Synthesis of l-prolinol substituted novel optically active phthalocyanines

Article abstract of DOI:10.1016/j.dyepig.2010.12.003

The novel optically active Pc-4 (neutral) and Pc-5 (ionic), zinc(II) phthalocyanines having four N-benzyl protected l-prolinol unit were synthesized. l-prolinol has binucleophilic character and can be anchored to phthalonitrile derivative from both nitrogen and oxygen atoms. In order to overcome this problem and to enhance the solubility of phthalonitrile (S)-(-)-3 and the target phthalocyanines, the nitrogen atom of l-prolinol was first protected with benzyl chloride. All the compounds were characterized by ¹H and ¹³C NMR, MALDI-TOF MS, IR, UV-vis, and Circular Dichroism (CD) spectroscopy. Pc-4 is highly soluble in most common organic solvents, whereas ionic Pc-5 is soluble in water. The CD results showed that the chiral information was transferred from the peripheral chiral l-prolinol side chains to the phthalocyanine chromophore at the molecular level.

Full text of DOI:10.1016/j.dyepig.2010.12.003

Dyes and Pigments 90 (2011) 100e105
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis of
L
-prolinol substituted novel optically active phthalocyanines
,
,
Hüseyin Karaca a b, Serdar Sezer a, Cihangir Tanyeli a
*
a Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
b Department of Chemistry, Sakarya University, 54187 Sakarya, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The novel optically active Pc-4 (neutral) and Pc-5 (ionic), zinc(II) phthalocyanines having four N-benzyl
protected L-prolinol unit were synthesized. L-prolinol has binucleophilic character and can be anchored
to phthalonitrile derivative from both nitrogen and oxygen atoms. In order to overcome this problem and
Received 16 October 2010
Received in revised form
30 November 2010
Accepted 7 December 2010
Available online 15 December 2010
to enhance the solubility of phthalonitrile (S)-(-)-3 and the target phthalocyanines, the nitrogen atom of
L
-prolinol was first protected with benzyl chloride. All the compounds were characterized by 1H and 13
C
NMR, MALDIeTOF MS, IR, UVevis, and Circular Dichroism (CD) spectroscopy. Pc-4 is highly soluble in
most common organic solvents, whereas ionic Pc-5 is soluble in water. The CD results showed that the
Keywords:
chiral information was transferred from the peripheral chiral
chromophore at the molecular level.
L
-prolinol side chains to the phthalocyanine
L-prolinol
Optically active phthalocyanine
Phthalocyanine
Ó 2010 Elsevier Ltd. All rights reserved.
Water soluble
Chiral peripheral unit
CD spectroscopy
1. Introduction
In this study, we report the synthesis and the photophysical
evaluation of a novel family of optically active phthalocyanines
Phthalocyanines (Pcs) have unique properties due to their
conjugated core units which have found widespread application as
dyes and catalysts [1]. Moreover, in the years, they have attracted
increasing interest for their application in the construction of
molecular devices. For example they have found utility in many
popular areas of research such as photodynamic therapy (PDT)
[2e4], organic photovoltaic (OPV) devices [5e9], and organic field-
effect transistors (OFETs) [10].
Although a wide range of studies on the synthesis, properties
and applications of many phthalocyanines has received more
research interest than porphyrins, chiral phthalocyanines have
received less attention than chiral porphyrins. However, optically
active Pcs are more available than porphyrins in some respects. For
instance, Pcs are prone to co-facial aggregation and may form
helical superstructures. In addition, to analyze their circular
dichroism (CD), Pcs are superior to porphyrins, since the Q-band is
much more intense. The studies on the chiral Pcs have emerged
over the last few decades. In particular, after 1990, Kobayashi and
co-workers [11e16] made very valuable contributions in this
emerging field [17e21].
with
L-prolinol peripheral units (Fig.1). The reason for choosing this
class of Pcs is that the bulky and ionic peripheral substitutions on
Pcs core enhance solubility in organic and aqueous media and
control the aggregation behavior [1,22]. In our synthetic strategy,
the N-benzyl protected
L-prolinol unit was first anchored to
the core scaffold of phthalocyanines and subsequent cyclo-
tetramerization afforded the optically active target ZnPcs. Since the
nitrogen atom of
ammonium salt, the neutral
transformed into the ionic Pc, which is soluble in water. To the best
of our knowledge, -prolinol type chiral peripheral units have never
been utilized before for the construction of optically active phtha-
locyanines. The combined structure of -prolinol and Pc may be
L-prolinol unit has the capacity to form quaternary
L-prolinol substituted Pc was easily
L
L
a valuable candidate as an organocatalyst in the application of
asymmetric transformation reactions.
2. Experimental
2.1. General
All experiments were carried out in pre-dried glassware (1 h,
150 ꢀC) under an inert atmosphere of argon. The following reaction
solvents were distilled from the indicated drying agents: DMAE
(CaH2), DMF (CaH2). Melting points were obtained on a Thomas
* Corresponding author. Tel.: þ90 312 210 32 22; fax: þ90 312 210 32 00.
E-mail address: tanyeli@metu.edu.tr (C. Tanyeli).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.12.003

H. Karaca et al. / Dyes and Pigments 90 (2011) 100e105
101
2.3.2. (S)-(-)-4-((1-Benzylpyrrolidin-2-yl)methoxy)phthalonitrile,
(S)-(-)-3
O
R1
=
R2 or R1
R1 or R2
N
(S)-(-)-(1-Benzylpyrrolidin-2-yl)methanol (S)-(-)-2, (3.52 g,
18.4 mmol) was added to a mixture of 4-nitrophthalonitrile
(3.18 g, 18.4 mmol), anhydrous potassium carbonate (20.33 g,
147.3 mmol) and 30 cm3 DMF at room temperature. The reaction
mixture was stirred at room temperature for 24 h under argon
atmosphere, and then distilled to remove DMF under reduced
pressure. Dilute hydrochloric acid (0.1 M) was then added. The
aqueous layer was shaken with ether and basified with ammo-
nium hydroxide, and extracted several times with DCM. The
organic layer was dried over MgSO4, and the solvent was then
removed under reduced pressure. The residue was purified by
column chromatography on silica gel eluting with ethyl acetate/
methanol (10/1) to afford (S)-(-)-4-((1-benzylpyrrolidin-2-yl)
methoxy)phthalonitrile (S)-(-)-3 as a yellow oil (1.45 g, 28%).
N
Zn
N
N
N
N
N
N
N
O
R2
=
N
H
R2 or R1
Cl
R1 or R2
Fig. 1. Target optically active phthalocyanine structures.
Hoover capillary melting point apparatus and are uncorrected. All
other chemicals were purchased from commercial suppliers and
used without further purification.
Flash column chromatography was performed by using thick-
walled glass columns with a flash grade (Merck Silica Gel 60). Reac-
tions were monitored by thin layer chromatography using precoated
silica gel plates (Merck Silica Gel PF-254), visualized by UV-light and
polymolybdenphosphoric acid in ethanol as appropriate. All extracts
were dried over anhydrous magnesium sulphate and solutions were
concentrated under vacuum by using rotary evaporator.
½ ꢁD ¼ ꢂ277.5 (c 3.9, CHCl3). FT-IR (ATR System, cmꢂ1): 3083,
a 25
3027, 2969, 2974, 2797, 2229, 1737, 1596, 1561, 1491, 1453, 1319,
1251, 1095, 1017. 1H NMR (400 MHz, CDCl3):
d
7.54 (d, J ¼ 8.8 Hz,
1H), 7.11e7.24 (m, 5H), 7.06 (d, J ¼ 2.6 Hz, 1H), 6.97 (dd,
J ¼ 2.6 Hz, J ¼ 8.8 Hz, 1H), 3.88 (d, JAB ¼ 13.1 Hz, 1H), 3.82 (dd,
JAB ¼ 5.1 Hz, JAB ¼ 9.4 Hz, 1H), 3.75 (dd, JAB ¼ 6.3 Hz, JAB ¼ 9.4 Hz,
1H), 3.53 (d, JAB ¼ 13.1 Hz, 1H), 2.90e2.97 (m, 2H), 2.28 (q,
J ¼ 9.9 Hz, 1H), 1.90e1.97 (m, 1H), 1.61e1.76 (m, 3H). 13C NMR
(100 MHz, CDCl3):
d 162.2, 139.5, 135.2, 128.8 (overlapped 2C
signals), 128.4 (overlapped 2C signals), 127.1, 119.8, 119.4, 117.2,
115.9, 115.4, 107.0, 72.4, 61.9, 60.0, 55.0, 28.6, 23.3. Exact mass:
317.15. GSeMS measured m/z: 317.2. HRMS: m/z [M þ H]þ calcd.
for C20H19N3O: 318.1606; found [M þ H]þ: 318.1601.
2.2. Spectroscopy
1H NMR and 13C NMR spectra were recorded in CDCl3 on Bruker
Spectrospin Avance DPX-400 spectrometer. 1H (400 MHz) and 13C
NMR were recorded in CDCl3 and D2O. The chemical shifts were
2.3.3. Synthesis of (S)-4-(1-benzylpyrrolidin-2-yl)methoxy
substituted Zn phthalocyanine, Pc-4
expressed in ppm relative to CDCl3
(d
7.26 and 77.0 for 1H and 13C
NMR, respectively) and D2O as the internal standards. Infrared
spectra were recorded on a Thermo Nicolet IS10 ATReFT-IR spec-
trophotometer. The mass spectra were recorded on Thermo
Scientific DSQ II Single Quadrupole GC/MS. HRMS and MALDIeTOF
spectra were detected on a Waters Synapt mass spectrometer at
central laboratory of Middle East Technical University. Optical
rotations were measured employing a Rudolph research analytical,
autopol III automatic polarimeter. Circular Dichroism (CD) meas-
urements were recorded on JASCO J-815 at UNAM of Bilkent
University. UVevisible spectroscopy was measured on a VARIAN
CARY 100 Bio Spectrophotometer.
(S)-(-)-3, (1.23 g, 3.86 mmol) was dissolved in 12 cm3 of dry
DMAE and DMF mixture (1:2) and then, stirred for 1 h. Zn(OAc)2
(0.21 g, 0.97 mmol) was added and stirred for another 1 h under
argon atmosphere and then refluxed at 160 ꢀC for 24 h. Reaction
mixture was poured into wateremethanol mixture (1:1). Precipi-
tate was filtered off and the residue was purified by column chro-
matography on silica gel eluting with ethyl acetate/methanol (10/1)
to afford Pc-4 as a dark-green solid (0.71 g, 55%). FT-IR (ATR System,
cmꢂ1): 2953, 2917, 2849, 1710, 1667, 1605, 1487, 1452, 1377, 1336,
1280, 1260, 1228, 1116, 1089, 1047, 936, 861, 845, 817, 745. 1H NMR
(400 MHz, CDCl3):
d
6.93e7.60 (m, 32H), 3.92e4.07 (d, JAB ¼ 13.1 Hz,
4H), 3.87 (dd, JAB ¼ 5.4 Hz, JAB ¼ 9.3 Hz, 4H), 3.77 (dd, JAB ¼ 6.5 Hz,
JAB ¼ 9.3 Hz, 4H), 3.26e350 (d, JAB ¼ 13.1 Hz, 4H), 2.81e2.97 (m, 8H),
2.20e2.28 (m, 4H), 1.90e2.00 (m, 4H), 1.60e1.75 (m, 12H). UVevis
2.3. Synthesis
2.3.1. (S)-(-)-(1-Benzylpyrrolidin-2-yl)methanol, (S)-(-)-2
lmax (nm) (log 3) in CHCl3: 345 (4.44), 623 (4.04), 683 (4.42).
To a stirred mixture of (S)-pyrrolidin-2-yl-methanol (1) (2.02 g,
20 mmol), benzyl chloride (3.80 g, 30 mmol), and anhydrous
potassium carbonate (2.76 g, 20 mmol) in 15 cm3 of toluene was
refluxed under argon for 16 h. Dilute hydrochloric acid was then
added until the aqueous layer was strongly acidic. The aqueous
layer was separated, shaken with ether, basified with ammonium
hydroxide, and extracted several times with DCM. The organic layer
was dried over MgSO4, and the solvent was then removed under
reduced pressure. The residue was purified by column chroma-
tography on silica gel eluting with ethyl acetate/methanol (10/1) to
afford (S)-(-)-(1-benzylpyrrolidin-2-yl)methanol (S)-(-)-2 as
MALDIeTOF MS: m/z [M]þ calcd. for C80H76N12O4Zn: 1334.9474;
found [M]þ:1334.4724.
2.3.4. Synthesis of (S)-4-((1-benzylpyrrolidinium-2-yl)methoxy)
substituted Zn phthalocyanine complex, Pc-5
To a solution of Pc-4, (0.50 g, 0.37 mmol) in DCM (50 cm3), dilute
hydrochloric acid (15 cm3, 0.1 M) was added and the stirring
continued at room temperature until pH became 1. The complete
dark-green colour transferring of organic phase to water phase was
observed. The water phase was separated and evaporated in vacuo
to afford quantitatively Pc-5. FT-IR (ATR System, cmꢂ1): 3210, 1710,
1635, 1404, 1327, 1080, 948, 741. 1H NMR (400 MHz, D2O):
a viscous oil (3.52 g, 92%) [23]. ½a D25
ꢁ
¼ ꢂ33.3 (c 1, EtOH). 1H NMR
(400 MHz, CDCl3):
d
7.07e7.17 (m, 5H), 3.84 (d, JAB ¼ 13.0 Hz, 1H),
d 7.01e7.56 (m, 32H), 4.28e4.44 (m, 4H), 4.04e4.14 (m, 6H),
3.46 (dd, JAB ¼ 4.2 Hz, JAB ¼ 10.8 Hz, 1H), 3.32 (dd, JAB ¼ 2.8 Hz,
JAB ¼ 10.8 Hz, 1H), 3.20 (d, JAB ¼ 13.0 Hz, 1H), 2.78e2.83 (m, 1H),
2.51e2.57 (m, 1H), 2.11 (q, J ¼ 8.8 Hz, 1H), 1.72e1.82 (m, 1H),
1.59e1.70 (m, 1H), 1.50e1.57 (m, 2H). 13C NMR (100 MHz, CDCl3):
3.86e3.96 (m, 3H), 3.73e3.77 (m, 3H), 3.32e3.54 (m, 8H),
2.31e2.35 (m, 4H), 2.07e2.20 (m, 4H), 1.75e2.01 (m, 12H). 13C NMR
(100 MHz, D2O):
d 169.3, 169.0, 160.7, 133.0, 129.0 (overlapped 2C
signals), 128.4, 128.3, 127.7 (overlapped 2C signals), 123.8, 123.2,
d
137.7, 127.2, 126.8, 125.5, 62.8, 60.2, 57.0, 52.9, 26.2, 21.9.
118.5, 107.7, 63.8, 61.0, 57.3, 53.8, 24.5, 20.3. UVevis lmax (nm) in

102
H. Karaca et al. / Dyes and Pigments 90 (2011) 100e105
H2O: 345, 623, 683. HRMS: m/z [M
þ
4H]þ calcd. for
yield after purification by column chromatography. Alternative
C80H84Cl4N12O4Zn: 1484.8230; found [M þ 4H]þ:1484.4760.
conditions (DBU and pentanol) were attempted but proved low
yielding. The solubility test of Pc-4 showed that it was highly
soluble in most organic solvents, such as CH2Cl2, CHCl3, toluene and
THF, however, it was insoluble in water. We turned our attention to
the synthesis of water soluble phthalocyanines that are potent
photosensitizers in the application of photodynamic therapy
3. Results and discussion
3.1. Synthesis
[2,24e26]. It is envisaged the aforementioned L-prolinol peripheral
From the documented literature on phthalocyanines, it is well
known that bulky peripheral substitutions can be used for
enhancing the solubility in organic and aqueous media and can
influence the aggregation behavior [1,22]. Moreover, as mentioned
above, chiral phthalocyanines remain extremely rare so far. Moti-
vated by the potential value of chirally anchored phthalocyanine
derivatives, we formulated a general strategy of synthesis based on
units could be available candidates for that purpose. For the
synthesis of water soluble phthalocyanine derivative, the Pc-4 was
reacted with dilute HCl solution (0.1 M) to afford water soluble Pc-5
in almost quantitative yield. The structures of novel Pc compounds
Pc-4 and Pc-5 were characterized by IR, UV, 1H and 13C NMR,
MALDIeTOF, LCeHRMS and CD techniques.
the use of commercially available
L-prolinol as the chiral peripheral
unit. Since -prolinol has binucleophilic character, it can be
L
3.2. Structure elucidation
anchored to 4-nitrophthalonitrile from both nitrogen and oxygen
atoms. In order to overcome this problem and to enhance the
solubility of phthalonitrile (S)-(-)-3 and the target phthalocyanines,
The FT-IR spectrum of the monomer (S)-(-)-3 exhibits a charac-
teristic absorption band at 2229 cmꢂ1 assignable to C^N vibration.
The disappearance of this signal in the FT-IR spectrum of Pc-4 is
a proof of cyclomerization. Absorption bands at 745, 817e861, 936,
1047e1280 and 1452e1487 cmꢂ1 are observed for Pc-4, these can
attribute to phthalocyanine skeletal vibrations [27]. FT-IR spectrum
of Pc-5 shows very similar absorption peaks at around
741e1404 cmꢂ1 which are broader than Pc-4 peaks. In addition to
these, we observed a very intense and broad band at 3210 cmꢂ1 for
Pc-5, this is due to newly formed NeH bond on the peripheral
chiral unit.
the nitrogen atom of L-prolinol was successfully functionalized to
the desired N-benzyl protected derivative (S)-(-)-2 with benzyl
chloride and anhydrous K2CO3 by refluxing in toluene in high
chemical yield [23]. The synthesis of novel chiral phthalonitrile
(S)-(-)-3 was performed by the SNAr type substitution reaction
between (S)-(-)-2 and 4-nitrophthalonitrile (Scheme 1). The chiral
phthalonitrile (S)-(-)-3 was isolated by column chromatography in
28% yield. The structure of (S)-(-)-3 was assigned on the basis of 1H
and 13C NMR spectra. The isomeric mixture of chiral phthalocya-
nine Pc-4 was synthesized under standard conditions by using Zn
(OAc)2.2H2O, DMEA (N,N-dimethylethanamine) afforded a 55%
The structures of Pc-4 and Pc-5 were mainly assigned on the
basis of 1H NMR spectra. The most conspicuous features in the 1H
O2N
CN
CN
CN
CN
O
Benzyl chloride
K2CO3
Toluene
OH
OH
N
N
N
H
DMF, K2CO3
60oC, 20 h
28%
24 h, 92%
(S)-(-)-1
(S)-(-)-3
(S)-(-)-2
Zn(OAc)2.2H2O
DMAE, DMF
150oC, 48 h, 55%
Cl-
NH
N
O
N
N
O
O
O
H
N
Cl-
N
N
N
N
N
N
N
N
HCl (0.1 N)
N
Zn
N
N
Zn
N
N
N
Cl-
HN
N
N
O
O
O
-
O
NH
N
Cl
Pc-5
Pc-4
Scheme 1. Synthesis of (S)-4-((1-benzylpyrrolidinium-2-yl)methoxy) substituted Zn phthalocyanine complexes Pc-4 and Pc-5.

H. Karaca et al. / Dyes and Pigments 90 (2011) 100e105
103
NMR spectrum of Pc-4 are the diastereotopic methylene proton
resonances of chiral -prolinol peripheral units. To determine the
exact structure of Pc-4, first we made full assignments for
the diastereotopic benzylic and CH2eO protons of phthalonitrile
(S)-(-)-3 with the help of the COSY spectrum. The diastereotopic
spectrum of Pc-4. Fortunately, expanding the 4.10e3.30 ppm part
of 1H NMR spectrum of Pc-4, it was observed that similar sets
of protons with almost the same coupling constant and with
slightly different chemical shift values were obtained as expected.
L
Diastereotopic methylene protons of Pc-4 resonate at
d 3.92e4.07
benzylic methylene protons resonate as two doublets at
d
3.88 and
and 3.30e3.50 ppm regions as two separate sets of doublets with
d
3.53 ppm with a coupling constant of J ¼ 13.1 Hz, whereas the other
coupling constants of J ¼ w13 Hz as well as (S)-(-)-3 diastereotopic
diastereotopic methylene protons next to the stereogenic center
methylene signals (Fig. 2, part b). The other diastereotopic methy-
reveal signal sets at
d
3.82 as doublet of doublets with coupling
lene protons next to stereogenic centers reveal signal sets at
3.86 ppm as doublet of doublets with coupling constants of J ¼ 9.1
and 5.3 Hz (A-component of AB system) and 3.76 ppm as
d
constants of J ¼ 9.4 and 5.1 Hz (A-component of AB system) and at
d
3.75 ppm as doublet of doublets with coupling constant values of
J ¼ 9.4 and 6.3 Hz (B-component of AB system) due to the coupling
with stereogenic center methine proton as given in Fig. 2 (part a).
Our expectation was to observe similar sets of signals in 1H NMR
d
a doublet of doublets with coupling constant values of J ¼ 9.1 and
6.6 Hz (B-component of AB system) as well as the phthalonitrile
derivative (S)-(-)-3 (Fig. 2, part c). 1H NMR spectrum of Pc-5 in D2O
shows similar signal sets to that of Pc-4 as given in experimental
part except that the signals shift to down field region and broaden
because of the ionic form of Pc-5. In addition, we compared the 13C
NMR spectra of phthalonitrile (S)-(-)-3 with Pc-5. 13C NMR spec-
trum of (S)-(-)-3 reveals two characteristic signals at 115.4 and
115.9 ppm for C^N carbons and another characteristic signal at
162.2 ppm for prolinol unit attached to aromatic carbon. In the 13C
NMR spectrum of Pc-5, disappearance of C^N carbon signals,
a slight shifting of prolinol attached carbon signal from 162.2 ppm
to 160.7 and the presence of newly formed inner core pyrrol unit
carbon signals at 169.0 and 169.3 ppm confirm strongly the struc-
ture of Pc-5.
The mass spectra of Pcs also confirm the proposed structures.
The linear mode positive ion MALDIeTOF mass spectrum of Pc-4 is
shown as an example in Fig. 3. The molecular ion peak was easily
identified at 1334.4724 Da. When the molecular mass region of
complex was expanded, we observed the protonated molecular ion
of Pc-4 at 1335, 1336, 1337 and 1338 Da as [M þ H], [M þ 2H],
[M þ 3H] and [M þ 4H], respectively.
3.3. UVevis and CD absorption spectra
The electronic absorption spectra of Pc-4 and Pc-5 were recorded
in CHCl3 and H2O over a wide concentration range (10ꢂ5e10ꢂ4 M),
respectively. Fig. 4 compares the electronic absorption spectra in the
range 300e750 nm of the two compounds. All the absorption spectra
show a typical phthalocyanine Soret band around 335 nm for both
Pc-4 and Pc-5. An intense long wavelength
pep
* transition, the
Q-band, which is characteristic of the UVevis absorption spectra
of phthalocyanines [1], and a peak at 683 nm with a shoulder at
the higher-energy side (620e640 nm) in the UVevis absorption
spectrum of Pc-4 in CHCl3, was assigned to this transition. The
Fig. 2. 1H NMR spectra (a) expanded 1H NMR spectrum of (S)-(-)-3 (3.50e4.00 ppm
region) for diastereotopic benzylic and methylene protons next to the stereogenic
center; (b) expanded 1H NMR spectrum of Pc-4 (3.30e4.10 ppm region) for diaster-
eotopic benzylic protons; (c) expanded 1H NMR spectrum of Pc-4 (3.30e4.10 ppm
region) for diastereotopic methylene protons next to the stereogenic center.
Fig. 3. The positive ion and linear mode MALDIeTOF MS spectrum of Pc-4, obtained in
a
-cyano-4-hydroxycinnamic acid (CHCA) MALDI matrix. Inset spectrum shows the
expanded molecular mass region.

104
H. Karaca et al. / Dyes and Pigments 90 (2011) 100e105
spectra. The CD spectra of Pc-4 and Pc-5 show the characteristic Q
and Soret bands at about 683, 630 nm and 335 nm, respectively. In
the CD spectra, the -prolinol-anchored phthalocyanines show
L
negative CD corresponding to these bands. These CD signals imply
the effective chiral information transfer from the peripheral chiral
L-prolinol side chains to the phthalocyanine chromophore at the
molecular level [33e35].
4. Conclusion
In summary, we have reported the synthesis of a novel chiral
L
-prolinol-anchored phthalocyanine Pc-4 with high solubility in
many common solvents. In our synthetic strategy, N-benzyl pro-
tected -prolinol was anchored to 4-nitrophthalonitrile via SNAr
L
type substitution reaction to yield optically active phthalonitrile
derivative (S)-(-)-3 and subsequent cyclotetramerization afforded
optically active target phthalocyanine Pc-4. Depending upon the
salt formation ability of nitrogen on the chiral peripheral unit, it
was transformed into its HCl salt Pc-5 in almost quantitative yield.
Thus, we have obtained optically active phthalocyanines which are
soluble in most common organic solvents and water. The structures
of all synthesized compounds were fully characterized by using
FT-IR, 1H NMR, 13C NMR, MALDIeTOF MS, LCeHRMS, UVevis and
CD spectroscopic techniques. In particular, the electronic absorp-
tion spectroscopy indicates that Pc-4 shows nonaggregated solu-
tion whereas, Pc-5 displays aggregated solution. The perfect CD
signals of both can prove the effective chiral information transfer
from peripheral chiral
L-prolinol units to the phthalocyanine
Fig. 4. Absorption spectra of Pc-4 in CHCl3 and Pc-5 in H2O at different concentrations.
chromophores at the molecular level. These findings may offer new
possibilities towards to use these chiral macrocyclic molecules as
catalyst in various asymmetric transformation reactions [36]. Our
ongoing studies will be published in due course.
sharpness of the peak indicates nonaggregated solution of Pc-4 [1].
The inset of Fig. 4a also displays nonaggregation behavior of Pc-4
solutions. The Q-band in the absorption spectrum of Pc-5 (Fig. 4b),
which is the HCl salt of Pc-4, was broadened, and the maximum
(630 nm) was blue shifted in H2O. This spectral change can be
attributed to the formation of aggregated phthalocyanine species
possessing a co-facial arrangement [28e32].
Since Pc-4 and Pc-5 have chiral peripheral units, they should
have circular dichroism (CD) activity. The CD spectra of Pc-4 and
Pc-5 were recorded in CHCl3 and H2O, respectively. Fig. 5 shows
the CD spectra in the range 300e750 nm. The shape of the CD
spectra of Pc-4 and Pc-5 is similar to the electronic absorption
Acknowledgments
We gratefully acknowledge the financial support of Middle East
Technical University DOSAP-Programme. Hüseyin Karaca thanks to
the Turkish Scientific and Technical Research Council, Department
of Science Fellowships and Grant Program.
References
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photodynamic therapy. Chemical Society Reviews 1995;24:19e33.
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