devices with TPPS4 layers on metallised substrates. For both types of sensors, the SAW velocity exhibits close-to-linear decrease with growing humidity. The sensor exhibited fast response and recovery times of from 0.8 to 0.5 s in both amplitude and phase of the output signal. The real-time monitoring of human breath with the help of the sensor was demonstrated.