Self‐assembled nanomaterials based on complementary sn(Iv) and zn(ii)‐porphyrins, and their photocatalytic degradation for rhodamine b dye

Article abstract of DOI:10.3390/molecules26123598

A series of porphyrin triads (1–6), based on the reaction of trans‐dihydroxo‐[5,15‐bis(3‐ pyridyl)‐10,20‐bis(phenyl)porphyrinato]tin(IV) (SnP) with six different phenoxy Zn(II)‐porphyrins (ZnLⁿ), was synthesized. The cooperative metal–ligand co

Full text of DOI:10.3390/molecules26123598

molecules
Article
Self-Assembled Nanomaterials Based on Complementary
Sn(IV) and Zn(II)-Porphyrins, and Their Photocatalytic
Degradation for Rhodamine B Dye
Nirmal K. Shee and Hee-Joon Kim *
Department of Applied Chemistry, Kumoh National Institute of Technology, Gumi 39177, Korea;
nirmalshee@gmail.com
* Correspondence: hjk@kumoh.ac.kr; Tel.: +82-54-478-7822
Abstract: A series of porphyrin triads (
pyridyl)-10,20-bis(phenyl)porphyrinato]tin(IV) (SnP) with six different phenoxy Zn(II)-porphyrins
ZnLn), was synthesized. The cooperative metal–ligand coordination of 3-pyridyl nitrogens in
1–6), based on the reaction of trans-dihydroxo-[5,15-bis(3-
(
the SnP with the phenoxy Zn(II)-porphyrins, followed by the self-assembly process, leads to the
formation of nanostructures. The red-shifts and remarkable broadening of the absorption bands in
the UV–vis spectra for the triads in CHCl3 indicate that nanoaggregates may be produced in the self-
assembly process of these triads. The emission intensities of the triads were also significantly reduced
due to the aggregation. Microscopic analyses of the nanostructures of the triads reveal differences
due to the different substituents on the axial Zn(II)-porphyrin moieties. All these nanomaterials
exhibited efficient photocatalytic performances in the degradation of rhodamine B (RhB) dye under
visible light irradiation, and the degradation efficiencies of RhB in aqueous solution were observed to
be 72~95% within 4 h. In addition, the efficiency of the catalyst was not impaired, showing excellent
recyclability even after being applied for the degradation of RhB in up to five cycles.
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Citation: Shee, N.K.; Kim, H.-J.
Self-Assembled Nanomaterials Based
on Complementary Sn(IV) and
Zn(II)-Porphyrins, and Their
Photocatalytic Degradation for
Rhodamine B Dye. Molecules 2021, 26,
3598. https://doi.org/10.3390/
molecules26123598
Keywords: complementary porphyrins; self-assembly; nanomaterial; photocatalytic degradation
Academic Editors: M. Graça P. M.
S. Neves, M. Amparo F. Faustino and
Nuno M. M. Moura
1. Introduction
Over the past two decades, nanomaterials have drawn the attention of material
chemistry researchers due to their extensive applicability in various fields, including catal-
ysis, solar energy conversion and storage, molecular recognition, sensing, and cancer
Received: 30 April 2021
Accepted: 9 June 2021
Published: 11 June 2021
treatment [
of materials, which include high electrical conductivity, excellent optoelectronics, and
corrosion resistance [ ]. There is no doubt that these highly ordered nanostructures
1–5]. These compounds have been widely used to improve the properties
6–8
exhibit tremendously useful features, including large surface areas, various chemical and
physical properties, as well as high thermal stability, compared to their parent compo-
nents. Therefore, the design and fabrication of these novel nano- and microstructured
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iations.
materials are important to their technological utility [
blocks have been used to endow the desired nanostructures with well-defined shapes and
dimensions [11 13]. Porphyrin compounds (free porphyrins or metalloporphyrins) are one
of the building blocks used for the construction of self-assembled functional nanomaterials
that possess a charge-transfer function and enhanced light-harvesting properties [14 17].
9,10]. A large number of building
–
–
Copyright:
© 2021 by the authors.
The porphyrinoid compounds form large-scale aggregates in solution via the self-assembly
process. The morphology of these structures is not always regular or suitable for many
practical applications. Thus, the construction of well-defined nanostructures from the
porphyrins with definite sizes, dimensions, and shapes is a formidable assignment. Various
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Attribution (CC BY) license (https://
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4.0/).
intermolecular non-covalent interactions (e.g., hydrogen bonding, ligand coordination,
interaction, electrostatics, van der Waals force, as well as hydrophobic and hydrophilic ef-
fects) are mainly responsible for the self-assembly of porphyrins [18 22]. Various methods,
π–π
–
Molecules 2021, 26, 3598. https://doi.org/10.3390/molecules26123598
https://www.mdpi.com/journal/molecules

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including re-precipitation, ionic self-assembly, metal–ligand coordination, sonication, and
surfactant-assisted methods, have been used for the fabrication of well-defined discrete
self-assembled porphyrin nanostructures [23–27].
Nowadays, among other metalloporphyrins, Sn(IV)-porphyrins are widely used as
a building block in the construction of functional porphyrin nanoaggregates, including
nanotubes, nanofibers, nanosheets, nanocomposites, and nanorods [28
tructures have been widely used for the photocatalytic degradation of organic dyes in an
aqueous solution, and the production of hydrogen gas under visible-light irradiation [33 34].
–32]. These nanos-
,
Sn(IV)-porphyrins are ideal scaffolds, as they can readily form stable six-coordinate com-
plexes with two trans-axial oxyanion ligands, such as carboxylates and alkoxides, due to the
oxophilic nature of the Sn(IV) center. In addition, these complexes have attractive optical
properties and are diamagnetic, meaning that structural information can be obtained from
the NMR-active Sn nuclei [35–39].
We are interested in the self-assembly of nanostructures based on combinations of
complementary hetero-metalloporphyrins, such as oxophilic Sn(IV)-porphyrins and nitro-
gen donor-ligating Zn(II)-porphyrins. Recently, we reported that metal–ligand cooperative
coordination between a pyridyl Sn(IV)-porphyrin and the phenoxy Zn(II)-porphyrins suc-
cessfully formed relevant triads, which were easily self-assembled into nanomaterials when
in non-coordinating solvents [40]. Here, we present six triads (Scheme 1) obtained from
the reaction of trans-dihydroxo-[5,15-bis(3-pyridyl)-10,20-bis(phenyl)porphyrinato]tin(IV)
(
SnP) with six different phenoxy Zn(II)-porphyrins (ZnLn). We explored the self-assembled
nanostructures of these triads with various substituents and utilized these materials for the
photocatalytic degradation of organic dye rhodamine B in an aqueous solution.
Scheme 1. Chemical structures of triads 1–6 and dye used in this study.

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2. Results and Discussion
2.1. Syntheses
We used the complementary coordination approach for the synthesis of these triads
(Scheme 2). The strong tendency of Sn(IV)-porphyrin to form bonds with aryloxides
drove the formation of stable porphyrin arrays [40–43]. All six triads were synthesized
by refluxing corresponding Zn(II) complexes of mono-hydroxyphenyl porphyrin with
trans-(dihydroxo)Sn(IV)-porphyrins SnP in anhydrous toluene for 48 h under an inert Ar
atmosphere. The average yields after proper work-up processes were 80% or higher. All
the synthesized compounds were fully characterized by various spectroscopic techniques,
including elemental analysis, 1H-NMR, UV–vis spectroscopy, fluorescence spectroscopy,
ESI-mass spectrometry, and scanning electron microscopy (SEM).
Scheme 2. Scheme for the synthesis of triads 1–6.
2.2. Spectroscopic Characterization
1
The H-NMR spectra of all six diamagnetic triads (
1–
6) along with the individual
unconnected monomers (free and Zn(II) porphyrin complexes) are shown in the Supple-
mentary Materials (Figures S1–S18). From the 1H-NMR spectra of six triads, it is clear that
the resonance positions of the
Sn(IV)-porphyrin are very similar to those of the starting SnP [Sn(OH)2(DPyDPP)] [40
The -pyrrolic protons of the triads appeared between 9.05 ppm and 9.17 ppm, whereas the
β-pyrrolic protons or the aromatic protons of the central
,
41].
β
protons at the pyridyl rings (H2,6-Py) appeared at ~9.55 ppm and ~9.28 ppm, respectively.
Other aromatic protons of the central Sn(IV)-porphyrin appeared at ~8.10 ppm. On the
other hand, due to the strong ring current effect of the central Sn(IV)-porphyrins, the reso-
nance positions and the splitting patterns of the axial Zn(II)-porphyrins were different from
those of the monomeric Zn(II)-porphyrins. The aryloxy protons appeared in monomeric
Zn(II)-porphyrins at ~7.17 and ~7.96 ppm (except for ZnL6, which appeared at ~7.23 and
8.20 ppm) as two set of doublets, respectively. When in triads, these two protons experience
a strong shielding effect caused by the ring current of the central Sn(IV)-porphyrins. These
protons resonated as two doublets at 2.62–2.70 and 6.65–6.80 ppm, respectively. The ∆δ
values (i.e.,
A similar kind of shielding effect was observed for the
porphyrins unit in triads compared to that seen in the monomeric Zn(II) complexes. The
δ
(
ZnLn)–
δ(triad)) of these protons were ~4.60 and ~1.30 ppm, respectively.
β–pyrrole protons of the axial

Molecules 2021, 26, 3598
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signals for the
β–pyrrole protons of the monomeric Zn(II)-porphyrins appeared at ~8.8 ppm
and ~8.9 ppm. These protons in the triads were shifted to the upfield zone and split into a
singlet at ~ 8.75 ppm, along with a pair of doublets at ~8.55 and ~8.40 ppm, respectively.
The 1H-NMR technique considers the interaction of the protons in axial porphyrins with
the central Sn(IV)-porphyrin, and manifests the ring current-induced shifts and resonance
couplings [40
,
41]. As such, this method has been extensively used in the literature to
43]. The electro-
explore the axial bonding-type architecture of similar compounds [40
–
spray ionization mass spectra (ESI-MS) of all the six triads are shown in Supplementary
Figures S19–S24. For each triad, we observed parent peaks at 769.13, corresponding to
[SnP(H)]+. However, a low-intensity molecular ion peak was also found for all six triads.
It is thus clear that all the compounds were fragmented during the mass spectrometry
experiments [40].
The UV–visible spectra of all six triads in the CHCl3 solution are depicted in Figure 1
along with an SnP spectrum for comparison. The peak positions, molar extinction co-
efficients ( ), and maximum absorbance (λmax) of all compounds, including monomeric
,
ε
Zn(II)-porphyrins, are reported in the experimental section.
Figure 1. UV–visible spectra of triads 1–6 and SnP in CHCl3.
All the monomeric Zn(II)-porphyrins showed a Soret band at ~421 nm and Q-bands
at ~548 and ~586 nm. The SnP also exhibited a Soret band at ~425 nm and Q-bands at
~558 and ~598 nm. The spectra obtained for the triads are different. Generally, the molar
extinction coefficient, as well as the peak position (λmax) values, of these triads are very
close to those of the total parent monomeric porphyrin units [40
of compounds show minimal perturbation in response to the minimal interactions between
the electronic structures of the discrete macrocyclic -systems. In our case, these spectra
–43]. In general, these types
π
are noticeably broad in the Soret band region (~380 nm to ~550 nm), with a red-shift (λmax
~455 nm) comparable to the corresponding monomeric units. In addition, the Q-bands
were red-shifted, with λmax values of ~578 nm and ~618 nm. These red-shifts and the
noticeable broadening of the absorption bands indicate that aggregation is possible in the
self-assembly process of these triads in solution [40]. Due to the different substituents on
the monomeric Zn(II)-porphyrins, small variations were observed in the spectral features
of these triads.

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The steady-state fluorescence spectra of all six triads and of SnP were recorded in
CHCl3, and are illustrated in Figure 2. The SnP gave two-banded fluorescence spectra
(
λext = 550 nm), with the emission maxima appearing at 610 and 656 nm. All the triads also
exhibited similar two-banded fluorescence spectra (λext = 550 nm), with the emission max-
ima appearing at 597 and 647 nm. The peak-to-peak intensity ratio decreased between the
SnP and the triad. The emission intensity of the triads was significantly reduced due to the
aggregation, and the patterns mostly depend on the substituents on the axial porphyrins.
Figure 2. Fluorescence spectra of triads 1–6 and SnP in CHCl3. The optical density (OD) of each
sample solution was fixed at 0.20.
2.3. Supramolecular Self-Assembly to Nanostructures
The self-assembly identity of all the compounds was analyzed via SEM. For sample
preparation, each compound was suspended in toluene at a fixed concentration (c = 1 mM)
and was centrifuged at 13,500 rpm for 10 s. Then, we drop-cast the solution on the surface
of copper tape for deposition, followed by drying in air. After deposition, a Pt coating was
required before the SEM could be carried out. All six triads assembled into nanoaggre-
gates and their morphologies are displayed in Figure 3 and Supplementary Figure S25.
Nanoflakes of different sizes were observed for triad
1 (Figure 3a and Supplementary
Figure S25a). These nearly spherical, spongy nanoflakes were interconnected indiscrim-
inately. The particle sizes were in the range of 100–500 nm (the population of smaller
particles was greater than bigger). A mixture of flake-shaped nano-aggregates was also
found for triad
arated. The lengths of these flakes ranged from approximately 150 nm to 1
width. In the case of triad , distinct and bigger nanoparticles were formed (Figure 3c
and Figure S25c). These stone-like particles were 300~800 nm in length and 150 nm in
width. Triad formed a petal-shaped nanostructure with the approximate dimensions
of 750 nm to 3 m, with a 200 nm width (Figure 3d and Supplementary Figure S25d).
Flower-shaped nanoaggregates were observed for triad (Figure 3e and Supplementary
2
(Figure 3b and Supplementary Figure S25b), but these particles were sep-
µm, with 50 nm
3
4
µ
5
Figure S25e). Finally, a nearly spherical nanostructure (closely packed) arose in the case of
triad 6 (Figure 3f and Supplementary Figure S25f), and these spheres were interconnected.
These particles were approximately 80 nm to 150 nm long.

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Figure 3. High-resolution FE-SEM (field emission scanning electron microscope) images for the
assembly patterns of triads: (a) 1; (b) 2; (c) 3; (d) 4; (e) 5; (f) 6.
Porphyrin molecules aggregate into nanostructures via self-assembly processes. Var-
ious interactions, including hydrogen bonding, π–π stacking, van der Waals forces, and
ligand coordination are responsible for this self-assembly process. Previously, we used
meso-[5-(4-hydroxyphenyl)-10,15,20-tris(3,5-di-tert-butylphenyl)porphyrinato]zinc(II) as
the source of axial porphyrins, leading to the creation of nanofibers [40]. It has been
suggested that the pyridyl groups in Sn(IV)-porphyrin probably coordinated with the
Zn ion in the axial Zn(II)-porphyrin intramolecularly. This coordination can prevent the
movement of the axial porphyrins, which facilitates the self-assembly processes. All the
triad molecules formed nanostructures via π–π stacking interactions between adjacent
porphyrin molecules through face-to-face-type interactions. Similarly, we observed dif-
ferent morphologies depending on the substituents on the axial Zn(II)-porphyrins. With
varying the substituent at the 4-position from H to Me and again to tBu, the features of the
nanoaggregates were also changed (Figure 3a–c). The nanoparticles were well separated,
and their sizes increased. The particle boundaries are clearly visible. It should be also
noted that the starting porphyrin monomer, either SnP or ZnLn, displayed no aggregation
under the present conditions [40].
On the other hand, triads
showed markedly different morphologies from triads
interactions based on their hetero-atomic functional groups may particularly contribute to
4
,
5
, and
6
possessing hetero-atomic functional groups,
1,
2
, and . The supramolecular
3

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constructing the nanostructured porphyrin assemblies. The halogen–halogen interaction
has been recently studied in the self-assembly of metalloporphyrins [44].
2.4. Photocatalysis for the Degradation of Rhodamine B (RhB) Dye
Our planet suffers from pollution resulting from meeting the needs of industry. Tex-
tile, leather, drugs and paper printing processes discharge large quantities of dye into
water ecosystems and damage the environment as a whole. Rhodamine B was one of the
20 dyes detected most frequently in wastewater, and it causes irritation to the skin, eyes,
gastrointestinal tract, and respiratory system. As such, there is an urgent need to remove
this dye from wastewater [45]. We have evaluated the photocatalytic activities of these
nanostructured materials under visible light irradiation for their ability to degrade RhB
dye in an aqueous solution. The minimal decay of RhB dye was observed in the absence
of visible light or any of the nanomaterials 1–6. Thus, visible light was determined to
be essential to the photocatalytic properties of all these porphyrin nanoaggregates. Each
experiment was performed with a 30 min delay after mixing the nanostructures and RhB
in the dark to reach an adsorption–desorption equilibrium between the photocatalyst and
RhB. Mass spectra were taken after 4 h for each experiment. New peaks (corresponding to
some small molecules) in the mass spectra compared to RhB indicated that the RhB was
successfully degraded in the presence of visible light irradiation and the photo-catalyst.
The degradation process was monitored by UV–vis spectroscopy. The time-dependent
absorption spectra of the aqueous RhB solution in the presence of nanostructures derived
from triad
3 under visible light irradiation are shown in Figure S26. Decreasing the ab-
sorption peak intensity at 554 nm over time caused the photocatalytic degradation of RhB.
Figure 4 shows the C/C0 versus time plot of RhB in the presence of various triad-based
nanomaterials. A negligible degradation of the RhB dyes with the starting porphyrin
monomer SnP or ZnLn was observed under the present experimental conditions.
Figure 4. Photocatalytic degradation of RhB dye by six triads in aqueous solution (pH 7, temperature
298 K) under visible light irradiation.
Figure 4 shows that all the nanomaterials were active in the photodegradation of RhB
in an aqueous solution. The degradation of RhB dye can be described by its degradation
efficiency, (C0
at time t. The observed degradation rates of RhB are 89%, 91%, 94%, 84%, 72%, and 79% for
the nanostructures derived from triads , and , respectively. The photocatalytic
−
C)/C0, where C0 is the initial concentration of RhB and C is the concentration
1,
2,
3,
4
,
5
6

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degradation efficiency of RhB dye in aqueous solution under visible light irradiation can
be ranked as follows:
3 > 2 > 1 > 4 > 6 > 5. Therefore, the nanoaggregates obtained from
triad show the best performance for the photocatalytic degradation of RhB. To further
3
interpret the reaction kinetics involved in the decomposition of RhB dye, we used the
pseudo-first-order model, as expressed by equation ln(C0/C) = kt, which is normally used
for photocatalytic degradation experiments in which the initial concentration of pollutant
or dye is low, where k is the pseudo-first-order rate constant. Based on the data plotted in
Figure 4, Figure S27 represents the reaction kinetics of RhB decomposition. The first-order
rate constant for the degradation of RhB by triad
3
(0.010 min−1) is higher than that for triad
(0.007 min−1), triad (0.006 min−1), and triad
(0.005 min−1). These values are impressive compared to other values in the literature [45].
2
5
(0.009 min−1), triad
1
(0.008 min−1), triad
4
6
The recovery of these photocatalysts was very simple; we filtered the reaction mixture after
the experiments and then washed it with water, followed by drying in air. Previously, we
demonstrated that these catalysts were stable enough for further use (confirmed via the
PXRD data after and before the reaction) [40]. Furthermore, the efficiency of the catalyst
was not impaired, and showed excellent recyclability even after using it for the degradation
of RhB in up to five cycles (Supplementary Figure S28).
A possible mechanism for the photocatalytic degradation of the RhB dye by porphyrin
nanomaterials in an aqueous solution has previously been given [40,45]. When these
nanomaterials are subjected to visible light irradiation along with RhB, the porphyrin
nanomaterials absorb light, and the valence band (VB) electrons are elevated to the con-
duction band (CB) after crossing the bandgap. This causes the generation of electron–hole
pairs (e−/h+) on the surfaces of the photo-catalysts. A strong intermolecular
π electronic
coupling occurs between the vicinal aggregations of these nanostructures. This can am-
plify the electronic delocalization occurring in the nanostructures that are held by strong
intermolecular π–π interactions. The excited electrons in the conduction band may move
without any constraint through the nanostructures. Therefore, the generated e−/h+ pairs
were successfully isolated, and their recombination energy was significantly minimized.
Hydroxyl radical (•OH) was produced by the reaction between photo-generated e−/h+
−
pairs and H2O or OH in the VB. On the other hand, the excited electrons in the CB interact
with the dissolved oxygen in the water to form superoxide radical anions (O2−•). These
photo-generated superoxide radical anions interact with H2O or OH− to form hydroxyl
radicals again. These highly active hydroxyl radical species oxidize the RhB molecules
until they become degraded products on the surfaces of the photo-catalysts [46]. To detect
the presence of hydroxyl radical during the photodegradation of RhB, we used coumarin
as a radical scavenger. We repeated our degradation experiment with our catalyst in
the presence of coumarin and irradiated the mixture with visible light for 30 min. After
that, the fluorescences of the solutions excited at 325 nm were measured. We observed
an intense peak at 460 nm compared to the coumarin (~400 nm). This result confirms
that •OH radicals were generated and reacted with coumarin to form a highly fluorescent
7-hydroxycoumarin (Supplementary Figures S29 and S30). In the presence of coumarin,
the degradation efficiency of RhB drastically decreased. This suggests that a portion of
the hydroxyl radicals was removed by coumarin to form 7-hydroxycoumarin, and the rest
reacted with RhB until decomposition [47]. Similarly, for the detection of the superoxide
radical anion, we used hydroethidine as a fluorescent probe. Upon reaction with the
superoxide radical anion, hydroethidine (blue fluorescent) underwent oxygenation to form
2-hydroxyethidium (red fluorescent) (Figure S29) and showed a bright “turn-on” fluores-
cence at 610 nm [48]. A negative response to the ADPA (anthracene-9,10-dipropionic acid
disodium salt) fluorescence test confirmed that singlet oxygen species were not generated
during the degradation reaction [47].
3. Conclusions
In summary, six Zn(II)-Sn(IV)-Zn(II) porphyrin triads were synthesized via the com-
plementary coordination approach. The cooperative metal–ligand coordination of the

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3-pyridyl nitrogen in the Sn(IV)-porphyrin with the phenoxy Zn(II)-porphyrins, followed
by the self-assembly process, determines the formation of these nanostructures. These
triads formed different nanostructures due to the different substituents present on the axial
Zn(II)-porphyrin moieties. Various types of interaction, including π–π stacking, Van der
Waals forces, halogen–halogen interactions, and repulsions among electronegative atoms
can contribute to the self-assembly of nanomaterials. These nanoaggregates also displayed
efficient photocatalytic performances for the degradation of RhB dyes under visible light
irradiation. The rate of the degradation of RhB by these nanomaterials in an aqueous solu-
tion varied from 72% to 95% within 4 h. The degree of self-assembly is mainly governed by
the substituents on the triads, and reflects the photocatalytic performances. Our study sug-
gests that the efficient photocatalytic performance of nanostructured porphyrin assemblies
can be achieved by tuning the substituents of porphyrin molecules to generate specific
morphologies. Furthermore, the easy synthesis, high efficiency, and high reproducibility of
these nanomaterials based on complementary metalloporphyrins make them feasible for
use in fabricating new porphyrin-based nanostructures for functional materials.
4. Materials and Methods
All the chemicals were procured from Sigma-Aldrich and used without further purifi-
cation unless otherwise mentioned. Trans-dihydroxo-[5,15-bis(3-pyridyl)-10,20-bis(phenyl)
porphyrinato]tin(IV) SnP was synthesized according to the previously reported proce-
dure [40]. All the experiments reported here were carried out under inert argon atmosphere
using standard Schlenk line techniques. The toluene was purified by distillation from a
sodium/benzophenone ketyl solution, whereas pyrrole was derived from a solution over
calcium hydride. Steady-state UV–vis spectra were recorded on a Shimadzu UV-3600
spectrophotometer (Shimadzu, Tokyo, Japan). The fluorescence spectra were recorded
with a Shimadzu RF-5301PC fluorescence spectrophotometer (Shimadzu, Tokyo, Japan).
The 1H-NMR spectra were obtained on a Bruker BIOSPIN/AVANCE III 400 spectrometer
at 293 K (Bruker BioSpin GmbH, Silberstreifen, Rheinstetten, Germany). Electrospray
ionization mass spectra (ESI-MS) were recorded on a Thermo Finnigan Linear Ion Trap
Quadrupole mass spectrometer (Thermo Fisher Scientific, Waltham, MA, USA). Elemental
analysis was performed using the EA 1110 Fisons analyzer (Used Lab Machines Limited,
London, UK). Field emission scanning electron microscope (FE-SEM) images were obtained
from MAIA III (TESCAN, Brno, Czech Republic).
4.1. General Procedure for the Synthesis of Free Porphyrin H2Ln
Free porphyrin was synthesized by mixing aldehydes condensation in propionic acid
using 1.0 equiv. of 4-hydroxybenzaldehyde, 3.0 equiv. of 4-substituted benzaldehyde,
and 4.0 equiv. of pyrrole. In a typical reaction, pyrrole (0.77 mL, 11.1 mmol) was added
dropwise to a solution of 4-substituted benzaldehyde (2.8 mmol) and benzaldehyde (0.89 g,
8.4 mmol) in propionic acid (2◦50 mL) at reflux. After this the mixture was stirred for 1 h.
The mixture was cooled to 0 C to precipitate the product. The solid was filtered and
◦
washed with hot water, and then dried at 50 C. Then, the mixture was purified by column
chromatography (SiO2, eluent: CH2Cl2/MeOH) to afford the compound H2Ln. The crude
was then recrystallized from CH2Cl2/acetonitrile mixture to give a violet purple powder.
4.1.1. Synthesis of Meso-5-(4-hydroxyphenyl)-10,15,20-tris(phenyl)porphyrin H2L1
A total of 0.89 g of benzaldehyde and eluent for column chromatography (CH2Cl2:
MeOH = 98:2) was used. Yield: 0.123 g (7%). Analysis calculated for C44H30N4O: C, 83.79;
1
H, 4.79; N, 8.88. Found: C, 84.02; H, 5.11; N, 8.80. H-NMR (400 MHz, CDCl3, ppm):
δ
–2.81 (s, 2H, NH), 7.14 (d, J = 8.4 Hz, 2H, H2,6-PhOH), 7.68–7.78 (m, 9H, Hm,p-Ph), 8.11–8.19
(m, 8H, meso-O-Ar), 8.83 (s, 8H, -pyrrole). UV–visible (CHCl3): λmax (log ), 418 (5.27),
517 (4.15), 554 (3.87), 593 (3.57), 649 (3.53) nm. Emission (CHCl3, λmax): 654, 713 nm.
β
ε

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4.1.2. Synthesis of Meso-5-(4-hydroxyphenyl)-10,15,20-tris(4-methylphenyl)porphyrin
H2L2
A total of 1.01 g of 4-methylbenzaldehyde and eluent for column chromatography
(CH2Cl2: MeOH = 99:1) was used. Yield: 0.150 g (8%). Analysis calculated for C47H36N4O:
1
C, 83.90; H, 5.39; N, 8.33. Found: C, 83.97; H, 5.57; N, 8.72. H-NMR (400 MHz, CDCl3,
ppm):
J = 6.8 Hz, 6H, H3,5-Ar), 8.04–8.10 (m, 8H, meso-O-Ar), 8.83 (s, 8H, β-pyrrole). UV–visible
(CHCl3): λmax (log ), 418 (5.25), 516 (4.14), 553 (3.86), 592 (3.56), 648 (3.52) nm. Emission
δ –2.79 (s, 2H, NH), 2.68 (s, 9H, Me), 7.15 (d, J = 8.4 Hz, 2H, H2,6-PhOH), 7.53 (d,
ε
(CHCl3, λmax): 654, 714 nm.
4.1.3. Synthesis of Meso-5-(4-hydroxyphenyl)-10,15,20-tris(4-tert-butylphenyl)porphyrin
H2L3
A total of 1.36 g of 4-tert-butylbenzaldehyde and eluent for column chromatography
(CH2Cl2: MeOH = 99:1) was used. Yield: 0.112 g (5%). Analysis calculated for C56H54N4O:
1
C, 84.17; H, 6.81; N, 7.01. Found: C, 84.02; H, 6.97; N, 6.88. H-NMR (400 MHz, CDCl3,
ppm):
J = 7.7 Hz, 6H, H3,5-Ar), 8.08–8.16 (m, 8H, meso-O-Ar), 8.87 (d, J = 4.4 Hz, 8H,
UV–visible (CHCl3): λmax (log ), 419 (5.24), 517 (4.15), 554 (3.84), 592 (3.57), 648 (3.55) nm.
Emission (CHCl3, λmax): 653, 715 nm.
δ
–2.74 (s, 2H, NH), 1.58 (s, 27H, tBu), 7.17 (d, J = 8.7 Hz, 2H, H2,6-PhOH), 7.70 (d,
β-pyrrole).
ε
4.1.4. Synthesis of Meso-5-(4-hydroxyphenyl)-10,15,20-tris(4-methoxyphenyl)porphyrin
H2L4
A total of 1.14 g of 4-methoxybenzaldehyde and eluent for column chromatography
(CH2Cl2: MeOH = 96:4) was used. Yield: 0.140 g (7%). Analysis calculated for C47H36N4O4:
1
C, 78.31; H, 5.03; N, 7.77. Found: C, 78.22; H, 5.41; N, 7.69. H-NMR (400 MHz, CDCl3,
ppm):
J = 7.6 Hz, 6H, H3,5-Ar), 8.08–8.14 (m, 8H, meso-O-Ar), 8.94 (s, 8H, β-pyrrole). UV–visible
(CHCl3): λmax (log ), 420 (5.27), 519 (4.16), 554 (3.86), 593 (3.56), 649 (3.54) nm. Emission
δ –2.75 (s, 2H, NH), 4.08 (s, 9H, OMe), 7.16 (d, J = 8.6 Hz, 2H, H2,6-PhOH), 7.36 (d,
ε
(CHCl3, λmax): 655, 719 nm.
4.1.5. Synthesis of Meso-5-(4-hydroxyphenyl)-10,15,20-tris(4-chlorophenyl)porphyrin H2L5
A total of 1.18 g of 4-chlorobenzaldehyde and eluent for column chromatography
(CH2Cl2: MeOH = 97:3) was used. Yield: 0.141 g (6%). Analysis calculated for C44H27N4Cl3O:
C, 71.99; H, 3.71; N, 7.63. Found: C, 71.87; H, 3.95; N, 7.57. 1H-NMR (400 MHz, CDCl3, ppm):
δ
–2.86 (s, 2H, NH), 7.12 (d, J = 7.2 Hz, 2H, H2,6-PhOH), 7.72 (d, J = 7.6 Hz, 6H, H3,5-Ar),
8.04–8.08 (m, meso-O-Ar), 8.84 (d, J = 4.0 Hz, 8H, -pyrrole). UV–visible (CHCl3): λmax (log
), 418 (5.29), 516 (4.17), 552 (3.89), 591 (3.59), 649 (3.56) nm. Emission (CHCl3, λmax): 654,
714 nm.
β
ε
4.1.6. Synthesis of Meso-5-(4-hydroxyphenyl)-10,15,20-tris(4-nitrophenyl)porphyrin H2L6
A total of 1.27 g of 4-nitrobenzaldehyde and eluent for column chromatography
(CH2Cl2: MeOH = 95:5) was used. Yield: 0.128 g (6%). Analysis calculated for C44H27N7O7:
1
C, 69.02; H, 3.55; N, 12.80. Found: C, 69.23; H, 3.87; N, 12.73. H-NMR (400 MHz, CDCl3,
ppm):
+ H3,5-PhOH), 8.65 (d, J = 7.8 Hz, 6H, meso-O-Ar), 8.90 (s, 8H,
(CHCl3): λmax (log ), 420 (5.26), 519 (4.16), 553 (3.87), 592 (3.58), 648 (3.55) nm. Emission
δ
–2.94 (s, 2H, NH), 7.22 (d, J = 8.6 Hz, 2H, H2,6-PhOH), 8.16–8.31 (m, 8H, H3,5-Ar
β-pyrrole). UV–visible
ε
(CHCl3, λmax): 653, 719 nm.
4.2. General Procedure for the Synthesis of Zn(II)-Porphyrin ZnLn
In each case, Zn(OAc)2
2H2O (0.053 g, 0.29 mmol) was added to a solution of H2Ln
·
(0.12 mmol) in a mixed solvent of tetrahydrofuran (20 mL) and methanol (20 mL). The
mixture was refluxed for 2 h. The solvent was then removed, and the solid product
was purified by column chromatography (SiO2, eluent: CH2Cl2/MeOH). The crude was
recrystallized from CH2Cl2/hexane to give a brownish red.

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4.2.1. Synthesis of Meso-5-(4-hydroxyphenyl)-10,15,20-tris(phenyl)porphyrinato)zinc(II)
ZnL1
A total of 0.076 g of H2L1 and eluent for column chromatography (CH2Cl2: MeOH = 98:2
)
was used. Yield: 0.075 g (90%). Analysis calculated for C68H76N4OZn: C, 76.14; H, 4.07; N, 8.07.
1
Found: C, 76.01; H, 4.39; N, 7.93. H-NMR (400 MHz, DMSO-d6, ppm):
δ 7.17 (d, J = 8.6 Hz,
2H, H2,6-PhOH), 7.76–7.82 (m, 9H, Hm,p-Ph), 7.97 (d, J = 8.8 Hz, 2H, H3,5-PhOH), 8.15–8.21 (m,
6H, meso-O-Ar), 8.77 (d, J = 4.0 Hz, 6H, -pyrrole), 8.86 (d, J = 3.6 Hz, 2H, -pyrrole), 9.87 (s, 1H,
), 421 (5.31), 547 (4.05), 585 (3.71) nm. Emission (CHCl3,
β
β
OH). UV–visible (CHCl3): λmax (log
λmax): 595, 642 nm.
ε
4.2.2. Synthesis of Meso-5-(4-hydroxyphenyl)-10,15,20-tris(4-methylphenyl)porphyrinato)
zinc(II) ZnL2
A total of 0.081 g of H2L2 and eluent for column chromatography (CH2Cl2: MeOH = 99:1
)
was used. Yield: 0.084 g (95%). Analysis calculated for C68H76N4OZn: C, 76.68; H, 4.66; N,
1
7.61. Found: C, 76.54; H, 4.79; N, 7.63. H-NMR (400 MHz, DMSO-d6, ppm):
δ 2.67 (s, 9H,
Me), 7.17 (d, J = 7.6 Hz, 2H, H2,6-PhOH), 7.58 (d, J = 6.8 Hz, 6H, H3,5-Ar), 7.95 (d, J = 7.6 Hz,
2H, H3,5-PhOH), 8.04 (d, J = 6.8 Hz, 6H, meso-O-Ar), 8.77 (d, J = 4.0 Hz, 6H, -pyrrole), 8.83
(d, J = 3.6 Hz, 2H, -pyrrole), 9.85 (s, 1H, OH). UV–visible (CHCl3): λmax (log ), 421 (5.29), 548
(4.04), 586 (3.70) nm. Emission (CHCl3, λmax): 597, 643 nm.
β
β
ε
4.2.3. Synthesis of Meso-5-(4-hydroxyphenyl)-10,15,20-tris(4-tert-butylphenyl)
porphyrinato)zinc(II) ZnL3
A total of 0.096 g of H2L3 and eluent for column chromatography (CH2Cl2: MeOH = 99:1
)
was used. Yield: 0.097 g (94%). Analysis calculated for C68H76N4OZn: C, 77.99; H, 6.08; N, 6.50.
1
Found: C, 77.65; H, 6.22; N, 6.45. H-NMR (400 MHz, DMSO-d6, ppm):
δ
1.58 (s, 27H, tBu),
7.17 (d, J = 8.8 Hz, 2H, H2,6-PhOH), 7.80 (d, J = 8.0 Hz, 6H, H3,5-Ar), 7.95 (d, J = 7.6 Hz, 2H,
H3,5-PhOH), 8.10 (d, J = 7.2 Hz, 6H, meso-O-Ar), 8.74–8.80 (m, 6H, -pyrrole), 8.83 (d, J = 4.4 Hz
2H, -pyrrole), 9.86 (s, 1H, OH). UV–visible (CHCl3): λmax (log ), 421 (5.27), 549 (4.03), 586
β
,
β
ε
(3.69) nm. Emission (CHCl3, λmax): 597, 644 nm.
4.2.4. Synthesis of
Meso-5-(4-hydroxyphenyl)-10,15,20-tris(4-methoxyphenyl)porphyrinato)zinc(II) ZnL4
A total of 0.086 g of H2L4 and eluent for column chromatography (CH2Cl2: MeOH = 97:3)
was used. Yield: 0.090 g (96%). Analysis calculated for C68H76N4OZn: C, 71.99; H, 4.37; N, 7.14.
1
Found: C, 71.74; H, 4.58; N, 7.07. H-NMR (400 MHz, DMSO-d6, ppm):
δ 4.05 (s, 9H, OMe),
7.17 (d, J = 8.4 Hz, 2H, H2,6-PhOH), 7.34 (d, J = 8.5 Hz, 6H, H3,5-Ar), 7.96 (d, J = 8.2 Hz, 2H,
H3,5-PhOH), 8.08 (d, J = 8.5 Hz, 6H, meso-O-Ar), 8.79 (d, J = 4.0 Hz, 6H, -pyrrole), 8.82 (d,
J = 3.8 Hz, 2H, -pyrrole), 9.85 (s, 1H, OH). UV–visible (CHCl3): λmax (log ), 422 (5.25), 550
(4.02), 588 (3.68) nm. Emission (CHCl3, λmax): 599, 645 nm.
β
β
ε
4.2.5. Synthesis of Meso-5-(4-hydroxyphenyl)-10,15,20-tris(4-chlorophenyl)
porphyrinato)zinc(II) ZnL5
A total of 0.088 g of H2L5 and eluent for column chromatography (CH2Cl2: MeOH = 97:3
)
was used. Yield: 0.088 g (92%). Analysis calculated for C68H76N4OZn: C, 66.27; H, 3.16; N, 7.03.
1
Found: C, 66.03; H, 3.27; N, 6.95. H-NMR (400 MHz, DMSO-d6, ppm):
δ 7.18 (d, J = 8.4 Hz,
2H, H2,6-PhOH), 7.85 (d, J = 7.6 Hz, 6H, H3,5-Ar), 7.96 (d, J = 8.4 Hz, 2H, H3,5-PhOH), 8.17 (d,
J = 7.2 Hz, 6H, meso-O-Ar), 8.78 (d, J = 6.0 Hz, 6H, -pyrrole), 8.87 (d, J = 4.4 Hz, 2H, -pyrrole),
), 420 (5.23), 547 (4.03), 585 (3.70) nm. Emission
β
β
9.89 (s, 1H, OH). UV–visible (CHCl3): λmax (log
(CHCl3, λmax): 598, 642 nm.
ε
4.2.6. Synthesis of Meso-5-(4-hydroxyphenyl)-10,15,20-tris(4-nitrophenyl)
porphyrinato)zinc(II) ZnL6
A total of 0.092 g of H2L6 and eluent for column chromatography (CH2Cl2: MeOH = 95:5
)
was used. Yield: 0.089 g (90%). Analysis calculated for C44H25N7O7Zn: C, 63.74; H, 3.04;

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N, 11.83. Found: C, 63.44; H, 3.42; N, 11.65. 1H-NMR (400 MHz, DMSO-d6, ppm):
(d, J = 8.5 Hz, 2H, H2,6-PhOH), 8.20 (d, J = 8.2 Hz, 2H, H3,5-PhOH), 8.34 (d, J = 7.6 Hz, 6H,
H3,5-Ar), 8.66 (d, J = 7.8 Hz, 6H, meso-O-Ar), 8.87 (d, J = 4.2 Hz, 6H, -pyrrole), 8.92 (d, J = 3.8
Hz, 2H, -pyrrole), 9.84 (s, 1H, OH). UV–visible (CHCl3): λmax (log ), 419 (5.25), 548 (4.04), 586
δ 7.23
β
β
ε
(3.67) nm. Emission (CHCl3, λmax): 600, 644 nm.
4.3. General Procedure for the Synthesis of the Triad
A mixture of ZnLn (0.08 mmol) and SnP (0.031 g, 0.04 mmol) was added to anhydrous
toluene (20 mL) and refluxed for 48 h under an argon atmosphere. Then, the reaction
mixture was cooled to room temperature, and we filtered the colored precipitate. After
that, it was washed with toluene, then dried under a vacuum.
4.3.1. Synthesis of Triad 1
A total of 0.056 g of ZnL1 was used, and light green precipitate was obtained. Yield:
(0.068 g, 80%). Analysis calculated for C130H80N14O2SnZn2: C, 73.66; H, 3.80; N, 9.25.
1
Found: C, 73.34; H, 4.12; N, 9.14. H-NMR (400 MHz, DMSO-d6, ppm):
δ
2.66 (d, J = 8.6
Hz, 4H,
α
-bridging phenyl), 6.70 (d, J = 8.8 Hz, 4H,
β-bridging phenyl), 7.19–7.31 (m, 18H,
{m,p-phenyl}-axial), 7.52–7.62 (m, 20H, meso-O-Phenyl-axial + H5-Py-central + m,p-Phenyl-
central), 8.07–8.11 (m, 6H, H4-Py-central + meso-O-phenyl-central), 8.40 (d, J = 7.8 Hz, 4H,
β-pyrrole-axial), 8.55 (d, J = 7.8 Hz, 4H,
β-pyrrole-axial), 8.65–8.75 (m, 8H,
β-pyrrole-axial),
9.05 (d, J = 8.2 Hz, 4H, -pyrrole-central), 9.15 (d, J = 8.2 Hz, 4H,
β
β-pyrrole-central), 9.28 (d,
J = 5.0 Hz, 2H, H6-Py), 9.58 (s, 2H, H2-Py). UV–visible (CHCl3): λmax (log
573 (5.21), 615 (5.19) nm. Emission (CHCl3, λmax): 592, 642 nm.
ε), 454 (5.65),
4.3.2. Synthesis of Triad 2
A total of 0.059 g of ZnL2 was used, and light green precipitate was obtained. Yield:
(0.074 g, 84%). Analysis calculated for C136H92N14O2SnZn2: C, 74.12; H, 4.21; N, 8.90.
1
Found: C, 73.94; H, 4.32; N, 8.74. H-NMR (400 MHz, DMSO-d6, ppm):
δ
2.64 (d, J = 8.6
Hz, 4H,
α
-bridging phenyl), 2.69 (s, 18H, Me), 6.70 (d, J = 8.8 Hz, 4H,
β-bridging phenyl),
7.24–7.32 (m, 12H, m-Ar-axial), 7.52–7.60 (m, 8H, H5-Py-central + m,p-Phenyl-central), 7.68–
7.74 (m, 12H, meso-O-Ar-axial), 8.08–8.14 (m, 6H, H4-Py-central + meso-O-phenyl-central),
8.42 (d, J = 7.8 Hz, 4H,
(m, 8H, -pyrrole-axial), 9.08 (d, J = 8.2 Hz, 4H,
-pyrrole-central), 9.26 (d, J = 5.0 Hz, 2H, H6-Py), 9.54 (s, 2H, H2-Py). UV–visible (CHCl3):
β-pyrrole-axial), 8.57 (d, J = 7.8 Hz, 4H,
β-pyrrole-axial), 8.70–8.80
β
β-pyrrole-central), 9.15 (d, J = 8.2 Hz, 4H,
β
λmax (log ε), 458 (5.88), 577 (5.68), 618 (5.69) nm. Emission (CHCl3, λmax): 592, 642 nm.
4.3.3. Synthesis of Triad 3
A total of 0.069 g of ZnL3 was used, and green precipitate was obtained. Yield: (0.082
g, 84%). Analysis calculated for C154H128N14O2SnZn2: C, 75.30; H, 5.25; N, 7.98. Found: C,
1
75.02; H, 5.32; N, 7.87. H-NMR (400 MHz, DMSO-d6, ppm):
δ
1.58 (s, 54H, tBu), 2.62 (d,
J = 8.6 Hz, 4H, α-bridging phenyl), 6.72 (d, J = 8.6 Hz, 4H, β-bridging phenyl), 7.42–7.52
(m, 20H, m,p-phenyl-central + H5-Py-central + m-Ar-axial), 7.65–7.73 (m, 12H, meso-O-Ar-
axial), 8.08–8.16 (m, 6H, H4-Py-central + meso-O-phenyl-central), 8.44 (d, J = 7.8 Hz, 4H,
β-pyrrole-axial), 8.56 (d, J = 7.8 Hz, 4H,
β-pyrrole-axial), 8.68–8.76 (m, 8H,
β-pyrrole-axial),
9.08 (d, J = 8.2 Hz, 4H, -pyrrole-central), 9.17 (d, J = 8.2 Hz, 4H,
β
β-pyrrole-central), 9.30 (d,
J = 5.0 Hz, 2H, H6-Py), 9.55 (s, 2H, H2-Py). UV–visible (CHCl3): λmax (log
577 (5.68), 619 (5.70) nm. Emission (CHCl3, λmax): 591, 640 nm.
ε), 454 (5.88),
4.3.4. Synthesis of Triad 4
A total of 0.063 g of ZnL4 was used, and dark blue precipitate was obtained. Yield:
(0.083 g, 90%). Analysis calculated for C136H92N14O8SnZn2: C, 71.03; H, 4.03; N, 8.53.
1
Found: C, 70.91; H, 4.30; N, 8.44. H-NMR (400 MHz, DMSO-d6, ppm):
δ
2.70 (d, J = 8.6
-bridging phenyl),
7.22–7.32 (m, 12H, m-phenyl), 7.35–7.43 (m, 8H, H5-Py-central + m,p-phenyl-central), 7.48–
Hz, 4H, α-bridging phenyl), 4.08 (s, 18H, OMe), 6.73 (d, J = 8.6 Hz, 4H, β

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7.58 (m, 12H, meso-O-Ar-axial), 8.06–8.12 (m, 6H, H4-Py-central + meso-O-phenyl-central),
8.38 (d, J = 7.8 Hz, 4H,
(m, 8H, -pyrrole-axial), 9.07 (d, J = 8.2 Hz, 4H,
-pyrrole-central), 9.28 (d, J = 5.0 Hz, 2H, H6-Py), 9.57 (s, 2H, H2-Py). UV–visible (CHCl3):
β-pyrrole-axial), 8.55 (d, J = 7.8 Hz, 4H,
β-pyrrole-axial), 8.65–8.75
β
β-pyrrole-central), 9.14 (d, J = 8.2 Hz, 4H,
β
λmax (log ε), 423 (5.71), 458 (5.32), 574 (5.12), 616 (5.09) nm. Emission (CHCl3, λmax): 596,
644 nm.
4.3.5. Synthesis of Triad 5
A total of 0.064 g of ZnL5 was used, and blue precipitate was obtained. Yield: (0.076 g,
82%). Analysis calculated for C130H74Cl6N14O2SnZn2: C, 67.12; H, 3.21; N, 8.43. Found:
1
C, 66.97; H, 3.55; N, 8.20. H-NMR (400 MHz, DMSO-d6, ppm):
δ
2.65 (d, J = 8.6 Hz, 4H,
α
-bridging phenyl), 6.74 (d, J = 8.6 Hz, 4H,
β-bridging phenyl), 7.22–7.30 (m, 8H, m,p-
phenyl-central + H5-Py-central), 7.42–7.52 (m, 12H, m-Ar-axial), 7.62–7.70 (m, 12H, meso-O-
Ar-axial), 8.06–8.12 (m, 6H, H4-Py-central + meso-O-phenyl-central), 8.36 (d, J = 7.8 Hz, 4H,
β
-pyrrole-axial), 8.48 (d, J = 7.8 Hz, 4H,
9.05 (d, J = 8.2 Hz, 4H, -pyrrole-central), 9.12 (d, J = 8.2 Hz, 4H,
J = 5.0 Hz, 2H, H6-Py), 9.52 (s, 2H, H2-Py). UV–visible (CHCl3): λmax (log
β
-pyrrole-axial), 8.60–8.70 (m, 8H,
-pyrrole-central), 9.28 (d,
), 422 (5.85),
β-pyrrole-axial),
β
β
ε
458 (5.69), 498 (5.69), 582 (5.61), 623 (5.65) nm. Emission (CHCl3, λmax): 595, 645 nm.
4.3.6. Synthesis of Triad 6
A total of 0.066 g of ZnL6 was used, and brown precipitate was obtained. Yield: (0.082
g, 86%). Analysis calculated for C130H74N20O14SnZn2: C, 65.34; H, 3.12; N, 11.72. Found:
C, 65.11; H, 3.40; N, 11.60. 1H-NMR (400 MHz, DMSO-d6, ppm):
δ
2.74 (d, J = 8.6 Hz,
4H, α-bridging phenyl), 6.80 (d, J = 8.6 Hz, 4H, β-bridging phenyl), 7.22–7.31 (m, 8H, m,p-
phenyl-central + H5-Py-central), 8.04–8.12 (m, 6H, H4-Py-central + meso-O-phenyl-axial),
8.15–8.16 (m, 12H, m-Ar-axial), 8.30–8.40 (m, 12H, meso-O-Ar-axial), 8.48 (d, J = 7.8 Hz, 4H,
β-pyrrole-axial), 8.62 (d, J = 7.8 Hz, 4H,
β-pyrrole-axial), 8.70–8.80 (m, 8H,
β-pyrrole-axial),
9.06 (d, J = 8.2 Hz, 4H, -pyrrole-central), 9.16 (d, J = 8.2 Hz, 4H,
β
β-pyrrole-central), 9.26 (d,
J = 5.0 Hz, 2H, H6-Py), 9.52 (s, 2H, H2-Py). UV–visible (CHCl3): λmax (log
455 (5.21), 572 (5.07), 618 (5.04) nm. Emission (CHCl3, λmax): 597, 647 nm.
ε), 424 (5.96),
4.4. Photocatalytic Degradation of Rhodamine B by Nanoaggregates of Triad 1–6
In the typical process, 10 mg of the photocatalyst was added to 100 mL of aqueous
RhB solution (4.5 mg L−1, pH 7) under stirring at room temperature. Before the visible light
irradiation, the mixture was kept in the dark for 30 min in order to reach an adsorption–
desorption equilibrium. After that, the mixture was exposed to visible light irradiation
from a 150 W Xenon arc lamp (ABET technologies, Milford, CT, USA) at room temperature.
All the samples were collected by centrifugation at given time intervals to determine the
RhB concentration via UV–vis spectroscopy at 554 nm.
Supplementary Materials: 1H-NMR spectra, mass spectra, FE-SEM images, and the photocatalytic
degradation of RhB are included in Figures S1–S30. Figure S1: 1H-NMR spectrum of H2L1, Figure S2:
1H-NMR spectrum of H2L2, Figure S3: 1H-NMR spectrum of H2L3, Figure S4: 1H-NMR spectrum
of H2L4, Figure S5: 1H-NMR spectrum of H2L5, Figure S6: 1H-NMR spectrum of H2L6, Figure S7:
1H-NMR spectrum of ZnL1, Figure S8: 1H-NMR spectrum of ZnL2, Figure S9: 1H-NMR spectrum of
ZnL3, Figure S10: 1H-NMR spectrum of ZnL4, Figure S11: 1H-NMR spectrum of ZnL5, Figure S12:
1H-NMR spectrum of ZnL6, Figure S13: 1H-NMR spectrum of 1, Figure S14: 1H-NMR spectrum of
2, Figure S15: 1H-NMR spectrum of 3, Figure S16: 1H-NMR spectrum of 4, Figure S17: 1H-NMR
spectrum of 5, Figure S18: 1H-NMR spectrum of 6, Figure S19: ESI-MS spectrum of 1, Figure S20: ESI-
MS spectrum of 2, Figure S21: ESI-MS spectrum of 3, Figure S22: ESI-MS spectrum of 4, Figure S23
:
ESI-MS spectrum of 5, Figure S24: ESI-MS spectrum of 6, Figure S25: Lower magnification of FE-SEM
images for the assembly patterns of triads (1–6), Figure S26: Absorption spectra of RhB in the presence
of nanostructures derived from triad 3 under visible light irradiation, Figure S27: Kinetics for the
photocatalytic degradation of RhB under visible light irradiation of the six triads (1–6), Figure S28:
Catalytic cycles (up to 5 cycles) using triad 3 as a photocatalyst for the degradation of RhB, Figure S29:

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Schematic representation of the detection of the hydroxyl and superoxide radical anion that were
generated during the photodegradation experiments, Figure S30: UV–visible spectra of coumarin in
the presence of triad 3 in water. λex = 325 nm and light exposure time (30 min).
Author Contributions: Investigation, methodology, formal analysis, data curation, visualization,
software, validation, resources, and writing, N.K.S.; conceptualization, project administration, su-
pervision, review, funding acquisition, and editing, H.-J.K. All authors have read and agreed to the
published version of the manuscript.
Funding: This work was supported by the National Research Foundation of Korea (NRF), and the
grant was funded by the Korean government (MSIT) (Grant No. 2017R1A2B2011585).
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Data are available in the article and supplementary materials.
Acknowledgments: H.-J.K. is grateful for the sabbatical provided by Kumoh National Institute
of Technology.
Conflicts of Interest: The authors declare no conflict of any interest.
Sample Availability: Samples of the compounds are not available from the authors.
References
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