Journal of Porphyrins and Phthalocyanines

Tris[tetra(15-crown-5)phthalocyaninato]dilutetium(III) (R₄Pc)₃Lu₂, whose structure had been confirmed earlier by X-ray analysis, was further examined by physicochemical studies. The redox properties of this complex were investigated by cyclic voltammetry. The spectroelectrochemical study of this compound has been performed for the first time. Based on the results obtained and analysis of literature data, an electrochemical criterion related to double- and triple-decker structure of lanthanide phthalocyanines has been proposed. IR and ¹H NMR data are also reported.

Association constants between α,α,α,β-ZnT(o-BocTyr)TAPP (1), α,α,α,β-ZnT(o-BocAla)-TAPP (2), and a series of amino acid esters were determined in chloroform by means of titrations monitored by UV-vis spectra. Association constants increased in the order K(AlaOMe) < K(ValOMe) < K(LeuOMe), showing the same preference for the electronic effect of bulky amino acid esters. For the guest SerOMe and ThrOMe, the association constants of two hosts showed different orders; the order of 1 is K(SerOMe) < K(ThrOMe), and that of 2 is the reverse. The host 2 shows a D-/L-selectivity of 6.9 for leucine methyl ester at 293 K in CHCl₃, which is the highest enantioselectivity achieved in our study. The host-guest system was studied by ¹H NMR spectra. On association, every proton experiences a small upfield shift. The intensity of circular dichroism (CD) spectra of 1 in the presence of optically active guests were reduced as compared with that of free 1, while that of 2 with optically active guests was of the induced split type. Molecular modeling of the host-guest systems were studied by simulated annealing on the basis of the Tripos force field. The minimal energies of the complexes were calculated, and the results show that the recognition behavior of hosts 1 and 2 toward amino acid esters is very different. The change of the interaction energy of 2 with guest molecules is larger than that of 1.

The optical properties of palladium phthalocyanine in dimethylformamide, toluene, acetonitrile, and dichloromethane solutions were studied in the visible range of energy. Palladium phthalocyanine in organic medium presented itself as a mixture of monomeric and dimeric species in equilibrium, and it was only in dichloromethane that the monomeric, non-aggregated form predominated. Palladium phthalocyanine films were prepared by casting, and studied by cyclic voltammetry and spectroelectrochemistry. The films showed an electrochromic response from blue to purple, and stability that depended on the applied potential. Electrochemical quartz crystal microbalance experiments indicated that the film exfoliates into solution after applying high values of final potentials. Raman spectroscopy was used to structurally characterize the palladium phthalocyanine film, which showed a central metal with +2 oxidation state that is not affected even when the film is oxidized.

Two high resolution single X-ray crystal structures of meso-substituted free-base corroles are presented: 5,10,15-triphenylcorrole (1) and 5,10,15-tris(pentafluorophenyl)corrole (2). The internal NH protons are clearly assignable to different nitrogens, which represents the two tautomer limits of corrole.

Reaction of the asymmetrically hexa(2-ethylhexyloxy) substituted nickel phthalocyanine PcNi1 with the pyridine N-oxides 2a-c to afford the nickel phthalocyanine adducts 3a-c containing furopyridine-type ring is described. The adducts are formed via 1,3-cycloaddtion followed by 1,5-sigmatropic rearrangement.

A new series of low-symmetry octasubstituted metal-free phthalocyanines with the general formula H₂N_xP^β_4−x(OBu)₈ (x = 0-4) were synthesized by mixed condensation of two different substituted precursors (4,5-dibutoxy- phthalonitrile and 1,4-dibutoxy-2,3-dicyanonaphthalene). Their electronic absorption spectra and MALDI-TOF-MS were investigated. The regiospecific, nonlinear and linear substituent effects of alkoxyl groups on the positions of the Q-bands of phthalocyanines with different substituent groups at different peripheral positions were systematically investigated. The results could provide a guide to the tuning of Q-band absorptions of phthalocyanine derivatives.

The electrochemistry of homoleptic bis(naphthalocyaninato) double-decker complexes for the whole series of tervalent rare earths M(TBNc)₂ (M = Y, La…Lu except Ce and Pm; H₂TBNc = 3(4),12(13),21(22),30(31)-tetra(tert-butyl)naphthalocyanine) has been systematically studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Up to three quasi-reversible one-electron oxidations and four quasi-reversible one-electron reductions have been revealed for these double-deckers.The half-wave potentials of all oxidations and the first reduction for double-decker complexes are dependent on the size of the metal center. The difference between the redox potentials of the first and second reductions for M^III(TBNc)₂, which represents the potential difference between the first oxidation and first reduction of [M^III(TBNc)₂]⁻, lies in the range 1.09-0.95 V and gradually diminishes along with the lanthanide contraction, indicating increased π-π interaction in the double-deckers in the same order. Comparison of electrochemical characteristics between M(TBNc)₂ and M(TBPc)₂ (H₂TBPc = 2(3),9(10),16(17),24(25)-tetra(tert-butyl)-phthalocyanine) reveals that extension of the ligand conjugated system upon going from phthalocyanine to naphthalocyanine attenuates the ring-to-ring separation effect on the redox potentials of the double-deckers of the whole series of tervalent lanthanides.

Three cationic zinc phthalocyanines (ZnPcs), tetrakis-(3-methylpyridyloxy)-, tetrakis-(3-hexyl-pyridyloxy)-, and tetrakis-(3-dodecylpyridyloxy)phthalocyaninezinc (ZnPcMe, ZnPcHe and ZnPcDo) have been studied as advanced fluorescent contrast agents for pigmented melanoma tumor. UV-vis spectroscopic properties of the monomers were investigated. Their photophysical behavior as a substantial part of dye-induced fluorescence was evaluated. The selective accumulation and labeling capacity towards B16F0 pigmented melanoma tumor were determined. Melanin containing cells were isolated and incubated with ZnPcs at several time intervals (1, 1.5 and 6 h) following the kinetics of cellular uptake. The highest accumulation was found for ZnPcHe. A lower uptake was detected for the more lipophilic ZnPcDo and more hydrophilic ZnPcMe. The fluorescence diagnostic potential of ZnPcs towards pigmented melanoma by using an argon-dye laser detection set-up was demonstrated.

The bis(octacyanophthalocyaninato)neodymium(III) was synthesized and its electrochemical behavior in N,N-dimethylformamide (DMF) was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV). Multiple redox reactions were observed on the cyclic voltammogram, although the voltammetric feature was complicated due to aggregation. With the aid of SWV, it was concluded that the redox potentials of the complex positively shifted by about 700 mV compared with potentials of the unsubstituted complex, which was ascribed to the strong electron-withdrawn effect of the substituted cyano group.

The effect of N-methyl substitution on photophysical and metal coordination properties of the respective derivatives of octaethylporphyrin (H₂OEP) and tetraphenylporphyrin (H₂TPP) was studied by means of steady-state and time-resolved optical spectroscopies combined with semi-empirical quantum-chemical calculations and coordination chemistry methods. In case of H₂TPP, the insertion of the methyl substituent into the center of the porphyrin macrocycle leads to noticeable nonplanar distortions of the molecule and is accompanied by changes of its photophysical and physicochemical properties towards those manifested by “classical” nonplanar porphyrins. Contrasting to that, N-methyl substituted H₂OEP does not undergo significant nonplanar distortions and possesses photophysical characteristics mainly similar to unsubstituted H₂OEP, except for the long-wavelength shift of the absorption and emission bands. The Zn coordination/Zn complex dissociation and macrocycle thermal stability parameters were also determined for both N-methyl substituted and parent unsubstituted macrocycles, which correlate well with a higher degree of nonplanarity of the N-methyl substituted H₂TPP as compared to H₂OEP. Basing on the results of this study the conclusion postulated is that N-methyl substitution has a different effect on the photophysical and coordination properties of H₂TPP vs. H₂OEP.

A unique salt composed of cationic and anionic phthalocyanine complexes has been prepared and structurally characterized. The cationic component is di(pyridine)(phthalocyaninato)cobalt(III) and the anionic one is dicyano(phthalocyaninato)cobalt(III). They arrange alternately in the crystal, forming a two-dimensional sheet with partial π–π overlaps.