Łukasz Łapok

Synthesis, X-ray Structure, Magnetic Resonance, and DFT Analysis of a Soluble Copper(II) Phthalocyanine Lacking C-H Bonds

The synthesis, crystal structure, and electronic properties of perfluoro-isopropyl-substituted perfluorophthalocyanine bearing a copper atom in the central cavity (F(64)PcCu) are reported. While most halogenated phthalocyanines do not exhibit long-term order sufficient to form large single crystals, this is not the case for F(64)PcCu. Its crystal structure was determined by X-ray analysis and linked to the electronic properties determined by electron paramagnetic resonance (EPR). The findings are corroborated by density functional theory (DFT) computations, which agree well with the experiment. X-band continuous-wave EPR spectra of undiluted F(64)PcCu powder, indicate the existence of isolated metal centers. The electron-withdrawing effect of the perfluoroalkyl (R(f)) groups significantly enhances the complexes solubility in organic solvents like alcohols, including via their axial coordination. This coordination is confirmed by X-band (1)H HYSCORE experiments and is also seen in the solid state via the X-ray structure. Detailed X-band CW-EPR, X-band Davies and Mims ENDOR, and W-band electron spin-echo-detected EPR studies of F(64)PcCu in ethanol allow the determination of the principal g values and the hyperfine couplings of the metal, nitrogen, and fluorine nuclei. Comparison of the g and metal hyperfine values of F(64)PcCu and other PcCu complexes in different matrices reveals a dominant effect of the matrix on these EPR parameters, while variations in the ring substituents have only a secondary effect. The relatively strong axial coordination occurs despite the diminished covalency of the C-N bonds and potentially weakening Jahn-Teller effects. Surprisingly, natural abundance (13)C HYSCORE signals could be observed for a frozen ethanol solution of F(64)PcCu. The (13)C nuclei contributing to the HYSCORE spectra could be identified as the pyrrole carbons by means of DFT. Finally, (19)F ENDOR and easily observable paramagnetic NMR were found to relate well to the DFT computations, revealing negligible isotropic hyperfine (Fermi contact) contributions. The single-site isolation in solution and solid state and the relatively strong coordination of axial ligands, both attributed to the introduction of R(f) groups, are features important for materials and catalyst design.

Synthesis of charged triazatetrabenzcorroles, phthalocyanines and tetrapyridylporphyrin, and their activities in the co-sensitized photooxidation of 2-mercaptoethanol

Water soluble zwitterionic, as well as cationic and anionic triazatetrabenzcorroles (TBC), phthalocyanines (Pc) and a porphyrin (P) were synthesized and their sensitizer properties investigated. Monomerization of the sensitizers, including their mixtures, in the presence of a detergent was used as a basis for studying the fundamental effect of co-sensitization upon a known model reaction, viz. the photooxidation of 2-mercaptoethanol in aqueous alkaline solutions. Compared to single-component sensitizers, a remarkable improvement of the photocatalytic activity is observed in the case of co-sensitization employing molecules that absorb in different Q and Soret regions.

Structures and Redox Characteristics of Electron-Deficient Vanadyl Phthalocyanines

The first single-crystal X-ray structures of substituted vanadyl phthalocyanine materials reveal the high-valence vanadium ions (denoted as V(IV)), whose coordination by a highly electron-deficient ligand is facilitated by an axial oxo group. The metal center of the hydrophilic V═O core, encapsulated in F-rich hydrophobic pockets, reaches a coordination number of 6 by binding an additional H(2)O that, in turn, hydrogen-bonds with ketones, resulting in solvent-induced variable solid-state architectures. Fluoroalkyl (R(f)) ligand substituents hinder π-π stacking interactions and favor ordered long-range packing, as well as the facile formation of film materials that exhibit high thermal stability and oxidation resistance. Reversible redox chemistry and spectroscopic studies in both solution and the solid-state indicate single-site isolation in both phases and an R(f)-induced propensity for electron uptake and inhibition of electron loss. Repeated redox cycles reorganize the thin films to accommodate Li(+) ions and facilitate their migration. The facile reduction, combined with high stability and ease of sublimation imparted by the R(f) scaffold that suppresses oxidations, recommends the new materials for sensors, color displays, electronic materials, and redox catalysts, as well as other applications.

Near Infrared Phosphorescent, Non‐oxidizable Palladium and Platinum Perfluoro‐phthalocyanines

New Pd(II) and Pt(II) complexes with a highly electron-deficient ligand (H2 PcF64 ) were conveniently prepared in a three-step synthesis. This is the first time that the phosphorescence of phthalocyanines with a H2 PcF64 framework has been measured. Based on these measurements, the triplet-state energies (ET ) were directly determined. Transient absorption experiments revealed broad T1 →Tn absorption spanning from ca. 350 to ca. 1000 nm and allowed determination of the triplet-state lifetimes. Removal of the Pd or Pt from the perfluoro-phthalocyanine resulted in a significant increase of the triplet lifetime for H2 PcF64 . The very efficient intersystem crossing observed for both PdPcF64 and PtPcF64 leads to residual fluorescence and suppresses the fluorescence lifetimes to less than 50 ps. The absence of Pd and Pt in the perfluoro-phthalocyanine ligand, viz. H2 PcF64 , led to a recovery of fluorescence. Cyclic voltamperometry studies pointed to complete resistance of PdPcF64 and PtPcF64 to oxidation and very strong electron affinity, which rendered these materials very good electron acceptors (n-type materials). The presence of d-orbital metals such as Pd(II) and Pt(II) in the phthalocyanine ring stabilizes their reduced forms, as indicated by the spectroelectrochemical experiments. PdPcF64 and PtPcF64 easily sensitize singlet oxygen production with very high quantum yields. Both phthalocyanines presented resistance to photodegradation in the solid state under aerobic conditions and under intense irradiation.

Photophysics and redox properties of aza-BODIPY dyes with electron-withdrawing groups

The optical and electrochemical properties are compared for aza-BODIPY dyes that differ by virtue of the substituents at 1,7- and 3,5-positions of the aza-BODIPY backbone. In particular, the impact of highly electron-withdrawing nitro substituents on these properties is of consideration. The aza-BODIPYs studied exhibit a broad absorption band spanning from ca. 600 nm to ca. 700 nm – a spectral region that is highly sought after for biomedical applications – and possess high molar absorption coefficients (e) ranging from 64 000 [M−1 cm−1] to 85 000 [M−1 cm−1] in THF. The compounds studied are weakly emissive as non-radiative decay is the predominant way of the excited state energy dissipation. Exemplarily, the fluorescence quantum yields (Φfl) measured in THF were in the range of 0.03 to 0.06 for the aza-BODIPYs studied. Transient absorption experiments revealed T1 → Tn absorption spanning from ca. 400 nm to ca. 600 nm and allowed determination of the triplet state lifetimes. The estimated triplet lifetimes (τT) in deaerated THF ranged from 77 µs to 130 µs. As estimated by the CV/DPV measurements, all aza-BODIPYs studied exhibited one irreversible oxidation and two quasi-reversible reductions. Estimation of the EHOMO gave a value of ca. −5.8 eV while the ELUMO was found to be located at ca. −4.5 eV. Extremely high photostability and thermal robustness up to approximately 300 °C were found for the nitro-substituted aza-BODIPYs.

Highly Thermostable, Non-oxidizable Indium, Gallium, and Aluminium Perfluorophthalocyanines with n-Type Character.

Perfluorophthalocyanines incorporating three-valent metals, namely In(Cl), Ga(Cl), and Al(Cl), have been synthesized and characterized. Thermogravimetric analysis revealed that these compounds exhibit outstanding thermal stability and a tendency to sublime at a temperature exceeding around 350 °C without thermal decomposition. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to probe the frontier orbital energy levels of these compounds in THF solution. All three compounds undergo three quasi-reversible reductions with the first one leading to the formation of an anion radical, namely MPc(-.) , as confirmed by spectroelectrochemistry. The compounds studied were intrinsically resistive to oxidation, which indicates that they are very good electron acceptors (n-type materials). The HOMO-LUMO energy gaps (Eg ) of the three compounds determined by UV/Vis spectroscopy were relatively unaffected by the three-valent metals incorporated into the phthalocyanine macrocycle. Similarly, the energies of the HOMO (EHOMO ) and LUMO (ELUMO ) orbitals remained virtually unaffected by the three-valent metals in the perfluorophthalocyanine. Importantly, all the perfluorophthalocyanines studied possess LUMO levels between -4.76 and -4.85 eV, which makes their reduced forms resistant to electron trapping by O2 and H2 O. This property opens up the possibility for the fabrication of electronic devices operating under ambient conditions. All three compounds demonstrated very good photostability as solid thin films.

Facile Synthesis, Triplet-State Properties, and Electrochemistry of Hexaiodo-Subphthalocyanine

In view of the ever-growing demand for efficient triplet photosensitizers and photoactive components of various optoelectronic devices, we herein report the synthesis and properties of hexaiodo-subphthalocyanines (I6 SubPcs). The improved five-step route to 4,5-diiodophthalonitrile, which serves as precursor for the synthesis of the I6 SubPcs, is reported. The improved synthesis merely required one chromatographic separation to afford the high-purity target product. Highly desirable photophysical and photochemical properties were induced in the I6 SubPcs due to the presence of six heavy iodine atoms. In particular, high values of the singlet-oxygen quantum yields (ΦΔ ) ranging from 0.83 to 0.9 were measured. The I6 SubPcs investigated proved to be phosphorescent at 77 K in 2-MeTHF with emission band maxima (λP ) located at λ=957 and 970 nm. The excited-triplet-state energies (ET ) were estimated to be approximately 1.30 eV, whereas the triplet lifetimes (τT ) were found to be 27.7 and 30.1 μs. The CV/DPV measurements indicated that both I6 SubPcs exhibited one irreversible oxidation and one quasi-reversible reduction. The spectroelectrochemical measurements pointed to a relative stability and reversibility of the electrochemically formed anion radical, that is, I6 SubPc.- , and an instability of the species formed upon one-electron oxidation, that is, I6 SubPc.+ . Estimation of EHOMO gave a value of approximately -5.8 eV whereas ELUMO was found to be located at around -3.8 eV.