11 research outputs found
Synthesis, Redox Properties, and Electronic Coupling in the Diferrocene Aza-dipyrromethene and azaBODIPY DonorāAcceptor Dyad with Direct FerroceneāĪ±-Pyrrole Bond
3,3ā²-Diferrocenylazadipyrromethene
(<b>3</b>) and
corresponding difluoroboryl (azaBODIPY) complex (<b>4</b>) were
synthesized in several steps from ferrocenecarbaldehyde, following
the well-explored chalcone-type synthetic approach. The novel diiron
complexes, in which ferrocene groups are directly connected to the
Ī±-pyrrolic positions were characterized by a variety of spectroscopic
techniques, electrochemistry, spectroelectrochemistry, and X-ray crystallography,
while their electronic structure, redox properties, and UVāvis
spectra were correlated with the density functional theory (DFT) and
time-dependent DFT calculations
Observation of the Strong Electronic Coupling in Near-Infrared-Absorbing Tetraferrocene aza-Dipyrromethene and aza-BODIPY with Direct FerroceneāĪ±- and FerroceneāĪ²-Pyrrole Bonds: Toward Molecular Machinery with Four-Bit Information Storage Capacity
The
1,3,7,9-tetraferrocenylazadipyrromethene (<b>3</b>) and the
corresponding 1,3,5,7-tetraferrocene aza-BODIPY (<b>4</b>) were
prepared via three and four synthetic steps, respectively, starting
from ferrocenecarbaldehyde using the chalcone-type synthetic methodology.
The novel tetra-iron compounds have ferrocene groups directly attached
to both the Ī±- and the Ī²-pyrrolic positions, and the shortest
FeāFe distance determined by X-ray crystallography for <b>3</b> was found to be ā¼6.98 Ć
. These new compounds
were characterized by UVāvis, nuclear magnetic resonance, and
high-resolution electrospray ionization mass spectrometry methods,
while metalāmetal couplings in these systems were probed by
electro- and spectroelectrochemistry, chemical oxidations, and MoĢssbauer
spectroscopy. Electrochemical data are suggestive of the well-separated
stepwise oxidations of all four ferrocene groups in <b>3</b> and <b>4</b>, while spectroelectrochemical and chemical oxidation
experiments allowed for characterization of the mixed-valence forms
in the target compounds. Intervalence charge-transfer band analyses
indicate that the mixed-valence [<b>3</b>]<sup>+</sup> and [<b>4</b>]<sup>+</sup> complexes belong to the weakly coupled class
II systems in the RobināDay classification. This interpretation
was further supported by MoĢssbauer spectroscopy in which two
individual doublets for FeĀ(II) and FeĀ(III) centers were observed in
room-temperature experiments for the mixed-valence [<b>3</b>]<sup><i>n</i>+</sup> and [<b>4</b>]<sup><i>n</i>+</sup> species (<i>n</i> = 1ā3). The
electronic structure, redox properties, and UVāvis spectra
of new systems were correlated with Density Functional Theory (DFT)
and time-dependent DFT calculations (TDDFT), which are suggestive
of a ferrocene-centered highest occupied molecular orbital and chromophore-centered
lowest unoccupied molecular orbital in <b>3</b> and <b>4</b> as well as predominant spin localization at the ferrocene fragment
attached to the Ī±-pyrrolic positions in [<b>3</b>]<sup>+</sup> and [<b>4</b>]<sup>+</sup>
Synthesis and Charge-Transfer Dynamics in a Ferrocene-Containing Organoboryl aza-BODIPY DonorāAcceptor Triad with Boron as the Hub
A <i>N</i>,<i>N</i>ā²-bisĀ(ferroceneacetylene)Āboryl
complex of 3,3ā²-diphenylazadiisoindolylmethene was synthesized
by the reaction of an <i>N</i>,<i>N</i>ā²-difluoroboryl
complex of 3,3ā²-diphenylazadiisoindolylmethene and ferroceneacetylene
magnesium bromide. The novel diiron complex was characterized by a
variety of spectroscopic techniques, electrochemistry, and ultrafast
time-resolved methods. Spectroscopy and redox behavior was correlated
with the density functional theory (DFT) and time-dependent DFT calculations.
An unexpected degree of coupling between the two Fc ligands was observed.
Despite a lack of conjugation between the donor and acceptor, the
complex undergoes very rapid (Ļ = 1.7 Ā± 0.1 ps) photoinduced
intramolecular charge separation followed by subpicosecond charge
recombination to form a triplet state with a lifetime of 4.8 Ā±
0.1 Ī¼s
Redox and Photoinduced Electron-Transfer Properties in Short Distance Organoboryl Ferrocene-Subphthalocyanine Dyads
Reaction between ferrocene lithium
or ethynylferrocene magnesium bromide and (chloro)Āboronsubphthalocyanine
leads to formation of ferrocene- (<b>2</b>) and ethynylferrocene-
(<b>3</b>) containing subphthalocyanine dyads with a direct
organometallic BāC bond. New donorāacceptor dyads were
characterized using UVāvis and magnetic circular dichroism
(MCD) spectroscopies, NMR method, and X-ray crystallography. Redox
potentials of the rigid donorāacceptor dyads <b>2</b> and <b>3</b> were studied using the cyclic voltammetry (CV)
and differential pulse voltammetry (DPV) approaches and compared to
the parent subphthalocyanine <b>1</b> and conformationally flexible
subphthalocyanine ferrocenenylmethoxide (<b>4</b>) and ferrocenyl
carboxylate (<b>5</b>) dyads reported earlier. It was found
that the first oxidation process in dyads <b>2</b> and <b>3</b> is ferrocene-centered, while the first reduction as well
as the second oxidation are centered at the subphthalocyanine ligand.
Density functional theory-polarized continuum model (DFT-PCM) and
time-dependent (TD) DFT-PCM methods were used to probe the electronic
structures and explain the UVāvis and MCD spectra of complexes <b>1</b>ā<b>5</b>. DFT-PCM calculations suggest that
the LUMO, LUMO+1, and HOMO-3 in new dyads <b>2</b> and <b>3</b> are centered at the subphthalocyanine ligand, while the
HOMO to HOMO-2 in both dyads are predominantly ferrocene-centered.
TDDFT-PCM calculations on compounds <b>1</b>ā<b>5</b> are indicative of the Ļ ā Ļ* transitions dominance
in their UVāvis spectra, which is consistent with the experimental
data. The excited state dynamics of the parent subphthalocyanine <b>1</b> and dyads <b>2</b>ā<b>5</b> were investigated
using time-resolved transient spectroscopy. In the dyads <b>2</b>ā<b>5</b>, the initially excited state is rapidly (<2
ps) quenched by electron transfer from the ferrocene ligand. The lifetime
of the charge transfer state demonstrates a systematic dependence
on the structure of the bridge between the subphthalocyanine and ferrocene
Tuning Electronic Structure, Redox, and Photophysical Properties in Asymmetric NIR-Absorbing Organometallic BODIPYs
Stepwise modification
of the methyl groups at the Ī± positions of BODIPY <b>1</b> was used for preparation of a series of mono- (<b>2</b>, <b>4</b>, and <b>6</b>) and diferrocene (<b>3</b>) substituted
donorāacceptor dyads in which the organometallic substituents
are fully conjugated with the BODIPY Ļ system. All donorāacceptor
complexes have strong absorption in the NIR region and quenched steady-state
fluorescence, which can be partially restored upon oxidation of organometallic
group(s). X-ray crystallography of complexes <b>2</b>ā<b>4</b> and <b>6</b> confirms the nearly coplanar arrangement
of the ferrocene groups and the BODIPY Ļ system. Redox properties
of the target systems were studied using cyclic voltammetry (CV) and
differential pulse voltammetry (DPV). It was found that the first
oxidation process in all dyads is ferrocene centered, while the separation
between the first and the second ferrocene-centered oxidation potentials
in diferrocenyl-containing dyad <b>3</b> is ā¼150 mV.
The density functional theory-polarized continuum model (DFT-PCM)
and time-dependent (TD) DFT-PCM methods were used to investigate the
electronic structure as well as explain the UVāvis and redox
properties of organometallic compounds <b>2</b>ā<b>4</b> and <b>6</b>. TDDFT calculations allow for assignment
of the charge-transfer and Ļ ā Ļ* transitions in
the target compounds. The excited state dynamics of the parent BODIPY <b>1</b> and dyads <b>2</b>ā<b>4</b> and <b>6</b> were investigated using time-resolved transient spectroscopy.
In all organometallic dyads <b>2</b>ā<b>4</b> and <b>6</b> the initially excited state is rapidly quenched by electron
transfer from the ferrocene ligand. The lifetime of the charge-separated
state was found to be between 136 and 260 ps and demonstrates a systematic
dependence on the electronic structure and geometry of BODIPYs <b>2</b>ā<b>4</b> and <b>6</b>
Tuning Electronic Structure, Redox, and Photophysical Properties in Asymmetric NIR-Absorbing Organometallic BODIPYs
Stepwise modification
of the methyl groups at the Ī± positions of BODIPY <b>1</b> was used for preparation of a series of mono- (<b>2</b>, <b>4</b>, and <b>6</b>) and diferrocene (<b>3</b>) substituted
donorāacceptor dyads in which the organometallic substituents
are fully conjugated with the BODIPY Ļ system. All donorāacceptor
complexes have strong absorption in the NIR region and quenched steady-state
fluorescence, which can be partially restored upon oxidation of organometallic
group(s). X-ray crystallography of complexes <b>2</b>ā<b>4</b> and <b>6</b> confirms the nearly coplanar arrangement
of the ferrocene groups and the BODIPY Ļ system. Redox properties
of the target systems were studied using cyclic voltammetry (CV) and
differential pulse voltammetry (DPV). It was found that the first
oxidation process in all dyads is ferrocene centered, while the separation
between the first and the second ferrocene-centered oxidation potentials
in diferrocenyl-containing dyad <b>3</b> is ā¼150 mV.
The density functional theory-polarized continuum model (DFT-PCM)
and time-dependent (TD) DFT-PCM methods were used to investigate the
electronic structure as well as explain the UVāvis and redox
properties of organometallic compounds <b>2</b>ā<b>4</b> and <b>6</b>. TDDFT calculations allow for assignment
of the charge-transfer and Ļ ā Ļ* transitions in
the target compounds. The excited state dynamics of the parent BODIPY <b>1</b> and dyads <b>2</b>ā<b>4</b> and <b>6</b> were investigated using time-resolved transient spectroscopy.
In all organometallic dyads <b>2</b>ā<b>4</b> and <b>6</b> the initially excited state is rapidly quenched by electron
transfer from the ferrocene ligand. The lifetime of the charge-separated
state was found to be between 136 and 260 ps and demonstrates a systematic
dependence on the electronic structure and geometry of BODIPYs <b>2</b>ā<b>4</b> and <b>6</b>
Outsourcing Intersystem Crossing without Heavy Atoms: Energy Transfer Dynamics in PyridoneBODIPYāC<sub>60</sub> Complexes
The
excited state dynamics in two fully characterized pyridoneBODIPYāfullerene
complexes were investigated using time-resolved spectroscopy. Photoexcitation
was initially localized on the pyridoneBODIPY chromophore. The energy
was rapidly transferred to the fullerene, which subsequently underwent
ISC to form a triplet state and returned the energy to the pyridoneBODIPY
via tripletātriplet energy transfer. This ping-pong energy
transfer mechanism resulted in efficient (>85%) overall conversion
of the excited state pyridoneBODIPY constituent despite a complete
lack of ISC in the pyridoneBODIPY in the absence of the fullerene
partner. The small difference in attachment chemistry for the fullerene
did not impact the initial singlet energy transfer. However, the N-methylpyrrolidine bridge did slow both the tripletātriplet
energy transfer and the ultimate relaxation rate of the final triplet
state when compared to an isoxazole-based bridge. The rates of each
step were quantified, and computational predictions were used to complement
the proposed mechanism and energetics. The result demonstrated efficient
triplet sensitization of a strong chromophore that lacks significant
spināorbit coupling
Tuning Electron-Transfer Properties in 5,10,15,20-Tetra(1ā²-hexanoylferrocenyl)porphyrins as Prospective Systems for Quantum Cellular Automata and Platforms for Four-Bit Information Storage
Metal-free (<b>1</b>) and zinc (<b>2</b>) 5,10,15,20-tetraĀ(1ā²-hexanoylferrocenyl)Āporphyrins
were prepared using an acid-catalyzed tetramerization reaction between
pyrrole and 1ā²-(1-hexanoyl)Āferrocencarboxaldehyde. New organometallic
compounds were characterized by combination of <sup>1</sup>H, <sup>13</sup>C, and variable-temperature NMR, UVāvis, magnetic
circular dichroism, and high-resolution electrospray ionization mass
spectrometry methods. The redox properties of <b>1</b> and <b>2</b> were probed by electrochemical (cyclic voltammetry and differential
pulse voltammetry), spectroelectrochemical, and chemical oxidation
approaches coupled with UVāvisānear-IR and MoĢssbauer
spectroscopy. Electrochemical data recorded in the dichloromethane/TBAĀ[BĀ(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] system (TBAĀ[BĀ(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] is a weakly coordinating tetrabutylammonium
tetrakisĀ(pentafluorophenyl)Āborate electrolyte) are suggestive of ā1e<sup>ā</sup> + 1e<sup>ā</sup> + 2e<sup>ā</sup>ā
oxidation sequence for four ferrocene groups in <b>1</b> and <b>2</b>, which followed by oxidation process centered at the porphyrin
core. The separation between all ferrocene-centered oxidation electrochemical
waves is very large (510ā660 mV). The nature of mixed-valence
[<b>1</b>]<sup><i>n</i>+</sup> and [<b>2</b>]<sup><i>n</i>+</sup> (<i>n</i> = 1 or 2) complexes
was probed by the spectroelectrochemical and chemical oxidation methods.
Analysis of the intervalence charge-transfer band in [<b>1</b>]<sup>+</sup> and [<b>2</b>]<sup>+</sup> is suggestive of the
Class II (in RobināDay classification) behavior of all mixed-valence
species, which correlate well with MoĢssbauer data. Density
functional theoryāpolarized continuum model (DFT-PCM) and time-dependent
(TD) DFT-PCM methods were applied to correlate redox and optical properties
of organometallic complexes <b>1</b> and <b>2</b> with
their electronic structures
Direct Synthesis of an Unprecedented Stable Radical of Nickel(II) 3,5-Bis(dimedonyl)azadiisoindomethene with Strong and Narrow Near-Infrared Absorption at Ī» ā¼ 1000 nm
An
unprecedented stable neutral radical nickelĀ(II) complex of 3,5-bisĀ(dimedonyl)Āazadiisoindomethene
(<b>1</b>) was prepared by the direct reaction between 1,3-diiminoisoindoline
and dimedone. A new radical complex <b>1</b> has an intense
and narrow absorption at 1008 nm and can be reduced to a less stable
anionic [<b>1</b>]<sup>ā</sup> with a typical azaĀ(dibenzo)Āboron
dipyrromethene (aza-BODIPY) UVāvis spectrum. Complex <b>1</b>, along with two other colored condensation reaction products <b>2</b> and <b>3</b>, was characterized by spectroscopy and
X-ray crystallography, while the paramagnetic nature of <b>1</b> was probed by EPR and SQUID methods. Complex <b>1</b> forms
dimers in the solid state with short (ā¼3.16 Ć
) Ni---Ni
contacts. Redox data on <b>1</b> are indicative of a reversible
reduction process in this complex; its magnetism suggests a <i>S</i> = <sup>1</sup>/<sub>2</sub> state with the spin density
delocalized over the aza-BODIPY core. The experimental data <b>1</b> and [<b>1</b>]<sup>ā</sup> were correlated
with the density functional theory (DFT) and time-dependent DFT calculations
Preparation, Xāray Structures, Spectroscopic, and Redox Properties of Di- and Trinuclear IronāZirconium and IronāHafnium Porphyrinoclathrochelates
The
first hybrid di- and trinuclear ironĀ(II)āzirconiumĀ(IV) and
ironĀ(II)āhafniumĀ(IV) macrobicyclic complexes with one or two
apical 5,10,15,20-tetraphenylporphyrin fragments were obtained using
transmetalation reaction between <i>n</i>-butylboron-triethylantimony-capped
or bisĀ(triethylantimony)-capped ironĀ(II) clathrochelate precursors
and dichlorozirconiumĀ(IV)- or dichlorohafniumĀ(IV)-5,10,15,20-tetraphenylporphyrins
under mild conditions. New di- and trinuclear porphyrinoclathrochelates
of general formula FeNx<sub>3</sub>((B<i>n</i>-Bu)Ā(MTPP))
and FeNx<sub>3</sub>(MTPP)<sub>2</sub> [M = Zr, Hf; TPP = 5,10,15,20-tetraporphyrinatoĀ(2-);
Nx = nioximoĀ(2-)] were characterized by one-dimensional (<sup>1</sup>H and <sup>13</sup>CĀ{<sup>1</sup>H}) and two-dimensional (COSY and
HSQC) NMR, high-resolution electrospray ionization mass spectrometry,
UVāvisible, and magnetic circular dichroism spectra, single-crystal
X-ray diffraction experiments, as well as elemental analyses. Redox
properties of all complexes were probed using electrochemical and
spectroelectrochemical approaches. Electrochemical and spectroelectrochemical
data suggestive of a very weak, if any, long-range electronic coupling
between two porphyrin Ļ-systems in FeNx<sub>3</sub>(MTPP)<sub>2</sub> complexes. Density functional theory and time-dependent density
functional theory calculations were used to correlate spectroscopic
signatures and redox properties of new compounds with their electronic
structures