Narrow Results

Singlet and triplet excited state data on two new core-modified expanded porphyrins and their protonated derivatives are reported. Absorption spectral studies indicate a gradual red shift of the absorption bands upon sulfur substitution into the core. The singlet lifetimes for expanded S₃-sapphyrin and S₄-rubyrin decrease steadily relative to STPPH and S₂TPP owing to a higher rate of intersystem crossing. Furthermore, the protonated derivatives of S₃-sapphyrin and S₄-rubyrin encapsulate fluoride ions into their cavities with binding constants of 807 and 48 M⁻¹ respectively. However, the triplet lifetime for S₃-sapphyrin is longer (58.80 μs) than for normal thiaporphyrins (STPPH, 37.45 μs; S₂TPP, 20.96 μs), suggesting that it could be very well suited for photosensitizing triplet oxygen.

An expanded heterocorrole, meso-tetraaryl-tellura[22]porphyrin(6.1.1.0), containing a bipyrrole moiety and a six-carbon long link, has been synthesized. The reaction path proceeds through a controlled acid-promoted extrusion of one tellurium atom from meso-aryl-26,28-ditellurasapphyrin, leading to a structure where one tellurophene ring of the substrate is replaced by a bridging acyclic four-carbon unit. This aromatic porphyrin-annulene hybrid is conformationally flexible in solution, on account of the C₄ unit adopting two different configurations: trans–cis–trans or all-trans. Studies of the dynamic behavior of tellura[22]porphyrin(6.1.1.0) in solution were performed by means of ¹H and ¹²⁵Te NMR spectroscopy. The X-ray structure of the all-trans form with trapezoid macrocyclic skeleton is also presented.

Synthesis of unsymmetrically substituted 2,3,7,13,16,17,22,23-octamethyl-8,12-di-$n$-butylsapphyrin dichloride (H₅P${}^{2+}$Cl${}_2)$ was carried out. The synthesized compound was identified by electron absorption, ¹H NMR spectroscopy, and mass spectrometry. The stability of the anionic complex and the acidic properties of H₅P${}^{2+}$Cl₂ were studied by spectrophotometric titration. The parameters of the electronic absorption spectra and the concentration range for the existence of deprotonated forms, as well as their acid dissociation constants, are determined. The geometric structure and electronic structure of the molecular and ionic forms of the resulting sapphyrin were calculated in terms of the density functional theory (B3LYP/Def2TZVPP with an empirical correction for GD3 dispersion). The calculations showed good agreement with the experimental data.

The UV-Vis spectra of the dicationic salt of 2,3,7,13,17,18,18,22,23-octamethyl-8,12-diethylsapphyrin {H₅β-Me₈Et₂Sap²⁺(Cl⁻)₂} in solutions with different polarity and acid-basic properties have been investigated. The tautomeric and acid-base equilibria of H₅β-Me₈Et₂Sap²⁺(Cl⁻)₂ in the presence of organic bases have been examined by spectrophotometric titration. It was demonstrated that an addition of small amounts of 1,8-diazabicyclo[5.4.0]undecene (DBU) and tetramethylammonium hydroxide (Me₄NOH) dissolved in methylene chloride (DCM) and MeOH, respectively results in a stepwise detachment of two protons from the basic nitrogen atoms of the macrocycle, with no anionic forms of sapphyrin being registered. The results obtained were supported using quantum-chemical calculations (DFT, B3LYP, cc-pVDZ including NBO analysis). The interactions of 2,3,7,13,17,18,18,22,23-octamethyl-8,12-diethylsapphyrin (H₃β-Me₈Et₂Sap) with a series of compounds of different acidity and basicity were studied and the formation of very weak hydrogen bond of H₃β-Me₈Et₂Sap as NH-acid with N,N-dimethylformamide (DMF) molecule with the value of the interaction energy (E_int equal -16.40 kJ/mol was revealed. The low acidity of bonds NH in the sapphyrin molecule was confirmed on the base of thermogravimetric data obtained for the solid samples of H₅β-Me₈Et₂Sap²⁺(Cl⁻)₂ evaporated from DMF and DCM concentrated solutions.

An expanded heterocorrole, meso-tetraaryl-tellura[22]porphyrin(6.1.1.0), containing a bipyrrole moiety and a six-carbon long link, has been synthesized. The reaction path proceeds through a controlled acid-promoted extrusion of one tellurium atom from meso-aryl-26,28-ditellurasapphyrin, leading to a structure where one tellurophene ring of the substrate is replaced by a bridging acyclic four-carbon unit. This aromatic porphyrin-annulene hybrid is conformationally flexible in solution, on account of the C4 unit adopting two different configurations: trans–cis–trans or all-trans. Studies of the dynamic behavior of tellura[22]porphyrin(6.1.1.0) in solution were performed by means of ¹H and ¹²⁵Te NMR spectroscopy. The X-ray structure of the all-trans form with trapezoid macrocyclic skeleton is also presented.