Protonation‐Induced Formation of a Stable Singlet Biradicaloid Derived from a Modified Sapphyrin Analogue

Ishida, Masatoshi; Karasawa, Satoru; Uno, Hidemitsu; Tani, Fumito; Naruta, Yoshinori

doi:10.1002/ange.200907350

Cited by 14 publications

(13 citation statements)

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“…Photoinduced electron transfer and Gibbs energy considerations : As inferred from the TA spectra of HP n and their Mg adducts, photoinduced electron‐transfer (PET) processes are expected to participate in the excited‐state dynamics of all of these derivatives. This result is consistent with emissive behavior that is eventually governed by donor‐excited PET (d‐PET) processes,32 owing to electron transfer from the excited fluorophore (i.e., the dipyrrin core) to the acceptor moiety (i.e., 1,10‐phenanthroline) 33. Support for this suggestion comes from the work of Nagano, Fukuzumi, and co‐workers, who reported the direct observation of radical‐ion pairs of fluorescein‐based probes by using EPR spectroscopy 32a.…”

Section: Resultssupporting

confidence: 82%

Photophysical Analysis of 1,10‐Phenanthroline‐Embedded Porphyrin Analogues and Their Magnesium(II) Complexes

Ishida

Lim

Lee

et al. 2012

Chemistry A European J

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The synthesis, characterization, photophysical properties, and theoretical analysis of a series of tetraaza porphyrin analogues (H-Pn: n=1-4) containing a dipyrrin subunit and an embedded 1,10-phenanthroline subunit are described. The meso-phenyl-substituted derivative (H-P1) interacts with a Mg(2+) salt (e.g., MgCl(2), MgBr(2), MgI(2), Mg(ClO(4))(2), and Mg(OAc)(2)) in MeCN solution, thereby giving rise to a cation-dependent red-shift in both the absorbance- and emission maxima. In this system, as well as in the other H-Pn porphyrin analogues used in this study, the four nitrogen atoms of the ligand interact with the bound magnesium cation to form Mg(2+)-dipyrrin-phenanthroline complexes of the general structure MgX-Pn (X=counteranion). Both single-crystal X-ray diffraction analysis of the corresponding zinc-chloride derivative (ZnCl-P1) and fluorescence spectroscopy of the Mg-adducts that are formed from various metal salts provide support for the conclusion that, in complexes such as MgCl-P1, a distorted square-pyramidal geometry persists about the metal cation wherein a chloride anion acts as an axial counteranion. Several analogues (HPn) that contain electron-donating and/or electron-withdrawing dipyrrin moieties were prepared in an effort to understand the structure-property relationships and the photophysical attributes of these Mg-dipyrrin complexes. Analysis of various MgX-Pn (X=anion) systems revealed significant substitution effects on their chemical, electrochemical, and photophysical properties, as well as on the Mg(2+)-cation affinities. The fluorescence properties of MgCl-Pn reflected the effect of donor-excited photoinduced electron transfer (d-PET) processes from the dipyrrin subunit (as a donor site) to the 1,10-phenanthroline acceptor subunit. The proposed d-PET process was analyzed by electron paramagnetic resonance (EPR) spectroscopy and by femtosecond transient absorption (TA) spectroscopy, as well as by theoretical DFT calculations. Taken together, these studies provide support for the suggestion that a radical species is produced as the result of an intramolecular charge-transfer process, following photoexcitation. These photophysical effects, combined with a mixed dipyrrin-phenanthroline structure that is capable of effective Mg(2+)-cation complexation, lead us to suggest that porphyrin-inspired systems, such as HPn, have a role to play as magnesium-cation sensors.

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Section: Resultssupporting

confidence: 82%

Photophysical Analysis of 1,10‐Phenanthroline‐Embedded Porphyrin Analogues and Their Magnesium(II) Complexes

Ishida

Lim

Lee

et al. 2012

Chemistry A European J

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“…For instance, a diradical was formed by double protonation and subsequent intramolecular electron transfer from donor to acceptor unit, as shown in Figure (a) . A singlet biradical was generated by protonation, coupled with oxidation, of a modified sapphyrin analog (Figure (b)) . A paramagnetic diradical dipyrilium salt in equilibrium with the corresponding closed‐shell dication was formed by protonation‐induced cyclization in a donor–acceptor–donor triad molecule, as shown in Figure (c) .…”

Section: Fluctuating Ground‐state Multiplicitymentioning

confidence: 99%

“…56 A singlet biradical was generated by protonation, coupled with oxidation, of a modified sapphyrin analog (Figure 9(b)). 57 A paramagnetic diradical dipyrilium salt in equilibrium with the corresponding closed-shell dication was formed by protonation-induced cyclization in a donor-acceptor-donor triad molecule, as shown in Figure 9(c). 58 The preference for high-spin state can also be employed as a synthetic strategy, for example to obtain building blocks for polaronic ferromagnetic polymer chains (Figure 9(d)).…”

Section: Exciting Casesmentioning

confidence: 99%

Theory and practice of uncommon molecular electronic configurations

Gryn’ova

Coote

Corminbœuf

2015

WIREs Comput Mol Sci

102

112

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The electronic configuration of the molecule is the foundation of its structure and reactivity. The spin state is one of the key characteristics arising from the ordering of electrons within the molecule's set of orbitals. Organic molecules that have open-shell ground states and interesting physicochemical properties, particularly those influencing their spin alignment, are of immense interest within the up-and-coming field of molecular electronics. In this advanced review, we scrutinize various qualitative rules of orbital occupation and spin alignment, viz., the aufbau principle, Hund's multiplicity rule, and dynamic spin polarization concept, through the prism of quantum mechanics. While such rules hold in selected simple cases, in general the spin state of a system depends on a combination of electronic factors that include Coulomb and Pauli repulsion, nuclear attraction, kinetic energy, orbital relaxation, and static correlation. A number of fascinating chemical systems with spin states that fluctuate between triplet and open-shell singlet, and are responsive to irradiation, pH, and other external stimuli, are highlighted. In addition, we outline a range of organic molecules with intriguing non-aufbau orbital configurations. In such quasi-closed-shell systems, the singly occupied molecular orbital (SOMO) is energetically lower than one or more doubly occupied orbitals. As a result, the SOMO is not affected by electron attachment to or removal from the molecule, and the products of such redox processes are polyradicals. These peculiar species possess attractive conductive and magnetic properties, and a number of them that have already been developed into molecular electronics applications are highlighted in this review. How to cite this article:WIREs Comput Mol Sci 2015Sci , 5:440-459. doi: 10.1002Sci /wcms.1233 INTRODUCTIONT he electronic configuration and state of a molecule characterize the distribution of electrons across the corresponding one-electron wavefunctions, i.e., orbitals. 1 This model description, albeit approximate, is nonetheless indispensable in explaining and predicting molecular geometry and various chemical and physical properties. As orbitals comprise not only the spatial component, but also the spin, they also give rise to such key features as the nature of configuration shell-open or closed-and the multiplicity of the electronic state. While the majority of stable organic molecules have a closed-shell singlet ground state, species with unpaired electrons display unique chemical reactivity and are capable of carrying magnetism and conductivity functionalities. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.Although historically the latter have been the domain of metals and, in particular, transition metal complexes, in the recent years the focus has ...

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“…A large number of studies have characterized different sapphyrin derivatives, including β‐alkylated sapphyrins, core‐modified sapphyrins with heteroatoms (O, S, or Se), N‐fused/N‐confused sapphyrins, and meso ‐tetraaryl‐substituted sapphyrins . Sapphyrins containing four meso ‐aryl substituents can serve as favorable building blocks for the further design of molecules, which are similar to meso ‐aryl‐substituted porphyrins, whose redox properties and chemical reactions can be finely tuned .…”

Section: Introductionmentioning

confidence: 99%

Synthesis, Characterization, and Electrochemistry of Open‐Chain Pentapyrroles and Sapphyrins with Highly Electron‐Withdrawing meso‐Tetraaryl Substituents

Shan

Desbois

Blondeau-Pâtissier

et al. 2017

Chemistry A European J

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A series of open-chain pentapyrroles and sapphyrins with highly electron-withdrawing substituents (i.e., CN, CF , or CO Me) on the meso-phenyl rings was synthesized and characterized as to the spectral properties, protonation reactions, and electrochemistry in non-aqueous media. The investigated compounds are represented as (Ar) PPyH and (Ar) SapH where PPy and Sap correspond to the tri-anion of the open-chain pentapyrrole and sapphyrin, respectively, and Ar=p-CNPh, p-CF Ph, or p-CO MePh. UV/Vis and H NMR spectroscopy as well as mass spectrometry data are given for the confirmation of the structures for the newly synthesized compounds. An X-ray structure for one of the pentapyrroles, that is, (p-CF Ph) PPyH (2), is also presented. The protonation processes were examined by UV/Vis absorption spectroscopy during the titration of the compounds with trifluoroacetic acid (TFA) in CH Cl . Equilibrium constants for the protonation reactions were calculated by using both the Hill equation and the mole ratio method. The protonation-initiated conversion of pentapyrroles to sapphyrins upon oxidation was also investigated. Cyclic voltammetry was used to measure the redox potentials in CH Cl , PhCN, and/or pyridine (Py). Electrochemical properties, protonation constants, and chemical reactions of the six compounds in the two series were then analyzed as a function of the solvent properties and the type of the electron-withdrawing groups on the meso-phenyl rings.

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Protonation‐Induced Formation of a Stable Singlet Biradicaloid Derived from a Modified Sapphyrin Analogue

Cited by 14 publications

References 60 publications

Photophysical Analysis of 1,10‐Phenanthroline‐Embedded Porphyrin Analogues and Their Magnesium(II) Complexes

Photophysical Analysis of 1,10‐Phenanthroline‐Embedded Porphyrin Analogues and Their Magnesium(II) Complexes

Theory and practice of uncommon molecular electronic configurations

Synthesis, Characterization, and Electrochemistry of Open‐Chain Pentapyrroles and Sapphyrins with Highly Electron‐Withdrawing meso‐Tetraaryl Substituents

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