Core-modified rubyrins with phenanthrene-fused pyrrole rings: Highly selective and tunable response to Hg2+ ions

Article abstract of DOI:10.1016/j.dyepig.2018.05.045

Three fused-ring-expanded rubyrins with modified macrocyclic core have been synthesized and characterized. A series of spectroscopic, electrochemical measurements and a set of theoretical calculations demonstrate that the core-modification of the inner co

Full text of DOI:10.1016/j.dyepig.2018.05.045

DyesandPigments158(2018)188–194
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Core-modified rubyrins with phenanthrene-fused pyrrole rings: Highly
selective and tunable response to Hg2+ ions
Xuemei Yuana, Minzhi Lib, Ting Menga, John Mackc,∗∗, Rodah Soyc, Tebello Nyokongc,
Weihua Zhub, Haijun Xua,∗∗∗, Xu Liangb,d,∗
a
College of Chemical Engineering, Jiangsu Key Lab of Biomass-based Green Fuels and Chemicals, Nanjing Forestry University, Nanjing 210037, PR China
School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, PR China
Centre for Nanotechnology Innovation, Department of Chemistry, Rhodes University, Grahamstown 6140, South Africa
State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210000, PR China
b
c
d
A R T I C L E I N F O
A B S T R A C T
Keywords:
Rubyrin
Electronic structure
Spectroscopy
Hg2+ ion sensors
Three fused-ring-expanded rubyrins with modified macrocyclic core have been synthesized and characterized. A
series of spectroscopic, electrochemical measurements and a set of theoretical calculations demonstrate that the
core-modification of the inner core of rubyrins has a large influence on the electronic structure. Colorimetric
changes are observe that demonstrate that these core-modified rubyrins could be used as selective Hg2+ ion
sensors. These properties can be fine-tuned by introducing lipophilic substituents on the meso-aryl rings.
1. Introduction
follow Huckel's (4N + 2) rule containing 18π-electrons delocalized on
the inner ligand perimeter [10]. Thus, the connection between the
In the past 20 years, a wide range of novel expanded porphyrin
structures have been successfully synthesized and characterized by
using a number of different structural modification strategies such as,
macrocycle ring-expansion, the introduction of heterocycles other than
pyrrole (core modification), meso-substitution, and heterocycle inver-
sion (i.e. “confused” porphyrins) [1–3]. Core-modified expanded por-
phyrins in which heteroatoms replace the pyrrole nitrogens have
seldom been studied despite being particularly attractive due to the
large influence that this structural modification strategy has on the
aromatic properties of the electronic structure [4–6]. The degree of
aromaticity of core-modified porphyrinoids can be quantified by ex-
perimental characterization and theoretical calculation by studying the
molecular and electronic structures, and the external magnetic field
induced diamagnetic ring current. For example, expanded porphyrins
could be explored by various spectroscopic and electrochemical tech-
niques [7–9]. On the other hand, the electronic structure of expanded
porphyrinoids can also be easily predicted by theoretical calculations
such as the use of molecular orbital (MO) theory, nucleus-independent
chemical shift (NICS) and anisotropy of the current-induced density
(ACID), and these approaches can be used to determine the extent to
which a novel macrocycle is aromatic [10,11].
electronic structures of core-modified expanded porphyrinoids and
their properties can be rationalized by using conceptual frameworks
such as Gouterman's 4-orbital [12] and Michl's perimeter model
[13–17] that consider how structural modifications change the relative
energies of the MOs that are derived from the HOMO and LUMO of a
2−
D16h symmetry C16H16
parent hydrocarbon cyclic perimeter. As a
relatively new class of functional molecules, ring-expanded porphyr-
inoids have attracted considerable attention recently as selective anion
receptors, ligands for transition and lanthanoid ions, use as photo-
sensitizers in photodynamic therapy and magnetic resonance imaging
contrast agents [18]. Expanded macrocycles of this type have also
proven useful in the study of aromatic effects in large heteroannulenes,
while, more recently, their large two-photon absorption cross sections,
have made these compounds attractive for use in the study of three-
dimensional micro-fabrication, optical data storage, and optical lim-
iting effects [19–22].
Herein, we report an in-depth analysis of the optical properties of
fused-ring-expanded rubyrins ([26]hexaphyrins (1.1.0.1.1.0)) that are
core-modified with group 16 heteroatoms. The Hg2+ ion is known to be
a ubiquitous heavy-metal pollutant and one of the most toxic metal ions
in the environment, which ranks sixth among the most toxic chemicals
in the list of hazardous compounds [23]. Hg2+ can cause many kinds of
Typically, porphyrins can be regarded as aromatic molecules that
∗
Corresponding author. School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, PR China. Tel.: +86 511 8879 1928.
Corresponding author.
Corresponding author.
∗∗
∗∗∗
E-mail addresses: j.mack@ru.ac.za (J. Mack), xuhaijun@njfu.edu.cn (H. Xu), liangxu@ujs.edu.cn (X. Liang).
https://doi.org/10.1016/j.dyepig.2018.05.045
Received 3 February 2018; Received in revised form 22 May 2018; Accepted 22 May 2018
Availableonline23May2018
0143-7208/©2018ElsevierLtd.Allrightsreserved.

X. Yuan et al.
DyesandPigments158(2018)188–194
diseases in the brain, heart, kidneys, lungs, central nervous system, and
immune system in humans even at ppm levels of mercury accumulation
[24]. The development of highly selective and sensitive optical probes
for the detection of Hg2+ is of great significance for both the en-
vironment and human health. In recent years, the design and con-
struction of optical sensors for the recognition of Hg2+ has attracted
considerable attention [25]. In this manuscript, the effect of fused-ring-
expansion, ring-expansion of the macrocycle and the electron-donating
properties of meso-aryl substituents on their electronic structures
through various spectroscopic and electrochemical measurements, and
theoretical applications.
solution was opened to air and 2,3-dichloro-5,6-dicyano-1,4-benzo-
quinone (DDQ, 227 mg, 1 mmol) was added, and the mixture was
stirred for a further 1 h. The solvents were removed under reduced
pressure by rotary evaporation. The crude product was purified by si-
lica-gel flash column chromatography and recrystallization from
chloroform/methanol afforded the rubyrin as deep blue solid (Scheme
1). 1H NMR spectroscopy and MS (ESI-HR, MALDI-TOF) are provided in
the Supporting Information (see ESI).
2.3. Structural characterization
5,5′-Bis(phenylhydroxymethyl)-2,2′-bithiophene (2a): 0.95 g,
66%; 1H NMR (300 MHz, DMSO-d6): δ 7.41 (d, J = 7.5 Hz, 4 H, phenyl-
H), 7.33 (t, J = 7.5 Hz, 4 H, phenyl-H), 7.24 (dd, J = 6.9, 7.2 Hz, 2 H,
phenyl-H), 6.98 (d, J = 3.6, 2 H, thiophene -H), 6.76 (d, J = 3.6, 2 H,
thiophene-H), 5.86 (s, 2 H, -CH-). 13C NMR (75 MHz, DMSO-d6): δ
149.9, 114.9, 136.1, 128.6, 127.7, 126.5, 125.1, 123.2, 70.8.
5,5′-Bis(4-tert-butyl-phenylhydroxymethyl)-2,2′-bithiophene
(2b): 1.03 g, 55%; 1H NMR (300 MHz, DMSO-d6): δ 7.30–7.36 (dd,
J = 9.0, 10.2 Hz, 8 H, phenyl-H), 6.98 (d, J = 3.6 Hz, 2 H, thiophene-
H), 6.76 (d, J = 3.6 Hz, 2 H, thiophene-H), 5.83 (s, 2 H, -CH-), 1.25 (s,
18 H, -t-Bu-H). 13C NMR (75 MHz, DMSO-d6): δ 150.0, 142.1, 136.0,
126.2, 125.4, 124.9, 123.2, 70.8, 57.5, 31.6.
5,5′-Bis(4-hexadecyloxy-phenylhydroxymethyl)-2,2′-bithio-
phene (2c): 1.25 g, 38%; 1H NMR (600 MHz, DMSO-d6): δ 7.29 (d,
J = 12.6 Hz, 4 H, phenyl-H), 6.96 (d, J = 4.8 Hz, 2 H, thiophene-H),
6.86 (d, J = 12.6 Hz, 4 H, phenyl-H), 6.73 (d, J = 4.8 Hz, 2 H, thio-
phene-H), 6.16 (br, 2 H，-OH), 5.81 (s, 2 H, -CH-), 3.92 (t, J = 9.6 Hz,
4 H, -OCH2-), 1.64–1.61 (m, 4 H, -OCH2-CH2-CH2-), 1.34–1.42 (m, 4 H,
-CH2-), 1.23 (s, 44 H, -CH2-), 1.14 (s, 4 H, -CH2-), 0.85 (t, J = 9.0,
10.2 Hz, 6 H, -CH3).
2. Results and discussion
2.1. Materials and methods
Unless otherwise noted, all chemicals and solvents were of com-
mercial reagent grade and used without further purification. Dry di-
chloromethane was freshly distilled over CaH2 under nitrogen. Dry n-
hexane and THF were distilled from sodium/benzophenone under an
inert atmosphere. Elemental analyses for C, H and N, were performed
on a Perkin-Elmer 240 C elemental analyzer. 1H NMR spectra were
recorded on a Bruker DRX300 and DRX600 spectrometer at ambient
temperatures. The chemical shifts are expressed relative to TMS as the
internal standard. MALDI-TOF-MS experiments were performed using
an Applied Biosystems 4800 proteomics analyzer equipped with an
Nd:YAG laser operating at the third harmonic wavelength of 355 nm, a
repetition rate of 200 Hz, and an acceleration voltage of 20 kV. ESI-
HRMS measurements were carried out using a Thermo Fisher Scientific
LTQ Orbitrap XL, USA. 2,2′-bithiophene (1a) [26], p-hexadecylox-
ybenzaldehyde [27] and phenanthropyrrole [28] were prepared ac-
cording to the literature methods. Cyclic voltammetry was carried out
on a Chi-730D electrochemistry station with a three-electrode cell. A
glassy carbon disk, a platinum wire and an Ag/AgCl electrode were
used as the working, counter and reference electrodes, respectively. The
UV and visible regions of the electronic absorption spectra were re-
corded with an HP 8453A diode array spectrophotometer.
Tetrathiarubyrin (3a): 89 mg, 32%; 1H NMR (600 MHz, CDCl3): δ
9.48–9.49 (br, 4 H, thiophene-H), 9.36–9.37 (br, 4 H, thiophene-H),
8.68–8.69 (m, 8 H, meso-phenyl-H), 8.57 (d, J = 7.8 Hz, 4 H, meso-
phenyl-H), 8.23 (d, J = 8.4 Hz, 4 H, meso-phenyl-H), 7.79 (dd, J = 7.2,
6.6 Hz, 8 H, fused ring-H), 7.65 (dd, J = 6.6, 7.2 Hz, 4 H, meso-phenyl-
H), 7.39 (dd, J = 6.6, 7.2 Hz, 4 H, fused ring-H), 7.12 (dd, J = 7.8,
7.2 Hz, 4 H, fused ring-H) ppm. Anal. Calcd. (%) for C76H44N2S4: C,
81.98; H, 3.98; N, 2.52; found: C, 82.02; H, 3.94; N, 2.55. ESI-HRMS:
2.2. General synthetic procedure
[M+H]+
=
1113.2537 (Calcd. [M+H]+ = 1113.2460).
ε
2.2.1. Preparation of diols
(L·mol⁻1·cm⁻1): 595 (71000), 716 (8600), 779 (9100).
n-Hexane (90 mL) was added to a 250 mL three-necked round-bot-
tomed flask flushed with argon for 10 min. TMEDA (1.8 mL, 11.4 mmol)
and n-BuLi (7.2 mL of ca. 1.6 M solution in hexane, 11.4 mmol) were
then added, and the solution was stirred under argon for 10 min. 2,2′-
bithiophene (3.82 mmol) was added, and the solution was gently re-
fluxed for 1 h. The reaction mixture was then allowed to attain 25 °C.
The reaction mixture was cooled to 0 °C in an ice bath, and then a so-
lution of aromatic aldehyde (9.53 mmol) in THF (25 mL) was added
dropwise. After the addition was over, the reaction mixture was stirred
at 0 °C for 15 min and then brought to room temperature. The reaction
was quenched by adding an ice-cold saturated NH4Cl solution (40 mL),
and it was then extracted with CHCl3 (50 mL × 3). The organic layers
were combined and washed with water and brine solution and dried
over anhydrous Na2SO4. The solvent was removed in a rotary eva-
porator under reduced pressure to obtain the crude compound, which
was recrystallized from CHCl3/n-hexane to afford the diol as a pale
white solid (Scheme 1).
Tetrathiarubyrin (3b): 98 mg, 29%; 1H NMR (600 MHz, CDCl3): δ
8.87–8.88 (br, 8 H, thiophene-H), 8.57 (d, J = 7.8 Hz, 4 H, meso-
phenyl-H), 8.42 (s, 8 H, meso-phenyl-H), 7.92 (d, J = 7.8 Hz, 4 H, meso-
phenyl-H), 7.71 (d, J = 7.8 Hz, 8 H, fused ring-H), 7.37 (dd, J = 6.6,
6.6 Hz, 4 H, fused ring-H), 7.06 (dd, J1 = 6.6, 7.2 Hz, 4 H, fused ring-
H), 1.51 (s, 36 H, t-Bu-H) ppm. Anal. Calcd. (%) for C92H76N2S4: C,
82.59; H, 5.73; N, 2.09; found: C, 82.55; H, 5.77; N, 2.14. ESI-HRMS:
[M+H]+
=
1337.5096 (Calcd. [M+H]+ = 1337.4964).
ε
(L·mol⁻1·cm⁻1): 595 (87000), 719 (9500), 788 (14500).
Tetrathiarubyrin (3c): 217 mg, 42%; 1H NMR (600 MHz, CDCl3): δ
9.08–9.09 (br, 4 H, thiophene-H), 8.86–8.89 (br, 4 H, thiophene-H),
8.50 (d, J = 6 Hz, 12 H, meso-phenyl-H), 8.00–8.01 (d, J = 2.4 Hz, 4 H,
meso-phenyl-H), 7.32 (s, 4 H, fused ring-H), 7.24–7.26 (m, 8 H, fused
ring-H), 7.06 (t, J = 6 Hz, 4 H, fused ring-H), 4.13 (s, 8 H, -OCH2-), 1.89
(ddd, J = 7.2, 7.2, 6.6 Hz, 8 H,-OCH2-CH2-), 1.55–1.57 (m, 16 H, -CH2-
), 1.43–1.44 (m, 8 H, -CH2-), 1.26–1.29 (m, 80 H, -(CH2)-), 0.88–0.90 (t,
J = 7.2 Hz, 12 H, -CH3) ppm. Anal. Calcd (%) for: C140H172N2O4S4: C,
81.03; H, 8.35; N, 1.35; found: C, 81.07; H, 8.41; N, 1.40. MALDI-TOF-
2.2.2. Preparation of rubyrin 3a-e
MS: [M+H]+
=
2074.752 (Calcd. [M+H]+ = 2074.227).
ε
The appropriate diol (0.5 mmol) was added to a stirred solution of
phenanthropyrrole (107 mg, 0.5 mmol) in freshly dry deoxygenated
dichloromethane (80 ml), and the resulting solution was purged with
argon for 10 min. After addition of boron trifluoride etherate (80 μl,
0.64 mmol) the reaction mixture was stirred for 1 h at −50 °C in the
dark, and then warmed to room temperature for 48 h. The resulting
(L·mol⁻1·cm⁻1): 595 (97000), 716 (10500), 779 (21000).
2.4. Theoretical calculations
B3LYP geometry optimizations were carried out for 3a-c and a series of
seven model complexes at the B3LYP/6-31G(d) level of theory by using
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DyesandPigments158(2018)188–194
Scheme 1. Synthetic procedures for core modified rubyrin 3.
the Gaussian 09 software package. The TD-DFT calculations were carried
out in a similar manner by using the CAM-B3LYP functional, which con-
transitions between the HOMO and LUMO levels of the π-system and the
intense B (or Soret) bands that arise from the allowed ΔML =
1 transi-
tains
a
long-range correction. The model complexes include tetra-
tions are expected to dominate their UV-visible absorption spectra (Fig. 3)
[10]. Ring-expansion of the macrocycle results in a narrowing of the
HOMO–LUMO gap and a red-shift of the L and B bands (Figs. 2 and 3) [10],
and the introduction of fused phenanthro rings to the tetraphenylporphyrin
and rubyrin ligands has a similar effect mainly due to a stabilization of the -s
MO due to strong bonding interactions at the points of attachment [5]. In
general, the B band of the parent rubyrin compound lies at ca. 550 nm and
the L band lies beyond 800 nm. In Fig. 4, rubyrin 3a has an intense B band
at 595 nm, while the L bands of 3a lie at 779 and beyond 1100 nm. The
introduction of the group 16 heteroatom has a large influence on the
electronic structure of rubyrin analogues in a similar manner to what has
been observed previously with tetraphenanthroporphyrins [5]. When tert-
butyl units were introduced at the meso-positions of the rubyrin 3b, only
minor changes are observed in the B band region, but the L hands are
slightly shifted to longer wavelength. The further red-shifts of the B and L
absorption bands of rubyrins 3c are consistent with the anticipated trends
(Fig. 4), since there is a relative destabilization of the HOMO when electron
donating –OR substituents are introduced at the para-positions of the meso-
aryl rings due to the large MO coefficients on the meso-carbons (Figs. 1 and
2).
phenylporphyrin (PN4), tetraphenyldiphenanthroporphyrin (N4), tetra-
phenyldithiaporphyrin (PN2S2), tetraphenyldiphenanthrodithiaporphyrin
(N2S2), tetraphenylrubyrin (PN6), tetraphenyldiphenanthrorubyrin (N6),
tetraphenyltetrathiarubyrin (PS4N2) and tetraphenyldiphenanthrotetra
thiarubyrin (S4N2). To simplify the calculations the structures of 3b and 3c
are modified to include methyl (3b_CH3) and methoxy (3b_OCH3) groups
respectively at the para-positions of the meso-aryl rings.
3. Results and discussion
3.1. Structural characterization
A series of fused-ring-expanded rubyrins 3a-c that are core-modified
with sulfur atoms were synthesized from a reaction of diols and phe-
nanthropyrroles in freshly dried and deoxygenated dichloromethane
and were purified by silica gel column chromatography and re-
crystallization. ESI-HRMS revealed an intense parent peak for 3a at [M
+H]+ = 1113.2537 (Calcd. [M+H]+ = 1113.2460) (Fig. S1, see ESI),
providing direct evidence that the target compound was successfully
prepared. In addition, similar parent peaks of HR-MS were also ob-
served for 3b and 3c (Figs. S2–S3, see ESI). The proton signals for the
meso-substituents, pyrrole and thiophene rings in the 1H NMR spectra of
3a-c lie beyond 7.40 ppm (Figs. S4–S6, see ESI). The purity of synthetic
compounds was further confirmed by elemental analysis, and the re-
sults are fully consistent with the theoretical results.
3.3. Electrochemistry
To gain further insight into the electronic structures of 3a-c, cyclic
and differential pulse voltammetry (CV and DPV) measurements were
carried out in o-dichlorobenzene (o-DCB) containing 0.1 M tetra-n-bu-
tylammonium perchlorate ([NBu]ClO4; TBAP) as a supporting electro-
lyte, so that redox potential (E1/2) values could be derived (Fig. 5). The
use of polar solvents including DMF, DMSO and PhCN was found to be
problematic due to the poor solubility of the compounds in these sol-
vents. Two reversible reduction curves are observed for 3a in o-DCB at
−0.63 and −1.70 V, while reversible oxidation waves are observed at
+0.54 and + 0.79 V. When tert-butyl groups are introduced, there is a
negative shift of the redox steps of 3b under the same conditions. It
should be noted that when n-OC16H33 groups are connected to the meso-
phenyl rings to form 3c, there are further shifts of the redox steps and a
decrease in the gap between the 1st oxidation and reduction steps were
observed in a similar manner to the narrowing in the predicted
3.2. Theoretical calculations and optical spectroscopy
Firstly, it is noteworthy that the nodal patterns of the four frontier π-
MOs of 3a (Fig. 1) are consistent with what would be anticipated for MOs
4−
derived from the HOMO and LUMO of a parent C22H22
aromatic hy-
drocarbon perimeter with D22h symmetry corresponding to the inner peri-
meter of the π-system [13–17]. Six angular nodal planes are observed for
the HOMO level, and seven for the LUMO level (Fig. 1) as part of an overall
ML = 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
13 sequence in terms of ascending energy. This is comparable to the
2−
ML = 0, 1, 2, 3, 4, 5, 6, 7, 8 sequence for the C16H16
Red
Ox
parent perimeter of tetraphenylporphyrin that results in frontier π-MOs with
four and five angular nodal planes (Figs. 1 and 2). To aid the comparison of
compounds with differing symmetries, Michl [13–17] referred to π-MOs
derived from the HOMO and LUMO, respectively, that have angular nodal
planes that lie on the y-axis as the a and -a MOs, while the MOs that have
significant MO coefficients on the y-axis are referred to as the s and -s MOs,
respectively. In the context of the parent porphyrin and rubyrin compounds,
there are only relatively minor energy splittings of the a and s, and -a and -s
MOs (the ΔHOMO and ΔLUMO values to use Michl's terminology) relatively
HOMO–LUMO gaps. The ip
and ip values, were determined from
CV measurements for 3a-c made at various scan-rates from 20 to
500 mV (Fig. S7, see ESI), and this provides an insight into the rever-
sibility of the system on an experimental time-scale. The good linear
½
correlations observed for plots of peak current vs v for 3a-c confirm
that all of the oxidation and reduction processes are diffusion con-
trolled.
weak L (or Q) bands associated with the forbidden ΔML =
9 or 13
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DyesandPigments158(2018)188–194
Fig. 1. The angular nodal patterns and the MO energies of the a, s, -a and -s MOs of the PN4 and S2N2 model complexes and 3a at the CAM-B3LYP/6-31G(d) level of
theory. The non-planarity of S2N2 and 3a are highlighted with views of the structures on the xz-plane.
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DyesandPigments158(2018)188–194
Fig. 2. Calculated MO energies of 3a-c and a series of tetraphenylporphyrin
(PN4), tetraphenyldiphenanthroporphyrin (N4), tetraphenyldithiaporphyrin
(PN2S2), tetraphenyldiphenanthrodithiaporphyrin (N2S2), tetraphenylrubyrin
(PN6), tetraphenyldiphenanthrorubyrin (N6), tetraphenyltetrathiarubyrin
(PS4N2) and tetraphenyldiphenanthrotetrathiarubyrin (S4N2) model complexes
at the CAM-B3LYP/6-31G(d) level of theory. Small black squares are used to
highlight occupied MOs. The a, s, -a and -s are denoted with thicker black lines
and black squares are used to highlight the s and -s MOs. Black circles are used
to highlight the s and -s MOs. The HOMO−LUMO band gap values are high-
lighted with red diamonds and are plotted against a secondary axis. (For in-
terpretation of the references to color in this figure legend, the reader is referred
to the Web version of this article.)
3.4. Tunable and specific response with Hg2+ ions
Upon the addition of Ag+, Cu2+, K+, Na+, Ca2+, Ni2+, Fe2+, Fe3+
,
Cd2+, Cr2+, Co3+, Pb2+ and Pd2+ ion to water/DMF (v:v = 8:2) so-
lutions of 3a-c, no significant changes were observed in the UV-visible
absorption spectra were observed in both the B and L band regions. In
contrast, when Hg2+ was added to a similar solution of 3a (Fig. 6), a
significant decrease is observed in the intensity of the B band at ca.
590 nm probably due to interactions with the sulfur atoms that were
introduced to the inner perimeter of the rubyrin macrocycles. When a p-
tert-butylphenyl substituent is introduced at the meso-positions of 3b, a
larger decrease in the B band intensity is observed. In contrast, in the
case of 3c which has a significantly longer lipophilic group on its meso-
p-C16H33O-phenyl rings, the main absorption band is shifted to longer
wavelength to ca. 630 nm and the intensity decreases, but a clear B
band remains apparent. When photographs of the water/DMF
(v:v = 8:2) solutions of 3a-c upon addition of 0.0–2.0 eq of Hg2+ are
compared, the colorimetric changes that occur to generate (Fig. 7),
purple (for 3a), transparent (for 3b) and blue (for 3c) colors become
apparent. The introduction of the lipophilic substituents of 3c decreases
the hydrophilic properties of the core-modified rubyrins, and in the
context of 3c this could create a hydrophobic environment surrounding
the inner cavity of the core-modified rubyrin in highly polar and aqu-
eous media. The selective response of the core-modified rubyrin to
Hg2+ ions can therefore be fine-tuned.
Fig. 3. Calculated TD-DFT spectra of 3a-c and a series of tetraphenylporphyrin
(PN4), tetraphenyldiphenanthroporphyrin (N4), tetraphenyldithiaporphyrin
(PN2S2), tetraphenyldiphenanthrodithiaporphyrin (N2S2), tetraphenylrubyrin
(PN6), tetraphenyldiphenanthrorubyrin (N6), tetraphenyltetrathiarubyrin
(PS4N2) and tetraphenyldiphenanthrotetrathiarubyrin (S4N2) model complexes
at the CAM-B3LYP/6-31G(d) level of theory. Red diamonds are used to high-
light the L and B bands. Details of the calculations are provided in Table S1.
(For interpretation of the references to color in this figure legend, the reader is
referred to the Web version of this article.)
solar cells and toxic ion sensors, the modification of optical properties
of rubyrins revealed in this research is useful for the design of func-
tional molecules based on conjugated systems of porphyrinoids.
Conflicts of interest
There are no conflicts of interests.
Acknowledgements
4. Conclusions
Financially supported by National Natural Scientific Foundation of
China (No. 21701058 and 21301092), Natural Scientific Foundation of
Jiangsu Province, P.R. China (No. BK20160499 and BK20151513), the
fund from the State Key Laboratory of Coordination Chemistry (No.
SKLCC1710, SKLCC1817), the fund from Key Laboratory of Functional
Inorganic Material Chemistry (Heilongjiang University) of Ministry of
Education, the Fok Ying Tung Education Foundation (Grant No.
141030) and Priority Academic Program Development of Jiangsu
Higher Education Institutions (PAPD). The theoretical calculations were
carried out at the Centre for High Performance Computing in Cape
Town.
A series of core-modified and fused-ring-expanded rubyrins have
been synthesized and characterized, with the structures confirmed by
MS and NMR data and elemental analyses. A series of spectroscopic,
electrochemical measurements and TD-DFT calculations demonstrate
that the modification of the inner perimeter of rubyrins through core-
modification with group 16 heteroatoms has a large influence on the
electronic structure. In addition, these rubyrins exhibit a highly selec-
tive and tuneable response to Hg2+ ions when lipophilic groups are
introduced onto the meso-aryl rings. Considering NIR region dyes are
being used in fields such as photo-energy conversion, dye-sensitized
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DyesandPigments158(2018)188–194
Fig. 4. UV-visible absorption spectra of rubyrins 3a-c in CHCl3.
Fig. 5. CV and DPV measurements of rubyrin 3a-c in o-dichlorobenzene (o-DCB) containing 0.1 M TBAP.
Fig. 6. UV-visible absorption spectra of 3a-c (1.0 × 10−5 mol/L, in 80: 20, DMF/water) upon addition of 0.0–2.0 eq of Hg2+
.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://dx.
doi.org/10.1016/j.dyepig.2018.05.045.
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