Synthesis and solvent effects on the spectroscopic properties of octatosylamido phthalocyanines

Article abstract of DOI:10.1039/b416286b

Octatosylamido-substituted metal-free, Ni(II) and Zn(II) phthalocyanines (pcs, 3a-c) have been synthesized from 4,5-dicyano-N,N′-ditosyl-o- phenylenediamine (2, tosyl: toluene-p-sulfonyl) in the presence of an anhydrous metal salt and a strong base. The new compounds have been characterized by elemental analysis, IR and UV-vis spectroscopy, different NMR techniques ( ¹H, ¹³C, ¹H-¹⁵N HSQC, ¹H-¹³C HSQC and ¹H-¹³C HMBC) and mass spectroscopy. The influence of the solvent on the ¹H, ¹³C NMR and UV-vis spectra has been determined. In chloroform, 3a-c are able to form intramolecular hydrogen bonds between four NH and oxygen atoms from neighbouring tosyl units and two tosyl groups occur in one single molecule: while four tosyl units are in the pc plane, the other four are nearly vertical to it. They have different chemical environments because of the magnetic anisotropy of the pc ring. For this reason, in chloroform, each of the protons and carbon atoms gives two sets of signals in the ¹H and ¹³C NMR spectra of pcs. In tetrahydrofuran, the intramolecular hydrogen bonding of pcs is disrupted and all tosyl units are located in the same environment. In the electronic spectra of 3a-c, all bands change with the solvent. This solvatochromism is caused by solvent basicity. Compounds 3a-c show rapid and reversible colour change upon addition of a base. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2005.

Full text of DOI:10.1039/b416286b

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P A P E R
Synthesis and solvent effects on the spectroscopic properties
of octatosylamido phthalocyanines
Fatma Yu l Gu
ksel,a Ays-e Gu rek,a Colette Lebrunb and Vefa Ahsen*ac
¨ ¨ ¨
a Department of Chemistry, Gebze Institute of Technology, P.O. Box 141, 41400 Gebze,
Kocaeli, Turkey. E-mail: ahsen@gyte.edu.tr; Fax: +90 262 754 23 85;
Tel: +90 262 754 23 60
b Laboratoire de Chimie Inorganique et Biologique (CNRS UMR 5046), DRFMC,
CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 09, France
c Materials and Chemical Technologies Research Institute, TUBITAK-Marmara Research
Center, P.O. Box 21, 41470 Gebze, Kocaeli, Turkey
Received (in Montpellier, France) 21st October 2004, Accepted 14th January 2005
First published as an Advance Article on the web 1st April 2005
Octatosylamido-substituted metal-free, Ni(II) and Zn(II) phthalocyanines (pcs, 3a–c) have been synthesized
from 4,5-dicyano-N,N’-ditosyl-o-phenylenediamine (2, tosyl: toluene-p-sulfonyl) in the presence of an
anhydrous metal salt and a strong base. The new compounds have been characterized by elemental analysis,
1
1
IR and UV-vis spectroscopy, different NMR techniques (1H, 13C, H–15N HSQC, H–13C HSQC and
1H–13C HMBC) and mass spectroscopy. The influence of the solvent on the H, 13C NMR and UV-vis
1
spectra has been determined. In chloroform, 3a–c are able to form intramolecular hydrogen bonds between
four NH and oxygen atoms from neighbouring tosyl units and two tosyl groups occur in one single
molecule: while four tosyl units are in the pc plane, the other four are nearly vertical to it. They have
different chemical environments because of the magnetic anisotropy of the pc ring. For this reason, in
1
chloroform, each of the protons and carbon atoms gives two sets of signals in the H and 13C NMR spectra
of pcs. In tetrahydrofuran, the intramolecular hydrogen bonding of pcs is disrupted and all tosyl units are
located in the same environment. In the electronic spectra of 3a–c, all bands change with the solvent. This
solvatochromism is caused by solvent basicity. Compounds 3a–c show rapid and reversible colour change
upon addition of a base.
chemical-switching systems and gas-controlled reversible
colour-change devices.13
Introduction
Phthalocyanines (pcs) have aroused extensive interest in the
past decades since their unique properties led to their use
in a wide number of applications in the area of materials
science, such as chemical sensors, liquid crystals, catalysis,
and nonlinear optics.1–7 In addition, their properties have
been considered to have potential applications in cancer
photodynamic therapy (PDT).8–10 Fundamental to their
specific properties is the delocalized electronic nature of the
pc ring system. Most of the applications of pcs are focused
on the electronic properties of the p-electron system of the
macrocycles. Strong light absorption by pcs to give clear
blue or green colours led to their use as pigments and dyes,
soon after their discovery, and these applications are still of
immense commercial importance. Pcs show typical electronic
spectra with strong absorption in two regions, the visible (Q
band at 600–700 nm) and the ultraviolet [B (Soret) band at 300
–350 nm]; the latter is generally much less intense. In the
absorption spectra of pcs, the bands can be changed by
changing the type of central metal ion and/or the nature of
substituents.
One of our main aims is the synthesis of new pcs with various
functional groups for potential applications such as chemical
gas sensors, liquid crystals, PDT and catalysis.14 Substituents
play an important role in tailoring pcs for various applications.
For example, aromatic diamines have interesting properties.
They are less basic than aliphatic amines due to the delocaliza-
tion of the electron pair on the nitrogen atom toward the
p-orbitals of the aromatic ring, the electron density on the
nitrogen atom available for bond formation thus being lower.15
Thanks to their protonation-deprotonation properties, aro-
matic diamines are useful for many applications such as
biosensors, mutagens, carcinogens and antitumor agents.15–18
Substitution of amines confers promising properties onto
pcs.19 In this respect, we have now designed and synthesized
octatosylamido-substituted metal-free, Ni(II) and Zn(II) pcs
(3a–c, respectively). These new compounds have been charac-
terized by elemental analysis, IR, NMR UV-vis and mass
spectroscopy. The influence of the solvent on the 1H, 13C
NMR and UV-vis spectra has been examined.
The electronic spectra of some molecules can be influenced
by the polarity (solvatochromism or perichromism11), tem-
perature (thermochromism), light (photochromism), pressure,
pH (acidichromism), etc., of the medium.12 In acidichromism,
the protonated form and the conjugate base may have
distinctly different absorption spectra. This phenomenon,
well-known for phenols and aromatic amines, has potential
applications in pH or acid and base gas sensors, photo- and
Experimental
Materials
4,5-Dibromo-N,N0-ditosyl-o-phenylenediamine (1) was pre-
pared according to the literature20 and spectroscopic results
are given below. All other reagents and solvents were of
T h i s j o u r n a l i s & T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 5
726
N e w J . C h e m . , 2 0 0 5 , 2 9 , 7 2 6 – 7 3 2

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reagent grade quality from commercial suppliers and were
dried before use as described in the literature.21
1348, 1333 (SO2), 1306, 1164 (SO2), 1086, 1019, 915, 883, 815,
750, 670, 580, 550, 538. MS (EI) m/z (%): 469 (16) [M + 2]+,
468 (15) [M + 1]+, 467 (51) [M]+, 312 (18) [M ꢀ (tosyl)]+, 157
(25) [M ꢀ 2tosyl]+, 155 (100) [M ꢀ 2(tosyl + H)]+.
Measurements
Elemental analyses were obtained from a Carlo Erba 1106
instrument. Infrared spectra from KBr pellets were recorded
on a Bio-Rad FTS 175C FT-IR spectrophotometer. UV-vis
spectra were recorded on a Schimadzu 2001 UV PC spectro-
photometer using 1 cm pathlength cuvettes at room tempera-
ture. The mass spectra were recorded on a VG Zab Spec
GC-MS spectrometer using electronic impact (EI) method
and on a LCQ ion trap (Thermofinnigan, San Jose, CA,
USA), equipped with an electrospray ionization (ES) source.
ES full scan spectra, in the range of m/z 50–2000 or 2000–3000
amu, were obtained by infusion through fused silica tubing at
2–10 ml minꢀ1. The solutions were analyzed in positive mode.
The LCQ calibration (m/z 50–2000) was achieved according to
the standard calibration procedure from the manufacturer
(mixture of caffeine, MRFA and Ultramark 1621). An ES-
Tuning Mix solution (Agilent) was used to calibrate the
spectrometer between 2000 and 3000 amu. The temperature
of the heated capillary of the LCQ was set in the range 180–
200 1C, the ion spray voltage was in the range 1–7 kV with an
injection time of 5–200 ms. 1H and 13C NMR spectra were
recorded in deuterated chloroform, THF and DMSO solutions
on a Bruker 500 MHz spectrometer using TMS as an internal
reference.
Octatosylamido phthalocyanine (3a). Freshly hexane-cleaned
lithium, 0.11 g (25.72 mmol), was dissolved in 3 ml of n-
pentanol and 0.4 g (0.86 mmol) of 2 were added to the solution.
The mixture was heated to reflux for 60 h under argon atmo-
sphere. The solvent was completely removed under reduced
pressure and the crude product was washed with hexane
several times, dissolved in 60 ml of a mixture of acetic acid–
CH2Cl2 (1 : 5). Then, it was extracted with distilled water (4 ꢁ
100 ml), and the organic layer was isolated, dried over anhy-
drous Na2SO4 and the solvent removed. The dark green-blue
crude product was purified by silica gel chromatography by
elution with CH2Cl2. Yield 0.022 g (5.5%); anal. calcd for
C88H74N16O16S8: C, 56.58; H, 3.99; N, 12.00; found C, 56.94;
H, 4.17; N 11.86%; IR nmax/cmꢀ1: 3546 (free NH), 3234 (H-
bonded NH), 3064 (CHAr), 2924 (CH ), 1650, 1620 (C N),
Q
3
1597, 1496, 1453, 1403, 1333 (SO2), 1291, 1263, 1161 (SO2),
1089 1019, 912, 812, 752, 704, 666, 596, 547. MS (ES-MS) m/z
(%): 1868 (100) [M + 1]+, 1867 (91) [M]+.
Octatosylamido phthalocyaninato nickel(II) (3b). A mixture of
1.87 g (4.00 mmol) of compound 2, 0.52 g (4.00 mmol) of
anhydrous NiCl2, 0.9 ml (6.00 mmol) of DBU and 6 ml of dried
n-hexanol was heated to reflux for 18 h under argon atmos-
phere. The solvent was completely removed under reduced
pressure and the crude product was washed with ethanol
several times, dissolved in 70 ml of a mixture of acetic acid–
CH2Cl2 (1 : 5). Then, it was extracted with distilled water (4 ꢁ
100 ml) and the organic solution was dried over anhydrous
Na2SO4 and concentrated. The dark green-blue product was
purified over silica gel with CH2Cl2 as the eluent. Yield 0.75 g
(%39); anal. calcd for C88H72N16NiO16S8: C, 54.91; H, 3.77;
The absorption spectra of 3a–c were taken on 7.5 ꢁ 10ꢀ3 mol
dmꢀ3 concentration solutions in various solvents. Acid-base
titrations of pcs were performed by addition of increasing
concentrations of KOH or HCl solutions in MeOH to the
fixed concentrations of pcs (3 ml; 7.5 ꢁ 10ꢀ6 mol dmꢀ3).
Syntheses
4,5-Dibromo-N,N0-ditosyl-o-phenylenediamine (1).
1 was
N, 11.64; found C, 54.63; H, 4.07; N 11.36%; IR nmax/cmꢀ1
3547 (free NH), 3233 (H-bonded NH), 3068 (CHAr), 2925
:
synthesized from o-phenylenediamine as described in the lit-
erature.20 Yield 94%; m.p.: 218–220 1C; anal. calcd for
C20H18Br2N2O4S2: C, 41.83; H, 3.16; N, 4.88; found: C,
41.92; H, 3.32; N, 4.59%; IR nmax/cmꢀ1: 3520 (free NH),
3257 (H-bonded NH), 3096 (CHAr), 2924 (CH3), 1597, 1503,
1468, 1426, 1391, 1361, 1335 (SO2), 1321, 1264, 1185, 1163
(SO2), 1118, 1090, 1018, 942, 900, 867, 835, 810, 723, 710, 676,
614, 589, 563, 483, 462; MS (EI) m/z (%): 576 (11) [M]+
(81Br81Br), 574 (19) [M]+ (81Br79Br), 572 (9) [M]+ (79Br79Br),
420 (59) [M ꢀ tosyl]+, 341 (25) [M ꢀ (tosyl + Br)]+, 265 (19)
[M ꢀ 2tosyl]+, 185 (12) [M ꢀ (2tosyl + Br)]+, 155 (79)
[M ꢀ (2tosyl + Br + 2NH)]+, 91 (100) [M ꢀ (2tosyl +
2Br + NH)]+, 78 (48) [M ꢀ (2tosyl + 2Br + 2NH)]+; 1H
NMR (DMSO-d6) d: 2.38 (s, 6H, CH3), 7.27 (s, 2H, CHAr),
(CH ), 1621 (C N), 1598, 1534, 1468, 1438, 1402, 1338
3
Q
(SO2), 1294, 1161 (SO2), 1090, 1055, 1020, 919, 812, 753, 706,
668, 546. MS (ES-MS), m/z (%): 1925 (100) [M + 1]+, 1924
(88) [M]+.
Octatosylamido phthalocyaninato zinc(II) (3c). The procedure
is the same as above with 0.88 g (4.00 mmol) of anhydrous
Zn(OAc)2 (instead of NiCl2) and 5 ml dried n-hexanol (instead
of
6
ml). Yield 0.64
g
(%33); anal. calcd for
C88H72N16O16S8Zn: C, 54.72; H, 3.76; N, 11.60; found C,
54.46; H, 4.07; N 11.41%; IR nmax/cmꢀ1: 3449 (free NH),
7.38 (d, 4H, CHAr), 7.61 (d, 4H, CHAr), 9.60 (br, 2H, NH); 13
NMR (DMSO-d6, APT) d: 20.98 (CH3), 125.80 (CAr–Br),
126.81 (CArH–C–Br and CArH–C–SO2–), 129.81 (CAr C–
C
3248 (H-bonded NH), 3070 (CHAr), 2927 (CH ), 1619 (C N) ,
Q
3
1599, 1492, 1460, 1403, 1339 (SO2), 1294, 1262, 1162 (SO2),
1090, 1037, 919, 812, 746, 706, 669, 548. MS (ES-MS) m/z (%):
1931 (100) [M + 1]+, 1930 (70) [M]+.
H
Q
CH3), 130.67 (CAr–NH–), 136.08 (CAr–SO2–), 143.78 (CAr
CH3).
–
Results and discussion
4,5-Dicyano-N,N0-ditosyl-o-phenylenediamine (2). A mixture
of 25.41 g (44.24 mmol) of 1, 12.32 g (137.56 mmol) of CuCN
and 120 ml of anhydrous DMF were heated to 140 1C for 20 h
under argon atmosphere. After cooling, the resulting dark
brown mixture was mixed with aqueous NH4OH (25%, 300
ml) and air was passed through the solution for 14 h. The
brown precipitate was filtered off and washed with water until
the filtrate was neutral. The solid product was recrystallized
first from acetic acid and then from ethanol. Yield 7.02 g
(34%); m.p.: 203–205 1C; anal. calcd for C22H18N4O4S2: C,
56.64; H, 3.89; N, 12.01; found: C, 56.36; H, 3.52; N, 11.91%;
IR nmax/cmꢀ1: 3535 (free NH), 3262 (H-bonded NH), 3065
(CHAr), 2925 (CH3), 2232 (CN), 1600, 1564, 1505, 1439, 1410,
Synthetic procedure and characterization
Pcs (3a–c) were prepared by the route shown in Scheme 1.
Commercially available o-phenylenediamine was employed as
the starting material for the synthesis of the pcs. It was first
tosylated, then brominated and converted into 4,5-dicyano-
N,N 0-ditosyl-o-phenylenediamine (2).
The synthesis of metal-free pc 3a from 2 was accomplished
through a dilithium pc intermediate followed by a proton-
lithium exchange. In the synthesis of 3b and 3c, the best yields
were obtained by a cyclotetramerization reaction in the pre-
sence of the metal salt and 8-diazabicyclo-[5.4.0]-undec-7-ene
(DBU) as a strong nitrogen base in n-hexanol at reflux of the
N e w J . C h e m . , 2 0 0 5 , 2 9 , 7 2 6 – 7 3 2
727

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Fig. 1 Molecular structure of metal-free pc 3a
and tosyl units. In order to form intramolecular hydrogen
bonding, two different tosyl groups occured: while four tosyl
units were at the pc plane, other four were nearly vertical to pc.
This structure was confirmed in the IR and NMR spectra
of pcs.
NMR spectra
The NMR spectra of compound 1 provided the characteristic
chemical shifts and confirmed the proposed structure. DMSO-
d6 was used as the solvent owing to good solubility. The methyl
signal was observed at 2.38 ppm as a singlet. Aromatic CH
protons of tosyl units gave two doublets at 7.38 and 7.61 ppm
and another aromatic CH proton gave a singlet signal at 7.27
ppm. The disappearance of the broad signal at 9.60 ppm upon
addition of D2O confirmed its attribution to the NH proton. In
the 1H NMR spectrum of compound 2 (Table 1) in DMSO-d6
methyl protons gave a singlet chemical shift at 2.40 ppm.
Aromatic protons of tosyl units gave two doublets at 7.40
and 7.70 ppm and other aromatic CH protons gave a singlet
signal at 7.55 ppm. When chloroform-d was used as solvent for
1H NMR spectroscopy of compound 2, methyl protons gave
rise to two singlet signals at 2.06 and 2.37 ppm and two NH
signals, at 7.49 and 8.50 ppm, disappeared upon deuterium
exchange. In the 13C NMR spectra of these two compounds all
of the carbon atoms showed the expected chemical shifts, as
listed in the Experimental and Table 2.
Scheme 1 Syntheses of the pc derivatives.
solvent. Silica gel column chromatography was employed to
obtain the pure products. The intense green-blue powders were
very soluble in a number of solvents such as chloroform,
acetone, tetrahydrofuran (THF), ethyl acetate and slightly
soluble in benzene, toluene, dimethyl sulfoxide (DMSO),
methanol and N,N’-dimethyl formamide (DMF).
Elemental analysis results and a close investigation of the
mass spectra of the intermediates (1, 2) and pcs confirmed the
proposed structures. Compound 1 gave [M]+ isotope peaks (at
572, 574, 576) in the ratio 1 : 2 : 1, respectively, because of the
presence of two bromine atoms. In the EI mass spectra of the
intermediates, fragmentation ion peaks appeared to corre-
spond to the stepwise loss of tosyl and NH groups from the
molecules. In the mass spectra of pcs obtained by the relatively
soft ES-MS technique, the molecule ion peaks were observed at
m/z 1867 for 3a, 1924 for 3b and 1930 for 3c. Another common
point in all pcs mass spectra is the clear appearance of the small
dimerization peaks.
Comparison of the IR spectra at each step gave some
insights on the nature of the products. In the IR spectrum of
2, CRN was responsible for an absorption at 2232 cmꢀ1. This
sharp peak disappeared in the IR spectra of pcs. The char-
acteristic vibration of SO2 groups appeared around 1335 and
1160 cmꢀ1 in the spectra of all compounds. For all compounds
the two NH groups gave rise to two bands around 3550 and
3235 cmꢀ1: the bands at ca. 3550 cmꢀ1 correspond to free NH
and the lower frequency bands at ca. 3235 cmꢀ1 arise from the
hydrogen-bonded NH.
Geometry optimization of the structure 3a was done by
means of the semi-empirical method AM1 (GAUSSIAN
03W program package) in the gas phase. As shown in Fig. 1,
four N–H units were found close to oxygen atoms of neigh-
bouring tosyls. Nitrogen atoms lead to rotation of hydrogen
These spectral data confirmed that compound 2 formed
intramolecular hydrogen bonds in chloroform. In general,
the formation of hydrogen bonds leads to significant shifts to
1
low field. Hence, in the H NMR spectrum of compound 2 in
chloroform-d, two hydrogen-bonded and free NH protons
appeared at two different chemical shifts. In the case of
intramolecular hydrogen bonding, two different types of tosyl
units occurred in one molecule: while one was in the same plane
as benzene, the other was nearly vertical to it. The methyl
protons of two tosyl units had different chemical environments
because of the magnetic anisotropy of the benzene.
1
Figs. 2 and 3 show the H and 13C NMR spectra of 3b in
deuterated chloroform and THF. In CDCl3, two NH signals
disappeared by deuterium exchange and the 1H–15N HSQC
(heteronuclear single quantum coherence) 2D NMR spectrum
showed two signals. Table 1 summarizes the 1H and 13C NMR
spectral data of 3a–c in deuterated chloroform and THF.
Similar to the nitrile derivative 2, 3a–c formed intramolecular
hydrogen bonds as confirmed by IR spectroscopy, giving the
special shown in Fig. 1. Here one of the NH groups forms a
H-bridge with the neighbouring tosyl moiety while the other
stays in the free form. Consequently, the chemical environ-
ments around the two tosylamido groups are totally different.
1
The H NMR spectra of phthalocyanines are known to show
large diamagnetic ring current shifts due to the macrocyclic
p-system. The signals of aromatic protons of pcs appear at low
field. Protons of axially bonded groups show a large shift to
higher field.2,22 In the case of dinitrile derivative 2, only the
methyl protons showed two different chemical shifts. Interest-
ingly, the 1H and 13C NMR spectra of pcs exhibited two sets of
728
N e w J . C h e m . , 2 0 0 5 , 2 9 , 7 2 6 – 7 3 2

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Table 1 1H NMR spectral data for dinitrile (2) and pc derivatives (3a–c)
Solvent
1, 10
3, 30
4, 40
7, 70
NH
Other
—
2
CHCl3-d
2.06 (s, 3H)
2.37 (s, 3H)
2.40 (s, 6H)
2.11 (s, 12H)
2.93 (s, 12H)
2.13 (s, 12H)
2.90 (s, 12H)
2.38 (s, 24H)
2.19 (s, 12H)
2.97 (s, 12H)
7.25 (d, 4H)
7.59 (d, 4H)
7.32 (s, 2H)
7.49 (s, 1H)
8.50 (s, 1H)
Not observed
7.92 (s, 4H)
8.89 (s, 4H)
7.90 (s, 4H)
8.82 (s ,4H)
9.30 (br, 8H)
7.99 (s, 4H)
8.86 (s, 4H)
2
3a
DMSO-d6
CHCl3-d
7.40 (d, 4H)
6.67 (d, 8H)
7.79 (d, 8H)
6.69 (d, 8H)
7.76 (d, 8H)
7.39 (d, 16H)
6.71 (d, 8H)
7.82 (d, 8H)
7.70 (d, 4H)
7.10 (d, 8H)
8.04 (d, 8H)
7.09 (d, 8H)
8.00 (d, 8H)
7.92 (d, 16H)
7.15 (d, 8H)
8.08 (d, 8H)
7.55 (s, 2H)
8.16 (s, 4H)
8.80 (s, 4H)
8.05 (s, 4H)
8.67 (s, 4H)
9.04 (s, 8H)
8.25 (s, 4H)
8.85 (s, 4H)
—
ꢀ3.46 (s, 2H, NH)
3b
CHCl3-d
—
3b
3c
THF-d8
CHCl3-d
—
—
signals for all protons and carbons except carbon atoms of the
pc core in chloroform-d but only one set of signals was
observed in THF-d8. The reason for this is that the benzene
ring in 2 possesses a smaller magnetic anisotropic effect than
the pc ring of 3a–c. All carbon signals obtained from 13C
of the molecules, thereby leaving all tosyl units in the same
chemical environment.
Electron absorption spectra
1
1
(APT) NMR were determined by H–13C HSQC and H–13C
HMBC (heteronuclear multiple bond coherence) 2D NMR
techniques (Table 2).
The blue-green phthalocyanines show typical electronic spectra
with two strong absorption bands: an ultraviolet Soret (B)
band around 300–350 nm and a visible Q band around 600–700
nm. In the case of metal-free phthalocyanine, the Q band splits
into two bands arising from its lower symmetry (D2h) com-
pared with that of metal phthalocyanines (D4h). The splitting of
the metal-free phthalocyanine is lost on deprotonation, using a
strong base to form the pc2ꢀ anion, which also has D4h
symmetry.1,2
The hydrogen-bonding capability of the solvent is very
important in the NMR spectra of these compounds. Chloro-
form is a weak hydrogen-acceptor solvent so it is not capable
of disrupting the intramolecular hydrogen bonds of dissolved
molecules. For this reason, when chloroform-d was used as the
solvent, the unexpected splitting of almost all bands was
observed in the NMR spectra of compounds 2 and 3a–c.
However, THF and DMSO are electron-donor (H-acceptor)
solvents so they break up the intramolecular hydrogen bonds
The colour of 3a–c changed in different solvents. In THF
and ethyl acetate they were green, in chloroform, benzene and
Table 2 13C (APT) NMR spectral dataa for dinitrile (2) and pc derivatives (3a–c)
Aromatic CHb
Aromatic Cc
CH3
1, 10
Solvent
3, 30
4, 40
7, 70
2, 20
5, 50
6, 60
8, 80
9
Other
2
CHCl3-d
DMSO-d6
CHCl3-d
21.73
21.50
20.60
21.44
20.61
21.41
21.37
20.60
21.42
130.33
130.49
128.52
130.01
128.53
129.98
129.84
128.45
129.89
127.50
127.36
125.96
126.26
125.97
126.21
128.13
125.89
126.29
b
127.50
124.95
122.22
123.42
121.46
122.62
118.16
121.87
123.10
145.79
144.8
134.29
136.31
135.82
136.07
135.73
135.84
137.08
135.54
135.95
133.95
133.98
133.11
133.59
132.71
133.60
133.07
132.11
133.80
112.78
110.33
135.42
135.60
133.79
134.29
134.04
135.06
135.76
—
—
114.45 (CN)
115.92 (CN)
—
2
3a
142.99
145.02
142.99
144.58
144.67
142.80
144.88
145.10
3b
CHCl3-d
145.03
—
3b
3c
THF-d8
CHCl3-d
146.04
151.79
—
—
a
c
1
Numbering of the atoms as shown in Table 1. Determined by 1H-13C HSQC 2D NMR technique. Determined by H-13C HMBC 2D NMR
technique.
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Fig. 2 1H NMR spectra of 3b in (A) CHCl3-d and (B) THF-d8
toluene blue, and reddish-brown in pyridine, DMF and
DMSO. This is demonstrated in Fig. 4, which shows the
absorption spectra of compounds 3a–c in THF, chloroform
and DMSO. In the case of THF, metal-free pc 3a gave a split Q
band at 710 and 681 nm as a result of the D2h symmetry. The
smaller two bands at shorter wavelengths (at 647 and 615 nm)
are vibrational progressions of the Q bands, which usually
appear in spectra of metal-free pcs.23 The nickel(II) pc 3b and
zinc(II) pc 3c exhibit intense Q bands at 683 and 687 nm,
respectively.
Electronic absorption spectra of 3a–c gave two Q bands in
chloroform: a monomeric Q band around 680 nm together
with a blue-shifted intense band around 640 nm corresponding
to aggregated species. In the case of most pcs, aggregation is
closely related to the concentration of the solution; any dilu-
tion usually results in lowering the intensity of the higher
energy band corresponding to aggregated species, together
with a relative increase in the lower energy band of the
monomers.24 When solvents such as chloroform, benzene,
toluene and nitromethane were used to obtain the UV-vis
spectra of pcs 3a–c, dilution brought out no appreciable
change in the relative intensities of both Q bands and the
absorbance values closely followed the Lambert–Beer law. This
means that there should be some additional interaction among
the pc units, so that they are kept in close contact even at very
low concentrations. Taking into account the usual spectra
obtained in the case of highly basic solvents (e.g., THF,
methanol, acetone, ethyl acetate, 1,4-dioxane), we expect an
interaction of the tosylamido groups of neighbouring pc
molecules, similar to the intramolecular H-bridge formation
shown in Fig. 1.
Fig. 3 13C (APT) NMR spectra of 3b in (A) CHCl3-d and (B) THF-d8
In the absorption spectra of pcs 3a–c in DMSO, Q bands
were appreciably shifted to the red and also the splitting of the
Q band of metal-free pc 3a disappeared. In addition to the Q
and B bands, a relatively weaker and broad new band appeared
around 500–550 nm. DMSO is basic enough to deprotonate
pcs via the NHTs (Ts ¼ tosyl) units, which produces the
anionic form and increases the number of lone pair electrons
on the nitrogen atoms. When this occurs, the new band around
500–550 nm appears, which is attributable to a n-p* transition.
Also, this new band is observed in the deprotonation of pc
derivatives in the presence of bases (KOH).
All these spectral changes are a result of the intermolecular
solute-solvent interaction forces. The ambitious approach of
Catalan et al. to quantify solvent effects on electronic absorp-
tion spectra includes comprehensive scales of solvent polarity/
polarizability (SPP), solvent basicity (SB), and solvent
acidity (SA).25 Table 3 summarizes the Q bands of 3a–c in
various solvents. In our case, solvatochromism is caused by a
combination of hydrogen bonding and deprotonation of the
NHTs units and it closely depends on the solvent basicity. Fig.
5 shows the relation between the peak wavelength of the
Q band maximum of compound 3b in various solvents on
the SB scale.
Deprotonation of pcs was also investigated in basic condi-
tions. The colour of 3a–c changed upon addition of a base to
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Table 3 Location of the Q bands (in nm) of pc derivatives 3a–c in
different solvents.
Solvent basicity
(from ref. 25)
Solvent
3a
3b
3c
Chloroform
Benzene
Toluene
0.071
0.124
0.128
0.236
0.444
0.475
0.542
0.545
0.591
0.581
0.613
0.647
686, 637
687, 639
687, 639
681, 637
717
673, 638
674, 639
673, 639
674, 637
683
682, 640
685, 643
684, 643
685, 643
688
Nitromethane
1,4-Dioxane
Acetone
708, 682
708, 678
710
681
681
686
686
Ethyl acetate
Methanol
THF
694
683
696
687
710, 681
722
734
Pyridine
DMF
DMSO
712
727
710
721
740
730
721
nitrogen atoms expand the delocalized p-system of the pcs,
resulting in the Q band shift to the red. The weaker broad
absorption band around 500–550 nm is possibly due to an n-p*
transition. A similar band (called the W band) has previously
been reported for pcs with peripheral alkoxy or alkylthio
groups as a broad band with intermediate intensity at ca. 400
–500 nm and has been assigned to the involvement of ether
oxygen or thioether sulfur lone pairs.26
When increasing concentrations of HCl was added to THF
solutions of 3a and 3b, the colour and spectra did not change.
But an additional new band was observed at a longer wave-
length (at 730 nm) and the intensity of the Q band decreased in
the absorption spectrum of ZnPc (3c, Fig. 7). In order to
eliminate the possibility of any effect of MeOH, a blank test
were run but no appreciable change was observed. The forma-
tion of this new band, which disappeared upon addition of a
base, can be attributed to protonation of the nitrogen atoms of
the pc ring. Metallated azaporphyrins have four meso nitrogen
atoms, which exhibit basic properties and are able to partici-
pate in acid-base interaction with an acid.27,28 Recently, spec-
tral changes consisting of shifts of the Q band to the red with
successive protonation of ZnPc complexes have been re-
ported.29
Fig. 4 Electronic spectra of 7.5 ꢁ 10ꢀ6 M solutions of metal-free pc
(3a), NiPc (3b). ZnPc (3c) in THF (—), CHCl3 (ꢂ ꢂ ꢂ) and DMSO (--).
the THF solutions, from green to red-brown. On the successive
addition of an acid to the basic solution, the colour turned
back to the original green. This colour change, which is caused
by deprotonation of the NHTs units, could be followed by UV
spectroscopy. Fig. 6 shows the evolution of the UV spectrum of
3b upon addition of first KOH (A), then HCl (B). Portionwise
addition of KOH (methanol solution) to the THF solution of
pc caused a red shift of all bands and the appearance of a new
band at around 500 nm. Addition of HCl to this solution
reversed this step-by-step back to the original spectrum. In
order to eliminate the possibility of any effect of MeOH, blank
tests were applied but no appreciable change was observed.
The bathochromic shift of the Q band in basic conditions can
be attributed to extension of the aromatic p-system of pc owing
to deprotonation of the NHTs units. Deprotonation of pcs via
the NHTs units by treatment with strong bases produces the
anionic form. In this case, the lone pair electrons of the
Fig. 5 Variation of the Q band wavelength of NiPc (3b) in different
solvents with the solvent basicity (SB) value.25 (1: chloroform, 2:
benzene, 3: toluene, 4: nitromethane, 5: 1,4-dioxane, 6: acetone, 7:
ethyl acetate, 8: THF, 9: methanol, 10: pyridine, 11: DMF, 12:
DMSO.)
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pounds were characterized by standard methods. All proton
and carbon atoms, except core carbons, gave two sets of signals
in the 1H and 13C NMR spectra of pcs in chloroform, but only
one set in THF. Solutions of 3a–c showed rapid and reversible
colour changes upon addition of a base. Because of the
hydrogen bonding and deprotonation of pcs via NHTs, these
compounds show solvatochromic features. These spectral
properties will be developed by modification of the substituents
and future investigations will focus on the chemical sensor
properties of these compounds.
Acknowledgements
¨
We are grateful to Prof. Ahmet GUL for fruitful discussions
and Prof. Anatoly DIMOGLO for geometry optimizations.
This work was supported by the Research Fund of Gebze
Institute of Technology.
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Conclusion
In this work, the synthesis of new octatosylamido-substituted
metal-free, Ni(II) and Zn(II) pcs were described and the com-
29 A. Ogunsipe and T. Nyokong, J. Mol. Struct., 2004, 689, 89.
732
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