Solvent Effect on Protonation Constants of 5, 10, 15, 20-Tetrakis(4-sulfonatophenyl)porphyrin in Different Aqueous Solutions of Methanol and Ethanol

Insights into the phototautomerism of free-base 5, 10, 15, 20-tetrakis(4-sulfonatophenyl) porphyrin

Phototautomerism in the excited states of free-base 5, 10, 15, 20-tetrakis(4-sulfonatophenyl) porphyrin (H₂TPPS^4-) has been investigated combining, for the first time, advanced Electron Paramagnetic Resonance (EPR) with fluorescence and Raman spectroscopy. Triplet EPR spectroscopy, performed in protic and deuterated solvents and in the presence of photoselection, confirms the occurrence of phototautomerization and additionally suggests the formation of the cis tautomer as a minor component. The zero-field splitting parameters and triplet sublevel populations indicate that the process is slow in the triplet state. The results obtained by EPR combined with photoselection and fluorescence anisotropy have been interpreted within a model which accounts for a fast trans-trans tautomerization promoted by a spin-vibronic coupling mechanism for intersystem crossing, with an even distribution of the two trans tautomers at liquid nitrogen temperatures for H₂TPPS^4-.

Solvent Effects in Highly Efficient Light-Induced Molecular Aggregation

It has been reported that when irradiated with laser light non-resonant with the main absorption peaks, porphyrin molecules (4-[10,15,20-tris(4-sulfophenyl)-21,24-dihydroporphyrin-5-yl]benzenesulfonic acid, TPPS) in an aqueous solution become 10,000 to 100,000 times more efficient in light-induced molecular aggregation than expected from the ratio of gradient force potential to the thermal energy of molecules at room temperature. To determine the mechanism of this phenomenon, experiments on the light-induced aggregation of TPPS in alcohol solutions (methanol, ethanol, and butanol) were performed. In these alcohol solutions, the absorbance change was orders of magnitude smaller than in the aqueous solution. Furthermore, it was found that the absorbance change in the aqueous solution tended to be saturated with the increase of the irradiation intensity, but in the ethanol solution, the absorbance change increased linearly. These results can be qualitatively explained by the model in which intermolecular light-induced interactions between molecules within a close distance among randomly distributed molecules in the laser irradiation volume are highly relevant to the signal intensity. However, conventional dipole–dipole interactions, such as the Keesom interaction, are not quantitatively consistent with the results.

Mechanical behavior of crystalline ionic porphyrins

Mechanical properties of six different binary ionic porphyrin crystals with variable morphologies were measured and correlated with their structural properties. These solids were formed from stoichiometric combinations of negatively charged tectons, meso-tetra(4-sulfonatophenyl)porphyrin (TSPP), Cu(II) meso-tetra(4-sulfonatophenyl)porphyrin (CuTSPP), Ni(II) meso-tetra (4-sulfonatophenyl)porphyrin (NiTSPP), and four different cationic tectons, namely, meso-tetra (4-pyridyl)porphyrin (TPyP), tetra([Formula: see text]-methyl-4-pyridyl)porphyrin (TMPyP), Cu(II) meso-tetra([Formula: see text]-methyl-4-pyridyl)porphyrin (CuTMPyP), Ni(II) meso-tetra([Formula: see text]-methyl-4-pyridyl)porphyrin (NiTMPyP), and tetra(4-aminophenyl)porphyrin (TAPP). Crystal structures were determined from single crystal and powder X-ray diffraction patterns. Scanning electron and atomic force microscopes (SEM and AFM) provided topographical information. The common arrangement of the porphyrin tectons within the crystals is consistent with alternating face-to-face molecular arrangement forming coherent columns along the fast-growing long axis which are held together by electrostatic and [Formula: see text]–[Formula: see text] interactions as well as hydrogen bonding. In acquiring the indentation data of the porphyrin crystals using AFM, stress was applied perpendicular to the direction where ionic and [Formula: see text]–[Formula: see text] bonds dominate the packing. At indent loads [Formula: see text]50 nN/nm2, all the porphyrin structures deformed elastically. Young’s modulus ([Formula: see text] values for the different crystals range from 6 to 28 GPa. In a broader perspective, this study highlights the extraordinary mechanical behavior of porphyrin assemblies formed by ionic self-assembly. Judicious selection of charged porphyrin synthons can yield crystalline materials with mechanical properties that combine the elastic characteristics of ‘soft’ polymers with the stiffness of composite materials. Such high-performance materials are excellent candidates for deformable optoelectronic devices.

Comparative study of binding interactions between porphyrin systems and aromatic compounds of biological importance by multiple spectroscopic techniques: A review

The specific spectroscopic and redox properties of porphyrins predestine them to fulfill the role of sensors during interacting with different biologically active substances. Monitoring of binding interactions in the systems porphyrin-biologically active compound is a key question not only in the field of physiological functions of living organisms, but also in environmental protection, notably in the light of the rapidly growing drug consumption and concurrently the production of drug effluents. Not always beneficial action of drugs on natural porphyrin systems induces to further studies, with commercially available porphyrins as the model systems. Therefore the binding process between several water-soluble porphyrins and a series of biologically active compounds (e.g. caffeine, guanine, theophylline, theobromine, xanthine, uric acid) has been studied in different aqueous solutions analyzing their absorption and steady-state fluorescence spectra, the porphyrin fluorescence lifetimes and their quantum yields. The magnitude of the binding and fluorescence quenching constants values for particular quenchers decreases in a series: uric acid > guanine > caffeine > theophylline > theobromine > xanthine. In all the systems studied there are characters of static quenching, as a consequence of the π-π-stacked non-covalent and non-fluorescent complexes formation between porphyrins and interacting compounds, accompanied simultaneously by the additional specific binding interactions. The porphyrin fluorescence quenching can be explain by the photoinduced intermolecular electron transfer from aromatic compound to the center of the porphyrin molecule, playing the role of the binding site. Presented results can be valuable for designing of new fluorescent porphyrin chemosensors or monitoring of drug traces in aqueous solutions. The obtained outcomes have also the toxicological and medical importance, providing insight into the interactions of the water-soluble porphyrins with biologically active substances.

Hyperbranched crystalline nanostructure produced from ionic π-conjugated molecules

We report the first synthesis of a hyperbranched sheaf-like nanostructure by ionic self-assembly of organic semiconductors that forms via combined oriented attachment and Ostwald ripening growth mechanisms.

Real-time analysis of porphyrin J-aggregation on a plant-esterase-functionalized surface using quartz crystal microbalance with dissipation monitoring

The J-aggregation of meso-tetra (4-sulfonatophenyl) porphine (TPPS4) on a plant-esterase-functionalized surface in a 1:1 v/v mixture of 0.05 M HCl/ethanol (pH ∼1.38) was analyzed in real time using a quartz crystal microbalance with dissipation monitoring (QCM-D). Simultaneous changes in frequency (Δf) and energy dissipation (ΔD) correlated well with mass and structural changes during the sequential phases of slow nucleation, rapid aggregation, and equilibration in J-aggregation. The time-dependent mass adsorption could be quantitatively analyzed with a model, which integrated two simple equations obtained when the surface concentration of TPPS4 (Γ(TPPS4)) was below and above the critical aggregation surface concentration (CASC). This study provides a new view for the protein-induced J-aggregation process, which may be helpful for understanding the interactions of self-assembled nanostructures with biomolecules.

Preferential solvation and solvation shell composition of free base and protonated 5, 10, 15, 20-tetrakis(4-sulfonatophenyl)porphyrin in aqueous organic mixed solvents

The solvatochromic properties of the free base and the protonated 5, 10, 15, 20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) were studied in pure water, methanol, ethanol (protic solvents), dimethylsulfoxide, DMSO, (non-protic solvent), and their corresponding aqueous-organic binary mixed solvents. The correlation of the empirical solvent polarity scale (E(T)) values of TPPS with composition of the solvents was analyzed by the solvent exchange model of Bosch and Roses to clarify the preferential solvation of the probe dyes in the binary mixed solvents. The solvation shell composition and the synergistic effects in preferential solvation of the solute dyes were investigated in terms of both solvent-solvent and solute-solvent interactions and also, the local mole fraction of each solvent composition was calculated in cybotactic region of the probe. The effective mole fraction variation may provide significant physico-chemical insights in the microscopic and molecular level of interactions between TPPS species and the solvent components and therefore, can be used to interpret the solvent effect on kinetics and thermodynamics of TPPS. The obtained results from the preferential solvation and solvent-solvent interactions have been successfully applied to explain the variation of equilibrium behavior of protonation of TPPS occurring in aqueous organic mixed solvents of methanol, ethanol and DMSO.