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.

The successful use of dipyrromethanecarbinols in rational routes to porphyrinic macrocycles requires catalysis conditions that enable irreversible condensation, thereby avoiding substituent scrambling and formation of undesired porphyrin products. Previously, successful conditions of trifluoroacetic acid (TFA) (30 mM) in acetonitrile were identified following a lengthy survey of TFA and BF₃-etherate catalysis in diverse solvents. In this study, focus was placed on the acid catalyst by examining 17 acids in CH₂Cl₂, the traditional solvent for two-step, one-flask porphyrin syntheses. In the self-condensation of the carbinol derived from 1-(4-methylbenzoyl)-5-phenyldipyrromethane, porphyrin yields of 9–55% were obtained from the various acids, compared to 20% under TFA catalysis in acetonitrile. A number of catalytic conditions that produce little to no porphyrin in reactions of pyrrole + benzaldehyde afforded good yields of porphyrin and the suppression of scrambling in reactions of dipyrromethanecarbinols. The four best acid catalysts (InCl₃, Sc(OTf)₃, Yb(OTf)₃, and Dy(OTf)₃) initially identified were then examined with dipyrromethanecarbinols bearing challenging substituents (alkyl, pyridyl, or no substituent). The greatest improvement was obtained with the pyridyl substrates. Selected reactions performed on a preparative scale (115 to 460 mg of isolated porphyrin) verified the results of the analytical-scale experiments and revealed the more facile isolation of the porphyrin from reactions performed in CH₂Cl₂ rather than acetonitrile. This study provides alternatives to the use of TFA/acetonitrile that offer advantages in terms of yield and isolation of the porphyrin without sacrificing suppression of scrambling. Furthermore, the finding that poor catalysts for the benzaldehyde + pyrrole reaction can be excellent catalysts for dipyrromethanecarbinols provides guidance for the identification of other catalysts for use with reactive precursors in porphyrin-forming reactions.

An approach toward molecular information storage employs redox-active molecules attached to an electroactive surface. The chief advantages of such molecular capacitors include higher charge density and more versatile synthetic design than is afforded by typical semiconductor charge-storage materials. An architecture containing two triple-decker sandwich coordination complexes and an S-acetylthiomethyl-terminated tether has been designed for multibit storage. Each triple decker is composed of two phthalocyanines, one porphyrin, and two europium atoms. The oxidation potentials of each triple decker are tuned through the use of different substituents on the phthalocyanines (t-butyl, methyl, H) and porphyrins (pentyl, p-tolyl). Interleaving of the four cationic oxidation states of each triple decker potentially affords eight distinct oxidation states. Two dyads were examined in solution and in self-assembled monolayers (SAMs) on a Au surface. One dyad exhibited eight distinct states in solution and in the SAM, thus constituting a molecular octal counter. The potentials ranged from −0.1-+1.3 V in solution and +0.1-+1.6 V in the SAM. Taken together, this approach provides a viable means of achieving multibit information storage at relatively low potential.

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.

A complete assignment of ¹³C NMR resonance peaks in the spectrum of heteroleptic triple-decker (porphyrinato)(phthalocyaninato) lanthanum of type [Br₄TPP]La[(15C5)₄Pc]La[Br₄TPP] (Br₄TPP = 5,10,15,20-tetrakis-(4-bromophenyl)-porphyrinato-ligand, (15C5)₄Pc = tetrakis-(15-crown-5)-phthalocyaninato-ligand) is performed. Application of set of gradient-enhanced homonuclear ¹H-¹H-correlation techniques (COSY and NOESY) allowed the unambiguous interpretation of proton spectrum of the complex. Application of INEPT polarization transfer technique allowed to separate quaternary carbon resonances from proton-bound carbon ones. Gradient-enhanced proton-detected HMQC and HMBC techniques allowed to correlate all the resonances in ¹³C-spectrum.

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.

Three lanthanide-vanadium porphyrins, [LnV(TPPS)H₂O]_n (Ln = Tb(1), Dy(2), Er(3); H₆TPPS = tetra(4-sulfonatophenyl)porphyrin), have been prepared from hydrothermal reactions and their structures were characterized by single crystal X-ray diffraction technique. The macrocyclic ring of H₆TPPS is coplanar and the center is occupied by the vanadium(III) ion. The lanthanide(III) ions are bound by eight oxygen atoms to yield a distorted square anti-prism geometry. They are characteristic of a three-dimensional (3-D) open framework with a void space of around 210 ų. Fluorescence studies reveal that compounds 1–3 exhibit an emission band in the red region with the quantum yields being of 2.0%, 1.4% and 5.0%, respectively. CV/DPV results discover one quasi-reversible wave (1), one reductive peak (2) and two reductive peaks (3). Compounds 1–3 show largely different photophysical and electrochemical properties, although their structures only show tiny difference in lanthanide metal ions. This is due to metal-induced properties variation.

A samarium hybrid with porphyrin and amino acid as mixed ligands {[Sm(His)(H₂O)][Sm(H₃O)₃](H₂TPPS)₂} • 5H₂O (1) (His = histidine; H₆TPPS = tetra(4-sulfonatophenyl)porphyrin) has been synthesized via a hydrothermal reaction and characterized by single-crystal X-ray diffraction. Compound 1is crystallized in the space group $P\bar{\mathrm{ı}}$ of the triclinic system. Compound 1is characteristic of a three-dimensional (3-D) open framework with the samarium ions in two types of coordinating environments and a saddle-distorted nonplanar porphyrin macrocycle. Compound 1 exhibits fluorescence in the red region. The fluorescence lifetime of 1 is 15.65 ns and the emission quantum yield is 4.1%. The CV/DPV, UV-vis and FT-IR are also reported in detail.

Using a hydrothermal reaction of SmCl₃•6H₂O, ZnBr₂ and TPPS, a crystalline metalloporphyrinic compound (MPC), [SmZn(TPPS)H₃O]${}_n$•2$n$H₂O (1), was synthesized. The crystal structure of the MPC exhibits a condensed and robust 3-D porous open framework. We studied the adsorption and desorption isotherms for N₂, H₂ and CO₂ conducted at 77 K and 273 K. They show different isotherms such as Type I, II and III isotherm behaviors. We found that low temperature is propitious for the title complex to adsorb more H₂, but less N₂. Compound 1 showed remarkably high selectivity for CO₂–N₂ separation, and good thermal stability. The temperature dependent magnetic susceptibility shows an antiferromagnetic-like behavior for 1.

A novel neodymium porphyrin [Nd(TPPS)]${}_n$•$n$H${}_{\mathrm{\text{3}}}$O (1) [H${}_{\mathrm{\text{6}}}$TPPS $=$ tetra(4-sulfonatophenyl)porphyrin] has been prepared through a solvothermal reaction and characterized by the X-ray single-crystal diffraction technique. Complex 1is crystallized in the $P$4/mcc space group of the tetragonal system. Complex 1 features a three-dimensional (3D) open framework with the pore size of the channels being of 6.9 $\AA$ × 8.2 $\AA$. A wide optical band gap of 4.98 eV is revealed by the solid-state UV/vis diffuse reflectance spectrum. The variable-temperature magnetic susceptibility obeys the Curie-Weiss law (${\chi }_m=c$/($T𝜃))$ with $C=$ 0.67 K and a negative Weiss constant $𝜃=$ -0.37 K as found by the magnetic measurements, suggesting the existence of an antiferromagnetic behavior. The N${}_{\mathrm{\text{2}}}$ adsorption and desorption curves show good reversibility and verify that the 3-D framework is flexible and can be compressed with the increasing pressure.