Electrochemical and Spectroscopic Behavior of Iron(III) Porphyrazines in Langmuir−Schäfer Films

Magnesium Porphine Supermolecules and Two-Dimensional Nanoaggregates Formed Using the Langmuir-Schaefer Technique

Porphyrins are functional elements of important biomolecules, whose assemblies play a central role in fundamental processes such as electron transfer, oxygen transport, enzymatic catalysis, and light harvesting. Here we report an approach to formation of porphyrin supermolecules, a particular type of nanoparticles with unusually strong noncovalent intermolecular interactions. Key differences between the supermolecules and noncovalent nanostructures described earlier are as follows. (1) Supermolecules consist of molecules of the same type without side groups promoting the self-assembly and without any spacers; no surfactant or catalyst to assist the process is needed. (2) They exhibit unusual photophysical properties and remain stable even in organic solvents. Their formation occurs under specially selected conditions at the air-water interface at room temperature. Following this route, we have formed supermolecules of magnesium porphine, a functional element of chlorophyll. The properties of these supermolecules are markedly different from those of the constituent molecules. For example, in contrast to the pink color of the monomer solution, solutions of supermolecules are transparent for visible light and absorb in the ultraviolet and near-infrared regions. We also present atomic force microscopy visualization of the porphyrin two-dimensional nanoaggregates forming at the air-water interface that were predicted in our previous works. This approach offers a guideline for the discovery of new supermolecules, including complex biological ones, and the formation of supermolecular materials with novel properties.

Direct observation by using Brewster angle microscopy of the diacetylene polimerization in mixed Langmuir film

Mixed Langmuir monolayers of 10,12-Pentacosadiynoic acid (DA) and amphiphilic hemicyanine (HSP) have been fabricated at the air-water interface. The mixed monolayer has been proved to be completely homogeneous. The DA molecules are arranged in a single monolayer within the mixed Langmuir monolayer, as opposed to the typical trilayer architecture for the pure DA film. Brewster angle microscopy has been used to reveal the mesoscopic structure of the mixed Langmuir monolayer. Flower shape domains with internal anisotropy due the ordered alignment of hemicyanine groups have been observed. Given the absorption features of the hemicyanine groups at the wavelength used in the BAM experiments, the enhancement of reflection provoked by the absorption process leads to the observed anisotropy. The ordering of such groups is promoted by their strong self-aggregation tendency. Under UV irradiation at the air-water interface, polydiacetylene (PDA) has been fabricated. In spite a significant increase in the domains reflectivity has been observed owing to the modification in the mentioned enhanced reflection, the texture of the domains remains equal. The PDA polymer chain therefore grows in the same direction in which the HSP molecules are aligned. This study is expected to enrich the understanding and design of fabrication of PDA at interfaces.

On the flexibility of carboranylalkylthio substituents in porphyrazines and its relevance to the photophysical properties

Ultrafast experiments reveal fast radiationless deactivation of the S₁(π,π*) state in carboranylalkylthio-porphyrazines, ascribed by DFT/TDDFT and VT ¹H NMR studies to the flexibility of the alkylthio groups.

Synthesis, coordination chemistry, and physico-chemical properties of the 2-chloroethoxy-iron(III)(ethylthio) porphyrazine

Reaction of octakis(ethylthio)porphyrazine ( H 2 OESPz ) with FeBr 2 in ClCH 2 CH 2 OH at 135 °C affords the 2-chloroethoxy-iron(III)-(ethylthio)porphyrazine, ( ClCH 2 CH 2 O ) Fe III OESPz , ( LFe III OESPz ) in good yield. The spectroscopic, redox, and coordination properties of the complex and its μ-oxo dimer derivative, [ Fe III OESPz ]2 O , are investigated and compared to those of the iron(III)porphyrin analogs.

Carboranylporphyrazines for anti-cancer therapies: synthesis and physicochemical properties

The synthesis, the salient physicochemical properties, and liposome insertion of carboranyl-alkylthio-porphyrazines, a new family of potential BNCT agents, are here reviewed together with recent progresses in their metalation and conversion in the water-soluble counterparts.

Photofunctional multilayer films by assembling naked silver nanoparticles and a tailored nitric oxide photodispenser at water/air interface

This contribution reports the design, preparation, and characterization of nanostructured hybrid films of silver nanoparticles (AgNPs) and a tailored nitric oxide (NO) photodonor. They were achieved by exploiting effective interfacial interactions between an amino-terminated NO photodonor spread onto water surface and naked AgNPs dissolved in the water subphase. The morphology, the spectroscopic features, and the interaction between the two components in the floating films at the air/water interface were inspected by Brewster Angle Microscopy, UV-Vis reflection, and polarization-modulation infrared reflection-absorption spectroscopy. AgNPs and the NO photodonor were successfully transferred onto hydrophobized quartz substrates by horizontal lifting deposition and the resulting multilayer films were characterized by UV-Vis absorption spectroscopy and transmission electron microscopy, respectively. The results obtained showed the presence of both isolated AgNPs and assemblies of AgNPs having nanodimensional character in the films. The photochemical properties of the NO photodonor were well preserved in the hybrid multilayers. In fact, they were able to release NO under visible light excitation, as unambiguously demonstrated by the direct and in real-time monitoring of this transient species using an ultrasensitive electrode, and the transfer of the released NO to a protein such as myoglobin.