Large Faraday Rotation in Optical-Quality Phthalocyanine and Porphyrin Thin Films

Article abstract of DOI:10.1021/jacs.1c02113

The magneto-optical phenomenon known as Faraday rotation involves the rotation of plane-polarized light as it passes through an optical medium in the presence of an external magnetic field oriented parallel to the direction of light propagation. Faraday rotators find applications in optical isolators and magnetic-field imaging technologies. In recent years, organic thin films comprised of polymeric and small-molecule chromophores have demonstrated Verdet constants, which measure the magnitude of rotation at a given magnetic field strength and material thickness, that exceed those found in conventional inorganic crystals. We report herein the thin-film magnetic circular birefringence (MCB) spectra and maximum Verdet constants of several commercially available and newly synthesized phthalocyanine and porphyrin derivatives. Five of these species achieved maximum Verdet constant magnitudes greater than 105 deg T-1 m-1 at wavelengths between 530 and 800 nm. Notably, a newly reported zinc(II) phthalocyanine derivative (ZnPc-OT) reached a Verdet constant of -33 × 104 deg T-1 m-1 at 800 nm, which is among the largest reported for an organic material, especially for an optical-quality thin film. The MCB spectra are consistent with resonance-enhanced Faraday rotation in the region of the Q-band electronic transition common to porphyrin and phthalocyanine derivatives, and the Faraday A-term describes the electronic origin of the magneto-optical activity. Overall, we demonstrate that phthalocyanines and porphyrins are a class of rationally designed magneto-optical materials suitable for applications demanding large Verdet constants and high optical quality.

Full text of DOI:10.1021/jacs.1c02113

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Article
Large Faraday Rotation in Optical-Quality Phthalocyanine and
Porphyrin Thin Films
Zachary Nelson, Leo Delage-Laurin, Martin D. Peeks, and Timothy M. Swager*
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ABSTRACT: The magneto-optical phenomenon known as Fara-
day rotation involves the rotation of plane-polarized light as it
passes through an optical medium in the presence of an external
magnetic field oriented parallel to the direction of light
propagation. Faraday rotators find applications in optical isolators
and magnetic-field imaging technologies. In recent years, organic
thin films comprised of polymeric and small-molecule chromo-
phores have demonstrated Verdet constants, which measure the
magnitude of rotation at a given magnetic field strength and
material thickness, that exceed those found in conventional
inorganic crystals. We report herein the thin-film magnetic circular
birefringence (MCB) spectra and maximum Verdet constants of
several commercially available and newly synthesized phthalocya-
nine and porphyrin derivatives. Five of these species achieved maximum Verdet constant magnitudes greater than 105 deg T−1 m−1 at
wavelengths between 530 and 800 nm. Notably, a newly reported zinc(II) phthalocyanine derivative (ZnPc-OT) reached a Verdet
constant of −33 × 104 deg T−1 m−1 at 800 nm, which is among the largest reported for an organic material, especially for an optical-
quality thin film. The MCB spectra are consistent with resonance-enhanced Faraday rotation in the region of the Q-band electronic
transition common to porphyrin and phthalocyanine derivatives, and the Faraday A-term describes the electronic origin of the
magneto-optical activity. Overall, we demonstrate that phthalocyanines and porphyrins are a class of rationally designed magneto-
optical materials suitable for applications demanding large Verdet constants and high optical quality.
nm to −0.3 × 104 deg T−1 m−1 at 980 nm,5 and is considered
INTRODUCTION
When plane-polarized light passes through any optically
■
the benchmark for Faraday materials.6 Although the high
optical quality, high laser damage threshold, and low
absorptivity of TGG and other inorganic crystals make them
ideal for many applications, future magneto-optical technolo-
gies may demand the lightness, flexibility, tunability, and
processability that are characteristics of many organic
materials. Over the past decade, several organic materials
have matched or exceeded the magneto-optical performance of
TGG by employing a variety of design strategies, including
extended conjugation,5,7−9 helical chromophores,10,11 the
inclusion of paramagnetic dopants,12−16 and spin-forbidden
transitions.17 To date, the largest Verdet constants reported in
organic thin-films are on the order of 105 deg T−1 m−1.7,11,18
However, many high-performance organic Faraday rotators are
not of optical quality because they incorporate light-scattering
transparent material in the presence of a magnetic field
oriented parallel to the direction of propagation, the plane of
polarization will rotate. This magneto-optical phenomenon is
known synonymously as magneto-optical rotation (MOR) and
the Faraday effect, and is caused by magnetically induced
circular birefringence (MCB). It may be described empirically
by the equation below.
φ = VBd
(1)
Here, the magnitude of the rotation φ of plane-polarized
light is proportional to the strength of the magnetic field B, the
path length d, and the wavelength-dependent Verdet constant
V (Figure 1a). Several key magneto-optical technologies rely
on materials with large Verdet constants, including optical
isolators crucial to our telecommunication infrastructure1,2 and
magneto-optical imaging devices used in aircraft fuselage
inspection.3,4 The development of materials with larger Verdet
constants may lead to lighter, less expensive, and more
sensitive instruments.
Received: February 23, 2021
Published: April 27, 2021
The inorganic material terbium gallium garnet (TGG)
exhibits a large Verdet constant across the visible and near-
infrared (IR) spectrum, from −1.0 × 104 deg T−1 m−1 at 532
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to the incident light beam, μx and μy are the electric dipole
moment operators perpendicular to the beam, and Im is the
function which returns the imaginary component of a complex
number. If the excited state is degenerate, then the expression
must be summed over all degenerate transitions j ← n. The
characteristic A-term line shape is shown in Figure 1b.
Crucially, the A-term only arises in electronic transitions
which involve degenerate electronic states that undergo
magnetic field induced Zeeman splitting.
In organic chromophores in the visible and near-IR regions,
degenerate electronic states are mostly limited to high-
symmetry molecules with degenerate frontier molecular
orbitals. The optical transition denoted as the Q-band found
in porphyrins and phthalocyanines fulfills this requirement as a
result of the degeneracy of the LUMOs (Figure 1c), which lead
to degenerate excited states of 1Eu symmetry and a non-
1
degenerate ground state of A1g symmetry. From eq 2, the
magnitude of the Faraday A-term for the Q-band transition
may be expressed as the product of isotropic reduced matrix
elements, as shown by Barron.20
i
1
A(1E ← 1A1) = −
⟨1E || m ||1E⟩|⟨ A1 || μ ||1 E⟩|2
(3)
2 2
The first term is the isotropic reduced magnetic moment of
1
the Eu excited state, and the second term is the isotropic
transition dipole strength. Such analysis has been used for
decades in the interpretation of solution-state magnetic circular
dichroism (MCD) spectra of phthalocyanines and porphyr-
ins.21,22 However, MCB spectra for these species is rarely
measured in the solution state,23,24 and to our knowledge, the
Faraday rotation has not been evaluated in the solid state,
especially in the context of thin-film devices. In this
contribution, we establish porphyrin and phthalocyanine
chromophores as a class of high-performance magneto-optical
materials with large Verdet constants in optical-quality thin
films.
Figure 1. (a) Illustration of the principle of Faraday rotation from a
thin film. (b) The characteristic line shape of the Faraday A-Term for
an arbitrary electronic transition. (c) The main orbital transitions
contributing to the Faraday rotation in the porphyrin and
phthalocyanine Q-band are from the HOMO to degenerate
LUMOs. (TD-DFT: ωB97X-D/6-31G*).
MATERIALS AND METHODS
■
nanoparticles14 or crystalline domains.18 Verdet constants in
optical-quality organic thin films beyond 104 deg T−1 m−1 are
key to realizing low cost and high sensitivity magneto-optical
imaging and future sensing technologies.
The synthetic routes to phthalocyanine derivatives ZnPc-OT, ZnPc-
(R)/(rac)/(S), and CuPc-(R)/(rac)/(S), as well as terbium double-
decker phthalocyanine TbPc2-(rac) are shown in Figure 2. The
bisthianthrene phthalonitrile (1) precursor to ZnPC-OT was
obtained from the addition of 1,2-dimercapto benzene to tetra-
fluorophthalonitrile as previously reported.25 The templated cycliza-
tion of 1 then proceeded under standard conditions26 to give ZnPc-
OT in modest overall yields. Bisalkoxy phthalonitrile (4) was
synthesized in a manner similar to previous reports;27 however,
synthesis of the (R)-enantiomer (4-(R)) is reported for the first time.
In brief, the alkylation of catechol by enantiopure bromo-alkanes
derived from citronellol gave bisalkoxybenzene 2, which was then
brominated twice to give 3. Cyanation of 3 was accomplished by the
Rosemund−von Braun reaction, giving bis-alkoxy phthalonitrile 4.
Phthalocyanine derivatives ZnPc-(R)/(rac)/(S) and CuPc-(R)/
(rac)/(S) were obtained from 4 via templated cyclization in a
manner analogous to previously reported procedures.28 Terbium
double-decker phthalocyanine TbPc2-(rac) only differs from well-
precedented species by the identity of the alkyl side chains and was
synthesized from 4-(rac) in an analogous manner.29 Subpthalocya-
nine SubPc was obtained following previously reported procedures.30
Zinc(II) tetraphenylporphyrin (ZnTPP) and ruthenium(II) tetraphe-
nylporphyrin carbonyl (RuTPP) were used as received from Sigma-
Aldrich. See the Supporting Information for detailed synthetic
methods.
One under-explored route to achieve optical-quality organic
thin films with large Verdet constants leverages the
phenomenon of resonance-enhanced Faraday rotation in
certain small-molecule chromophores. The quantum-mechan-
ical underpinnings of Faraday rotation enhancement near
optical transitions are well described by the equations of
Buckingham and Stephens.19 These equations may be broken
down into three independent terms, the A-, B-, and C-terms,
which when summed are directly proportional to the Verdet
constant at a given wavelength. In diamagnetic organic
materials, the A-term (eq 2) often dominates and guides the
analysis reported in this investigation.
3
dn
A(j ← n) =
[⟨j|m |j⟩ − ⟨n|m |n⟩]Im{⟨n|μ |j⟩⟨j|μ |n⟩}
x y
∑
z
z
n
(2)
In eq 2, the magnitude of the A-term for a transition from
electronic state j ← n is denoted, where dn is the degeneracy of
the ground electronic states, ∑n is the sum over all degenerate
transitions, mz is the magnetic dipole moment operator parallel
Thin films were prepared by being spin-coated onto thin (170
μm) glass substrates from concentrated chloroform solutions (10−20
5
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Figure 2. Synthetic routes to novel phthalocyanine derivatives (a) octathianthrene-substituted zinc pththalocyanine (ZnPc-OT), (b) bisalkyloxy
phthalonitrile (4), and (c) Zn- and Cu-phthalocyanines (ZnPc-(rac)/(R)/(S) and CuPc-(rac)/(R)/(S)) and Tb-double-decker phthalocyanine
(TbPc2-(rac)).
mg mL−1) at a rate of 1000 rpm. Only samples of high optical quality
(cobalt(II) tetraphenylporphyrin, iron(III) tetraphenylpor-
were measured, as evidenced by polarized optical microscopy images
phyrin chloride, and metal-free tetraphenylporphyrin). The
(Leica DMRXP) taken of the thin films in transmission (Figure S1).
MCB and UV−vis spectra of thin films of ZnTPP and RuTPP
The thickness of each thin film was determined using contact
showed large magneto-optical responses in the Q-band region
profilometry (Dektak 6 M Profilometer) or atomic force microscopy
(Figure 3). The maximum absolute value of the Verdet
constant for both species was achieved at the wavelength
corresponding to maximum absorbance, reaching −6 × 104
deg T−1 m−1 at 560 nm for ZnTPP and −24 × 104 deg T−1
m−1 at 530 nm for RuTPP. The characteristic line shape of the
Faraday A-term (cf. Figure 1b) was observed most clearly in
the RuTPP thin film. The more complex line shape observed
in the ZnTPP thin film may be attributed to overlapping A-
term contributions from vibrational replicas of the Q-band,
which were also observed in the solution state MCB spectrum
(Figure S6a). Thermal annealing to 150 °C had little effect on
the magnitude or line shape of the Verdet constant spectra of
RuTPP and ZnTPP thin films (Figure S3a,b), although the
optical quality of the ZnTPP thin film was lowered due to the
formation of scattering crystalline domains (Figure S4b). The
figure-of-merit (FOM), defined as the magnitude of the
Faraday rotation (deg T−1) divided by the absorbance
(unitless) at a given wavelength, reached 0.052 deg T−1 in
RuTPP thin films. Although this FOM value is smaller than is
observed in many inorganic crystals such as TGG, the larger
Verdet constant and fabrication advantages of RuTPP make it
an especially attractive material in technologies in which the
use of short optical path lengths minimize absorption, such as
magneto-optical imaging.
(Nanoscope V with Dimension 3100) and ranged from 65 to 320 nm.
Thermal annealing was conducted using a Linkam TMS 94 hot stage
with the following temperature profile: heated from room temperature
to 150 °C at 30 °C min−1 and then cooled to room temperature at 1
°C min−1 under an ambient atmosphere. MCB and UV−vis spectra
were obtained from a home-built measurement system based on
established designs.14,17,31 At each wavelength, the magnitude and
sign of the rotation of plane polarized light was measured at five
different magnetic field strengths ranging from −0.5 to 0.5 T to
ensure a linear response consistent with eq 1. The performance of the
system was validated using reference samples of BK7 glass and TGG,
giving values consistent with those found in the literature.5 The
spectrometer is fully described in the Supporting Information.
RESULTS AND DISCUSSION
■
Two metal tetraphenylporphyrin (TPP) derivatives, zinc(II)
tetraphenylporphyrin (ZnTPP) and ruthenium(II) tetraphe-
nylporphyrin carbonyl (RuTPP), produced optical-quality thin
films and also displayed large Verdet constants (Figure 3).
Other metal tetraphenylporphyrin derivatives were screened,
but these either did not form optical quality films as a result of
crystallization or poor surface coverage (nickel(II) tetraphe-
nylporphyrin and metal-free tetrakis(pentafluorophenyl)-
porphyrin), or their apparent Verdet constants were below
the detection limit of our instrument (ca. 1 × 104 deg T−1 m−1
for ∼100 nm thin films) in the region of the Q-band
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Figure 4. (a) Chemical structure and (b) Faraday rotation and
absorbance spectra of a SubPc thin film.
lower symmetry (C3v) than their phthalocyanine and
porphyrin counterparts (D4h generally), they contain formally
degenerate frontier molecular orbitals similar to those found in
metal porphyrins (Figure S13).32 This leads to the analogous
electronic state diagrams in subphthalocyanines, resulting in
comparable Faraday rotation.
The synthetic flexibility of the phthalocyanine core structure
enabled us to study the effects of side-chain chirality and the
presence of paramagnetic metal centers on the magneto-optical
performance of their thin films. Previous studies of Faraday
rotation have demonstrated the impact of appended chiral side
chains in organic thin-film magneto-optical materials on both
the sign and magnitude of the Faraday rotation; however, the
magneto-optical responses of these systems were not attributed
to Faraday A-term mechanisms.10,11,17 As shown in Figure 5a−
b, for ZnPc and CuPc derivatives, the line shape of the MCB
spectrum in the region surrounding the Q-band is consistent
with a Faraday A-term. However, the appended chiral side
chains had little effect on the magnitude, line shape, or sign of
the Faraday rotation of diamagnetic zinc(II) phthalocyanine
derivatives ZnPc-(R), ZnPc-(S), and ZnPc-(rac). The largest
apparent effect is found in minor variations in the Verdet
constant maxima, which range from −9.0 × 104 deg T−1 m−1 in
ZnPc-(S) to −15.2 × 104 deg T−1 m−1 in ZnPc-(R) at 640
nm. The effect of chiral side chain substitution was also small
in copper(II) phthalocyanine derivatives CuPc-(R), CuPc-(S),
and CuPc-(rac), ranging from −6.2 × 104 deg T−1 m−1 in
CuPc-(rac) to −10.6 × 104 deg T−1 m−1 in CuPc-(S) at 630
nm. Thermal annealing of ZnPc-(R), ZnPc-(S), and ZnPc-
(rac) thin films induced partial crystallization as evidenced by
polarized optical microscopy (Figure S4d−f). As a result, the
Figure 3. (a) Chemical structures and Faraday rotation and
absorbance spectra of (b) ZnTPP and (c) RuTPP thin films.
The subphthalocyanine derivative SubPc also formed optical
quality thin films when it was spin-coated from concentrated
chloroform solutions. The solubility of SubPc and the optical
clarity of its thin films were enhanced by the inclusion of bulky
thioarene solubilizing groups (Figure 4a). These films achieved
a maximum Verdet constant of −11 × 104 deg T−1 m−1 at 650
nm and displayed the characteristic A-term line shape centered
at the subphthalocyanine Q-band transition (Figure 4b).
Neither the Faraday rotation nor the optical quality of SubPc
thin films were impacted when thermally annealed (Figures
S3c and S4c). Although subphthalocyanine derivatives are of
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Figure 5. Faraday rotation and absorbance spectra of (a) ZnPc-(R)/(S)/(rac), (b) CuPc-(R)/(S)/(rac), (c) TbPc2-(rac), and (d) ZnPc-OT thin
films.
optical quality of the thin films was lowered, and the maximum
Verdet constants decreased to −4.4−9.9 × 104 deg T−1 m−1
(Figure S3d−f). Overall, the effect of thermal annealing on the
MO activity was consistent between the enantiomers and the
racemic mixture. These results suggest that remote chirality
(via side chain introduction) does not strongly contribute to
Faraday rotation in materials in which the Faraday A-term
dominates. Presumably, the perturbation of the π and π*
molecular orbitals which contribute to the Faraday A-term
(Figure 1c) by the remote chiral centers is small. Additionally,
the Faraday A-term mechanism is thought to be insensitive to
chirality, and any MO activity resulting from magnetochiral
dichroism (MChD) or birefringence (MChB) should be both
small and not detectable with the spectrometer used in this
experiment.20
Substitution of a diamagnetic metal ion with a paramagnetic
metal ion at the center of phthalocyanine allowed us to study
the impact of spin magnetic moments due to unpaired
electrons on the magneto-optical properties of phthalocyanine
thin films. Studies of Faraday rotation in other organic thin
films have suggested that the presence of paramagnetic species
enhances the magneto-optical activity of adjacent polymeric
chromophores.11,12 The substitution of diamagnetic zinc(II)
with paramagnetic copper(II) had little effect on the
magnitude of the Faraday rotation as demonstrated in Figure
5a−b, with a range of −9.0−15.2 × 104 deg T−1 m−1 in ZnPc-
(R)/(S)/(rac) and −6.2−10.6 × 104 deg T−1 m−1 in CuPc-
(R)/(S)/(rac). This difference, even if treated as significant,
was much smaller than that observed in previously mentioned
polymeric systems.11,12 However, the observed Faraday
rotation in the polymeric systems displaying a paramagnetic
enhancement was not consistent with the Faraday A-term line
shape, and eq 3 does not include a term for the ground state
magnetic moment of the chromophore. Ground state magnetic
moments are instead expected to influence Faraday rotation in
materials with resonance enhancement due to Faraday C-term
mechanisms, which require degenerate electronic ground
states. The π to π* transitions which are responsible for the
Q-band are confined to the phthalocyanine ligand, and do not
posess degenerate electronic ground states. The absence of a
large paramagnetic effect on the magneto-optical performance
of the phthalocyanine chromophore is consistent with our
assignment of the A-term mechanism as the dominant factor
giving rise to Faraday rotation in phthalocyanine derivatives.
Phthalocyanine lanthanide complexes are also of interest for
the study of Faraday rotation, as they incorporate highly
polarizable metal centers containing high numbers of unpaired
electrons. Some multidecker Pc structures have even been
shown to act as single-molecule magnets,33 presenting
thermally activated magnetic relaxation with relatively high
effective barriers. Similar features, namely, high polarizability,
numerous unpaired spins, and magnetic ordering, are found in
the highest performance inorganic garnets, such as TGG. With
this in mind, the terbium double-decker phthalocyanine
complex TbPc2-(rac) was targeted, and the recorded MCB
spectrum is shown in Figure 5c. The 320 nm thick thin film of
TbPc2-(rac) achieved a maximum Verdet constant of −7.3 ×
104 deg T−1 m−1 at 680 nm, with a line shape consistent with
the Faraday A-term. This value is similar to other transition
metal phthalocyanines reported in this work. Therefore, it can
be concluded that proximity of a polarizable and spin-rich
lanthanide ion does not greatly perturb the π-electron system
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of the phthalocyanine ligands, at least not in a manner which
affects the resonance-enhanced Faraday rotation associated
with the Q-band of phthalocyanines. As in CuPc, this result
highlights the primacy of the π-electron system of the
phthalocyanine ligand in determining the Faraday rotation of
the material.
Table 1. Measured Verdet constants and Figures-of-Merit
for Phthalocyanine, Subphthalocyanine, and Porphyrin
Derivatives
λmax
Faraday
Rotation
(nm)
Verdet Constant
a
× 104
Figure of Merit
(deg T−1
Entry Species
(deg T−1 m−1
)
)
In contrast, increased substitution at the periphery of the
phthalocyanine core in octathianthrene-substituted zinc
phthalocyanine ZnPc-OT led to a Verdet constant of −33 ×
104 deg T−1 m−1 at 800 nm, which is among the largest
reported Verdet constants for an organic material. The
observed line shape supports a Faraday A-term origin (Figure
5d). The pronounced redshift in the Q-band absorption is
consistent with behavior observed in other phthalocyanines
having substitution at the “inner” sites34 and is thought to arise
from sterically induced twisting of the chromophore’s π-
electron system.35 The figure-of-merit value of −0.046 deg T−1
was smaller in magnitude for ZnPc-OT than that for both
ZnPc-(R) and ZnPc-(rac), indicating that optical absorption
and magneto-optical activity increase simultaneously in this
system. This observation is consistent with eq 3, in that, the
magnitude of the Faraday A-term is proportional to the
magnitude of the electric transition dipole moment. Thin films
of ZnPc-OT formed microscopic cracks when subjected to
thermal annealing, lowering their optical-quality and Verdet
constant (Figures S3g and S4g). The combination of large
magneto-optical activity, near-infrared absorption, good
optical-quality thin films, and simple preparation make
ZnPc-OT an attractive candidate for incorporation into
magneto-optical devices wherein low optical density is not a
requirement.
1
2
3
RuTPP
ZnTPP
CuPc-
(S)
CuPc-
(rac)
CuPc-
(R)
ZnPc-
(S)
ZnPc-
(rac)
ZnPc-
(R)
SubPc
TbPc2-
(rac)
530
560
620
−24.2 2.9
−6.2 0.7
−10.6 1.4
−0.05210 0.0007
−0.01915 0.0006
−0.05278 0.0011
4
5
6
7
8
620
630
640
640
640
−6.2 0.6
−9.9 1.1
−9.0 0.9
−14.1 1.6
−15.2 1.8
−0.03873 0.0015
−0.05316 0.0012
−0.04785 0.0012
−0.06981 0.0014
−0.06897 0.0014
9
10
650
680
−11.1 0.7
−7.3 1.2
−0.03497 0.0004
−0.05520 0.0030
11
ZnPc-
OT
800
−33.1 2.6
−0.04615 0.0005
a
Defined as Faraday rotation divided by absorbance.
coating, such as hot-pressing or blade-coating, are ongoing.
Given the massive structural diversity of phthalocyanines and
porphyrins in the literature, there are abundant opportunities
to create high-performance Faraday rotator materials from
these structures.
CONCLUSION
■
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.1c02113.
■
In summary, our investigation of 11 porphyrin, subphthalo-
cyanine, and phthalocyanine derivatives demonstrates the
rational tunability of the large magneto-optical response
observed in a series of electronically similar chromophores.
The key magneto-optical properties of these optical-quality
thin films are summarized in Table 1. The spectral coverage of
the species that were studied spans much of the visible and
near-infrared regions, bookended by RuTPP and ZnPc-OT,
which reached maximum absolute Verdet constants of −24 ×
104 deg T−1 m−1 at 530 nm and −33 × 104 deg T−1 m−1 at 800
nm, respectively. Five other species in this study also achieved
maximum absolute Verdet constants greater than 105 deg T−1
m−1, which is comparable to those of other high-performance
thin-film Faraday rotator materials. The origin of the large
magneto-optical response is attributed to Faraday A-term
resonance enhancement associated with the degenerate
electronic transitions that are responsible for the Q-band in
porphyrins, subphthalocyanines, and phthalocyanines. Chem-
ical modifications of the chromophore cores, like the addition
of chiral side chains and the introduction of paramagnetic
metal centers, were shown to have little effect on the
magnitude of the maximum Verdet constant. However, both
the introduction of different metal centers in tetraphenyl
porphyrin derivatives and increased peripheral substitution in a
phthalocyanine derivative made significant impacts on the
magnitude of the Verdet constant. The maximum thin film
thickness of 320 nm achieved here by TbPc2-(rac) was less
than the 1 to 5 μm typical for applications of MO thin
films,3,4,36 such as those in magneto optical imaging. Efforts to
fabricate thicker films using alternative techniques to spin-
sı
Experimental procedures, details of the characterization
of the chromophores and synthetic intermediates, details
of the Faraday rotation measurement and instrument,
theoretical calculations, UV−vis, H and 13C NMR, and
1
MALDI mass spectra (PDF)
AUTHOR INFORMATION
Corresponding Author
■
Timothy M. Swager − Department of Chemistry,
Massachusetts Institute of Technology, Cambridge,
Massachusetts 02139, United States; orcid.org/0000-
0002-3577-0510; Email: tswager@mit.edu
Authors
Zachary Nelson − Department of Chemistry, Massachusetts
Institute of Technology, Cambridge, Massachusetts 02139,
United States; orcid.org/0000-0002-3949-682X
Leo Delage-Laurin − Department of Chemistry, Massachusetts
Institute of Technology, Cambridge, Massachusetts 02139,
United States; orcid.org/0000-0002-9174-5416
Martin D. Peeks − Department of Chemistry, Massachusetts
Institute of Technology, Cambridge, Massachusetts 02139,
United States; School of Chemistry, University of New South
Wales, Sydney, NSW 2052, Australia; orcid.org/0000-
0002-9057-9444
Complete contact information is available at:
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Composites with Tunable Magneto-Optical Activity: Role of
Nanoparticle Dispersion for High Verdet Constant Materials. J.
Mater. Chem. C 2020, 8 (16), 5417−5425.
https://pubs.acs.org/10.1021/jacs.1c02113
Notes
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This research was funded by the Air Force Office of Scientific
Research grant: 17RT0904; FA9550-18-1-0341.
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