Pressure‐induced d–π charge transfer in one‐dimensional phthalocyanine conductors, NiPc(AsF6)0.5 and CoPc(AsF6)0.5

Phthalocyanines as materials for advanced technologies: some examples

Metallophthalocyanine complexes and related compounds play an important role in many advanced applications and modern technologies mostly by virtue of their characteristic optical absorption and high chemical stability. As a class of materials made well-known by their vivid and fast colors, it is expected that metallophthalocyanines and analogues, e.g. naphthalocyanines, are going to keep their role with the increasing use of natural and artificial light in the technologies of the future. In the present review some relevant properties of phthalocyanines and related macrocycles for technological applications are analyzed. In particular the electrical conductivity and photoconductivity as well as some nonlinear optical properties (mostly optical limiting), of phthalocyanines and related compounds are discussed.

Spectroscopic studies of solid phthalocyanines and their charge transfer salts

We present the polarized reflection spectra of several MPcs ( M ≡ Co , Ni , Cu , Zn , Pb ) in the Q-band region and interpret them based on conventional exciton theory. We compare the polarized reflection spectra of the phthalocyanine radical salts NiPc ( AsF 6)0.5, H 2 Pc ( AsF 6)0.67 and LiPc and interpret the new absorption band near the Q-band using the relationship between the degree of oxidation and the intensity of this new band. Based on the pressure dependence of this new band and the diagnostic phonon modes, we prove a pressure-induced charge transfer in NiPc ( AsF 6)0.5. A metal–insulator phase transition is predicted from the analysis of the plasmon absorption and is confirmed by the high-pressure electrical resistivity. We propose the origin of the pressure-induced charge transfer and the mechanism of the metal–insulator transition. We find the optical transition associated with the 3 d z2 band in the reflection spectrum of CoPc ( AsF 6)0.5, which is proved by comparison with the mixed crystals Co x Ni 1 − x Pc ( AsF 6)0.5. A new weak intermolecular optical transition is found through the resonance enhancement of a local phonon in the mixed crystals Co x Ni 1 − x Pc ( AsF 6)0.5.

Electronic states and infrared spectroscopy of Ni- and Co-phthalocyanines: neutral and oxidized forms

Quantum chemical calculations reproduced the experimental infrared spectra of NiPc , NiPc ( AsF 6)0.5, CoPc , and CoPc ( AsF 6)0.5. The agreement in the changes of line intensities supports the ligand-centered oxidation in both NiPc ( AsF 6)0.5 and CoPc ( AsF 6)0.5. Whereas, electron configurations of NiPc and NiPc + as well as CoPc represent standard cases, i.e. they can be taken as a closed-shell and open-shell system, respectively, the electron configuration of CoPc + must be taken as an open-shell system (while the number of electrons is even) to get an agreement of theoretical and experimental infrared spectra.

Technique for anisotropic extension of organic crystals: application to temperature dependence of electrical resistance

We have developed a technique for the anisotropic extension of fragile molecular crystals. The pressure medium and the instrument, which extends the pressure medium, are both made from epoxy resin. Since the thermal contraction of our instrument is identical to that of the pressure medium, the strain applied to the pressure medium has no temperature dependence down to 2 K. Therefore, the degree of extension applied to the single crystal at low temperatures is uniquely determined from the degree of extension in the pressure medium and thermal contractions of the epoxy resin and the single crystal at ambient pressure. Using this novel instrument, we have measured the temperature dependence of the electrical resistance of metallic, superconducting, and insulating materials. The experimental results are discussed from the viewpoint of the extension (compression) of the lattice constants along the parallel (perpendicular) direction.

Potassium Phthalocyanine, KPc: one-dimensional molecular stacks bridged by K+ ions

We report the synthesis of potassium phthalocyanine (KPc) and its structural characterization by synchrotron X-ray powder diffraction. We find that while KPc adopts the beta-polymorphic structural type (monoclinic space group P21/a) common for many MPc solids, its structure is characterized by unique features. The K+ ions, which are statistically disordered over two symmetry-equivalent positions, reside in the intrastack spacing of the rodlike molecular assemblies and strongly bond equidistantly to selected N atoms of the two neighboring Pc rings along the chain direction with an unusual 5-fold coordination. The K+-stuffed slipped stacks of Pc units display much greater intrastack and slippage distances than those of other beta-MPc polymorphs. They may be thought as comprising disordered dimeric (Pc)22- units; this leads to electron pairing and is consistent with the observed nonmagnetic response of the system.