Conjugated porphyrin arrays that possess delocalised electronic networks have, for the most part, been assembled by using alkene or alkyne type bridging units or by directly connecting individual porphyrin chromophores with multiple bonds to form fused porphyrin arrays. Throughout the last two decades, such conjugated porphyrin arrays have been actively explored due to their attractive electronic, optical and electrochemical properties. This review aims to cover the multitude of synthetic methodologies that have been developed for the construction of conjugated porphyrin arrays as well as to summarise their structure-property relationships and use in various applications such as near infrared (NIR) dyes, nonlinear optical materials and electron-conducting molecular wires.

Since the discovery of its facile synthesis in 2001, meso-aryl-substituted expanded porphyrins have been developed as a new class of azaannulenes in light of their facile redox interconversions, conformational flexibilities involving flipping of the constitutional pyrroles, rich metal coordination behaviors, unprecedented chemical reactivities, effective platforms to realize versatile electronic states including Möbius aromatic and antiaromatic species, and abilities to stabilize organic radicals. In this Review, the syntheses, structures, and optical, electronic, and magnetic properties of meso-aryl-substituted expanded porphyrins and their metal complexes have been updated with a particular focus on the relationship between "aromaticity and molecular twist (molecular topology)". While the importance of the interplay of these two characteristics has been long recognized from the theoretical viewpoint, meso-aryl-substituted expanded porphyrins offered solid experimental evidence to provide Möbius aromatic and antiaromatic molecules with distinct diatropic and paratropic ring currents, respectively. This attribute is not shared with β-alkylated expanded porphyrin counterparts, underlining the importance and uniqueness of meso-aryl-substituted expanded porphyrins.

Tetrabenzotetraaza[8]circulene (1) has been synthesized in good yield by a "fold-in" oxidative fusion reaction of a 1,2-phenylene-bridged cyclic tetrapyrrole. X-ray diffraction analysis of 1 has revealed a planar square structure with a central cyclooctatetraene (COT) core that shows little alternation of the bond lengths. Despite these structural features, 1 shows aromatic-like character, such as sharp absorption bands, high fluorescence quantum yields (Φ(F)=0.55 in THF), and a single exponential fluorescence decay with τ(F)=3.8 ns. These observations indicate a dominant contribution of an [8]radialene-like π conjugation and hence aromatic character of the local aromatic segments in 1.

Various aromatic segments have been fused onto the porphyrin periphery to create porphyrinoids that have expanded p-conjugated networks and thus exhibit red-shifted absorption spectra. Fused coplanar porphyrin oligomers, represented by meso-meso, b-b, b-b triply linked porphyrin arrays (porphyrin tapes), are endued with more red-shifted absorption spectra and better nonlinear optical properties.These fused porphyrinoids have emerged as promising near-infrared (NIR) absorbing dyes, pointing to future applications such as conducting wire, NIR emitter, photovoltaics, and nonlinear optical materials.Developments of the fused porphyrinoid chemistry are reviewed in this feature article with focus on the synthesis, the relationships between their absorption spectra and molecular structures, and the applications in materials science.

We have grown epitaxial thin sheets of graphene on BC 3 /NbB 2 (0001) and measured phonon dispersion curves of the graphene sheets by means of high-resolution electron energy-loss spectroscopy (HREELS). The phonon dispersion curves have been calculated on the basis of ab initio calculations. The observed curves were in good agreement with theoretical curves. The quality of crystallinity of the graphene layers was high compared with the bulk graphite crystals. In this paper, we demonstrate that the combination of HREELS measurement and ab initio calculations is extremely effective for investigation of honeycomb-structured materials.

β-to-β Directly linked cyclic Ni(II) porphyrin trimer, tetramer, and pentamer ([3]CP, [4]CP, and [5]CP) have been synthesized by reaction of a 2,12-diborylated Ni(II) porphyrin with Pt(cod)Cl2 followed by reductive elimination. The structures of these cyclic porphyrin arrays have been revealed by X-ray diffraction analysis. The strain energies of these cyclic oligomers are calculated to be 77, 57, and 47 kcal/mol for [3]CP, [4]CP, and [5]CP, respectively. Intramolecular excitation energy hopping was observed between the (3)(d,d) states of the Ni(II) porphyrins with rates of 3.0, 4.4, and 4.6 ps for [3]CP, [4]CP, and [5]CP, respectively, reflecting the close proximity of the Ni(II) centers.

Deprotonation of nonaromatic octakis-(pentafluorophenyl)-substituted [36]octaphyrin(1.1.1.1.1.1.1.1) with tetrabutylammonium fluoride (TBAF) afforded monoanionic twisted Möbius aromatic species and dianinonic square Hückel antiaromatic species, depending upon the amount of TBAF.

The entire phonon-dispersion curves along the Gamma-M direction of a BC3 honeycomb sheet have been determined both experimentally and theoretically for the first time. Most of the observed curves agreed with the theoretical ones calculated on the basis of ab initio theory. From the stretching force constants of the nearest-neighbor C-C and B-C bonds, together with that of the B-B bond, we clarified the characteristic feature of the C-C and B-C bonds. From the experimental and theoretical results, we discussed the possibility of high T(c).