SubPc-ZnPorphyrin conjugates - Synthesis, characterization and properties

Article abstract of DOI:10.1016/j.dyepig.2014.07.012

A set of SubPc-Porphyrin dyads and triads have been synthesized by the nucleophilic substitution reaction of hydroxyl-containing meso-substituted porphyrins and a good electron acceptor, dodecafluorosubphthalocyanine. Acid-catalyzed condensation of p-hydr

Full text of DOI:10.1016/j.dyepig.2014.07.012

Dyes and Pigments 112 (2015) 283e289
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
SubPc-ZnPorphyrin conjugates e Synthesis, characterization and
properties
Lakshmi C. Kasi Viswanath, Laura D. Shirtcliff, Sadagopan Krishnan, K. Darrell Berlin*
Department of Chemistry, Oklahoma State University, Stillwater, OK 74078, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
A set of SubPc-Porphyrin dyads and triads have been synthesized by the nucleophilic substitution re-
action of hydroxyl-containing meso-substituted porphyrins and a good electron acceptor, dodecafluor-
osubphthalocyanine. Acid-catalyzed condensation of p-hydroxybenzaldehyde and the corresponding
dipyrromethane, followed by zinc metallation, afforded the appropriate metalloporphyrins. Subsequent
nucleophilic substitution occurred between the porphyrin and the axial chlorine atom of the sub-
phthalocyanine when reacted in a sealed tube at 180 ꢀC. The structures of all the synthesized compounds
were characterized by 1H NMR, 13C NMR and mass spectroscopy. The photophysical and electrochemical
studies have also been performed by using UVeVis, fluorescence spectroscopy and cyclic voltammetry
experiments.
Received 11 February 2014
Received in revised form
24 June 2014
Accepted 14 July 2014
Available online 23 July 2014
Keywords:
Meso-substituted
Dodecafluorosubphthalocyanine
Tetraarylporphrins
© 2014 Elsevier Ltd. All rights reserved.
Donoreacceptor conjugates
NMR spectroscopy
Electrochemical properties
1. Introduction
[10e13], depending on the nature of the counterpart. Due to the
synthetic versatility and the tunable properties of the sub-
In the recent years, the field of organic solar cells have chal-
lenged scientists in various aspects. A great deal of research has
been invested towards improving the efficiency of solar cells by not
only collecting the solar energy throughout the entire solar spec-
trum, but also in the effectual conversion of solar energy into
resourceful chemical energy [1]. This conversion involves three
sequential steps: (i) light absorption, (ii) excitation energy trans-
duction, and (iii) photoinduced electron transfer [2e4]. Notwith-
standing, fullerene derivatives are considered to be among the
most employed n-type material for photovoltaic applications [5,6].
With exceptional electron accepting properties, they display only
weak absorption cross sections in the visible part of the solar
spectrum. This alters the sunlight capture, thereby impeding the
output of photon-to-electron conversion [7].
phthalocyanines, several peripheral substituted derivatives of sub-
phthalocyanines have been prepared [14]. However, there are only a
few axially coordinated subphthalocyanine derivatives where the
electronic characteristics of the macrocycle are preserved [15e18].
Donor acceptor conjugates of subphthalcyanines are particularly
interesting because their excited states can be potentially applied in
various molecular electronic devices and artificial photosynthetic
systems [12,13]. Furthermore, the incorporated subphthalocyanines
impart additional solubility to the conjugates. Thus, in order to
achieve highly soluble donoreacceptor conjugates covering a broad
range of the solar spectrum, and with increased efficiency of solar
energy conversion, the construction of dyads and triads comprised
of porphyrin and subphthalocyanine units has been established. A
covalently linked BeO bond in the axial position can act as the
electron donor and acceptor pair.
Tetraarylporphyrins (A4) containing nucleophilic sites in the pe-
ripheral positions have been employed as building blocks for various
assemblies that are of interest to material scientists and bioinorganic
chemists. These assemblies include multiporphyrin arrays [19] and
also porphyrins with appended axial ligands. Although many of the
meso-substituted porphyrins used for such purposes have four
identical aryl substituents, less symmetric porphyrins (A3B, A2B2) are
expected to permit more varied structures. Particularly, the trans
meso-A2B2 porphyrins may be utilized to form macrocyclic
In the quest to find promising alternatives to fullerenes, sub-
phthalocyanines (SubPcs) [8,9] have been identified as suitable
candidates which possess strong absorption in the visible region
with high extinction coefficients. Additionally, subphthalocyanines
can play a dual role acting as both electron acceptor and donor
* Corresponding author. Tel.: þ1 405 744 5950.
E-mail addresses: kenneth.d.berlin@okstate.edu, kdb@okstate.edu (K. Darrell
Berlin).
http://dx.doi.org/10.1016/j.dyepig.2014.07.012
0143-7208/© 2014 Elsevier Ltd. All rights reserved.

284
L.C. Kasi Viswanath et al. / Dyes and Pigments 112 (2015) 283e289
assemblies that are difficult to make from the conventional meso-A4
porphyrins. The construction of trans meso-substituted porphyrins
containing two eOH groups in the aryl moiety was considered for the
convenient nucleophilic substitution with the axial chlorine atom of
the subphthalocyanine. Owing to the geometry of the two incorpo-
rated SubPc units, the proposed trans meso-substituted Porphyrin-
SubPc Conjugate was expected to possess improved solubility
properties compared to the corresponding monosubstituted de-
rivatives. The present work focusses on the synthesis, characteriza-
tion and properties of novel A3B and trans A2B2 porphyrins, SubPc
derivatives, Porphyrin-SubPc dyads and triads.
2. Results and discussion
2.1. Synthesis
The synthesis of A3B and trans meso-substituted A2B2 porphy-
rins began with the preparation of dipyrromethane (Scheme 1).
Two different dipyrromethanes 1a and 1b were synthesized from
the corresponding aldehydes (benzaldehyde or methyl 3-
formylbenzoate) via a condensation with freshly distilled pyrrole
in the presence of TFA [20]. Condensation of the dipyrromethanes
1a or 1b with p-hydroxybenzaldehyde in acetic acid under reflux
conditions with air as the oxidant afforded a mixture of A3B-(2a,
3a) and A2B2-(2b, 3b), plus a trace of A4-(2c, 3c) porphyrins
(Scheme 1). Since the base porphyrin intermediates were difficult
to handle, conversion to zinc complexes (ZnP) was accomplished
with Zn(OAc)2.2H2O. Initially, with a 1:1 ratio of dipyrromethane 1a
and p-hydroxybenzaldehyde, a mixture of monohydroxy triphenyl
porphyrin, A3B (4a-28%), dihydroxydiphenylporphyrin A2B2 (4b-
13%), and tetraphenylporphyrin, A4 (4c-3%) was isolated [21].
However, in our hands with 1:1.5 ratio of the starting materials, the
yield of 4b was increased to 24% and 4a was decreased to 12% while
a trace amount of tetraphenylporphyrin A4 was also isolated.
Scheme 2. Synthesis of eOBu substituted SubPcs.
Adopting similar conditions (ratio 1:1.5), the synthesis of mono (5a,
15%), dihydroxy-substituted (5b, 26%), and a trace of 5c derivatives
was achieved.
For the synthesis of the OBu-SubPc 6a (43%), a dinitrile pre-
cursor, 4,5-dibutoxyphthalonitrile, was cyclotrimerized with 1 M
BCl3 in p-xylene at 160 ꢀC using o-dichlorobenzene as the co-
solvent (Scheme 2). Attempts were also made to synthesize the
SubPc fused dimer by the condensation of dibutoxyphthalonitrile
with tetracyanobenzene. To our surprise, we were able to isolate a
Scheme 1. Synthesis of A3B and trans meso-substituted A2B2 zinc porphyrins.

L.C. Kasi Viswanath et al. / Dyes and Pigments 112 (2015) 283e289
285
butoxy-substituted SubPc derivative, 6b (22%) containing two
active nitrile groups in the peripheral position which can act as a
potential building blocks for various supramolecular assemblies. To
initiate the formation of a covalent linkage of the SubPc with the
ZnP, efforts were taken by reacting SubPc 6a and ZnP 4b with/
without base (DMAP, DBU, pyridine, NaH, K2CO3/18-crown-6).
However, no product was isolated in any of the conditions. This may
be attributed to the electron donating properties of the peripheral
butoxy groups in the subphthalocyanine which made the boron
atom less electropositive. Studies on the electronic and mechanistic
aspects of the different SubPc derivatives led us to investigate the
Hence SubPc-F (7) was synthesized by the cyclotrimerization
of tetrafluorophthalonitrile with BCl3 (1.0 M solution in p-
xylene) using the standard reaction conditions. A conventional
nucleophilic substitution required 1:5 M ratio of the Sub-
Pc:nucleophile concentration and reflux temperature. The
nucleophilic substitution of the chlorine atom by the phenoxy
group was first attempted with the monohydroxy substituted
ZnP 4a. Reaction of 7 and 4a in 1:5 ratio in dry toluene at reflux
conditions afforded the product 8 in low yield (12%) after 4 days.
However in order to reduce the concentration of nucleophile to a
1:1 M ratio, the reaction was performed in a sealed tube at 180 ꢀC
using an equimolar mixture of 4a:7 and afforded the SubPc-
nucleophilic substitution of porphyrin with
a good electron
acceptor, SubPc-F (7).
Porphyrin conjugate 8 in 33% yield (Scheme 3). Adopting
Scheme 3. Synthesis of porphyrin-SubPc-F conjugates.

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L.C. Kasi Viswanath et al. / Dyes and Pigments 112 (2015) 283e289
similar conditions, the reaction of trans- A2B2 porphyrin 4b with
the SubPc-F 7 gave two products 9a and 9b which were isolated
by column chromatography. The ester substituted compounds
10a and 10b were also prepared employing similar conditions.
In summary, a series of SubPc-Porphyrin conjugates were syn-
thesized by the nucleophilic substitution of the axial chlorine atom
by the phenoxy group of the meso-substituted zinc porphyrins. All
2.3. Electrochemical properties
The redox behavior of the dyads and triads was investigated by
cyclic voltammetry experiments. The results were compared with
those of the reference compounds SubPc-F, MPP and DPP. All ex-
periments were performed at room temperature in deaerated
acetonitrile solution containing tetra-n-butylammonium hexa-
fluorophosphate (TBAPF6, 0.1 M) as the supporting electrolyte, with
glassy carbon as the working electrode, platinum-wire as the
counter electrode, and Ag/AgNO3 as the reference electrode. The
representative cyclic voltammograms (CVs) of porphyrins, SubPc-F
and SubPc-porphyrin conjugates (MPS, DPPS1 and DPPS2) are
shown in Fig. 2. The CVs of the SubPc-Porphyrin conjugates share
common features with respect to those of the parent porphyrins,
and SubPc-F. SubPc-F presents several characteristic reduction
waves of SubPcs with a reversible one electron reduction process
occurring at ꢁ0.986 V versus Ag/AgNO3. In the cathodic direction
(between 1 and ꢁ2.5 V), MPS showed successive three reduction
processes, which are electrochemically reversible, two waves cor-
responding to the porphyrin (0.481 V and ꢁ1.878 V) and one wave
corresponding to the SubPc-F located at ꢁ0.948 V versus Ag/AgNO3.
In comparison to the unsubstituted SubPc-F, the conjugate MPS
exhibited a more positive reduction peak ~40 mV vs Ag/AgNO3
which supports a strong coupling between the subphthalocyanine
and the porphyrin units. Moreover, an irreversible oxidation pro-
cesses was exhibited by the conjugate MPS which occurred
at ꢁ1.43 V (Table 1). This supports the concept that, in general, the
fluoro-subphthalocyanines are difficult to oxidize. The dyad DPPS2
and the triad DPPS1 retain the common features of MPS. A close
inspection of the redox features of these compounds reveals that,
although the reduction waves based on both porphyrin and SubPc-
F do not change significantly, both the oxidative and reductive
voltammograms of MPS, DPPS1 and DPPS2 are not exactly the sum
of those of the parent SubPc-F and porphyrins. These are good in-
dications that electronic communications between the chromo-
phores are present in the conjugate which can form the Porþ-
SubPc-Fꢁ species. Thus, the electrochemical investigation confirms
the formation of different porphyrin-SubPc conjugates and addi-
tionally provide further insights into the electronic properties of
the synthesized complexes.
of the synthesized compounds were characterized by 1H NMR, 13
NMR and Mass Spectroscopy.
C
2.2. Optical properties
The electronic interactions between the SubPc and A3B/
A2B2eZnP were investigated via absorption and emission studies.
The steady-state absorption spectra of the parent compounds and
the conjugates in CH2Cl2 are shown in Fig. 1(Right A). The absorp-
tion spectra of MPP (4a) and DPP (4b) exhibited an intense Soret
band at 420 nm and two weak Q bands at 546 nm and 591 nm
corresponding to the Zn(II) metalloporphyrin. The SubPc-F moiety
also displayed the characteristic Q bands (575 nm, 555 nm-sh)
associated with the
p-p* transition. The absorption spectra of
conjugates [MPS (8), DPPS1 (9a), DPPS2 (9b)] revealed common
features of the SubPc-F and ZnP retaining their individual identities
in the ground state. The emission spectra of the compounds
recorded in CH2Cl2 are shown in Fig. 1(Right-B). Excitation of the
porphyrins DPP and MPP at 420 nm in CH2Cl2 produced two
emission bands centered at 597 nm and 644 nm. Whereas excita-
tion of the conjugates displayed diminished intensities of the two
bands (MPS, DPPS1 and DPPS2 in Fig. 1).
Additionally, the intensity of the typical Soret band corre-
sponding to the porphyrin moiety is also reduced. The conjugates
exhibited altered emission intensities due to charge transfer be-
tween the donor metalloporphyrin and the acceptor SubPc-F. In
order to confirm this, the fluorescence quantum yields were
determined for MPS, DPPS1 and DPPS2 by steady state comparative
method using cresyl violet (quantum efficiency, ФF ¼ 0.54) [22] as
the standard. In comparison to the free SubPc-F, 5 (ФF ¼ 0.58), the
fluorescence quantum yields of the conjugates decreased signifi-
cantly (MPS-ФF ¼ 0.089; DPPS2-ФF ¼ 0.082; DPPS1-ФF ¼ 0.063),
which correlates well with the fluorescence emission spectra. A
similar trend has also been reported in the case of PDI-SubPc Dyad
[23]. It is also interesting to note that a more pronounced drop in
fluorescence quantum yield was observed in the case of the triad
9a, which contains two SubPc-F units. All these findings suggest the
occurrence of a charge transfer process between the ZnP and SubPc
species.
3. Experimental
3.1. General
Melting points were determined using a Stuart SMP10 instru-
ment. NMR spectra (1H, and 13C) were acquired in CDCl3, CD2Cl2, or
Fig. 1. Absorption spectra of the compounds in CH2Cl2 at room temperature; (b) emission spectra in CH2Cl2 at 25 ꢀC (420 nm).

L.C. Kasi Viswanath et al. / Dyes and Pigments 112 (2015) 283e289
287
(b)
(a)
Fig. 2. Cyclic voltammogram recorded in deareated acetonitrile using TBAPF6 (0.1 M) as the supporting electrolyte. (a) parent SubPc-F, MPP, DPP: (b) SubPc-poprhyrin Conjugates
MPS, DPPS1 and DPPS2.
DMSO using a Varian Inova 400 MHz spectrometer. Chemical shifts
) are expressed in ppm relative to residual chloroform (1H:
3.3. General method for the synthesis of porphyrin (B)
(d
7.26 ppm, 13C: 77.0 ppm), DMSO (1H: 2.5 ppm, 13C: 39.5 ppm), and
dichloromethane (1H: 5.32 ppm, 13C: 54.0 ppm). Fourier Transform
Infrared measurements were performed on a Varian 800 FTeIR
spectrometer. UVeVis spectra were recorded on Cary 5000
UVeVISeNIR spectrophotometer. Fluorescence spectra were
recorded on a Cary Eclipse fluorescence spectrophotometer. The
sealed tube reaction was conducted in a unit from Chem Glass,
Model 1880. Column chromatography was carried out with silica
gel (Sorbent Technologies, 230e400 mesh), and TLC was performed
with polyester sheets precoated with silica gel (Sorbent Technolo-
gies). Compounds 3-methylformyl benzoate, pyrrole, TFA (Acros
Metallation of the base porphyrin was achieved by treating the
crude black solid and an excess of Zn(OAc)2∙2H2O with a 1:1
mixture of CH2Cl2:MeOH (10 volumes w.r.t crude) in a 100-mL,
single-necked, round-bottomed flask fitted with a magnetic stirrer
at room temperature for 12 h. The progress of the reaction was
monitored by TLC. The solvent from the reaction mixture was
evaporated, and the residue obtained was extracted with ethyl
acetate (10 volumes). The extracts were combined and were
washed with brine, dried (Na2SO4), and concentrated to provide a
dark purple solid containing a mixture of A3B and A2B2 porphyrins.
Flash chromatography of the mixture using ethyl acetate:hexane
(1:3) afforded pure mono and di-substituted porphyrins.
Organics),
p-hydroxybenzaldehyde
(Fisher),
tetra-
fluorophthalonitrile (TCI), benzaldehyde, Zn(OAc)2∙2H2O, 1.0 M
BCl3 solution in p-xylene (Sigma Aldrich) were purchased from
commercial suppliers and used as received unless otherwise
indicated.
3.4. General method for the synthesis of porphyrin-SubPc-F
conjugates (C)
A mixture of porphyrin (1.0 equiv) and dodecafluorosubph-
thalocyanine (1.0e2.0 equiv) dissolved in dry toluene (10 volumes
w.r.t porphyrin) was taken in a sealed tube and heated to 180 ꢀC for
3 days. The progress of the reaction was monitored by TLC. The
solvent from the reaction mixture was removed under vacuum and
the residue was purified by column chromatography over silica gel
using ethyl acetate:hexane in varying ratios.
3.2. General method for the synthesis of porphyrin (A)
A mixture of the dipyrromethane (1.0 equiv) and p-hydrox-
ybenzaldehyde (1.5 equiv) was taken in a 250-mL, single-
necked, round-bottomed flask fitted with a condenser and a
magnetic stir bar. Acetic acid was added to the reaction mixture,
and the resulting pale yellow solution was refluxed with
continuous stirring for 7 h. After allowing the thick, black
mixture to cool to room temperature, the solvent was removed
under vacuum to give a black solid. The solid was then redis-
solved in dichloromethane and filtered over a pad of silica which
was finally washed with THF. The filtrate and washings were
combined, and the solvent was evaporated to afford the crude
base porphyrin. Without further purification, the crude base
porphyrin intermediate was taken to the next step of complex-
ation with zinc.
3.5. Synthesis of 5a and 5b
A mixture of dipyrromethane 1b, (1 g, 0.0035 mol), p-hydrox-
ybenzaldehyde (0.653 g, 0.0053 mol), and acetic acid (200 mL)
were reacted according to general procedure A. This was then fol-
lowed by the metallation with Zn(OAc)2$2H2O (1.53 g, 0.007 mol) in
CH2Cl2:MeOH solution (50 mL, 1:1) according to the standard
procedure B to afford a mixture of A3B and trans A2B2 porphyrins
corresponding to the mono hydroxyl 5a and di-hydroxy porphyrins
5b, respectively. Purification of the mixture by column chroma-
tography using ethyl acetate:hexane (1:3) afforded pure 5a and 5b.
5a: yield: 0.46 g (15%), mp: >250 ꢀC. IR (CH2Cl2) cmꢁ1: 3052, 2989,
1719, 1484, 1422, 1264, 1170, 1109, 735, 709. 1H NMR (400 MHz,
Table 1
Electrochemical properties of SubPc-F, parent porphyrins (MPP, DPP) and SubPc-
Porphyrin Conjugates (MPS, DPPS1, DPPS2). The reduction and oxidation poten-
tials presented are in V vs Ag/AgNO3 at 25 ꢀC.
CDCl3):
d
8.95 (d, J ¼ 4.8, 2H), 8.86 (m, 9H), 8.42 (d, J ¼ 8 Hz, 3H),
8.39 (d, J ¼ 8 Hz, 3H), 8.02 (d, J ¼ 7.2 Hz, 2H), 7.80 (t, J ¼ 7.6 Hz, 3H),
7.12 (d, J ¼ 7.2 Hz, 2H), 3.92 (s, 9H). 13C NMR (100 MHz, CDCl3):
Compound E1(red) E2(red) E3(red) E1(ox)
E2(ox)
E3(ox)
E4(ox)
d
167.2, 157.3, 150.6, 149.3, 143.5, 138.9, 135.3, 134.7, 133.4, 132.4,
SubPc-F
MPP
DPP
MPS
DPPS1
DPPS2
0.265
0.430
0.421
0.481
0.447
ꢁ0.986 ꢁ1.593 ꢁ1.541
ꢁ1.725 ꢁ1.811
e
e
e
ꢁ0.937 0.706
131.3, 128.4, 128.3, 127.9, 121.9, 121.3, 119.1, 114.0, 52.8. MS (MALDI-
TOF) m/z for C50H34N4O7Zn: Calcd: 868.2132; Found: 868.2654. 5b:
yield: 0.76 g (26%). mp: >250 ꢀC. IR (CH2Cl2) cmꢁ1: 3055, 2985,
1721, 1422, 1264, 1169, 895.53, 734, 707, 619. 1H NMR (400 MHz,
e
ꢁ0.885
e
ꢁ0.931 ꢁ1.531
e
ꢁ1.026 0.510
ꢁ0.948 ꢁ1.878 ꢁ1.861 ꢁ1.431 ꢁ0.942 0.538
ꢁ0.919 ꢁ1.844 ꢁ1.919 ꢁ1.424 ꢁ0.925 0.493
0.4815 ꢁ0.925 ꢁ1.96
ꢁ1.93
ꢁ1.450 ꢁ0.953 0.510
DMSO-d6):
d
9.97 (s, broad, 1H), 8.84 (d, J ¼ 4.8, 4H), 8.69 (d,

288
L.C. Kasi Viswanath et al. / Dyes and Pigments 112 (2015) 283e289
J ¼ 4.8 Hz, 4H), 8.67 (s, 2H), 8.43 (d, J ¼ 8 Hz, 2H), 8.38 (d, J ¼ 8 Hz,
2H), 7.93e7.96 (m, 6H), 7.15 (d, J ¼ 8.8 Hz, 4H), 3.92 (s, 6H). 13C NMR
3.9. Synthesis of 9a and 9b
mixture of 4b (0.055 g, 0.07 mmol) and 7 (0.1 g,
(100 MHz, DMSO-d6):
d
167.1, 157.4, 150.5, 149.4, 143.7, 138.8, 135.9,
A
134.5, 133.6, 132.6, 131.6, 128.8, 128.5, 127.8, 121.8, 121.4, 119.2, 114.1,
52.9. MS (MALDI-TOF) m/z for C48H32N4O6Zn: Calcd: 826.1716;
Found: 826.1532.
0.154 mmol) was reacted in dry toluene (2 mL) using a sealed
tube according to the general procedure C. Repeated washing of
the products with pentane and drying under vacuum did remove
all of the solvent impurities and water. 9a: yield: 14 mg (10%).
mp: >250 ꢀC. IR (CH2Cl2) cmꢁ1: 3052, 2925, 2854, 1531, 1480,
1265, 1095, 1003, 964, 799, 740. 1H NMR (400 MHz, CD2Cl2):
3.6. Synthesis of 6a
d
8.90 (d, J ¼ 4.4 Hz, 4H), 8.67 (d, J ¼ 4.8, 2H), 8.18 (d, J ¼ 6.4 Hz,
4H), 7.76e7.81 (m, 6H), 7.63 (d, J ¼ 6.8 Hz, 4H), 5.73 (t, J ¼ 8.8 Hz,
4H). 13C NMR (100 MHz, CD2Cl2):
151.5, 150.4, 148.8, 144.5,
A solution of dicyanodibutoxybenzene (0.819 g, 3.0 mmol) in o-
dichlorobenzene (20 mL) under Ar blanket was placed in a 100-mL,
two-necked, round-bottomed flask fitted with a condenser, a gas
inlet, and a stir bar. Boron trichloride (1 mL, 1 M solution in p-
xylene) was then added dropwise, maintaining the temperature
between 25e30 ꢀC. The reaction mixture was heated to reflux at
160 ꢀC for 5 h. The solution slowly turned from a pale yellow to a
deep red colored solution upon refluxing. After cooling to room
temperature, the mixture was passed through a plug of silica gel,
followed by washing the plug with CH2Cl2 to remove impurities
and then with THF to extract the product. The organic extract was
dried, (Na2SO4) and evaporated to dryness. Column purification of
the crude product using ethyl acetate:hexane (1:1) afforded 10 as a
pink solid; yield: 1.11 g (43%). mp: > 300 ꢀC. 1H NMR (400 MHz,
d
144.2, 142.9, 141.1, 141.4, 137.4, 135.4, 134.7, 1322.2, 131.9, 132.2,
131.9, 127.9, 126.9, 121.4, 120.4, 117.4, 115.5. MS (MALDI-TOF) m/z
for C92H26B2F24N16O2Zn: Calcd: 1930.1675; Found: 1930.1643.
9b: yield: 23 mg (23%). mp: >250 ꢀC. IR (CH2Cl2) cmꢁ1: 3053,
2924, 2854, 1531, 1481, 1264, 1224, 1094, 1000, 965, 799, 740. 1H
NMR (400 MHz, CD2Cl2):
d
8.97 (d, J ¼ 4.8 Hz, 2H), 8.92 (d, J ¼ 4.8,
2H), 8.90 (d, J ¼ 4.8 Hz, 2H), 8.69 (d, J ¼ 4.8 Hz, 2H), 8.18 (d,
J ¼ 7.2 Hz, 4H), 8.04 (d, J ¼ 8.4 Hz, 2H), 7.75e7.80 (m, 6H), 7.64 (d,
J ¼ 8.4 Hz, 2H), 7.20 (t, J ¼ 6.4 Hz, 2H), 5.77 (d, J ¼ 8.4 Hz, 2H). 13C
NMR (100 MHz, CD2Cl2):
d 155.6, 151.2, 150.7, 150.3, 150.2, 148.6,
144.3, 143.9, 142.9, 141.6, 141.1, 137.3, 135.7, 135.2, 134.6, 132.1,
131.7, 127.6, 126.7, 121.2, 120.1, 117.3, 115.3, 113.6. MS (MALDI-
TOF) m/z for
1320.1418.
CDCl3):
d
8.20 (s, 4H), 4.29e4.40 (m, 10H), 1.96e2.01 (q, J ¼ 7.4 Hz,
8H), 1.51e1.62 (q, J ¼ 7.6 Hz, 8H), 1.06e1.08 (q, J ¼ 7.6 Hz, 20H). 13C
C68H27BF12N10O2Zn: Calcd: 1320.1668; Found:
NMR (100 MHz, CDCl3):
d 148.2, 146.0, 145.6, 145.4, 144.1, 141.4,
119.3, 114.8. MS (MALDI-TOF) m/z for C48H60BClN6O4: Calcd:
862.4356; Found: 862.4903.
3.10. Synthesis of 10b
A mixture of 5b (0.064 g, 0.077 mmol) and 7 (0.1 g, 0.154 mmol)
was reacted in dry toluene (2 mL) in a sealed tube according to the
general procedure C. Repeated washing of the product with
pentane and drying under vacuum did remove all of the solvent
impurities and water; yield: 24 mg (22%). mp: >250 ꢀC. IR
(CH2Cl2) cmꢁ1: 3058, 2924, 2854, 1532, 1483, 1392, 1265, 1223,
1169, 1114, 995, 966, 797, 741, 718. 1H NMR (400 MHz, CD2Cl2):
3.7. Synthesis of 6b
Dry dicyanodibutoxybenzene (1.22 g, 4 mmol) and tetracyano-
benzene (0.1 g, 0.05 mmol) were placed in a 100-mL, two-necked,
round-bottomed flask fitted with a condenser, gas inlet, and a stir
bar. The system was flushed with argon for ~10 min to remove air
and moisture. Boron trichloride (2 mL, 1 M solution in p-xylene)
was then added dropwise, maintaining the temperature between
25e30 ꢀC. The mixture was stirred at 140 ꢀC for 7 h. A change of
color was observed from pale yellow, to pink and to a final thick,
reddish-blue solution. After cooling, the solvent was evaporated to
give a dark blue solid which was chromatographed by eluting with
ethyl acetate:hexane (1:10) to afford 6b as reddish blue solid; yield:
d
8.95 (d, J ¼ 4.4 Hz, 2H), 8.84 (d, J ¼ 4.8 Hz, 2H), 8.83 (d, J ¼ 4.8 Hz,
2H), 8.80 (s, 2H), 8.69 (d, J ¼ 4.8 Hz, 2H), 8.42 (d, J ¼ 8.4 Hz, 2H), 8.40
(d, J ¼ 7.8 Hz, 2H), 8.01 (d, J ¼ 7.8 Hz, 2H), 7.84 (t, J ¼ 7.8 Hz, 2H), 7.63
(d, J ¼ 7.6 Hz, 2H), 7.15 (d, J ¼ 8.4 Hz, 2H), 5.72 (d, J ¼ 7.8 Hz, 2H). 3.91
(s, 6H). 13C NMR (100 MHz, CD2Cl2):
d 167.5, 155.9, 151.0, 150.3,
144.1, 143.1, 138.1, 135.1, 132.6, 132.1, 131.9, 129.1, 127.1, 120.1, 117.4,
115.4, 113.5, 52.5. MS (MALDI-TOF) m/z for C72H31BF12N10O6Zn:
Calcd: 1436.1777; Found: 1436.1654.
0.66 g (22%).mp: >250 ꢀC. 1H NMR (400 MHz, CDCl3):
8.20 (s, 4H), 4.29e4.40 (m, 10H), 1.96e2.01 (m, 8H), 1.51e1.62 (m,
8H), 1.06e1.08 (m, 20H). 13C NMR (100 MHz, CDCl3):
155.2, 153.4,
d 9.25 (s, 2H),
d
152.7, 151.1, 143.8, 129.1, 128.7, 126.5, 124.6, 116.1, 112.3, 105.0, 104.6,
69.4, 31.0, 31.0, 19.2, 13.9. MS (MALDI-TOF) m/z for C48H60BClN6O4:
Calcd: 768.3111; Found: 768.4312.
4. Conclusions
We have synthesized different SubPc-Zn-Porphyrin conjugates
which are linked in the axial position. All the synthesized com-
pounds were characterized by 1H NMR and 13C NMR spectroscopy
and their properties have been studied by absorption, emission
spectroscopy and electrochemical measurements. The electro-
chemical measurements, coupled with the emission results,
demonstrate the existence of the electronic communication
occurring between the SubPc and the porphyrin moieties. The
synthesized ZnP-SubPc conjugates are expected to find applications
in artificial photosynthetic systems and various molecular elec-
tronic devices.
3.8. Synthesis of 8
A mixture of 4a (0.026 g, 0.03 mol) and 7 (0.025 g, 0.03 mmol)
was reacted in dry toluene (2 mL) using a sealed tube according to
the general procedure C. Repeated washing of the product with
pentane and drying under vacuum did remove all of the solvent
impurities and water; yield: 16.3 mg (33%). mp: >250 ꢀC. IR
(CH2Cl2) cmꢁ1: 3058, 2924, 2853, 1531, 1480, 1264, 1107, 1002,
965, 798, 741. 1H NMR (400 MHz, CD2Cl2):
d 8.94 (s, 4H), 8.92 (d,
J ¼ 4.8, 2H), 8.70 (d, J ¼ 4.4 Hz, 2H), 8.20 (d, J ¼ 6.8 Hz, 6H),
7.75e7.78 (m, 9H), 7.64 (d, J ¼ 8 Hz, 2H), 5.73 (d, J ¼ 8 Hz, 2H). 13C
Acknowledgments
NMR (100 MHz, CD2Cl2):
d 151.5, 150.5, 148.8, 144.2, 143.0, 142.2,
137.4, 135.4, 132.2, 131.9, 127.8, 126.9, 121.4, 120.4, 117.4, 115.5. MS
(MALDI-TOF) m/z for C68H27BF12N10OZn: Calcd: 1304.1719; Found:
1304.1516.
We thank the Oklahoma State University, Chemistry Depart-
ment for financial support provided for this project. We also thank
Dr. Barry Lavine for providing the fluorescence accessories.

L.C. Kasi Viswanath et al. / Dyes and Pigments 112 (2015) 283e289
289
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