17 research outputs found
Siamese-Twin Porphyrin Goes Platinum: Group 10 Monometallic, Homobimetallic, and Heterobimetallic Complexes
No full textNew Insight into an Old Problem: Analysis, Interpretation, and Theoretical Modeling of the Absorption and Magnetic Circular Dichroism Spectra of Monomeric and Dimeric Zinc Phthalocyanine Cation Radical
No full textThe
chemically or spectroelectrochemically generated formation and aggregation
of zinc(II) tetra-tert-butylphthalocyanine cation
radical [ZnPctBu]+•, which was highly
soluble in common organic solvents, were investigated using UV−vis
and magnetic circular dichroism (MCD) spectroscopies with an emphasis
on the influence of the axial ligand on the fingerprint (∼500
nm) and NIR (720∼1000 nm) spectral envelopes. MCD spectroscopy
is suggestive that the NIR band at ∼1000 nm observed for the
antiferromagnetically coupled cation radical dimer, [ZnPctBu]22+, has no degeneracy, the monomer–dimeric
equilibrium is temperature dependent, and higher degree aggregates
can be formed at specific conditions. Sixteen different exchange-correlation
functionals were tested to accurately predict the energies, intensities,
and profiles of the UV–vis and MCD spectra of the phthalocyanine
cation radical monomer and dimer. It was found that the M05 exchange-correlation
functional (along with several other functionals that include 27–42%
of Hartree–Fock exchange) provided an excellent agreement (∼0.1
eV for the degenerate excited states observed by MCD spectroscopy)
between theory and experiment for the phthalocyanine cation-radical
monomer and dimer. Not only did time-dependent density functional
theory (TDDFT) calculations with M05 exchange-correlation functional
correctly predict the nondegenerate NIR charge-transfer band at ∼1000
nm, all degenerate excited states, monomer and dimer energies, and
oscillator strengths, but also they correctly described the nature
of the experimentally observed at ∼500 nm MCD B-term (fingerprint band) detected for both the monomeric and dimeric
phthalocyanine cation radicals. The TDDFT data explain the similarities
in the UV–vis and MCD spectra of the monomeric and dimeric
species observed between the UV and fingerprint spectral envelopes
as well as correctly predicted the antiferromagnetic coupling between
the two singly oxidized phthalocyanine macrocycles in the dimer
Charge-Transfer Spectroscopy of Bisaxially Coordinated Iron(II) Phthalocyanines through the Prism of the Lever’s <i>E</i><sub>L</sub> Parameters Scale, MCD Spectroscopy, and TDDFT Calculations
No full textThe position of the experimentally
observed (in the UV–vis
and magnetic circular dichroism (MCD) spectra) low-energy metal-to-ligand
charge-transfer (MLCT) band in low-spin iron(II) phthalocyanine complexes
of general formula PcFeL2, PcFeL′L″, and
[PcFeX2]2– (L, L′, or L″
are neutral and X– is an anionic axial ligand) was
correlated with the Lever’s electrochemical EL scale values for the axial ligands. The time-dependent
density functional theory (TDDFT)-predicted UV–vis spectra
are in very good agreement with the experimental data for all complexes.
In the majority of compounds, TDDFT predicts that the first degenerate
MLCT band that correlates with the MCD A-term observed
between 360 and 480 nm is dominated by an eg (Fe, dπ) → b1u (Pc, π*) single-electron excitation
(in traditional D4h point group notation)
and agrees well with the previous assignment discussed by Stillman
and co-workers[Inorg. Chem. 1994, 33, 573–583]. The TDDFT calculations also suggest a small
energy gap for b1u/b2u (Pc, π*) orbital splitting
and closeness of the MLCT1 eg (Fe, dπ) → b1u (Pc, π*) and MLCT2 eg (Fe, dπ) → b2u (Pc,
π*) transitions. In the case of the PcFeL2 complexes
with phosphines as the axial ligands, additional degenerate charge-transfer
transitions were observed between 450 and 500 nm. These transitions
are dominated by a2u (Pc
+ L, π) → eg (Pc, π*) single-electron excitations and are unique for the
PcFe(PR3)2 complexes. The energy of the phthalocyanine-based a2u orbital has large axial
ligand dependency and is the reason for a large energy deviation for
B1 a2u (Pc + L, π)
→ eg (Pc, π*)
transition. The energies of the axial ligand-to-iron, axial ligand-to-phthalocyanine,
iron-to-axial ligand, and phthalocyanine-to-axial ligand charge-transfer
transitions were discussed on the basis of TDDFT calculations
Catalytic Synthesis of Donor-Acceptor-Donor (D-A-D) and Donor-Acceptor-Acceptor (D-A-A) Pyrimidine-Ferrocenes via Acceptorless Dehydrogenative Coupling: Synthesis, Structures, and Electronic Communication
No full textThe synthesis and full characterization of a series of ferrocene-decorated pyrimidines with donor-acceptor-donor (D-A-D) and donor-acceptor-acceptor (D-A-A) architectures are reported. The three novel compounds share a pyrimidine core and single ferrocenyl donor arm, with an additional substituent varied from donor ferrocene (1) to acceptor pyrenyl (2) to donor (4-diphenylamino)phenyl groups (3). The compounds could be easily constructed in acceptable yields in one-pot reactions via acceptorless dehydrogenative coupling reactions mediated by a ruthenium coordination complex supported by a simple bidentate P^N ligand. The solution and solid-state structures of the new pyrimidines are described along with photophysical and computational characterization. The lack of near IR (NIR) transitions upon single-electron oxidation of the compounds implies that the pyrimidinyl unit is less effective at mediating electronic communication compared with pyridine or pyrrole cores. Nevertheless, strong absorption in the far visible and NIR is observed upon formation of a dicationic species from 3 and is attributed to efficient charge transfer from the pyrimidine core to the oxidized donor units.Natural Sciences and Engineering Research Council of Canada (RGPIN-2014-03733
Unsymmetric Pentacene- and Pentacenequinone-Fused Porphyrins: Understanding the Effect of Cross- and Linear-Conjugation
No full textArticle says that unsymmetric pentacenequinone-fused (cross-conjugated) and pentacene-fused (linear-conjugated) porphyrins were designed and synthesized. This work provides important and useful information on guiding new material designs
Identifying charge-transfer and trip-multiplet states in Co(i), Co(ii), and Co(iii) phthalocyanines using (magneto)optical spectroscopy and (TD)DFT calculations
No full textClick on the DOI link to access this article at the publishers website (may not be free).Herein we compare the electronic structures of the Co(i), Co(ii), and Co(iii) phthalocyanines, which were elucidated using UV-vis-NIR and magnetic circular dichroism (MCD) spectroscopy as well as density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. The NIR triplet-multiplet bands in PcR4(2-)CoIIL2 (L = nil, Py, or nBuNH2; R = H or tert-Bu) complexes were studied by MCD spectroscopy for the first time and compared to those reported earlier by us in PcR4(2-)Cu (R = tert-Bu or SO3Na) compounds (J. Porphyrins Phthalocyanines 2025, 29, 110-122). In all cases, a Faraday MCD pseudo A-term was observed for this transition. DFT and TDDFT calculations successfully explained a systematic blue-shift in the metal-to-ligand charge-transfer (MLCT) and B1-band transitions going from [PcR4(2-)CoI]− to PcR4(2-)CoIIL2 to [PcR4(2-)CoIIIX2]− (X = CN− or Br−) complexes. Additionally, absorption bands observed in the 370-530 nm spectral envelope in [PcR4(2-)CoIIIX2]− complexes were assigned with a high level of confidence for the first time. This work provides the first combined systematic experimental and theoretical study that highlights similarities and differences in (magneto)optical spectroscopy of cobalt phthalocyanines spanning three oxidation states at the central metal ion. © 2025 The Royal Society of Chemistry.University of Tennessee; Minnesota Supercomputing Institute, University of Minnesota; National Science Foundation, NSF, (CHE-2153081); National Science Foundation, NSF; Division of Graduate Education, DGE, (2152168); Division of Graduate Education, DGEGenerous support from the NSF(CHE-2153081), Minnesota Supercomputing Institute, and the University of Tennessee to V. N. is greatly appreciated. B. J. M. acknowledges generous support from the University of Tennessee. BEM is a recipient of the fellowship provided by the NSF - Division of Graduate Education (grant #2152168). We wish to acknowledge Katelyn Llewellyn for her help with some data collection
Evaluation of the Intramolecular Charge-Transfer Properties in Solvatochromic and Electrochromic Zinc Octa(carbazolyl)phthalocyanines
No full textMagnetic Circular Dichroism of Porphyrinoid Silver Complexes: Evidence of the Electronic Structure Inversion upon Protonation of the N‑Confused Core
No full textWe report a systematic investigation of a series of Ag(II)
and
Ag(III) complexes of porphyrins and their analogues using UV–vis
magnetic circular dichroism (MCD) spectroscopies and theoretical calculations.
Ag(II) and Ag(III) octaethyl- and tetraarylporphyrins show the usual
sign sequence in the Q-band region (i.e., negative to positive intensities
with increasing energy) of their MCD spectra, indicative of the ΔHOMO
> ΔLUMO relationship (ΔHOMO is the energy difference
between
Michl’s a and s orbitals,
and ΔLUMO is the energy difference between Michl’s -a and -s pair of MOs). In contrast, Ag(II)
complexes of β,β′-pyrrole-modified porphyrins (with
an effective chlorin-type π-system) and Ag(III) corroles have
sign reverse features in the MCD spectra of their Q-band region (ΔHOMO
< ΔLUMO relationships). The Ag(III) complex of N-confused
porphyrin shows the ΔHOMO > ΔLUMO relationship in the
neutral state and the ΔHOMO < ΔLUMO relationship in
the protonated form
Siamese-Twin Porphyrin Goes Platinum: Group 10 Monometallic Homobimetallic, and Heterobimetallic Complexes
No full textUnsymmetric Pentacene- and Pentacenequinone-Fused Porphyrins: Understanding the Effect of Cross- and Linear-Conjugation
No full textUnsymmetric pentacenequinone-fused (cross-conjugated)
and pentacene-fused
(linear-conjugated) porphyrins were designed and synthesized. The
cross-conjugated (AM1–AM3) and linear-conjugated (AM5–AM7) porphyrins displayed strikingly different sets of
optical and electronic properties, both of which are unusual and nontypical
of porphyrins. MCD, DFT, and TDDFT calculations suggest that multiple
charge transfer states exist in both π-conjugated systems, which
contributes to the complex absorption and MCD spectra of these molecular
systems. The general Gouterman’s four-orbital model used to
explain porphyrin spectroscopy led to contradicting theoretical and
experimental data, and is thus not applicable for these molecular
systems. The “2 + 4” and “3 + 3” active
spaces have been deduced and have proven effective to interpret the
absorption and MCD spectra of the pentacenequinone-fused (cross-conjugated)
and pentacene-fused (linear-conjugated) porphyrins, respectively.
Spectroelectrochemistry of AM5–AM7 revealed broad and
intense IR absorptions in the range of 1500–2500 nm, illustrating
the exceptional ability of these pentacene-fused systems to accommodate
positive charges. A pronounced metal effect was observed for pentacene-fused
porphyrins. While pentacene-fused Ni(II) porphyrin (AM6) demonstrated an abnormal ability to stabilize pentacene
with a half-life of >28.3 days, the half-life of the free base
and
Zn(II) counterparts were normal, similar to those of pentacene analogues.
This work provides important and useful information on guiding new
material designs
