A two-step, one-pot route to swap the pyrroline moiety in meso-tetraaryldihydroxy-chlorins with an O/N-substituted oxazoline

New Fluorine-Containing Diamine Monomers for Potentially Improved Polyimides

Two new fluorine-containing diamine monomers were designed with the goal of reducing charge transfer complex (CTC) interactions between neighboring chains in polyimides (i.e., high transparency/low color) while hopefully maintaining the well-known thermal stability and flexibility generally associated with polyimides. The proposed diamines have been prepared through (1) the functionalization of 1,3-bis[(pentafluorobenzyl)oxy]benzene with 4-aminophenol and (2) the addition of 2-chloro-5-nitrobenzotrifluoride to 4,4'-bicyclohexanol followed by reduction of the resulting dinitro compound. The new compounds have been characterized by multinuclear NMR and IR spectroscopy and high-resolution liquid chromatography-mass spectrometry as well as single-crystal X-ray diffraction on the new diamine prepared from 4,4'-bicyclohexanol. Not only was the structure of the proposed new diamine confirmed, but another interesting example of hydrogen bonding between an N-H proton and the π-system of an aromatic ring was observed and documented. Initial polymerizations have been carried out via the two-step imidization process.

Metal Complexes of Porphyrinoids Containing Nonpyrrolic Heterocycles

The replacement of one or more pyrrolic building block(s) of a porphyrin by a nonpyrrolic heterocycle leads to the formation of so-called pyrrole-modified porphyrins (PMPs), porphyrinoids of broad structural variability. The wide range of coordination environments (type, number, charge, and architecture of the donor atoms) that the pyrrole-modified frameworks provide to the central metal ions, the frequent presence of donor atoms at their periphery, and their often observed nonplanarity or conformational flexibility distinguish the complexes of the PMPs clearly from those of the traditional square-planar, dianionic, N₄-coordinating (hydro)porphyrins. Their different coordination properties suggest their utilization in areas beyond which regular metalloporphyrins are suitable. Following a general introduction to the synthetic methodologies available to generate pyrrole-modified porphyrins, their general structure, history, coordination chemistry, and optical properties, this Review highlights the chemical, electronic (optical), and structural differences of specific classes of metalloporphyrinoids containing nonpyrrolic heterocycles. The focus is on macrocycles with similar "tetrapyrrolic" architectures as porphyrins, thusly excluding the majority of expanded porphyrins. We highlight the relevance and application of these metal complexes in biological and technical fields as chemosensors, catalysts, photochemotherapeutics, or imaging agents. This Review provides an introduction to the field of metallo-PMPs as well as a comprehensive snapshot of the current state of the art of their synthesis, structures, and properties. It also aims to provide encouragement for the further study of these intriguing and structurally versatile metalloporphyrinoids.

Modifications of Porphyrins and Hydroporphyrins for Their Solubilization in Aqueous Media

The increasing popularity of porphyrins and hydroporphyrins for use in a variety of biomedical (photodynamic therapy, fluorescence tagging and imaging, photoacoustic imaging) and technical (chemosensing, catalysis, light harvesting) applications is also associated with the growing number of methodologies that enable their solubilization in aqueous media. Natively, the vast majority of synthetic porphyrinic compounds are not water-soluble. Moreover, any water-solubility imposes several restrictions on the synthetic chemist on when to install solubilizing groups in the synthetic sequence, and how to isolate and purify these compounds. This review summarizes the chemical modifications to render synthetic porphyrins water-soluble, with a focus on the work disclosed since 2000. Where available, practical data such as solubility, indicators for the degree of aggregation, and special notes for the practitioner are listed. We hope that this review will guide synthetic chemists through the many strategies known to make porphyrins and hydroporphyrins water soluble.

Porphyrin Macrocycle Modification: Pyrrole Ring-Contracted or -Expanded Porphyrinoids

In recent years, several synthetic strategies aiming at the peripheral functionalization of porphyrins were developed. Particularly interesting are those involving the modification of β-pyrrolic positions leading to pyrrole-modified porphyrins containing four-, five-, six- or seven-membered heterocycles. Azeteoporphyrins, porpholactones and morpholinoporphyrins are representative examples of such porphyrinoids. These porphyrin derivatives have recently gained an increasing interest due to their potential application in PDT, as multimodal imaging contrast agents, NIR-absorbing dyes, optical sensors for oxygen, cyanide, hypochlorite and pH, and in catalysis.

Fluorinated porphyrinoids as efficient platforms for new photonic materials, sensors, and therapeutics

Porphyrinoids are robust heterocyclic dyes studied extensively for their applications in medicine and as photonic materials because of their tunable photophysical properties, diverse means of modifying the periphery, and the ability to chelate most transition metals. Commercial applications include their use as phthalocyanine dyes in optical discs, porphyrins in photodynamic therapy, and as oxygen sensors. Most applications of these dyes require exocyclic moieties to improve solubility, target diseases, modulate photophysical properties, or direct the self-organization into architectures with desired photonic properties. The synthesis of the porphyrinoid depends on the desired application, but the de novo synthesis often involves several steps, is time consuming, and results in low isolated yields. Thus, the application of core porphyrinoid platforms that can be rapidly and efficiently modified to evaluate new molecular architectures allows researchers to focus on the design concepts rather than the synthesis methods, and opens porphyrinoid chemistry to a broader scientific community. We have focused on several widely available, commercially viable porphyrinoids as platforms: meso-perfluorophenylporphyrin, perfluorophthalocyanine, and meso-perfluorophenylcorrole. The perfluorophenylporphyrin is readily converted to the chlorin, bacteriochlorin, and isobacteriochlorin. Derivatives of all six of these core platforms can be efficiently and controllably made via mild nucleophilic aromatic substitution reactions using primary S, N, and O nucleophiles bearing a wide variety of functional groups. The remaining fluoro groups enhance the photo and oxidative stability of the dyes and can serve as spectroscopic signatures to characterize the compounds or in imaging applications using (19)F NMR. This review provides an overview of the chemistry of fluorinated porphyrinoids that are being used as a platform to create libraries of photo-active compounds for applications in medicine and materials.

High pH sensing with water-soluble porpholactone derivatives and their incorporation into a Nafion® optode membrane

The known optical high pH sensing chromophores, free base and metal complexes (M = 2H, Zn(ii), Pt(ii)) of meso-tetrakis(pentafluorophenyl)porpholactone, and the as yet untested Ga(iii) complex, were made freely water-soluble by derivatization at the aryl group with PEG chains. Their halochromic response profiles were determined and found to be surprisingly shifted toward greater base sensitivity when compared to the parent sensors in aqueous solution in the presence of a surfactant. Select PEG-derivatized chromophores were also incorporated into Nafion®-based membranes. The immobilized sensor was shown to be suitable for a moderately rapid (response time in minutes) sensing of high concentrations of hydroxides (pH 11 and above, up to 5 M NaOH concentrations). The lesser sensitivity of the indicators in the membrane is rationalized by the anionic nature of the membrane material. The membrane shows a perfectly reversible response and remains transparent and stable even under extended times of exposure to very caustic environments, and no leaching of the chromophore is observed. The membrane might find use in fiber optics-based optodes suitable for the monitoring of high hydroxide environments inside chemical reactors or fuel cells.

PEGylated meso-arylporpholactone metal complexes as optical cyanide sensors in water

A number of water-soluble metal complexes of PEGylatedmeso-fluorophenylporpholactones display a specific optical response upon addition of cyanide.

MS/MS fragmentation behavior study of meso-phenylporphyrinoids containing nonpyrrolic heterocycles and meso-thienyl-substituted porphyrins

Free base and cobalt(II) complexes of six meso-tetraphenylporphyrinoids containing nonpyrrolic heterocycles and of three meso-thienylporphyrins were investigated using electrospray ionization tandem mass spectrometry (ESI-MS/MS). Their fragmentation was studied in a quadrupole ion trap as a function of the porphyrinoid macrocycle structure and compared with the fragmentation behavior of the benchmark compound meso-tetraphenylporphyrin. In situ oxidation of the neutral cobalt(II) complexes under ESI conditions produced singly charged cobalt(III) porphyrinoid ions; the free bases were ionized by protonation. For the porphyrinoids with an intact porphyrin core, the major fragmentation pathways observed were the losses of the meso-substituent (for meso-phenyl groups) and characteristic fragmentations of one or more meso-substituents (for the meso-thienyl group). Complex fragmentation pathways were observed for porphyrinoids with modifications to the porphyrin core but chemically reasonable structures could be assigned to most fragments, thus delineating general patterns for the behavior of pyrrole-modified porphyrins under CID conditions. ᅟ

Oxazolochlorins 11: Tuning the dynamic high pH sensing range of [meso-tetraarylporpholactonato]M(II) complexes by variation of the central metal ion, the aryl substituents, and introduction of a β-nitro group

Based on the high pH-sensing ability of [meso-tetrakis(pentafluorophenyl) porpholactonato]-platinum(II), we investigated the influence of the metal ( M = Zn ( II ), Ni ( II ), Cu ( II ), Pd ( II ), Ag ( II ), Pt ( II )), the aryl group ( Ar = C 6 H 5, C 6 F 5), and the presence of a β- NO 2 group on the pH sensing range. The syntheses of the novel β-nitroporpholactone derivatives are described, and their regiochemistry deduced by spectroscopic and single crystal X-ray diffraction methods. The UV-vis base titration midpoints for all derivatives were determined in an aqueous solution containing a surfactant, showing that the metal has the least influence, thus identifying a cheaper and easier method to prepare porpholactone M complex-based high pH-sensors. The influence of the pentafluorophenyl groups and the β-nitration were comparable with respect to their ability to increase the nucleophilicity of the porpholactone toward hydroxide, but the optical response for the pentafluorophenyl-substituted derivative were stronger. β-Nitration and pentafluorophenyl-substitution had additive effects.