On-Surface Synthesis of Polyene-Linked Porphyrin Cooligomer.

π-Conjugated molecules are viewed as fundamental components in forthcoming molecular nanoelectronics in which semiconducting functional units are linked to each other via metallic molecular wires. However, it is still challenging to construct such block cooligomers on the surface. Here, we present a synthesis of [18]-polyene-linked Zn-porphyrin cooligomers via a two-step reaction of the alkyl groups on Cu(111) and Cu(110). Nonyl groups (-C9H19) substituted at the 5,15-meso positions of Zn-porphyrin were first transformed to alkenyl groups (-C9H10) by dehydrogenation. Subsequently, homocoupling of the terminal -CH2 groups resulted in the formation of extended [18]-polyene-linked porphyrin cooligomers. The structures of the products at each reaction step were investigated by bond-resolved scanning tunneling microscopy at low temperatures. A combination of angle-resolved photoemission spectroscopy and density functional theory calculations revealed the metallic property of the all trans [18]-polyene linker on Cu(110). This finding may provide an approach to fabricate complex nanocarbon structures on the surface.

[22]Pentaphyrins(2.0.1.1.0) Displaying N-Fusion, Pyrrole-Rearrangement, and Dimerization Reactions Upon Oxidation and Metalation.

Exploration of expanded porphyrins with unprecedented reactivities has remained important. Here [22]pentaphyrins(2.0.1.1.0) were synthesized as a constitutional isomer of sapphyrin by acid-catalyzed cyclization of 1,14-dibromo-5,10-diaryltripyrrin with 1,2-di(pyrro-2-ly)ethenes. These pentaphyrins display roughly planar structures and varying aromaticities depending upon the vinylene structures. The 19,20-ditolyl pentaphyrin gave an N-fused product and an unprecedented pyrrole-rearranged product, depending upon the oxidation conditions. Remarkably, upon the metalation with CuCl, the N-fused product and the pyrrole-rearranged product afforded an inner b-b coupled face-to-face CuII complex dimer and an outer b-b coupled lateral CuII complex dimer, respectively, in fairly good yields. Further, [22]pentaphyrin(2.0.1.1.0) fused with a NiII porphyrin was effectively dimerized upon oxidation with MnO2 to give a 16-16' directly linked dl-dimer.

Carbazole Based Smaragdyrins: Synthesis, Aromaticity Switching, and Formation of a Spiro-Dimer.

Carbazole-incorporated smaragdyrin BF2-complex 3 was synthesized by SNAr reaction of 3,5-dibromo-8-mesityl-BODIPY 1 with 3,6-di(tert-butyl)-1,8-di(pyrrol-2-yl)carbazole 2 as a nucleophile. Demetalation of 3 with ZrCl4 gave the corresponding smaragdyrin free base 4 in a good yield. Oxidations of 3 and 4 with MnO2 gave smaragdyrins 5 and 6, respectively, both followed by aromaticity switching, since the oxidized products showed a moderate paratropic ring current owing to their 20π-electronic circuits. Further, treatment of 4 with [RhCl(CO)2]2 in the presence of NaOAc gave RhI complex 7, and oxidation of 3 with RuCl3 in the presence of triethylamine led to the formation of a spiro dimer product, 8.

BIII-Subporphyrins Bearing Distorted Metal-Coordinating Straps: CuII-Assisted meso-Fabrications.

BIII-subporphyrins 4, 5, and 6 possessing metal-coordinating carbaporphyrin-like pockets were synthesized by Suzuki-Miyaura coupling reactions. Compounds 4 and 5 gave PdII complexes 4-Pd and 5-Pd upon metalation with Pd(OAc)2 but did not give either their NiII or CuII complexes. Conversely, 6 was expected to induce distorted square planar coordination because of its 2,5-di(pyrid-2-yl)pyrrole strap. Indeed reaction of 6 with Cu(OAc)2 did not give its CuII complex but produced meso-alkoxy and meso-phenoxy products in the presence of alcohols and phenol, possibly via CuII-mediated C-H bond functionalization, which was further extended to meso-C-C bond-forming fabrications by using organoboronic acids. These CuII-mediated C-H bond meso-fabrications are the first example for porphyrinoid substrates.

A Green-to-Near-Infrared Photoswitch Based on a Blended Subporphyrazine-Dithienylethene System.

A subporphyrazine (SubPz)-dithienylethene (DTE) photochromic device with 1o and 1c states, was developed and characterized. In this device, the DTE unit can reversibly switch the SubPz absorbance from green to near-infrared [λmax (o/c) = 527 nm/740 nm], as well as the SubPz fluorescence and singlet oxygen quantum yields. The core of this design involves using a highly tunable SubPz chromophore that shares its quasi-isolated ethene moiety with a DTE photoswitch.

A Triply Linked Porphyrin-Norcorrole Hybrid with Singlet Diradical Character.

Norcorrole Ni(II) complexes have recently received considerable attention because they are readily accessible antiaromatic molecules. Their high stability under ambient conditions and ease of synthesis have enabled the exploration of the intrinsic properties of antiaromatic molecules. Here, we report the synthesis and properties of meso-meso singly linked porphyrin-norcorrole hybrids and a triply linked porphyrin-norcorrole hybrid. The singly linked and triply linked porphyrin-norcorrole hybrids were fully characterized, including an X-ray structural analysis. Due to their orthogonal conformation, the singly linked hybrids maintain the individual electronic properties of their porphyrin and norcorrole subunits, while the triply linked hybrid shows a significantly smaller electrochemical HOMO-LUMO gap (0.45 eV) than that of Ni(II) dimesitylnorcorrole (1.08 eV). Furthermore, the triply linked hybrid exhibits singlet diradical characteristics, as confirmed by VT NMR, ESR, and SQUID experiments.

Copper(II) Carbaporphyrins: Oxygenation Reactivities Dependent upon Coordinating Structures.

CuII metalations of carbaporphyrins 1-4 gave the corresponding CuII complexes 1-Cu, 2-Cu, 3-Cu, and 4-Cu with varying degrees of distortions in CuII square-planar coordination. Upon treatment with Cu(OAc)2, 1-Cu was inert but 2-Cu and 3-Cu gave the respective O-atom-inserted complexes 2-OCu and 3-OCu. Further, 3-Cu and 4-Cu were converted to meso-methoxynickel(II) porphyrins 3-OMe and 4-OMe, respectively, via treatment with Cu(OAc)2 in methanol. meso-Hydroxynickel(II) porphyrin 3-OH was obtained by the treatment of 3-OCu by acetic acid. The treatment of 4-Cu with Cu(OAc)2 in the presence of acetic acid gave 5,15-diketoporphyrinogen 4-O. CuII complexes of carbaporphyrins became more reactive with an increased distortion in CuII square-planar coordination.

Cyclic Azobenzene-BODIPY Hybrids.

Cyclic azobenzene-BODIPY hybrids were synthesized via cyclization by 1) acid-catalysed condensation of azobenzene-bridged dipyrroles with 3,5-di-tert-butylbenzaldehyde, 2) oxidation with DDQ, and 3) metalation with BF3 ⋅ Et2 O. The structures of many cyclic hybrids have been confirmed by single crystal X-ray analysis. The absorption spectra of the hybrids reveal the effective cyclic conjugation. The ultrafast measurements reveal that the photoexcited decays of these cyclic hybrids depend upon the ring size and connectivity.

Di(p-dibenzi)[40]decaphyrin(1.0.0.0.0.1.0.0.0.0) PdII Complex: A Weakly Hückel 38π-Aromatic Macrocycle.

Di(p-benzi)[40]decaphyrin(1.0.0.0.0.1.0.0.0.0) BF2 complex and tris(p-benzi)[60]pentadecaphyrin(1.0.0.0.0.1.0.0.0.0.1.0.0.0.0) BF2 complex were synthesized by Suzuki-Miyaura coupling of α,α'-diborylated tetrapyrrole BF2 -complex with 1,4-diiodobenzene. Bis-BF2 complex was converted to bis-PdII complex via its free base. Macrocycles bis-BF2 and tris-BF2 complex take Möbius topology but are nonaromatic, since the macrocyclic conjugation is disrupted by the locally aromatic 1,4-phenylene units. In contrast, bis-PdII complex is a weakly Hückel 38π-aromatic macrocycle as evinced by its red-shifted, enhanced, and structured Q-like bands and a small electrochemical HOMO-LUMO gap. Interestingly, one 1,4-pheylene part of bis-PdII complex takes a quinonoidal distorted structure and the other takes a usual benzene structure in a figure-eight conformation with Hückel topology.

Synthesis of Pyrrole-Sharing Fused Porphyrinoid Hybrids by Post-fabrication of Ni(II) Porphyrins.

Pyrrole-sharing fused hybrids of NiII porphyrin with PdII N-confused(NC)-corrole and PdII NC-oxaporphyrin were synthesized by post-fabrication of NiII porphyrins. Specifically this consists of Friedel-Crafts type aromatic substitution reaction of meso-free NiII porphyrin with α,α'-dibromotripyrrin and Pd(OAc)2 assisted cyclization, and final heating to induce a Pd-C bond formation. NiII porphyrins fused with PdII NC-corrole and with PdII NC-oxaporphyrins show coplanar structures with a shared pyrrole unit. In these hybrids, the PdII NC-oxaporphyrin is aromatic and the PdII NC-corrole is moderately antiaromatic and these local electronic properties interact to influence the whole network.

Stable Antiaromatic [24]Hexaphyrin(1.1.0.0.1.0) and Its Metal Complexes.

5,10,23-Trimesityl-substituted [24]hexaphyrin(1.1.0.0.1.0) was synthesized as a stable antiaromatic molecule by base-catalyzed twofold SNAr reaction and was reduced to the corresponding [26]hexaphyrin, which was an unstable aromatic molecule because it easily oxidized to the [24]hexaphyrin. The [24]hexaphyrin served as a ligand to give the bis-PdII complex and tris-RhI complex with unique structures. The former complex has two square-planar-coordinated PdII ions bridged by an acetate anion and shows a strong paratropic ring current, while the latter complex has three RhI ions coordinated with two pyrrolic nitrogen atoms and two carbonyl groups, but one carbonyl group is shared with two RhI ions in a unique manner.

Synthesis of Naphthalene- and Phenanthrene-Fused Smaragdyrins and Their BF2 Complexes.

Naphthalene- and phenanthrene-fused [22]smaragdyrin BF2 -complexes were synthesized by 1) Suzuki-Miyaura coupling of ß-brominated [22]smaragdyrin BF2 complexes with 2-formylarylboronates, 2) Witting-type methoxymethylenation of the formyl group, and 3) methanesulfonic acid-catalyzed cyclization reaction. Subsequently these BF2 complexes were deboronized and oxidized to the corresponding antiaromatic [20]smaragdyrin free bases. The installed fused structures led to decrease of the aromatic characters of the [22]smaragdyrin BF2 complexes and the antiaromatic characters of the [20]smaragdyrin free bases.

Doubly N-confused and ring-contracted [24]hexaphyrin Pd-complexes as stable antiaromatic N-confused expanded porphyrins.

As isomers of the regular porphyrins, N-confused porphyrins have attracted extensive attention of chemists because of their unique chemical structures, chemical reactivities, and physical properties, which result in their promising applications in the fields of catalytic chemistry, biochemistry and material science. Typically, N-confused porphyrins are synthesized via acid catalyzed condensation and following oxidation during which lactams are often formed as the byproducts. Here we report doubly N-confused and ring-contracted [24]hexaphyrin(1.1.0.1.1.0) mono- and bis-Pd-complexes as stable antiaromatic N-confused expanded porphyrins, which are synthesized through Pd-catalyzed Suzuki-Miyaura coupling of 1,14-dibromotripyrrin. These macrocycles show a paratropic ring currents, an ill-defined Soret band, a red-shifted weak absorption tail, and a small HOMO-LUMO gap. NBS bromination of the bis Pd-complex give its mono- and dibromides regioselectively, which are effectively used to synthesize a [24]hexaphyrin dimer and a NiII porphyrin-[24]hexaphyrin-NiII porphyrin triad, respectively.

Gated Photochromism of Dithienylethene-Embedded Expanded Calixphyrins.

Dithienylethene (DTE)-embedded expanded porphyrins were synthesized and confirmed to be photochemically inactive due to the lowest excited state of the expanded porphyrins. On the other hand, DTE-embedded expanded calixphyrins exhibited reversible photochromism upon UV-irradiation to form colored closed forms, which reverted to colorless open forms upon red-light irradiation. The closed forms were oxidized with DDQ or the air to lock the recorded information by converting to photochemically inactive expanded porphyrins. This was unlocked by reduction with NaBH4 to restore expanded calixphyrins with photochromism activity. These gated photochromic behaviors were demonstrated in PMMA (polymethyl methacrylate) film.

Post-Installation of Fused Benzoheptagons at the Periphery of NiII Porphyrins: Helical Structures and Conformation-Adjustable Fullerenes Binding.

Fused-benzoheptagon-installed NiII porphyrins were synthesized by a protocol consisting of (2-formyl)arylation at the meso-position(s) of NiII porphyrins, conversion of formyl group to methoxyethene group by Wittig reaction, and final Bi(OTf)3 -catalyzed cyclization. The structures of these porphyrins have been revealed by X-ray analysis. Owing to the installed heptagon ring(s), these porphyrins show curved structures with conformational flexibility. Dimer has been shown to have a small activation barrier for inversion and to capture C60 and C70 with large association constants with adjustable conformational changes.

Rearrangements of Internally-bridged Octaphyrin(1.1.1.1.1.1.1.1)s to Porphyrin Dimers.

Internally-bridged octaphyrin(1.1.1.1.1.1.1.1) underwent a rearrangement to meso-meso linked porphyrin dimer as a new metamorphosis. Extensive examination suggests that hydride-addition is a key step for the rearrangements to afford thermodynamically more stable porphyrin framework. Further, ß-tetrabromo[36]octaphyrin was transformed to meso-meso, ß-ß, ß-ß triply linked porphyrin dimer via a similar mechanism combined with Pd-mediated reductive homocoupling.

Rhodium-Catalyzed [5 + 2] Annulation of Pyrrole Appended BODIPYs: Access to Azepine-Fused BODIPYs.

Rhodium-catalyzed C-H/N-H [5 + 2] annulations of 8-(pyrrol-2-yl)-appended boron-complexed dipyrromethenes (BODIPYs) with internal alkynes have been established to afford a series of azepine-fused BODIPYs with good yields and excellent regioselectivity, in which the pyrrol-2-yl unit serves as the directing group as a rare example. A RhI intermediate was obtained to indicate a RhI/RhIII catalytic process involved in this reaction. Importantly, the [5 + 2] C-H annulation is demonstrated as a concise strategy to change the optical properties of BODIPY.

Aromatic-bridged and meso-meso-linked BF2-smaragdyrin dimers exhibit fast decays in polar solvents by symmetry-breaking charge transfer.

Symmetry-breaking charge transfer is one of the key process in photosynthetic reaction centers and specific artificial optoelectronic devices such as dye-sensitized solar cells. Here we report the synthesis of aromatic-bridged BF2-smaragdyrin dimers, meso-free BF2-smaragdyrin, and its meso-meso-linked BF2-smaragdyrin dimer. The decays of S1-states of these dimers are accelerated with an increase in solvent polarity and a decrease in the distance between the two BF2-smaragdyrin units, suggesting symmetry-breaking charge transfer. The fluorescence lifetimes of the dimers become shortened in polar solvents. However, ultrafast transient absorption spectroscopy do not detect charge-separated ion pairs. On the basis of these results, we conclude that the decays of the excited states of the BF2-smaragdyrin dimers are accelerated by solvation-induced symmetry-breaking charge transfer, depending on the degree of the electronic interaction between the smaragdryin units as a rare case for porphyrinoids. The degree of charge transfer is larger for dimers with larger electronic interactions.

Heptagon/Octagon-Fused Diporphyrins or Spiro-Pentagon-Bridged Dichlorin from p-Terphenylene-Bridged Diporphyrin.

Intramolecular fusion reactions of a p-terphenylene-bridged NiII porphyrin dimer gave different products, depending upon reaction conditions. Oxidation with Fe(OTf)3 provided syn- and anti-doubly heptagon-fused NiII porphyrin dimers showing enlarged π-electronic networks, probably via a radical mechanism, while treatment with methanesulfonic acid provided a spiro-pentagon-bridged NiII chlorin dimer via acid-catalyzed Friedel-Crafts type cyclization. Further, a doubly octagon-fused NiII porphyrin dimer was synthesized via a sequence of double meso-formylation, reduction to corresponding diol, and BF3 -catalyzed cyclization.