Journal of Porphyrins and Phthalocyanines

The tremendous potential for the manifold applications of porphyrins, porphyrazines, and phthalocyanines derives from their photophysical and electrochemical properties, their remarkable stability, and their predictable and rigid structure. These applications include nonlinear optics, catalysts, sensors, actuators, molecular sieves, and therapeutics. All of these properties are modulated by appending various chemical moieties onto the macrocycles, by choice of metallo derivative, and by the choice of environment. In multichromophoric systems, furthermore, the relative orientation of the chromophores, the nature of the linker, and the size of the system also dictate the properties. The synthesis of multichromophoric systems – both via covalent and noncovalent linkers – is driven by the desire to make new materials and to understand biological processes such as the various aspects of photosynthesis. Though electron and energy transfer processes continue to drive the synthesis of ever more complex systems, more recent focus has shifted toward other applications and functionalities of these structures. The focus of this perspective is on four recent developments in formation and characterization of functional, porphyrinic materials and devices: (1) self-assembly and self-organization of porphyrin arrays and aggregates into phototransistors and photonic devices; (2) self-assembled porphyrin squares for sensors, sieves, and catalysts; (3) covalently bound arrays of different chromophores as photonic materials; and (4) spatially separated arrays of metalloporphyrins as cross-reactive sensors.

Recent advances in the chemistry of main group porphyrin complexes are surveyed. New, unprecedented structural types for porphyrin complexes which have been revealed from the recent reports of boron and tellurium porphyrins are described. Advances in the preparation and reactivity of Group 14 (silicon and tin) and Group 15 porphyrin complexes are discussed. A systematic variation in the out-of-plane distortion (ruffling) of light element Group 14 and 15 porphyrin complexes has become apparent now that a significant number of structurally characterized examples are at hand.

To meet recent requirement of sensors, new optical sensor technology by molecules of functional chemical compounds as nano-scale sensor probes is developing. In this overview, the background and the concept of optical sensor technology are briefly introduced and a new optical sensing system by triplet-triplet absorption is discussed as an example.

Heme, resulting from hemoglobin digestion by the malaria parasite is one of the main target of antimalarial drugs like chloroquine and artemisinin. This later molecule contains a trioxane which is activated by the reduced form of heme to generate a strong alkylating agent able to react with heme itself. Taking advantage of these studies, we prepared new antimalarial drugs, trioxaquines, containing a trioxane motif covalently linked to an aminoquinoline.

A brief overview is presented on the status of the synthesis of unsymmetric phthalocyanines and related compounds. The main aim of this paper is to describe the key problems and the interest in synthesizing new functionalized unsymmetric phthalocyanine systems. Some phthalocyanine homologues and analogues like subphthalocyanines and expanded phthalocyanines are also treated.

Recent developments in the electrochemistry of metalloporphyrins and metallophthalocyanines are reviewed briefly by focusing on the electroanalytical, electrocatalytic and electrochemical sensor applications.

Recent advances in electron transfer chemistry of electron donor-acceptor ensembles reported containing porphyrins and metalloporphyrins reported in ICPP-2 are reviewed briefly by focusing on the fundamental aspects of electron transfer reactions.

The development of theoretical models that describe the electronic structures of the porphyrins and phthalocyanines using ZINDO and DFT techniques is rapidly approaching the point where the major spectral bands over a wide energy range, for both symmetric and non–symmetric molecules can be fully accounted for. However, although there has been much recent progress, theoretical models should always be tested accuracy by reference to the most recent electronic absorption and magnetic circular dichroism spectra available. This must be carried out by calculating absorption spectra to determine whether the major spectral features determined are accurately described. Spectroscopists need to provide fully analyzed data for this purpose as well as data recorded at low temperatures to enhance resolution. Since the porphyrin and phthalocyanine rings readily undergo oxidation and reduction, and well-characterized spectral data are available for many different redox states, new theoretical studies should also include the bands observed in the anion and cation radical species, as well as those of the neutral complex. This symposium addresses these goals by bringing together theoreticians and experimentalists to discuss their results.

The main topics in resonance Raman spectroscopy presented at ICPP-2 in Kyoto are briefly discussed. These include: (i) coherent spectroscopy and low frequency vibrations of ligand-photodissociated heme proteins, (ii) vibrational relaxation revealed by time-resolved anti-Stokes Raman spectroscopy, (iii) electron transfer in porphyrin arrays, (iv) vibrational assignments of tetraazaporphyrins and (v) resonance Raman spectra of an NO storing protein, nitrophorin.