Homoconjugation in diporphyrins: excitonic behaviors in singly and doubly linked Zn(ii)porphyrin dimers

Yoon, Min Chul; Lee, Sangsu; Tokuji, Sumito; Yorimitsu, Hideki; Osuka, Atsuhiro; Kim, Dongho

doi:10.1039/c3sc22151b

Cited by 17 publications

(19 citation statements)

References 44 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition to exciton coupling, we can consider homoconjugation through the central sp 3 hybridized carbon atom, which allows orbital overlap of π‐systems located on different arms. This phenomenon has previously been invoked to explain the redshift in similar tetramers41 and has recently been shown to contribute to conjugation in Zn II porphyrin dimers 42. In the case of 1 4+ , the LUMO π* orbitals are considerably delocalized on the four arms.…”

Section: Resultsmentioning

confidence: 75%

A Highly Luminescent Tetramer from a Weakly Emitting Monomer: Acid‐ and Redox‐Controlled Multiple Complexation by Cucurbit[7]uril

Bergamini

Fermi

Marchini

et al. 2014

Chemistry A European J

View full text Add to dashboard Cite

The tetrahedral, shape-persistent molecule 1(4+), containing four pyridylpyridinium units connected through a central carbon atom, exhibits unexpected photophysical properties including a substantially redshifted absorption (2350 cm(-1)) and a very strong fluorescence (Φem = 40 %), compared with the monomer 2(+) (Φem = 0.4 %). Density functional theory calculations on the structure and spectroscopic properties of 1(4+) and 2(+) show that exciton interactions, homoconjugation, and orbital nature account for the observed differences in their photophysical properties. The protonated tetramer binds four cucurbit[7]uril molecules and the host/guest interactions can be controlled by chemical (acid/base) as well as redox stimuli.

show abstract

Section: Resultsmentioning

confidence: 75%

A Highly Luminescent Tetramer from a Weakly Emitting Monomer: Acid‐ and Redox‐Controlled Multiple Complexation by Cucurbit[7]uril

Bergamini

Fermi

Marchini

et al. 2014

Chemistry A European J

View full text Add to dashboard Cite

show abstract

“…TD-DFT calculations for the BS and triplet solutions for [2CC] 2 + both predict two NIR transitions in close agreement with experiment. [68,70,71] We have used Equation (5) to calculate the distance R [] between the transition moment dipoles of the monomer units in [2CC] 2 + . A number of reports have described the presence of multiple low-energy bands in organic biradical systems.…”

Section: Discussionmentioning

confidence: 99%

“…In oblique dimers having intermediate geometries, such as [2CC] 2 + with an approximate 608 between the salen units, both transitions are partially allowed and band splitting is observed. [68,70,71] We have used Equation (5) to calculate the distance R [] between the transition moment dipoles of the monomer units in [2CC] 2 + . [72] R ¼…”

Section: Discussionmentioning

confidence: 99%

“…This analysis is further confirmation that [2CC] 2 + functions as a mixture of oxidized monomers [1C] + , and that the NIR band splitting of [2CC] 2 + can be adequately described by the exciton model. [68][69][70][71] In addition, this model assumes that negligible electron delocalization between the two chromophores occurs in the groundstate. [69] Although we cannot discount the possibility that the observed spectrum is due to equal populations of cis and trans forms of [2CC] 2 + , the experimental and theoretical data strongly favor the exciton model.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Class III Delocalization and Exciton Coupling in a Bimetallic Bis‐ligand Radical Complex

Dunn

Chiang

Ramogida

et al. 2013

Chemistry A European J

View full text Add to dashboard Cite

The geometric and electronic structure of an oxidized bimetallic Ni complex incorporating two redox-active Schiff-base ligands connected via a 1,2-phenylene linker has been investigated and compared to a monomeric analogue. Information from UV/Vis/NIR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, electrochemistry, and density functional theory (DFT) calculations provides important information on the locus of oxidation for the bimetallic complex. The neutral bimetallic complex is conformationally dynamic at room temperature, which complicates characterization of the oxidized forms. Comparison to an oxidized monomer analogue 1 provides critical insight into the electronic structure of the oxidized bimetallic complex 2. Oxidation of 1 provides [1˙](+), which is characterized as a fully delocalized ligand radical complex; the spectroscopic signature of this derivative includes an intense NIR band at 4500 cm(-1). Oxidation of 2 to the bis-oxidized form affords a bis-ligand radical species [2˙˙](2+). Variable temperature EPR spectroscopy of [2˙˙](2+) shows no evidence of coupling, and the triplet and broken symmetry solutions afforded by theoretical calculations are essentially isoenergetic. [2˙˙](2+) is thus best described as incorporating two non-interacting ligand radicals. Interestingly, the intense NIR intervalence charge transfer band observed for the delocalized ligand-radical [1˙](+) exhibits exciton splitting in [2˙˙](2+), due to coupling of the monomer transition dipoles in the enforced oblique dimer geometry. Evaluating the splitting of the intense intervalence charge transfer band can thus provide significant geometric and electronic information in less rigid bis-ligand radical systems. Addition of excess pyridine to [2˙˙](2+) results in a shift in the oxidation locus from a bis-ligand radical species to the Ni(III) /Ni(III) derivative [2(py)4](2+), demonstrating that the ligand system can incorporate significant bulk in the axial positions.

show abstract

“…52a, 53 This is further emphasized by the appearance of a 57 Co hyperfine interaction, observed as shoulders on the S = ½ peak although not fully resolved due to broadening of the experimental spectrum. The hyperfine coupling is on the order of ~1.2 mT which is in agreement with hyperfine coupling constants observed in the EPR spectra of other Co(III)-phenoxyl radical complexes.…”

Section: T / Kmentioning

confidence: 92%

Electronic Structure Description of a Doubly Oxidized Bimetallic Cobalt Complex with Proradical Ligands

et al. 2015

View full text Add to dashboard Cite

The geometric and electronic structure of a doubly oxidized bimetallic Co complex containing two redox-active salen moieties connected via a 1,2-phenylene linker was investigated and compared to an oxidized monomeric analogue. Both complexes, namely, CoL 1 and Co2L 2 , are oxidized to the mono- and dications, respectively, with AgSbF6 and characterized by X-ray crystallography for the monomer and by vis–NIR (NIR = near-infrared) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, superconducting quantum interference device (SQUID) magnetometry, and density functional theory (DFT) calculations for both the monomer and dimer. Both complexes exhibit a water molecule coordinated in the apical position upon oxidation. [CoL1-H2O]+ displays a broad NIR band at 8500 cm–1 (8400 M–1 cm–1), which is consistent with recent reports on oxidized Co salen complexes (Kochem, A. et al., Inorg. Chem. , 2012, 51, 10557–10571 and Kurahashi, T. et al., Inorg. Chem. , 2013, 52, 3908–3919). DFT calculations predict a triplet ground state with significant ligand and metal contributions to the singularly occupied molecular orbitals. The majority (∼75%) of the total spin density is localized on the metal, highlighting both high-spin Co(III) and Co(II)L• character in the electronic ground state. Further oxidation of CoL1 to the dication affords a low-spin Co(III) phenoxyl radical species. The NIR features for [Co2L2-2H2O]2+ at 8600 cm–1 (17 800 M–1 cm–1) are doubly intense in comparison to [CoL1-H2O]+ owing to the description of [Co2L2-2H2O]2+ as two non-interacting oxidized Co salen complexes bound via the central phenylene linker. Interestingly, TD-DFT calculations predict two electronic transitions that are 353 cm–1 apart. The NIR spectrum of the analogous Ni complex, [Ni2L2]2+, exhibits two intense transitions (4890 cm–1/26 500 M–1 cm–1 and 4200 cm–1/21 200 M–1 cm–1) due to exciton coupling in the excited state. Only one broad band is observed in the NIR spectrum for [Co2L2-2H2O]2+ as a result of the contracted donor and acceptor orbitals and overall CT character.

show abstract

Homoconjugation in diporphyrins: excitonic behaviors in singly and doubly linked Zn(ii)porphyrin dimers

Cited by 17 publications

References 44 publications

A Highly Luminescent Tetramer from a Weakly Emitting Monomer: Acid‐ and Redox‐Controlled Multiple Complexation by Cucurbit[7]uril

A Highly Luminescent Tetramer from a Weakly Emitting Monomer: Acid‐ and Redox‐Controlled Multiple Complexation by Cucurbit[7]uril

Class III Delocalization and Exciton Coupling in a Bimetallic Bis‐ligand Radical Complex

Electronic Structure Description of a Doubly Oxidized Bimetallic Cobalt Complex with Proradical Ligands

Contact Info

Product

Resources

About