Porphyrin-Ryleneimide Hybrids: Low-Bandgap Acceptors in Energy-Transfer Cassettes.

Energy-transfer cassettes consisting of naphthaleneimide-fused metalloporphyrin acceptors (M=Zn and Pd) and BODIPY donors have been designed and synthesized. These systems have rigid pseudo-tetrahedral structures with a donor-acceptor separation of ca. 17.5 Å. Spectroscopic investigations, including femtosecond transient absorption measurements, showed efficient excitation energy transfer (EET) occurring according to the Förster mechanism. Strong fluorescence of the donor units and significant spectral overlap of the donor and acceptor subunits are prerequisites for the efficient EET in these systems.

Noncovalent Intermolecular Interaction in Cofacially Stacked 24π Antiaromatic Hexaphyrin Dimer.

π-π Stacking is omnipresent not only in nature but in a wide variety of practical fields applied to our lives. Because of its importance in a performance of natural and artificial systems, such as light harvesting system and working layer in device, many researchers have put intensive effort into identifying its underlying nature. However, for the case of π-π stacked systems composed of antiaromatic units, the understanding of the fundamental mechanisms is still unclear. Herein, we synthesized a new type of planar ß,ß'-phenylene-bridged hexaphyrin (1.0.1.0.1.0), referred as naphthorosarin which possesses the 24π-electron conjugated pathway. Especially, the corresponding antiaromatic porphyrinoid shows the unique property to form dimeric species adopting the face-to-face geometry which is unprecedented in cases of known annulated naphthorosarins. In order to elucidate the intriguing properties derived from the stacked dimer, the current study focuses on the experimental support to rationalize the observed π-π interactions between the two subunits.

Synthesis of a Black Dye with Absorption Capabilities Across the Visible-to-Near-Infrared Region: A MO-Mixing Approach via Heterometal Coordination of Expanded Porphyrinoid.

An expanded metalloporphyrin-based "black dye" Au-Pd oxohexaphyrin (AuPd-1) with absorption capabilities across the visible-to-near-infrared (NIR) range was synthesized. This black dye, AuPd-1, possessed efficient light-harvesting and photostable capabilities, which were indicative of superior photothermal (PT) conversion abilities. Encapsulation of AuPd-1 with a micellar nanocapsule resulted in a compound that demonstrated intense photoacoustic (PA) properties in the NIR region in water. This finding indicated how metal (d)-ligand (π) molecular orbital interactions in metalloporphyrins could aid in the design of visible-to-NIR light-harvesting black dyes for PT and PA applications.

Rational Synthesis of 5,10-Diazaporphyrins via Nucleophilic Substitution Reactions of α,α'-Dibromotripyrrin and Dihydrogenation to Give 5,10-Diazachlorins.

We report here the first rational synthesis of 5,10-diazaporphyrins via nucleophilic substitution reactions of α,α'-dibromotripyrrin. Uses of 1,3-diiminoisoindoline and 3,4-di(ethylsulfanyl)pyrrole-2,5-diimine as nucleophiles allowed for synthesis of 5,10-diazabenzoporphyrin (2) and 5,10-diaza-7,8-di(ethylsulfanyl)porphyrin (3). 3 was reduced to 5,10-diazaporphyrin (4), 5,10-diaza-2,3-dihydrogenated porphyrin (5), and 5,10-diaza-7,8-dihydrogenated porphyrin (6) with yields that were dependent upon reduction conditions. All the structures of these products were confirmed by X-ray crystallographic analysis. Their optical and electrochemical properties have been comparatively studied with those of 5,15-diazaporphyrin (7) and 5,15-diazachlorin (8). Furthermore, NH tautomers of 2 and 4 were observed as different species in solution, and the dynamic NH tautomeric behavior was studied in 4.

meso-Triaryl-Substituted Smaragdyrins: Facile Aromaticity Switching.

All-aza smaragdyrin, a historic but elusive pentapyrrolic macrocycle, was successfully synthesized and characterized for the first time. [22]Smaragdyrin BF2-complex 3 was smoothly synthesized by 2-fold SNAr reaction of 1,9-dibromo-5-mesityldipyrrin with 5,10-dimesityltripyrrane. Treatment of 3 with methanesulfonic acid gave [20]smaragdyrin 5 as a stable antiaromatic compound. Reduction of 5 with NaBH4 under inert conditions gave [22]smaragdyrin 6 as an aromatic congener, which was easily oxidized back to 5 in the air. Complex 3 was interconvertible with its 20π-congener 4 via oxidation with MnO2 and reduction with NaBH4. Treatment of 3 or 4 with CuCl2 in the presence of NaOAc gave hetero bimetal complex 8.

Diazachlorin and diazabacteriochlorin for one- and two-photon photodynamic therapy.

Diazachlorin and diazabacteriochlorin have been prepared through reduction of diazaporphyrin and their in vitro and in vivo activity in photodynamic therapy has been investigated.

Proton-Coupled Redox Switching in an Annulated π-Extended Core-Modified Octaphyrin.

Proton-coupled electron transfer (PCET) is an important chemical and biological phenomenon. It is attractive as an on-off switching mechanism for redox-active synthetic systems but has not been extensively exploited for this purpose. Here we report a core-modified planar weakly antiaromatic/nonaromatic octaphyrin, namely, a [32]octaphyrin(1.0.1.0.1.0.1.0) (1) derived from rigid naphthobipyrrole and dithienothiophene (DTT) precursors, that undergoes proton-coupled two-electron reduction to produce its aromatic congener in the presence of HCl and other hydrogen halides. Evidence for the production of a [4 n + 1] π-electron intermediate radical state is seen in the presence of trifluoroacetic acid. Electrochemical analyses provide support for the notion that protonation causes a dramatic anodic shift in the reduction potentials of octaphyrin 1, thereby facilitating electron transfer from halide anions (viz. I-, Br-, and, Cl-). Electron-rich molecules, such as tetrathiafulvene (TTF), phenothiazine (PTZ), and catechol, were also found to induce PCET in the case of 1. Both the oxidized and two-electron reduced forms of 1 were characterized by X-ray diffraction analyses in the solid state and in solution via spectroscopic means.

Stable 2D anti-ferromagnetically coupled fluorenyl radical dendrons.

We report the first class of stable, two-dimensional (2D) anti-ferromagnetically coupled dendritic polyradicaloids. A kinetically blocked fluorenyl radical was used to build up the first and second generation dendrons FR-G1 and FR-G2 containing three and seven fluorenyl units, respectively. The neighboring fluorenyl radicals in FR-G1 and FR-G2 show moderate anti-ferromagnetic exchange interaction, resulting in a doublet and quartet ground state, respectively, with a small doublet-quartet energy gap. From FR-G1 to FR-G2, the energy gap decreased and the two-photon absorption was enhanced owing to more extended 2D π-conjugation. Both compounds showed multiple redox waves due to their polyradical character.

The First Silicon(IV) Corrole Complexes: Synthesis, Structures, Properties, and Formation of a µ-Oxo Dimer.

The first SiIV corrole complexes were synthesized in good yields by treatment of meso-triarylcorroles with tetrachlorosilane in 1,2-dichloroethane at 60 °C. The central silicon atom possesses a square-pyramidal coordination geometry with slightly longer Si-N bond lengths as compared with those of known triazacorrole SiIV complexes. The SiIV corrole complexes exhibit sharp and blue-shifted absorption spectra and larger fluorescence quantum yields as compared with the corresponding free-base corroles. A µ-oxo dimer of a SiIV corrole was synthesized upon treatment with methanesulfonyl chloride in pyridine at 100 °C. This dimer shows a face-to-face structure with a 90° twist in the solid state. Although the dimer exhibits a blue-shifted Soret band, reflecting the face-to-face geometry, it displays a largely red-shifted and broad fluorescence spectrum with a large Stokes shift, suggesting a large structural change in the S1 state. These intriguing optical properties have been comprehensively studied by magnetic circular dichroism (MCD) spectroscopy, femtosecond transient absorption (fs-TA) measurements, and theoretical calculations.

Strategic Construction of Directly Linked Porphyrin-BODIPY Hybrids.

A powerful and concise synthesis of directly linked porphyrin-BODIPY hybrids has been demonstrated, which consists of condensation of directly linked meso-pyrroyl NiII -porphyrin with arylaldehyde, oxidation with p-chloranil, and complexation with BF3 ⋅Et2 O. Synthesized hybrids include porphyrin dimer 6Ni, trimers 8Ni, 9Ni, tetramer 12Ni, pentamer 16Ni, hexamer 13Ni, and nonamers 17Ni and 18Ni. The structures of 6Ni, 9Ni and 12Ni were unambiguously confirmed by X-ray diffraction analysis. Some NiII porphyrins were effectively converted to the corresponding ZnII porphryins. In these hybrids, the pigments are three-dimensionally arranged with a face-to-face dimeric porphyrin unit in a well-defined manner, featuring their potential as light-harvesting antenna and functional hosts.