Narrow Results

Absorption and MCD spectra of the two-electron oxidized lutetium phthalocyanine trimer [(Pc)Lu(CRPc)Lu(Pc)]²⁺ (Pc ≡ phthalocyanine;CRPc ≡ 15-crown-5-substituted Pc) as well as the MCD spectrum of the oxidized lutetium Pc dimer [Lu(Pc)₂]⁺ are reported. These ‘two-electron-deficient’ Pc stacks show absorption bands in the NIR region whose intensities are comparable with those of the Q bands. The band of [Lu(Pc)₂]⁺ showed only an MCD B term with no A term contribution, from which we assign the band to a non-degenerate transition whose transition moments are perpendicular to the Pc planes. In both trimer and dimer cases the excitation energy is higher than that of the corresponding NIR band in the ‘one-electron-deficient’ Pc stack [(Pc)Lu(CRPc)Lu(Pc)]⁺ or [Lu(Pc)₂], but the magnitudes of the shift were significantly different (1500 cm⁻¹ in the trimer and 4500 cm⁻¹ in the dimer). The energy shifts are shown to be represented by a pair of two-electron repulsion integrals in a localized orbital basis. The model reproduced well the direction and magnitude of the shifts using numerical values of the integrals.

This paper reviews the studies on the electronic structures and spectroscopic properties of sandwich-type complexes M(Pc)₂ and M₂(Pc)₃. The subjects discussed are as follows. (1) Electronic spectra of closed-shell Pc dimers and trimers. The complexes with closed-shell systems, such as [Lu(Pc)₂]⁻, Sn(Pc)₂ and Lu₂(Pc)₃, can be thought of as stacked systems composed only of Pc²⁻. The excited states of these complexes can be described by locally excited and charge transfer configurations. The coupling terms of the configurations are written using orbitals localized on each Pc ring. Assignments of the observed absorption bands are discussed. Computational studies on the band assignments were carried out using a localized molecular orbital (LO) basis which maximizes orbital populations on one of the Pc rings. (2) Electronic structures of πelectron-deficient Pc dimers and trimers. Oxidation of [Lu(Pc)₂]⁻ or Lu₂(Pc)₃ yields systems with π-electron deficiency or π-hole(s) residing on multiple Pc sites. The delocalized nature of the π-hole in Lu(Pc)₂ is elucidated by comparison of the electronic spectra of symmetric and asymmetric dimers composed of Pc and Nc(H₂Nc ≡ naphthalocyanine). The band assignments of the dimer radicals are discussed. The Pc trimer radical shows an intense absorption band at about 5000 cm⁻¹, which is 2000 cm⁻¹ lower than the valence resonance band of Lu(Pc)₂. The two-electron-deficient complexes [Lu(Pc)₂]⁺ and [Lu₂(Pc)₃]²⁺ also show intense near-IR bands at higher energy than the corresponding monoradical species. The interactions that determine the excitation energies of the near-IR bands of the π-electron-deficient species are elucidated.

A novel one-pot method for the regioselective preparation of early heteroleptic lanthanide (porphyrinato)(phthalocyaninato) complexes of double- and triple-decker structure [(Por)Ln(Pc) and (Por)Ln(Pc)Ln(Por), respectively] is developed. Sandwich-type complexes are synthesized for La, Ce and Pr following this procedure, with yields up to 30%. Tetrakis(15-crown-5)-phthalocyanine [(15C5)₄PcH₂] and tetrakis-meso-(4-methoxyphenyl)-porphyrin (An₄PH₂) are used as macrocyclic tetrapyrrolic ligands. The complexes are widely characterized with various physico-chemical methods (NMR and UV-vis spectroscopy, MALDI-TOF mass spectrometry). Quantum chemistry calculations for intermediates of the process are performed. The results of calculations explain the high regioselectivity of the triple-decker complex formation in the developed method.

For the first time, bis[octakis-(2,2,3,3-tetrafluoropropoxy)phthalocyaninato] rare-earth metal(III) double-decker phthalocyanine complexes (Pc₂Sm, Pc₂Eu, Pc₂Gd, Pc₂Dy and Pc₂Lu) are synthesized. The new phthalocyanine complexes are characterized using mass, FT-IR and UV-vis spectroscopic techniques as well as elemental analysis. All these compounds exhibit excellent solubility in organic solvents. The photophysical and photochemical properties of the rare-earth metal(III) double-decker complexes are investigated and discussed.

The synthesis of trifluoroethoxy-substituted double-decker phthalocyanines was investigated for the first time. Trifluoroethoxy-substituted phthalonitriles reacted with lanthanide acetylacetonate hydrate in n-octanol in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene when refluxed. La and Eu were chosen as central metals. Phthalonitriles, including one trifluoroethoxy substituent at the α- or β-position, were nicely induced to double-decker phthalocyanines. Phthalonitrile having two trifluoroethoxy substituents at α-positions did not react, although we succeeded in leading β-di-substituted phthalonitrile to double-decker phthalocyanines. Fully trifluoroethoxy-coated phthalonitrile did not react at all. Fluorophobic repulsion and steric hindrance caused by outlying trifluoroethoxy groups could be responsible for the difficulty in the formation of a double-decker structure. Absorption and fluorescence spectra of trifluoroethoxy-substituted double-decker phthalocyanines obtained were also investigated.

An efficient enzymatic-free electrochemical sensor is firstly developed based on the self-assemblied film of a sandwich mixed (phthalocyaninato) (porphyrinato) europium(III) double-decker complex, Eu(Pc)[T(OH)PP], [Pc = phthalocyaninate, T(OH)PP = 5,10,15,tris (4-tert-butylphenyl)-20-(4-hydroxyphenyl)porphyrinate] prepared by using a solution-processing QLS method. The Eu(Pc)[T(OH)PP]semiconducting active layer on an ITO working electrode leads to a good sensing property for the detection of dopamine with an excellent selectivity, due to the high Eu(Pc)[T(OH)PP] molecular ordering/packing in the QLS film and more favorable interaction between the Eu(Pc)[T(OH)PP] and DA molecules. The amperometric responses are linearly proportional to the concentration of dopamine in the range of 8–100 $\mu$M, with a low detection limit of 4.8 $\mu$M and good sensitivity, indicating the great potential of electroactive tetrapyrrole rare earth sandwich type complexes in the field of nonenzymatic electrochemical sensors.

The location of the unpaired electron in neutral bis(phthalocyaninato) yttrium double-decker complexes, with different substituents, has been studied on the basis of both experimental methods and density functional theory (DFT) calculations over the molecular structures, atomic charges, electronic absorption, infrared spectra, and electron paramagnetic resonance. The results reveal the location of the unpaired electron mainly on the carbon atoms of both tetrapyrrole chromophores with the population distribution obviously affected by the peripheral substituents.