S₂ Fluorescence from [26]Hexaphyrin Dianion

S₂ fluorescence from <i>meso</i>-hexakis­(pentafluorophenyl)-substituted [26]­hexaphyrin dianion was observed as the first example of expanded porphyrins despite its large molecular size and small HOMO–LUMO gap. The population kinetics among S₂, S₁, and S₀ states have been studied by using femtosecond time-resolved absorption and fluorescence spectroscopies. Broad-band fluorescence upconversion spectroscopy allowed for simultaneous observation of S₂ fluorescence decay in the visible region and S₁ fluorescence rise in the NIR region, both with a time constant of 0.22 ps. The transient absorption spectroscopy revealed the presence of a direct decay path from the S₂ state to the S₀ state. The observation of S₂ fluorescence from highly conjugated molecular systems is quite rare, and S₂ fluorescence beyond 700 nm is also quite rare

A Hybrid Macrocycle with a Pyridine Subunit Displays Aromatic Character upon Uranyl Cation Complexation

Reported here is a new hybrid macrocycle, cyclo[1]­furan[1]­pyridine[4]­pyrrole (<b>1</b>), that bears analogy to the previously reported mixed heterocycle system cyclo[2]­pyridine[4]­pyrrole (<b>2</b>) and cyclo[6]­pyrrole <b>3</b>, an all-pyrrole 22 π-electron aromatic expanded porphyrin. The oxidized, dianionic form of <b>1</b>, [<b>1</b> – 4H]^2–, has been characterized as its uranyl complex. In contrast to <b>2</b> and <b>3</b> and in spite of the presence of a 2,6-disubstituted pyridine subunit, the uranyl complex of [<b>1</b> – 4H]^2– displays solid-state structural and solution-phase spectroscopic features consistent with contributions to the overall electronic structure that involve a conjugated, (4<i>n</i> + 2) π-electron aromatic periphery

Near-Infrared S₂ Fluorescence from Deprotonated Möbius Aromatic [32]Heptaphyrin

This study revealed S₂ fluorescence from deprotonated <i>meso</i>-pentafluorophenyl-substituted Möbius aromatic [32]­heptaphyrin(1.1.1.1.1.1.1) that was formed upon treatment of neutral antiaromatic [32]­heptephyrin with tetrabutylammonium fluoride. Higher excited-state dynamics and emission were studied by fs-transient absorption spectroscopy and a broad-band fluorescence upconversion technique. This is the first S₂ fluorescence from chromophores with twisted Möbius topology, and the observation of S₂ fluorescence in the near-infrared region has been unprecedented. The higher excited-state dynamics of neutral and deprotonated [32]­heptaphyrins were compared by ultrafast transient absorption spectroscopy to understand the S₂ fluorescence origin. In the antiaromatic [32]­heptaphyrin, a fast time component of 65 fs was assigned as an internal conversion process from the S_B state to the S_Q state, which occurs prior to relaxation to the optically dark, lowest electronic state (S_D). Therefore, the S_Q state of the antiaromatic [32]­heptaphyrin acts as a trap state intervening radiative transitions from the S_B state to the S₀ state. In deprotonated [32]­heptaphyrin, the internal conversion from the S_B state to the S_Q state proceeds with a slower time constant of 150 fs for owing to its rigid structure, helping the observation of its S₂ fluorescence

Hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1): A Dual Site Ligand That Supports Thermal Conformational Changes

A new expanded porphyrin, hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1), is reported. It was obtained via the condensation of a hexapyrrolic derivative prepared in turn from a bipyrrole dialdehyde and a stable quaterpyrrole precursor. This hexadecaphyrin contains eight direct α-pyrrole-to-α-pyrrole linkages in its structure. It supports the formation of bimetallic complexes of both zinc and cobalt that are characterized by different conformational structures. Furthermore, a mixed zinc/cobalt macrocycle has been prepared. The cobalt bimetallic complex shows two stable conformations with the same oxidation state that are in equilibrium. All compounds have been characterized by common spectroscopic means, and single crystal X-ray diffraction structures were obtained for all macrocyclic compounds. DFT calculations and transient absorption spectra were used to study the electronic features of the complexes and the effect of conformational changes. This system shows promise as an accumulated heat sensor

Hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1): A Dual Site Ligand That Supports Thermal Conformational Changes

A new expanded porphyrin, hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1), is reported. It was obtained via the condensation of a hexapyrrolic derivative prepared in turn from a bipyrrole dialdehyde and a stable quaterpyrrole precursor. This hexadecaphyrin contains eight direct α-pyrrole-to-α-pyrrole linkages in its structure. It supports the formation of bimetallic complexes of both zinc and cobalt that are characterized by different conformational structures. Furthermore, a mixed zinc/cobalt macrocycle has been prepared. The cobalt bimetallic complex shows two stable conformations with the same oxidation state that are in equilibrium. All compounds have been characterized by common spectroscopic means, and single crystal X-ray diffraction structures were obtained for all macrocyclic compounds. DFT calculations and transient absorption spectra were used to study the electronic features of the complexes and the effect of conformational changes. This system shows promise as an accumulated heat sensor

Hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1): A Dual Site Ligand That Supports Thermal Conformational Changes

A new expanded porphyrin, hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1), is reported. It was obtained via the condensation of a hexapyrrolic derivative prepared in turn from a bipyrrole dialdehyde and a stable quaterpyrrole precursor. This hexadecaphyrin contains eight direct α-pyrrole-to-α-pyrrole linkages in its structure. It supports the formation of bimetallic complexes of both zinc and cobalt that are characterized by different conformational structures. Furthermore, a mixed zinc/cobalt macrocycle has been prepared. The cobalt bimetallic complex shows two stable conformations with the same oxidation state that are in equilibrium. All compounds have been characterized by common spectroscopic means, and single crystal X-ray diffraction structures were obtained for all macrocyclic compounds. DFT calculations and transient absorption spectra were used to study the electronic features of the complexes and the effect of conformational changes. This system shows promise as an accumulated heat sensor

Hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1): A Dual Site Ligand That Supports Thermal Conformational Changes

A new expanded porphyrin, hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1), is reported. It was obtained via the condensation of a hexapyrrolic derivative prepared in turn from a bipyrrole dialdehyde and a stable quaterpyrrole precursor. This hexadecaphyrin contains eight direct α-pyrrole-to-α-pyrrole linkages in its structure. It supports the formation of bimetallic complexes of both zinc and cobalt that are characterized by different conformational structures. Furthermore, a mixed zinc/cobalt macrocycle has been prepared. The cobalt bimetallic complex shows two stable conformations with the same oxidation state that are in equilibrium. All compounds have been characterized by common spectroscopic means, and single crystal X-ray diffraction structures were obtained for all macrocyclic compounds. DFT calculations and transient absorption spectra were used to study the electronic features of the complexes and the effect of conformational changes. This system shows promise as an accumulated heat sensor

Cyclo[6]pyridine[6]pyrrole: A Dynamic, Twisted Macrocycle with No Meso Bridges

A large porphyrin analogue, cyclo[6]­pyridine[6]­pyrrole, containing no meso bridging atoms, has been synthesized through Suzuki coupling. In its neutral form, this macrocycle exists as a mixture of two figure-eight conformers that undergo fast exchange in less polar solvents. Upon protonation, the dynamic twist can be transformed into species that adopt a ruffled planar structure or a figure-eight shape depending on the extent of protonation and counteranions. Conversion to a bisboron difluoride complex via deprotonation with NaH and treatment with BF₃ acts to lock the macrocycle into a figure-eight conformation. The various forms of cyclo[6]­pyridine[6]­pyrrole are characterized by distinct NMR, X-ray crystallographic, and spectroscopic features

Hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1): A Dual Site Ligand That Supports Thermal Conformational Changes

A new expanded porphyrin, hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1), is reported. It was obtained via the condensation of a hexapyrrolic derivative prepared in turn from a bipyrrole dialdehyde and a stable quaterpyrrole precursor. This hexadecaphyrin contains eight direct α-pyrrole-to-α-pyrrole linkages in its structure. It supports the formation of bimetallic complexes of both zinc and cobalt that are characterized by different conformational structures. Furthermore, a mixed zinc/cobalt macrocycle has been prepared. The cobalt bimetallic complex shows two stable conformations with the same oxidation state that are in equilibrium. All compounds have been characterized by common spectroscopic means, and single crystal X-ray diffraction structures were obtained for all macrocyclic compounds. DFT calculations and transient absorption spectra were used to study the electronic features of the complexes and the effect of conformational changes. This system shows promise as an accumulated heat sensor