Synthesis and photophysical properties of novel hexadeca-substituted phthalocyanines bearing three different groups

Article abstract of DOI:10.1016/j.jorganchem.2013.12.044

The synthesis of novel, hexadeca-substituted metal-free and zinc(II)phthalocyanines bearing naphthoxy groups and chloro groups in peripheral positions and hexyloxy groups in non-peripheral positions is described. These phthalocyanines were characterized w

Full text of DOI:10.1016/j.jorganchem.2013.12.044

Journal of Organometallic Chemistry 754 (2014) 8e15
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and photophysical properties of novel hexadeca-substituted
phthalocyanines bearing three different groups
_
*
Özge Kurt, Ibrahim Özçes¸ meci, Ahmet Gül, Makbule Burkut Koçak
Department of Chemistry, Istanbul Technical University, Maslak TR34469, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of novel, hexadeca-substituted metal-free and zinc(II)phthalocyanines bearing naphthoxy
groups and chloro groups in peripheral positions and hexyloxy groups in non-peripheral positions is
described. These phthalocyanines were characterized with elemental analyses, mass, proton nuclear
magnetic resonance (1H NMR), fourier transform infrared spectroscopy (FT-IR) and ultravioletevisible
spectroscopy (UVevis) techniques. Aggregation properties of these compounds were investigated in the
different concentration range. The influences of the substituent on the hexadeca-substituted phthalo-
cyanine framework and metal ion on the spectroscopic and photophysical properties have been inves-
tigated. The energy transfer to phthalocyanine core and radiative decays of the naphthol emission and
phthalocyanine core were examined.
Received 1 October 2013
Received in revised form
16 December 2013
Accepted 19 December 2013
Keywords:
Phthalocyanine
Hexadeca-substitution
Energy transfer
Naphthol
Ó 2014 Elsevier B.V. All rights reserved.
Fluorescence
Quantum yield
1. Introduction
in the related fields. Thus many strategies have been investigated to
prevent self-association of Pc-based materials [6].
Phthalocyanines (Pcs) are widely investigated organic com-
pounds for many high-technology applications, such as nonlinear
optics, photoconductivity, photovoltaic cells, low-dimensional
conductors, chemical sensors, optical data storage, Langmuire
Blodgett films, liquid crystals, photodynamic cancer therapy, etc.
[1]. Improving the solubility of phthalocyanines is an important
aspect of their chemistry, as the insolubility of unsubstituted
phthalocyanine molecules in common organic solvents causes
difficulties for many applications [2]. The introduction of a diverse
substituents on peripheral, non-peripheral or axial positions, metal
insertion, variation of the main structure of the macrocycle and
Placing bulky substituents or aryl groups simultaneously at both
peripheral and non-peripheral positions of the phthalocyanine core
(i.e. hexadeca-substituted phthalocyanines) perfectly prohibit close
self-association of the macrocycle even within solid thin film [7]
and results in a shift of the Q-band in the visible spectrum into
the near-IR region so that the Pc does not display its characteristic
blue or green colour [8]. Besides, addition of substituent groups to
both peripheral and non-peripheral sides of the phthalocyanine
core disrupt
p-stacking between macrocycles and therefore in-
crease the solubility of the substituted Pcs even in non-polar sol-
vents such as hexanes [9]. The non-aggregation behaviour, high
solubility and red shifted Q-band properties of hexadeca-
substituted phthalocyanines make such new chromophore mate-
rials to be attractive candidates for several applications such as PDT
as photosensitiser, optoelectronics, optical limiters and near-IR
devices [10].
Phthalocyanines are ideal photoactive units with outstanding
electronic properties, namely strong absorption in the visible re-
gion and fine-tunable redox properties, related to their aromatic p-
conjugated system. In this regard, many phthalocyanine-based
multicomponent systems in which one of these chromophores is
covalently or nonconvalently linked to another electro- or photo-
active unit have been prepared and their mutual electronic in-
teractions studied [11]. One of the main advantages of using
multichromophoric systems is to harvest a wide range of the solar
extension of p-electron density have strong influence on the elec-
tronic and absorption characteristics of Pcs [3].
The nature of the substituents is important not only in terms of
the solubility of Pcs but also in context of the state of their aggre-
gation. Aggregation causes a drastic decay of Pcs optical properties
[4]. For example, aggregation behaviour of Pcs leads to degrade
their optical modulating capabilities through reducing the active
absorbing excited state lifetime [5]. This has led to a growing in-
terest in designing nonaggregated Pcs and controlling the archi-
tecture of these macrocycles tailored to the intended applications
* Corresponding author. Tel.: þ90 212 285 69 64; fax: þ90 212 285 63 86.
E-mail address: mkocak@itu.edu.tr (M.B. Koçak).
0022-328X/$ e see front matter Ó 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.12.044

Ö. Kurt et al. / Journal of Organometallic Chemistry 754 (2014) 8e15
9
spectrum, which is of general interest for optical and photovoltaic
applications. The phthalocyanine skeleton permits to attach easily
many energy donor arms in the near periphery, and such a light-
harvesting system can be expected to show antenna effect [12].
Although non-aggregation and photophysical properties of
hexadeca-substituted phthalocyanines are investigated in number
of papers [13e15], the light-harvesting phenomena due to addi-
tional fluorophore groups has not been studied. This paper con-
cerns with the preparation of novel, hexadeca-substituted
phthalocyanines with hexyloxy groups in non-peripheral and
chloro and naphthoxy groups in peripheral positions. Aggregation
behaviour and photophysical properties of hexadeca-substituted
metal-free and zinc(II)phthalocyanine complexes were investi-
gated. The effects of naphthol groups on the efficiency of energy
transfer from naphthol group to the phthalocyanine core have been
also studied.
precipitated with methanolewater mixture, filtered, washed with
the same solvent, and finally dried in vacuo. The purification of the
crude product was accomplished by column chromatography on
silica gel first with 1:5 Ethyl acetate:n-hexane then with ethyl-
acetate as the eluent. Yield: 32 mg (15.5%); m.p. > 200 ꢀC. IR
n
(cmꢁ1): 2955e2924 (CeH aliphatic), 1207 (AreOeC); UVeVis
(tetrahydrofuran (THF)): lmax nm (log ε) 337 (4.31), 651 (4.4), 725
(4.96); 1H NMR (DMSO-d6): 4.18 (16H, t, OeCH2), 2.21 (16H, p, Oe
CeCH2), 1.58e1.39 (32H, m, OeCeCeCH2eCH2), 0.96 (16H, m, Oe
CeCeCeCeCH2), 0.88 (24H, t, eCH3); MS: m/z 1655.48 [M þ H]þ.
2.2.3. {1,4,8,11,15,18,22,25-Octahexyloxy-3,9(10),16(17),23(24)-
tetrachloro-2,9(10),16(17), 23(24)-tetrakis(naphth-2-yloxy)
phthalocyaninato}zinc(II) (4)
A mixture of compound 2 (101 mg, 0.2 mmol), anhydrous metal
salt Zn(CH3COO)2, (9.2 mg, 0.05 mmol) and catalytic amount of DBU
(1,8-diazabicyclo[5.4.0]undec-7-ene) in 2.0 cm3 of n-pentanol was
irradiated in a microwave oven at 155 ꢀC, 200 W for 15 min. After
cooling to room temperature the green suspension was precipi-
tated with methanolewater mixture, filtered, washed with the
same solvent, and finally dried in vacuo. The purification of the
crude product was performed by preparative chromatography on
silica gel (THF and hexane 1:1 v/v). Pure compound 4 was obtained
as an isomeric mixture. Yield: 20 mg, 19%; IR, gmax (cmꢁ1): 3055
(CeH, aromatic), 2953e2924 (CeH aliphatic), 1210 (AreOeAr);
UVeVis (THF): lmax nm (log ε) 328 (4.73), 653 (4.61), 727 (5.37); 1H
2. Experimental
2.1. Equipments and materials
IR spectra were recorded on a PerkineElmer Spectrum One FT-
IR (ATR sampling accessory) spectrometer and electronic spectra on
a Scinco S-3100 spectrophotometer using 1 cm path length cuvettes
at room temperature. 1H NMR spectra were recorded on Agilent
VNMRS 500 MHz spectrometer using TMS as internal reference.
Mass spectra were performed on a Micromass Quatro LC/ULTIMA
LCeMS/MS spectrometer. Fluorescence excitation and emission
spectra were measured by using PerkineElmer LS-55 fluorescence
spectrophotometer. Single mode reactor (CEM DISCOVER SP) were
used for microwave heating. All reagents and solvents were of re-
agent grade quality obtained from commercial suppliers. The ho-
mogeneity of the products was tested in each step by TLC (SiO2).
4,5-dichloro-3,6-bis(hexyloxy)phthalonitrile (1) was prepared ac-
cording to reported procedures [13e15].
NMR (CDCl3 d): 7.86e7.18 (28H, b, AreH), 4.93 (16H, b, OeCH2e),
1.86e0.80 (88H, b, aliphaticeCH); MS [m/z]: 2086 [M þ H]þ
2.2.4. {1,4,8,11,15,18,22,25-Octahexyloxy-2,3,9,10,16,17,23,24-
octachloro-phthalocyanine} (5)
Lithium metal (20 mg, 2.88 mmol) was heated to dissolve in
pentanol (1.5 mL) and allowed to cool to room temperature.
Compound 1 (95 mg, 0.24 mmol) was added to the above solution
and was heated at 180 ꢀC for 3 h. After cooling to room temperature
the green mixture was treated with methanolewater mixture to
precipitate the product completely. The green precipitate was
collected by centrifuging and then it was washed with methanole
water. It was dissolved in a small amount of methanol and
precipitated by diluted hydrochloric acid (HCl) (2 M). In this
mixture, the Li2Pc formed was converted into H2Pc. The green
precipitate was centrifuged and washed successively with water,
warm ethanol, warm methanol, and then dried in vacuo. This
product was then further purified by preparative thin layer chro-
matography on silica gel using an ethylacetate:hexane (1:5) solvent
mixture as the eluting system. Yield: 35 mg, 36%; IR, gmax (cmꢁ1):
3299 (NeH), 2954e2925 (CeH aliphatic), 1242 (AreOeC); UVeVis
(THF): lmax nm (log ε) 340 (4.39), 730 (5.04), 752 (5.12); 1H NMR
2.2. Synthesis
2.2.1. 4-Chloro-5-bis(2-naphthoxy)-3,6-bis-(hexyloxy)
phthalonitrile (2)
4,5-Dichloro-3,6-dihexyloxyphthalonitrile (1) (1.2 g, 3 mmol)
was dissolved in 10 cm3 dry dimethylformamide (DMF) at 45 ꢀC and
2-naphthol (0.43 g, 3 mmol) was added to this solution. After
stirring for 15 min, 1.26 g of finely ground anhydrous K2CO3
(9 mmol) was added portion wise during 2 h with efficient stirring.
The reaction mixture was stirred under nitrogen at 45 ꢀC for further
48 h. After being cooled to room temperature, the mixture was
poured into ice/water (100 cm3). The resulting deep brown solid
was extracted with ethylacetate. The organic solution was dried
with Na2SO4 and the solvent was evaporated to give the crude
product. Finally pure product is obtained by recrystallization from
ethanol. Yield: 0.635 g (42%) m.p. 52e54 ꢀC 1H NMR (DMSO-d6):
(CDCl3, d) ppm: 4.93 (16H, t, OeCH2), 2.19 (16H, p, OeCeCH2),1.58e
1.39 (32H, m, OeCeCeCH2eCH2), 0.96 (16H, m, OeCeCeCeCe
CH2), 0.89 (24H, t, eCH3); MS [m/z]: 1591 [M]þ, 1535
[M ꢁ 3CH2 ꢁ CH3]þ
d
8.03e7.35 (m, HeAr), 4.29 (t, OeCH2), 4.16(t, OeCH2) 1.84 (dd,
CH2), 1.51 (dd, CH2), 1.36 (dd, CH2), 1.09 (q, CH2), 0.73 (t, CH3); IR (
n
,
2.2.5. {1,4,8,11,15,18,22,25-Octahexyloxy-3,9(10),16(17),23(24)-
tetrachloro-2,9(10),16(17), 23(24)-tetrakis(naphth-2-yloxy)
phthalocyanine)} (6)
cmꢁ1): 3058 (HeAr), 2952, 2929, 2854 (H-Alifatik), 2235 (C^N),
1632 (Ar C]C), 1161 (AreOeAr), MS [m/z]: 507 [M þ H]þ, 471
[M ꢁ Cl]þ, 362 [M ꢁ C10H7O]þ.
Lithium metal (18 mg, 2.6 mmol) was heated to dissolve in
pentanol (2 mL) and allowed to cool to room temperature. Com-
pound 2 (130 mg, 0.26 mmol) was added to the above solution and
was heated at 180 ꢀC for 3 h. After cooling to room temperature the
green mixture was treated with methanolewater mixture to pre-
cipitate the product completely. The green precipitate was collected
by centrifuging and then it was washed with methanol. It was
dissolved in a small amount of THF and precipitated by HCl solution
(2 M). In this mixture, the Li2Pc formed was converted into H2Pc.
2.2.2. {1,4,8,11,15,18,22,25-Octahexyloxy-2,3,9,10,16,17,23,24-
octachloro-phthalocyaninato}zinc(II) (3)
A mixture of compound 1 (200 mg, 0.5 mmol), anhydrous
Zn(CH3COO)2, (23 mg, 0.125 mmol) and catalytic amount of DBU
(1,8-diazabicyclo[5.4.0]undec-7-ene) in 1.0 cm3 of n-pentanol was
irradiated in a microwave oven at 155 ꢀC, 200 W for 15 min. After
cooling to room temperature the green suspension was

10
Ö. Kurt et al. / Journal of Organometallic Chemistry 754 (2014) 8e15
Scheme 1. Structure of hexadeca-substituted metal-free and zinc(II)phthalocyanines (4e6). i: DMF, K2CO3, 45 ꢀC, 48 h, ii: n-pentanol, Zn(Ac)2, DBU, MW, 15 m (for 3 and 4), iii: n-
pentanol, lithium, 180 ꢀC, 3 h, HCl (for 5 and 6).
The green precipitate was centrifuged and washed several times
with water, hot ethanol, hot methanol and then dried in vacuo. This
product was then further purified by preparative thin layer chro-
matography on silica gel using a THF:hexane (1:10) solvent mixture
as the eluting system. Yield: 40 mg, 30%; IR, gmax (cmꢁ1): 3296 (Ne
H), 3057 (CeH aromatic), 2959e2926 (CeH aliphatic), 1244e1207
(AreOeAr); UVeVis (THF): lmax nm (log ε) 326 (4.63), 736 (4.90),
Conversion of the dinitrile derivatives 1 and 2 into the metal-free
Pcs (5) and (6) was accomplished in a mixture of pentanol in the
presence of lithium. Dilithium Pc complexes are unstable towards
water and acid, and can easily be converted to the metal-free Pcs. In
this study, hexadeca-substituted zinc (4) and metal-free (6)
phthalocyanines were obtained as a mixture of four structural
isomers (D2h:Cs:C2v:C4h) owing to the possible positions of the
naphthoxy and chloro groups relative to one another. No attempt
was made to separate the isomers of complexes 4 and 6.
All compounds were identified through various spectroscopic
techniques such as 1H NMR, FT-IR, UVeVis and MALDI-TOF. The
spectral data for the newly synthesized compounds were in
accordance with the assigned formulations. Generally, phthalocy-
anine complexes are insoluble in most organic solvents; however
introduction of substituents on the ring increases the solubility
[15,16]. All studied phthalocyanine complexes (3e6) exhibited high
solubility in organic solvents such as n-hexane, acetone, diethyl
ether, dichloromethane (DCM), THF, DMF and dimethyl sulfoxide
(DMSO).
759 (4.99); 1H NMR (CDCl3
d): 7.95e7.75, 7.70e7.55, 7.50e7.20
(28H, m, AreH), 4.80 (16H, m, OeCH2), 1.60e0.47 (88H, m,
aliphaticeCH); MS [m/z]: 2023 [M]þ
3. Results and discussion
3.1. Synthesis and characterization
The synthetic procedure as outlined in Scheme 1 started with
the synthesis of namely 4-chloro-5-(2-naphthoxy)-3,6-bis-(hex-
yloxy)phthalonitrile (2) by the reaction of 2-naphthol with 4,5-
dichloro-3,6-dihexyloxyphthalonitrile (1). Cyclotetramerization of
the dinitrile 1 and 2 separately to the hexadeca-substituted zinc
phthalocyanine (3) and (4) was accomplished in the presence of
anhydrous Zn(CH3COO)2 in a high-boiling solvent such as n-pen-
tanol for 24 h in a sealed tube. Compound 3 and 4 was isolated by
preparative chromatography on silica gel using ethylacetate:n-
hexane (1:5) for 3 and THF:n-hexane (5:2) for 4 mixtures as eluent.
In the IR spectrum of compound 2, stretching vibrations of C^N
groups at 2235 cmꢁ1
, aliphatic CH groups at 2952e2929e
2854 cmꢁ1, aromatic CH groups at 3058 cmꢁ1, and ether (AreOeAr)
units at 1161 cmꢁ1 appeared at expected frequencies. In the 1H
NMR spectrum of compound 2 in DMSO-d6, the aromatic protons
are present at around d
: 8.03e7.35 ppm. 1H NMR spectrum of 2

Ö. Kurt et al. / Journal of Organometallic Chemistry 754 (2014) 8e15
11
showed two different triplets for AreOeCH2 protons at 4.29 and at
4.16 ppm corresponding to asymmetric configuration. The CH2
protons of hexyloxy group resonate at : 1.84, 1.51, 1.36 and
1.09 ppm as multiplets. For the terminal methyl protons of the side
chains exhibited as a triplet at : 0.73 ppm. In the mass spectra of 2
d
d
the presence of the characteristic molecular ion peaks at m/z 507
[M]þ confirmed the proposed structure.
After conversion into phthalocyanines (3, 5) the characteristic
sharp C^N stretch at 2236 cmꢁ1 for phthalonitrile 1 disappeared in
the FT-IR spectra of phthalocyanine derivatives. Similarly, cyclo-
tetramerization of 2 to (4) and (6) can be seen clearly by the
absence of the C^N peaks at 2235 cmꢁ1 in the FT-IR spectrum. The
FT-IR spectra of zinc (3, 4) and metal-free (5, 6) phthalocyanines are
very similar. The significant difference is the presence of NeH vi-
brations of the inner phthalocyanine core which are assigned to a
weak vibration at 3299 cmꢁ1 for (5) and 3296 cmꢁ1 for (6).
The 1H NMR spectrum of zinc (3, 4) and metal-free (5, 6)
phthalocyanine derivative was slightly different from the starting
compound 1 and dinitrile derivative 2 except for somewhat broad
signal and small shifts in the positions of signals. In the H NMR
spectrum of 3 and 5, AreOeCH2 protons of hexyloxy group were
observed as triplets at 4.93 ppm and remaining protons of hexyloxy
groups were observed between 2.21e1.40 ppm and 0.97e0.91 ppm.
In the 1H NMR spectrum of 4 and 6, resonances belonging to aro-
matic protons were observed between 7.90 and 7.06 ppm and in-
tegrated for 28 protons. CH2 and CH3 protons, integrating for a total
of 104, were observed around 4.93e4.80 ppm and 1.86e0.47 ppm.
It is probable that the phthalocyanine derivative obtained as posi-
tional isomers mixture shows chemical shifts that are similar to
each other [17e19].
Fig. 2. Maldi-Tof mass spectrum of 6.
with substituents at the non-peripheral positions and have been
explained as being due to a linear combination of the atomic orbital
(LCAO) coefficients at the non-peripheral positions of the highest
occupied molecular orbital (HOMO) being greater than those at the
peripheral positions [26,27]. As a result, the HOMO level is more
destabilized upon non-peripheral substitution than peripheral
substitution. Besides, simultaneous peripheral and non-peripheral
substitution as in the case of hexadeca-substituted phthalocya-
nine increases this destabilization. Essentially, the energy gap (DE)
between the highest occupied molecular orbital (HOMO) and the
lowest unoccupied molecular orbital (LUMO) becomes smaller,
resulting with a w30e60 nm bathochromic shift [28].
In the mass spectral results of phthalocyanines (3e6) obtained
by the Maldi-TOF technique, the molecular ion peaks were
observed at m/z 1655.48 [M þ H]þ for 3 (Fig.1), 2086 [M þ H]þ for 4,
1591.5 [M]þ for 5 and 2023 [M]þ for 6 (Fig. 2).
3.2. Aggregation studies
The aggregation behaviour was assessed by UVeVis spectros-
copy in THF solution. Usually, the aggregation of the phthalocya-
nines is indicated by the hypsochromic shift of the Q-band at
700 nm and gradual broadening of this region in a hypochromic
fashion [29]. As anticipated, the UVeVis absorption spectra of
hexadeca-substituted phthalocyanine complexes (3e6) show no
evidence of aggregation as shown by the position and the appear-
ance of the intense Q-bands (Fig. 4). Aggregation behaviours of 3e6
were examined by UVevis spectroscopy in different concentrations
ranging from 4 ꢂ 10ꢁ6 to 14 ꢂ 10ꢁ6 M. As depicted in Fig. 4, the
appearance of the Q-band absorption maxima remained un-
changed as the concentration increases as well as its apparent
molar extinction coefficient remains almost constant indicating
purely monomeric form which obeyed the BeereLambert Law in
the outlined range of concentration (Fig. 5) [30]. By evaluating
these observations, it can clearly be concluded that the hexadeca-
substituted phthalocyanine derivatives (3e6) did not show aggre-
gation behaviour in THF at studied concentration range.
The phthalocyanines show typical electronic spectra with two
characteristic strong absorption regions, one in the UV region at
about 300e400 nm (B-band) and the other one is in the visible
region at 600e750 nm (Q-band), both correlate to pep* transitions
[20e24]. The UVeVis absorption spectra of zinc phthalocyanines 3
and 4, in THF exhibited intense Q absorption at 728 and 732,
respectively. For the metal-free phthalocyanine 5 and 6 in THF, Q
band observed at 751 nm with a shoulder at 730 nm and 752 nm
with a shoulder at 732 nm, respectively (Table 1) (Fig. 3) [25]. The Q
bands of hexadeca-substituted zinc (3 and 4) and metal-free (5 and
6) phthalocyanine complexes were red-shifted compared to the
peripherally substituted metal-free and zinc phthalocyanine com-
plexes [13,15]. The observed red spectral shifts are typical of Pcs
3.3. Fluorescence spectra
The steady-state fluorescence spectra of the hexadeca-
substituted phthalocyanines derivatives were performed in THF,
upon excitation at the 660 nm Q-band vibration for 3 and 4 and
excitation at the 675 nm Q-band vibration for 5 and 6. Emission
around 739 nm for 3 and 750 nm for 4 (Fig. 6), emission around
772 nm for 5 and 780 nm for 6 (Fig. 7), occurred almost entirely
from the phthalocyanine moiety (Table 1). The Q bands of the
hexadeca-substituted phthalocyanines’ luminescent spectra are
red shifted when compared to the corresponding peripheral
substituted phthalocyanine complexes. The red shifts observed in
Fig. 1. Maldi-Tof mass spectrum of 3.

12
Ö. Kurt et al. / Journal of Organometallic Chemistry 754 (2014) 8e15
Table 1
Photophysical and photochemical parameters of hexadeca-substituted phthalocyanine complexes (3e6) in THF.
Comp.
Q band
Log ε
Excitation
Emission
Stokes shift
(nm)
FF
sF
so
kF
lmax, (nm)
lEx, (nm)
lEm, (nm)
(ns)
(ns)
(sꢁ1)(ꢂ108)a
3
4
5
6
728
732
730, 751
732, 752
666b
5.33
5.27
5.37, 5.44
5.25, 5.30
5.19b
724
730
746
756
666b
739
750
772
780
673b
11
18
21
28
7b
0.042
0.059
0.037
0.057
0.25b
0.16
0.05
0.10
0.20
2.72b
3.81
0.85
2.89
2.63
11.75
3.72
3.65
2.85
ZnPc
10.9b
0.92b
a
kF is the rate constant for fluorescence. Values calculated using kF
Ref. [24].
¼
FF/sF.
b
emission maxima are 40e60 nm bathochromic shifted in compar-
ison with peripheral substituted phthalocyanine complexes [10].
The observed red shifts are typical of Pcs with substituents at the
non-peripheral positions and have been explained in the literature
[25,26].
The excitation spectra of 3 and 4 were similar to absorption
spectra and both were mirror images of the fluorescent spectra in
THF. The proximity of the wavelength of each component of the Q-
band absorption to the Q-band maxima of the excitation spectra for
ZnPc’s suggest that the nuclear configurations of the ground and
excited states are similar and are not affected by excitation in THF.
Excitation spectrum of hexadeca-substituted H2Pc’s (5 and 6) show
two shoulder in the red spectral region and emission maxima of
hexadeca-substituted H2Pc’s (5 and 6) appears at lower energy than
those of the corresponding hexadeca-substituted ZnPc’s (3 and 4).
It means that hexadeca-substituted metal-free phthalocyanines
shows red shift in emission maxima compared to hexadeca-
substituted zinc(II)phthalocyanines because of symmetry
lowering [31]. The observed Stokes shifts (Table 1) were typical of
phthalocyanine complexes [32].
Fig. 3. UVevis spectra of 3e6 in THF. Concentration ¼ 5.0 ꢂ 10ꢁ6 M.
Fluorescence quantum yields (FF) were determined by the
comparative method (Eq. (1)) [33]:
ꢀ
ꢁ
FF
¼
FFðStdÞ FAStdh2=FStd
A
h2Std
(1)
where F and FStd are the areas under the fluorescence curves of
phthalocyanines derivatives and the standard, respectively. A and
AStd are the respective absorbance of the sample and standard at
the excitation and
h and hStd are the refractive indices of solvents
used for the sample and standard, respectively. ZnPc was employed
as a standard in DMF (FF ¼ 0.23) [34]. Both the sample and the
standard were excited at the same wavelength. Radiative or natural
Fig. 4. Aggregation behaviour of 4 in THF at different concentrations.
lifetimes (so) were estimated using PhotochemCAD program which
Fig. 6. Excitation and emission spectra of 3 and 4 in THF. Excitation wavelengths:
660 nm. Concentration ¼ 1.0 ꢂ 10ꢁ6 M.
Fig. 5. Plot of the Log ε of 3e6 against concentration in THF.

Ö. Kurt et al. / Journal of Organometallic Chemistry 754 (2014) 8e15
13
substituted Pc complexes (3e6) are lower compared to unsub-
stituted ZnPc in THF (Table 1) [37], suggesting more quenching by
substitution. The natural radiative lifetime (so) and the rate con-
stants for fluorescence (kF) values were also shown in Table 1. The kF
values of studied hexadeca-substituted Pc complexes (3e6) are
higher than unsubstituted ZnPc and have lower natural radiative
lifetime (so) values than unsubstituted ZnPc in THF.
3.4. Energy transfer
In this study we examined also the fluorescence and energy
transfer properties of the hexadeca substituted metal free and
zinc(II)phthalocyanines. This avenue studying excitation energy
transfer through donor group has been of much current interest
because of its relevance to biological light-harvesting antennae
[38]. Excitation and emission spectra of the hexadeca substituted
metal free and zinc(II)phthalocyanines were obtained in THF so-
lution. Fig. 8 shows the excitation spectra of 2-naphthol, 3, 4,
mixture of 2-Naphthol-3 (4/1) and emission spectra of 2-naphthol.
As shown in Fig. 8, the naphthol groups exhibit two absorption
bands peaking at 275 and 327 nm and an emission at 356 nm upon
excitation at 275 nm. A considerable overlap between the emission
spectrum of 2-naphthol and the B-band excitation spectra of 3 and
4 is observed in this figure. This overlap is a clear evidence of the
energy transfer from naphthol units to the Pc core of 4 after
covalently binding of naphthol as substituents to phthalocyanine
core [39,40]. Excitation energy transfer occurred from naphthol
units of 4 to ZnPc core of 4. Fig. 9 shows the excitation spectra of 2-
Naphthol, 5, 6, a mixture of 2-Naphthol-5 (4/1) and emission
spectra of 2-naphthol. 2-Naphthol groups exhibit broad emission
peak at 356 nm upon excitation at 327 nm. The results obtained
from the excitation spectrum of 5 and 6 are very similar to the
results obtained for 3 and 4. There are overlap between the emis-
sion spectrum of 2-Naphthol and the excitation spectra of 5 and 6
and this overlap is a clear evidence of the energy transfer from
naphthol units to the Pc core of 6 after covalently binding of
naphthol as substituent to Pc [41].
Fig. 7. Excitation and emission spectra of 5 and 6 in THF. Excitation wavelengths:
675 nm. Concentration ¼ 1.0 ꢂ 10ꢁ6 M.
uses the StricklereBerg equation [35]. Finally, the fluorescence
lifetimes (sF) were calculated using the following equation (Eq. (2)):
FF
¼
sF
=
so
(2)
The fluorescence quantum yields (FF) of hexadeca-substituted
phthalocyanines are given in Table 1. To our surprise, the
measured fluorescence quantum yields for hexadeca-substituted
phthalocyanines were much lower than those for ZnPc, for which,
in DMF and unsubstituted ZnPc in THF [24], both quantum yield of
0.23 and 0.25 respectively at room temperature, this being roughly
four times greater than that of hexadeca-substituted phthalocya-
nines in THF. An apparent reason may be non-peripheral hexyloxy
groups enhanced vibrational and rotational motion that may
deactivate the excited states [13]. The FF values of the Zn (II) Pc
complexes (3, 4) are higher than for the metal-free Pc complexes (5,
6) [36].
The fluorescence lifetime statements to the average time the
molecule stays in its excited state before emitting a photon, and its
value is directly related to that of fluorescence quantum yield; i.e.
the longer the lifetime, the higher the quantum yield of fluores-
cence. Many factors such as internal conversion and intersystem
crossing, shorten the fluorescence lifetime of a molecules and
Upon excitation at 275 nm for 4 (Fig. 10) and 327 nm for 6
(Fig.11) where the naphthol units absorb and hexadeca-substituted
phthalocyanines compounds emit weakly at about 356 nm for 4
and 6 due to the naphthol units, together with an emission at
indirectly decreases the value of FF. The sF values of the hexadeca-
Fig. 8. Excitation spectra of 2-Naphthol (4.0
ꢂ
10ꢁ6 M),
3
(1.0
ꢂ
10ꢁ6 M),
4
Fig. 9. Excitation spectra of 2-Naphthol (4.0
ꢂ
10ꢁ6 M),
5
(1.0
ꢂ
10ꢁ6 M),
6
(1.0 ꢂ 10ꢁ6 M), mixture of 2-Naphthol þ 3 (4:1) (4.0 ꢂ 10ꢁ6 Me1.0 ꢂ 10ꢁ6 M) and
emission spectra of 2-Naphthol in THF, emission excited at 275 nm. Excitation spectra
were recorded for emission peak at 356 nm. Excitation and emission spectra of 2-
Naphthol and mixture of 2-Naphthol þ 3 (4:1) were lowered by 10-fold.
(1.0 ꢂ 10ꢁ6 M), mixture of 2-Naphthol þ 5 (4:1) (4.0 ꢂ 10ꢁ6 Me1.0 ꢂ 10ꢁ6 M) and
emission spectra of 2-Naphthol in THF, emission excited at 327 nm. Excitation spectra
were recorded for emission peak at 356 nm. Excitation and emission spectra of 2-
Naphthol and mixture of 2-Naphthol þ 5 (4:1) were lowered by 10-fold.

14
Ö. Kurt et al. / Journal of Organometallic Chemistry 754 (2014) 8e15
observed in 4, after covalently binding of 2-naphthol to H2Pc to
produce 6, the fluorescence emission intensity of naphthol units of
6 decreased considerably and the fluorescence emission of H2Pc
core of 6 increased and a red-shift from 772 nm to 780 nm occurred.
This decrease in the fluorescence emission intensity of naphthol
units of 4 and 6 can be considered as an indication of the excitation
energy transfer from naphthol units to the phthalocyanine core of 4
and 6 as suggested before due to the overlap between the emission
spectrum of 2-naphthol and the excitation spectrum of 4 and 6 in
Figs. 6 and 7.
These energy transfers from donor (naphthol units) to acceptor
(H2Pc and ZnPc core of 4 and 6) studies were estimated according to
the Förster theory by accumulating both the donor and acceptor
[44]. Transfer efficiency, εT, from donor to acceptor is given by Eq.
(3) [12]:
εT
¼
DIA=ðID*FA
Þ
(3)
Fig. 10. Emission spectra of 2-Naphthol (4.0
ꢂ
10ꢁ6 M),
3
(1.0
ꢂ
10ꢁ6 M),
4
(1.0 ꢂ 10ꢁ6 M), mixture of 2-Naphthol þ 3 (4:1) (4.0 ꢂ 10ꢁ6 Me1.0 ꢂ 10ꢁ6 M) in THF,
emission excited at 275 nm. Emission spectra of 2-Naphthol and mixture of 2-
Naphthol þ 3 (4:1) were lowered by 5-fold in B band region.
where D A is the increase in the integral of the fluorescence emis-
I
sion spectra of the acceptor upon binding of donor to acceptor, ID is
the integral of fluorescence spectrum of the donor before binding to
the acceptor and FA is the quantum yield of the acceptor in the
absence the acceptor. By using the data in Figs.10 and 11 and Eq. (3),
the energy transfer efficiency from naphthol units to ZnPc core of 4
and H2Pc core of 6 were calculated as 0.20 and 0.14, respectively.
750 nm for 4 (inset Fig. 10) and at 780 nm for 6 (inset Fig. 11) due to
a singletesinglet energy transfer from the excited arms to the
central phthalocyanine cores. The fluorescence of naphthol units
was quenched and emission intensity of phthalocyanine part
around 750 nm and 780 nm were increased because of the radiative
energy transfer resulting from the inner filter effect of the phtha-
locyanine core [42].
For comparison, fluorescence spectra of the mixture of 2-
naphthol-3 and 2-naphthol-5 have 4:1 M ratios are represented
in Figs. 8e11. It is clearly seen in these figures that the fluorescence
emission intensity of the 2-naphthol is bigger than that of the
conjugated naphthol units in 4. Since the distance between 2-
naphthol and 3 in the mixture solution is greater, naphthol
groups cannot transfer its excitation energy exactly to ZnPc core.
But after covalently binding of 2-naphthol to ZnPc to produce 4, the
fluorescence emission intensity of naphthol units of 4 decreased
considerably and the fluorescence emission of ZnPc core of 4
increased and a red-shift from 735 nm to 750 nm. These red shifts
indicate molecular rearrangement in the excited state originating
from intramolecular interactions [43]. The results obtained from
the fluorescence spectrum of mixture of 2-naphthol-5 are very
similar to the results obtained for 2-naphthol-3 (Figs. 8e11). As
4. Conclusions
The synthesis, characterization, energy transfer and fluores-
cence properties of newly synthesized hexadeca-substituted
metal-free and zinc(II)phthalocyanines with naphthoxy and
chloro groups in peripheral positions and hexyloxy groups in non-
peripheral positions have been presented in this work for the first
time. All hexadeca-substituted novel phthalocyanine derivatives
have not shown any aggregation behaviours in the concentration
range from 4 ꢂ 10ꢁ6 to 14 ꢂ 10ꢁ6 M. The fluorescence behaviours of
the hexadeca-substituted phthalocyanine complexes (3e6) were
studied in THF. Generally, the FF values of the hexadeca-substituted
phthalocyanine complexes (3e6) are lower than unsubstituted
ZnPc. These hexadeca-substituted phthalocyanines emit essentially
red light after selective ultraviolet or visible irradiation. In the case
of ultraviolet irradiation, these systems comprising central phtha-
locyanines linked to peripheral photon-harvesting naphthol moi-
eties have been shown to act as antennas.
Acknowledgement
This work was supported by the Research Fund of the Istanbul
Technical University and TUBITAK (Project#109T163). AG thanks
Turkish Academy of Sciences (TUBA) for partial support.
References
[1] N.B. McKeown, Phthalocyanine Materials Synthesis, Structure and Function,
Cambridge University Press, 1998.
[2] M.K. S¸ ener, A. Koca, A. Gül, M.B. Koçak, Polyhedron 26 (2007) 1070e1076.
[3] C.C. Leznoff, A.B.P. Lever, Phthalocyanines: Properties and Applications, vols.
1e4, VCH, New York, 1989.
[4] J. Vacus, J. Simon, Adv. Mater. 7 (1995) 797e800.
[5] E.M. Maya, A.W. Snow, J.S. Shirk, R.G.S. Pong, S.R. Flom, G.L. Roberts, J. Mater.
Chem. 13 (2003) 1603e1613.
[6] M. Brewis, G.J. Clarkson, M. Helliwell, A.M. Holder, N.B. McKeown, Chem. Eur.
J. 6 (2000) 4630e4636.
[7] B.M. Hassan, H. Li, N.B. McKeown, J. Mater. Chem. 10 (2000) 39e45.
[8] N. Bhardwaj, J. Andraos, C.C. Leznoff, Can. J. Chem. 80 (2002) 141e147.
[9] C.C. Leznoff, L.S. Black, A. Hiebert, P.W. Causey, D. Christendat, A.B.P. Lever,
Inorg. Chim. Acta 359 (2006) 2690e2696.
[10] S. Makhseed, M. Al-Sawah, J. Samuel, H. Manaa, Tetrahedron Lett. 50 (2009)
165e168.
Fig. 11. Emission spectra of 2-Naphthol (4.0
ꢂ
10ꢁ6 M),
5
(1.0
ꢂ
10ꢁ6 M),
6
(1.0 ꢂ 10ꢁ6 M) and mixture of 2-Naphthol þ 5 (4:1) (4.0 ꢂ 10ꢁ6 Me1.0 ꢂ 10ꢁ6 M) in
THF, emission excited at 327 nm. Emission spectra of 2-Naphthol and mixture of 2-
Naphthol þ 5 (4:1) were lowered by 5-fold in B band region.

Ö. Kurt et al. / Journal of Organometallic Chemistry 754 (2014) 8e15
15
[11] S.I. Yang, J. Li, H.S. Cho, D. Kim, D.F. Bocian, D. Holten, J.S. Lindsey, J. Mater.
[29] A.W. Snow, K.M. Kadish, K.M. Smith, R. Guilard, The Porphyrin Handbook, in:
Phthalocyanine Aggregation, vol. 17, Elsevier Science, Amsterdam, 2003, pp.
129e173.
Chem. 10 (2000) 283e296.
_
[12] I. Özçes¸ meci, A. Gelir, A. Gül, Dyes Pigm. 92 (2012) 954e960.
[13] S.Y. Al-Raqa, Dyes Pigm. 77 (2008) 259e265.
[30] A. Lyubimtsev, Z. Iqbala, G. Cruciusa, S. Syrbub, E.S. Taraymovich, T. Ziegler,
M. Hanack, J. Porphyrins Phthalocyanines 15 (2011) 39e46.
[31] A. Ogunsipe, D. Maree, T. Nyokong, J. Mol. Struct. 650 (2003) 131e140.
[32] Y. Zorlu, F. Dumoulin, M. Durmus¸ , V. Ahsen, Tetrahedron 66 (2010) 3248e
3258.
[33] A. Ogunsipe, T. Nyokong, J. Photochem. Photobiol. A 173 (2005) 211e220.
[34] I. Scalise, E.N. Durantini, Bioorg. Med. Chem. 13 (2005) 3037e3045.
[35] H. Du, R.C.A. Fuh, J. Li, L.A. Corkan, J.S. Lindsey, Photochem. Photobiol. 68
(1998) 141e148.
[14] J.P. Fox, D.P. Goldberg, Inorg. Chem. 42 (2003) 8181e8191.
[15] E. Güzel, A. Atsay, N.S. Nalbantoglu, L. Dogan, A. Gül, M.B. Koçak, Dyes Pigm.
97 (2013) 238e243.
[16] H.R.P. Karaoglu, A. Koca, M.B. Koçak, Dyes Pigm. 92 (2012) 1005e1017.
[17] A. Koca, H.A. Dinçer, H. Çerlek, A. Gül, M.B. Koçak, Electrochim. Acta 52 (3)
(2006) 1199e1205.
_
[18] I. Özçes¸ meci, I. Sorar, A. Gül, Inorg. Chem. Commun. 14 (2011) 1254e1257.
_
[19] H.Y. Yenilmez, I. Özçes¸ meci, A. Okur, A. Gül, Polyhedron 23 (2004) 787e791.
[20] A. Atsay, A. Koca, M.B. Koçak, Transit. Met. Chem. 34 (2009) 877e890.
[21] M.K. S¸ ener, A. Koca, A. Gül, M.B. Koçak, Transit. Met. Chem. 33 (2008)
867e872.
[22] M.B. Koçak, A. Gürek, A. Gül, Ö. Bekaroglu, Chem. Ber. 127 (1994) 355e358.
[23] H.A. Dinçer, A. Gül, M.B. Koçak, Dyes Pigm. 74 (2007) 545e550.
[24] E.T. Saka, M. Durmus¸ , H. Kantekin, J. Organomet. Chem. 696 (2011) 913e924.
[25] N.B. McKeown, H. Li, M. Helliwell, J. Porphyrins Phthalocyanines 9 (2005)
841e845.
[26] A.B. Anderson, T.L. Gorden, M.E. Kenney, J. Am. Chem. Soc. 107 (1985)
192e195.
[27] M. Konami, M. Hatano, A. Tajiri, Chem. Phys. Lett. 166 (1990) 605e608.
[28] M. Göksel, M. Durmus¸ , D. Atilla, J. Porphyrins Phthalocyanines 16 (2012)
898e906.
[36] M. Çamur, M. Durmus¸ , M. Bulut, Polyhedron 30 (2011) 1935e1945.
[37] M. Durmus¸ , T. Nyokong, Spectrochim. Acta, Part A 69 (2008) 1170e1177.
[38] D.L. Jiang, T. Aida, J. Am. Chem. Soc. 120 (1998) 10895e10901.
[39] B. Valeur, Molecular Fluorescence Principles and Applications, Wiley-VCH,
Germany, Weinheim, 2002.
[40] J.R. Lakowicz, Principles of Fluorescence Spectroscopy, third ed., Springer,
Berlin, 2006.
[41] A.C.H. Ng, X. Li, D.K.P. Ng, Macromolecules 32 (1999) 5292e5298.
[42] D.K.P. Ng, C.R. Chim. 6 (2003) 903e910.
[43] C.A. Barker, X. Zeng, S. Bettington, A.S. Batsanov, R. Martin, M.R. Bryce,
A. Beeby, Chem. Eur. J. 13 (2007) 6710e6717.
[44] M. Durmus¸ , J.Y. Chen, Z.X. Zhao, T. Nyokong, Spectrochim. Acta, Part A 70
(2008) 42e49.