The Hyperporphyrin Concept: A Contemporary Perspective

The Gouterman four-orbital model conceptualizes porphyrin UV-visible spectra as dominated by four frontier molecular orbitals-two nearly degenerate HOMOs and two exactly degenerate LUMOS under D _4h symmetry. These are well separated from all the other molecular orbitals, and normal spectra involve transitions among these MOs. Unusual spectra occur when additional orbitals appear in this energy range, typically as a consequence of the central coordinated atom. For example, metals with empty d orbitals in a suitable energy range may lead to charge transfer from porphyrin (ligand) to metal, that is, so-called LMCT transitions. Metals with filled p or d orbitals may lead to charge transfer from metal to porphyrin, MLCT transitions. These cases lead to additional peaks and/or significant redshifts in the spectra and were classified as hyperporphyrins by Gouterman. Cases in which spectra are blueshifted were classified as hypsoporphyrins; they are common for relatively electronegative late transition metal porphyrins. Many of the same principles apply to porphyrin analogues, especially corroles. In this Perspective, we focus on two newer classes of hyperporphyrins: one reflecting substituent effects in protonated or deprotonated free-base tetraphenyporphyrins and the other reflecting "noninnocent" interactions between central metal ions and corroles. Hyperporphyrin effects on spectra can be dramatic, yet they can be generated by relatively simple changes and subtle structural variations, such as acid-base reactions or the selection of a central metal ion. These concepts suggest strategies for engineering porphyrin or porphyrinoid dyes for specific applications, especially those requiring far-red or near-infrared absorption or emission.

Mosquito larvae control by photodynamic inactivation of their intestinal flora - a proof of principal study on Chaoborus sp

Mosquitoes are carriers of dangerous infectious disease pathogens all over the world. Owing to travelling and global warming, tropical disease-carrying species such as Aedes, Anopheles and Culex spread beyond tropical and subtropical zones, even to Europe. The aim of this study is to investigate the potential of photodynamic agents to combat mosquito larvae. Three different photosensitizers were tested on Chaoborus sp. larvae: TMPyP and TPPS as antimicrobial photosensitizers, and mTHPC as a PDT drug against eukaryotic animal and human cells. Chaoborus sp. is a commercially available harmless species developing translucent larvae similar to the larvae of Aedes, Anopheles and Culex. The uptake of photosensitizers by the larvae was tested by fluorescence microscopy. All tested photosensitizers were observed in the intestinal tract of the living larvae, and none of the photosensitizers was found in the larval tissues. In phototoxicity tests, mTHPC and TPPS did not have any effect on the larvae, while TMPyP killed the larvae efficiently. TPPS is an antimicrobial photosensitizer, mainly phototoxic to Gram-positive bacteria. TMPyP is well known as an efficient photosensitizer against Gram-negative bacteria like most species of the intestinal flora. From this result, we conclude that the photodynamic inactivation of the intestinal flora leads to the death of mosquito larvae. The feasibility of mosquito larvae control by photodynamic inactivation of their intestinal flora instead of the direct killing of the larvae is a promising alternative to other highly toxic insecticides. Compared to insecticides and other biochemical toxins, photosensitizers are not dark toxic. No resistance against photosensitizers is known so far. Thus, the dilution of the active substances by being distributed in the environment, which promotes the development of resistance in biocides of all kinds, does not pose danger. Thus, it reduces the potential side effects on environment and human health.

Porphyrin Supramolecular 1D Structures via Surfactant-Assisted Self-Assembly

One-dimensional (1D) solid-state supramolecular structures based on porphyrin chromophores arouse numerous expectations from the interdisciplinary scientific communities of supramolecular chemistry and advanced soft materials science. This stems from the intrinsic assembly capability of porphyrins to form various well-defined 1D assemblies, which have broad opportunities in the fields of advanced soft matter. A brief review on 1D porphyrin micro-/nanoassemblies constructed via surfactant-assisted self-assembly is presented here, in terms of addressing new ideas recently developed for controlled assembly, hierarchical organization, and new-type functional surfactants etc. The functionalization of the as-assembled 1D structures with regard to supramolecular photocatalysis, non-linear optics, nanoelectronic gas sensors, photoelectrochemical solar cells, etc. is highlighted.

Aggregation behavior of tetraphenylporphyrin in aqueous surfactant solutions: Chiral premicellar J-aggregate formation

Porphyrin-surfactant interactions in aqueous solutions are known to result in the selfassembly of various supramolecular structures, including pigment-surfactant complexes, J- and H-aggregates, and solubilized dye species. Detailed studies on the mechanisms of the intermolecular interactions governing the above self-assembly processes allow to predict the aggregation state and hence, the photophysical properties of the dye-surfactant assemblies in order to perform a direct synthesis of the desired porphyrin-based nanostructures at the appropriate experimental conditions. This paper describes a novel example of the surfactant-induced J-aggregate formation from the diprotonated hydrophobic tetraphenylporphyrin species in submicellar aqueous anionic surfactant solutions. The above assemblies are characterized by a rod-like morphology and possess supramolecular chirality according to the CD measurements.

Charge and substituent effects on the stability of porphyrin/G-quadruplex adducts

The adduct ions of two tetramolecular G-quadruplexes formed from the d(TGGGGT) and d(TTGGGGGT) single strands with a group of cationic porphyrins, with different charges and substituents, and one neutral porphyrin, were investigated by ESI-MS and ESI-MS/MS in the negative ion mode. Formation of [Q + nNH(4)(+)+P(p+)-(z + n + p)H(+)](z-) adduct ions (where Q = quadruplex, n = number of quartets minus 1, P = porphyrin and p(+) = 0,1,2,3,4) indicates that the porphyrins are bound outside the quadruplexes providing an additional stabilization to those structures. The fragmentation pathways of the [Q + nNH(4)(+)+P(p+)-(z + n + p)H(+)](z-) adduct ions depend on the number of positive charges (p(+)) of the porphyrins and on the overall complex charge (z(-)), but do not show a significant dependence on the type of the substituent groups in the porphyrins. Formation of the 'unfilled' ions [Q + P(p+)-(z + p)H(+)](z-) predominates for porphyrins with a higher number of positive charges. Strand separation with the formation of [T + P(p+)-(z-2 + p)H(+)]((z-2)-) and (SS-2H(+))(2-) ions, where T = [d(TG(4)T)](3) and [d(T(2)G(5)T)](3) and SS = d(TG(4)T) and d(T(2)G(5)T) is only observed for the complexes with a higher overall negative charge. Porphyrin loss with the formation of [Q + nNH(4)(+)-(z + n)H(+)](z-) ions occurs predominantly for the neutral and monocharged porphyrins. The predominant formation of the 'unfilled' ions, [Q + P(p+)-(z + n)H(+)](z-), for porphyrins with a higher number of charges shows that these porphyrins can prevent strand separation and preserve, at least partially, the quadruplex structure.

Effects of environment on the photophysical characteristics of mesotetrakis methylpyridiniumyl porphyrin (TMPyP)

Porphyrins are an important class of organic molecules, with interesting linear and nonlinear optical properties given mainly by their extended π-conjugation structure. Their photophysical properties can be greatly affected by the surrounding environment, which can be used to tune its final properties. Here we report on an experimental study of the photophysical properties of meso-tetrakis (methylpyridiniumyl) porphyrin (TMPyP) in aqueous and in several organic solvents and its interaction with micelles formed from negatively charged sodium dodecylsulphate (SDS), positively charged cetyl trimethyl ammonium bromide (CTAB) and neutral TRITON X-100. By using the Z-scan technique, flash-photolysis and time-resolved fluorescence techniques, we were able to evaluate the excited state dynamics of the TMPyP, and observed that the tetrapyrrole ring plays important role due to hydrogen bonds formation between nitrogen atom and water, while the side groups determine the porphyrin localization in non-aqueous micelle part.