Through-space electronic communication of zinc phthalocyanine with substituted [60]Fullerene bearing O2Nxaza-crown macrocyclic ligands

Article abstract of DOI:10.1016/j.saa.2016.08.031

Two new macrocyclic ligands containing 17- and 19-membered O₂N₃-donor aza-crowns anchored to [60]Fullerene were synthesized and characterized by employing HPLC, electrospray ionization mass (ESI-MS), ¹H and ¹³C NMR, UV–vis, IR spectroscopies, as well as powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA) in solid state. TGA measurements revealed that upon linking each of these macrocycle rings to [60]Fullerene, the decomposition point measured for [60]Fullerene moiety was increased, indicating on the promoted stability of [60]Fullerene backbone during binding to these macrocyclic ligands. Moreover, the ground state non-covalent interactions of [60]Fullerene derivatives of O₂N_x (x?=?2, and 3) aza-crown macrocyclic ligands namely, L¹–L⁴ with zinc phthalocyanine (ZnPc) were also investigated by UV–vis absorption, steady state and time resolved fluorescence spectrophotometry in N-methyl-2-pyrrolidone (NMP). The calculation of Stern-Volmer constants (K_SV) indicated on existence of an efficient quenching mechanism comprising of the excited singlet state of ZnPc in the presence of L¹–L⁴. The observation of an appropriate correlation between decrease in fluorescence intensity and lifetime parameters led us to propose the occurrence of a static mechanism for the fluorescence quenching of ZnPc in the presence of L¹–L³. The binding constants (K_BH) of L¹–L⁴/ZnPc were also determined applying the fluorescence quenching experiments. Meanwhile, the incompatibility of both K_SV and K_BH values found for L⁴ was also described in terms of structural features using DFT calculations using the B3LYP functional and 6-31G* basis set.

Full text of DOI:10.1016/j.saa.2016.08.031

Through-space electronic communication of zinc phthalocyanine with substi-
tuted [60]fullerene bearing O2NxAza-crown macrocyclic ligands
Bahram Ghanbari, Leila Shahhoseini, Niloofar Mahlooji, Parisa Gho-
lamnezhad, Zahra Taheri Rizi
PII:
DOI:
Reference:
S1386-1425(16)30484-X
doi: 10.1016/j.saa.2016.08.031
SAA 14617
To appear in:
Received date:
Revised date:
Accepted date:
1 May 2016
13 August 2016
16 August 2016
Please cite this article as: Bahram Ghanbari, Leila Shahhoseini, Niloofar Mahlooji, Parisa
Gholamnezhad, Zahra Taheri Rizi, Through-space electronic communication of zinc ph-
thalocyanine with substituted [60]fullerene bearing O2NxAza-crown macrocyclic ligands,
(2016), doi: 10.1016/j.saa.2016.08.031
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ACCEPTED MANUSCRIPT
Through-Space Electronic Communication of Zinc Phthalocyanine with Substituted
[
60]Fullerene bearing O N Aza-Crown Macrocyclic Ligands
2 x
a
a
a
a
Bahram Ghanbari* , Leila Shahhoseini , Niloofar Mahlooji , Parisa Gholamnezhad , Zahra
b
Taheri Rizi
a
Department of Chemistry, Sharif University of Technology, Tehran, Iran
b
Research Institute of Petroleum Industry, Tehran, Iran
Two new macrocyclic ligands containing 17- and 19-membered O N -donor aza-crowns
2
3
anchored to [60]Fullerene were synthesized and characterized by employing HPLC, electrospray
1
13
ionization mass (ESI-MS), H and C NMR, UV-vis, IR spectroscopies, as well as powder x-ray
diffraction (PXRD) and thermogravimetric analysis (TGA) in solid state. TGA measurements
revealed that upon linking each of these macrocycle rings to [60]Fullerene, the decomposition
point measured for [60]Fullerene moiety was increased, indicating on the promoted stability of
[
60]Fullerene backbone during binding to these macrocyclic ligands. Moreover, the ground state
non-covalent interactions of [60]Fullerene derivatives of O N (x = 2, and 3) aza-crown
2
x
1
4
macrocyclic ligands namely, L -L with zinc phthalocyanine (ZnPc) were also investigated by
UV–vis absorption, steady state and time resolved fluorescence spectrophotometry in N-methyl-
2
-pyrrolidone (NMP). The calculation of Stern-Volmer constants (K ) indicated on existence of
SV
an efficient quenching mechanism comprising of the excited singlet state of ZnPc in the presence
1
4
of L -L . The observation of an appropriate correlation between decrease in fluorescence
intensity and lifetime parameters led us to propose the occurrence of a static mechanism for the
1
3
1
fluorescence quenching of ZnPc in the presence of L -L . The binding constants (K ) of L -
BH
4
L /ZnPc were also determined applying the fluorescence quenching experiments. Meanwhile, the
4
incompatibility of both KSV and KBH values found for L was also described in terms of structural
features using DFT calculations using the B3LYP functional and 6-31G* basis set.
Keywords: [60]Fullerene; zinc phthalocyanine; aza-Crown; fluorescence; quenching
1
. Introduction
Amongst the eminent subjects of the current worldwide research, study on donor-acceptor
molecular assemblies is of central topics for light-to-electricity and light to fuel conversion as
well as for the purpose of investigation on artificial photosynthetic systems [1–5]. In molecular
systems combining various donors and [60]Fullerene acceptors, photoinduced electron transfer
and energy transfer have been widely investigated applying mainly their electrochemical and
photophysical properties [6–9].
After the initial discovery in 1984, [60]Fullerene and higher fullerenes display a remarkable
chemical feature, that is the chemical functionalization of fullerenes [10]. Chemical
functionalization of the fullerene cage can be easily achieved, allowing the introduction of
various functional groups which can help to both control and manipulate the fullerene molecules
and tune the properties of the resulting hybrid compounds. On one hand, the combination of
fullerene cages with those of other interesting materials, such as photoactive and/or electroactive

ACCEPTED MANUSCRIPT
units [11] and recently macrocyclic units [12] are diverse strategies which can enhance and tune
the physiochemical properties of the resulting fullerene-containing compound. On the other
hand, macrocyclic units anchored to [60]Fullerene could be useful for creating
fullerene/transition-metal complexes. Besides, as good electron donors and also excellent light
acceptors, transition-metal complexes are largely ideal candidates to association with the
fullerene cages to create photoactive donor-acceptor dyads for green energy production.
Numerous researches have been directed to assess the performance of fullerene/transition-metal
complexes as components of solar cell assemblies [13,14]. Molecular assemblies comprising of
[
60]Fullerene and transition metal complexes in separate molecules could potentially yield
unique compounds which display the properties of their single molecular structures as well as
diversified properties. Based on the chemical nature of the transition metal and the type of the
fullerene-transition metal linkage, these compounds are potentially applicable in various
fields[11]. Correspondingly, the application of such dyads containing [60]Fullerene derivatives
as the electron acceptor with diverse donors, such as tetracene, tetrathiafulvalene, chlorines,
amine, porphyrins, and ferrocenes, has drawn certain attention of researchers to donor–acceptor
interactions.
From the practical point of view, phthalocyanines (Pcs) are the structural analogues of
porphyrins which are planar 18 π-electron aromatic macrocycles and perfectly capable to fit to
the buckyball structure of fullerenes according their saddle-like macrocycle ring. Meanwhile
they could experimentally act as light energy conversion systems. Associated to porphyrins, Pcs
enjoy their advantage of having higher absorption around 700 nm which covers the maximum
spectra received from the solar photon flux. Numerous systems bearing Pcs as electron donor
and [60]Fullerene as electron acceptor have been reported and investigated by researchers during
the past decade [15].
In order to identify and study on the charge transfer phenomenon of [60]Fullerene derivatives as
the acceptor in donor-acceptor hybrids, spectroscopic techniques have been extensively used
[
16–19] . As a well-known donor-acceptor hybrid, [60]Fullerene-Pcs have been studied as charge
transfer assemblies employing spectroscopic techniques [20–23]. Furthermore, photoactive
supramolecular assemblies, in which both donor and acceptor moieties are non-covalently linked
together, are principally attractive either as prototypes of the conversion of light into electric
current or natural photosynthesis [24–26]. Basically, two mechanisms were introduced for
electron transfer phenomena in [60]Fullerene-metallophthalocyanine and/or metalloporphyrin
dyads [27]. In the first mechanism the covalent bonding guarantees linking of both donor-
acceptor moieties while the other approach enjoys from supramolecular self assembling of the
aforesaid moieties by virtue of so-called interactions as H bonding, electrostatic interactions,
metal−ligand coordination, and π−π plane-to-plane stacking of their aromatic rings [27].
On the other hand, a collection of bidentate and tridentate N-donor ligands have been shown to
be chemically linked to the [60]Fullerene cage, including 2,2′-bipyridine, 1,10-phenanthroline,
diazafluorene, dipyrromethene, and terpyridine. They were capable to bind simultaneously to
various transition metal ions creating charged complexes [11]. To the best of our knowledge,
however, there is no report on photochemical study of aza-crown derivative of [60]Fullerene
with Pcs.
1
2
Recently, we reported L and L (Fig. 1) as new [60]Fullerene derivatives [12] potentially
capable to bind to various transition metal cations as ligands through their macrocycle rings [28].

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CH2 2
CH2 2
CH2 4
CH2 4
O
O
O
O
O
O
O
O
N
N
2
NH
N
HN
3
NH
N
HN
N
N
1
2
3
4
L
L
L
L
Fig. 1. The structures of O N and O N aza-crown macrocyclic ligands
2
2
2
3
3
4
In the present work, we developed the synthesis of new [60]Fullerene derivatives, L and L
Fig. 1) to elaborate a systematic study on their basic photochemical behavior as electron
acceptor in the presence of ZnPc as a well-known electron donor, in the course of a charge
(
1
4
transfer process. Herein, the possibility of non-covalent interactions between L -L (Fig. 1) with
ZnPc are investigated by employing various spectroscopic methods, e.g. absorption, steady state
fluorescence and time-resolved fluorescence spectrophotometry in solution as well as DFT
calculations.
2
. Experimental
2
.1. Materials and methods
[
60]Fullerene (98%) and ZnPc were purchased from BuckyUSA and Sigma-Aldrich
respectively. The other reagents were obtained in analytical and/or chemical grade from Merck
without further purification.
UV–vis spectrophotometry was performed on a Rey Leigh UV-2601 equipped with thermo bath
o
1
13
applying N-Methyl-2-pyrrolidone (NMP) at 25 C. H and C NMR spectra were recorded in
CDCl on a Bruker-ARX500 instrument at room temperature. Micro analytical measurements
3
were performed on Truspec CHNS-Com Leco (USA). The fluorescence spectra was run on a
Varian Cary Eclipse fluorescence spectrophotometer (Springvale, Victoria, Australia) equipped
with 1cm×1cm quartz cells and a xenon lamp which was applied for recording the fluorescence
spectra. In these experiments, both of the excitation (340 nm) and emission (671 nm) bands were
set at the slit width of 5 nm. TGA was recorded on STA instrument from Germany Linseis (gas
-1
flow 30 mL min ). Mass spectroscopic measurements were carried out on a ThermoFisher
Scientific (Bremen, Germany) ion trap mass spectrometer (model LTQ, mass range m/z 10–
2
000) equipped with an electrospray ionization (ESI) interface. Instrument control, data
acquisition and processing were conducted by the Xcalibur 2.0 SR2 software. Typical positive
ESI-MS conditions were: capillary voltage −2.0 kV and skimmer cone voltage −20V.
-1
The HPLC measurements were carried out using C column and flow rate 0.8 mL min with
18
methanol–toluene (30/70 v/v) mixture as mobile phase. Based on the method of Jinno et al. [29],
the eluent was monitored at 330, 206 nm since the absorbance associated with toluene at 254 nm
would not interfere with the absorbance of [60]Fullerene.

ACCEPTED MANUSCRIPT
The PXRD patterns were collected on X’Pert PRO MPD PANalytical Company using Cu K 


(40 kV, 40 mA) radiation and a secondary beam graphite monochromator. The patterns were
recorded in the 2-theta (2) range from 2to 80
2
.2. The synthesis of the parent aza-crown macrocyclic ligands 1-4
The precursor dialdehydes as well as the respective O N and O N -azacrowns 1-4 were prepared
2
2
2
3
according to the similar method reported before [30,31,32] shown in Scheme 1.
n
n
O
O
O
O
O
O
I
II
Br n Br
n= 2 or 4
OH
NaOH
NH2 NH2
N
N
O
X
X
X=CH2
n
O
X=CH NHCH
III
O
N
2
2
NaBH4
X
y
N
n
IV
O
O
[60]Fullerene
NH HN
X
1 n=2, X=CH2
1
L n=2, X=CH y=1
2,
2
3
4
n=4, X=CH2
n=2, X=CH NHCH2
2
L n=4, X=CH , y=2
2
3
2
L n=2, X=CH NHCH , y=3
2
2
n=4, X=CH NHCH2
4
2
L n=4, X=CH NHCH , y=1
2
2
1
4
Scheme 1. The synthetic procedure for the preparation of L –L ; The reaction conditions were as
follow: I. ethanol, reflux, 2 (for n=2) and 4 (for n=4) days, II. dry methanol, reflux, 20 min, III.
stirring at room temperature, IV. toluene, reflux for 10 days.
The compounds were purified by using flash column chromatography; their purity was checked
1
13
by H and C NMR.
1
4
2
.3. General procedure for the synthesis of L –L
3
4
The [60]Fullerene-linked macrocyclic ligands L and L (Fig. 1) were synthesized using a
general method shown in Scheme 1 employing the similar method reported before for the
1
2
preparation of L and L [12] as follow: 1 g of 3 and/or 4 (in excess) was added to stirred
solution of 0.2 g [60]Fullerene in 50 mL toluene under nitrogen atmosphere at ambient
temperature. After 10 days, a dark brown solid product was filtered off and decanted several
times with toluene to remove any unreacted starting materials. The dark brown-colored products
3
were separated and used as the samples applied for the analyses. The separated yields of L and
4
L were determined as 71, and 62%, respectively. The following analytical data was also found
for:

ACCEPTED MANUSCRIPT
3
Macrocyclic derivative L
+
Mass spectral parent peak for [M+H] , m/z 1746.6.
1
H NMR: 2.40 (broad s, ArCH NH), 2.61 (t, ArCH NHCH CH ), 2.72 (t, ArCH NHCH CH ),
2
2
2
2
2
2
2
3
.83 (s, Ar-CH N) 4.41 (t, OCH ), 6.92-7.31 (m, aromatic H)
2 2
1
3
C NMR: 48.54 (ArCH NHCH CH ), 41.03, 48.90 (ArCH NHCH ), 50.68 (Ar-CH N), 67.05
2
2
2
2
2
2
(
OCH ), 110.91, 120.66, 120.92, 125.32, 128.24, 128.46, 128.52, 129.06, 131.12, 131.38,
2
1
37.88, 143.10, 157.25 (aromatic C)
-1
IR ν (cm ) 758, =C-H; 526, 1488, 1450 C=C;2846, 2937, C-H , 3392, N-H.
4
Macrocyclic derivative L
+
Mass spectral parent peak for [M+H] , m/z 1091.2
1
H NMR: 1.95 (broad s, ArCH NH), 2.08 (m, OCH CH ), 2.73-2.80 (t, ArCH NHCH ), 3.80 (s,
2
2
2
2
2
Ar-CH N) 4.ꢀ3(t, OCH ), 6.89-7.29 (m, aromatic H)
2
2
1
3
C NMR: 18.48 (OCH CH ), 26.39 (ArCH NHCH CH ), 49.48, 49.82 (ArCH NHCH ), 51.14
2
2
2
2
2
2
2
(
Ar-CH N), 67.17 (OCH ), 110.56, 11.03, 120.41, 128.06, 128.56, 130.84, 143.10, 157.27
2
2
(
aromatic C)
-1
IR ν (cm ) 758, =C-H; 526, 1488, 1450 C=C; 2846, 2937, C-H; 3392, N-H.
2
.4. Photophysical measurements
n
1
4
The quantum yields of the complexes, L /ZnPc (L -L ), were recorded in NMP. The absorption
and the emission intensities in the fluorescence spectra of L /ZnPc were measured at fixed
concentrations of ZnPc and variable concentrations of L -L (1.8x10 , 3.6x10 , 5.4x10 ,
7
n
1
4
-5
-5
-5
-5
-5
-4
-3
.2x10 , 9x10 , 1.1x10 mol dm ). Then, the absorption and emission intensities of ZnPc were
employed as the standard fluorophore [33]. The other operative parameters as source of light, slit
width, and cuvette were fixed during the measurements. Moreover, the absorption intensities
were plotted against emission intensities and the slopes of these graphs were calculated for the
n
complexes of L /ZnPc as well as the standard sample. Employing these slopes and Eq. (1), the
n
relative quantum yield for L /ZnPc (∅ ) were calculated.
F
Eq. (1)
n
where F and FZnPc are the slopes of L /ZnPc and the standard samples, respectively. A and A
ZnPc
n
represent the absorbance of the complexes of L /ZnPc and ZnPc, respectively, at the excitation
wavelength (in 1% pyridine in toluene) while the quantum yield for the standard sample was
ZnPc
∅
F
=
0.30 [33] and n and nZnPc are correspondingly the refractive indices of the solvent
applied for dissolution of the complexes of L /ZnPc as well as the standard samples [34].
n
3
3
. Results and Discussion
.1. The synthesis and characterization of L and L
3
4
3
4
The synthesis of L and/or L was accomplished by stirring the mixture containing 15 equivalent
weight of 3 and/or 4 in the presence of one equivalent weight of [60]Fullerene in toluene at
ambient temperature stirring for several days. The excess mole ratio of the

ACCEPTED MANUSCRIPT
macrocycle:[60]Fullerene was applied to ensure the maximum derivatization capability of
[
60]Fullerene with 3 and/or 4 [35].
From the practical point of view, ESI-MS has been conventional as the method of choice for the
mass spectrometric study on [60]Fullerene derivatives [36–38]. Recently, we successfully
1
2
applied ESI-MS for the characterization of L and L [12]. In similar experiments based on the
3
4
+
ESI-MS results obtained for L and L , the molecular ion [M+H] afforded the main peak in the
3
3
spectrum of L at m/z 1746.6 which indicated on a 3:1 mole ratio for 3:[60]Fullerene in L .
In the meantime, a 1:1 mole ratio of 4:[60]Fullerene in L was found by observing the protonated
molecular ion [M+H] at m/z 1091.2. Then, the purity of L was also checked by employing
HPLC method in order to phase out the presence of any other mole ratios of 3:[60]Fullerene in
L sample except for 3:1 mole ratio which was found in its mass spectrum . Basically, liquid
4
+
3
3
chromatography (LC) is the most effective separation technique which is applicable for the
separation of Fullerenes as well as their derivatives [39]. The chromatogram in Fig. 1S specifies
3
the purity of L in terms of any other derivatives as by-product.
In conclusion, Table 1 summarizes the ratio of macrocycle:[60]Fullerene for L -L calculated by
1
4
ESI-MS results.
1
4
Table 1. The calculated number of macrocyclic ligands linked to [60]Fullerene in L - L
compound
mole ratio of
aza-crown:[60]Fullerene
1:1 [12]
1
L
2
L
2:1 [12]
3:1
3
L
4
L
1:1
3
Moreover, TGA results (Fig. 2S) illustrated significant variations in thermal behaviour of L and
4
L comparing with pristine [60]Fullerene. Fig. 2S generally showed no upsurge in weight due to
added oxygen was experienced before weight loss begins for these samples. Besides, the
recorded TGA curves for 3 and 4 represented two main weight-loss steps; 65-80%
o
o
decomposition at 350-450 C and subsequent 20-35% decomposition at 450-800 C. Fig. 2S also
3
o
displayed that decomposition of L consists of two steps of weight loss: 51% from 100 to 390 C,
o
4
and 49% from 460 to 590 C. Similarly, TGA curve for L (Fig. 2S) demonstrated a 30% weight
o
4
loss from 220 to 480 C essentially assigned to the first major decomposition step of L (by
comparison with TGA curve for 4), following a 70% weight loss from 490 to 780 C mainly
o
assigned to the decomposition of [60]Fullerene backbone. Taking into account the
3
4
o
abovementioned discussion for the comparison of TGA curve of L with L at <400 C (Fig. 2), it
3
4
was found that more weight loss for L was observed than the corresponding curve for L . This
3
was another indication of 3:1 mole ratio proposed for 3:[60]Fullerene (in L ). The HF/3-21G
optimized structure for 3:1 mole ratio of 1:[60]Fullerene resulted in the structure shown in Fig.
3
S.
3
Besides, These TGA curves indicated on significant differences in thermal behaviour of both L ,
and L with respect to the corresponding results for their paten macrocyclic ligands, 3, 4 as well
4

ACCEPTED MANUSCRIPT
as [60]Fullerene. Meanwhile, the temperature of thermal decomposition reported for pure
o
o
[
60]Fullerene was 475 to 625 C (mainly at 545 C) [40] which was far from the observed value
3
4
3
4
found for L as well as L (in Fig. 2S). The TGA results found for L and L were also consistent
with our recent observation for L and L [12].
1
2
Comparing the thermal decomposition temperature of pure [60]Fullerene [41] in Table 2 with
3
4
those found in Fig. 2S for L and L unveiled that [60]Fullerene moiety generally received more
stabilization upon linking to 3 and 4.
Table 2. Thermal decomposition temperature obtained for free and the bonded forms of
3
4
[
60]Fullerene to 3 (in L ) and 4 (in L )
Decomposition Temperature (ºC) for
60]Fullerene in
[
free [60]Fullerene
70 [41]
3
4
L
L
4
500-600
550-750
3
4
The presence of [60]Fullerene backbone in L and L derivatives was also examined by
3
employing powder X-ray diffraction (PXRD) analysis. The patterns of PXRD found for L and
4
L were compared with the pattern of pristine [60]Fullerene in Fig. 4S.
The first three peaks in the XRD pattern of pristine [60]Fullerene powder shown in Fig. 4S were
assigned to Bragg diffractions from (111), (220), and (311) crystal planes [42]. On one hand, the
3
4
corresponding peaks of L , and L (in Fig. 4S) are much broader than those of the pristine
[
[
60]Fullerene powder. On the other hand, it should be noted that the peak indexed to (111) of
60]Fullerene in the XRD pattern of L , and L (in Fig. 4S) was blue-shifted from that in the
3
4
XRD pattern of the [60]Fullerene. These evidence suggested that the interplanar distance of d
1
11
3
4
3
was little larger in L , and L than that in the pristine [60]Fullerene powder. Furthermore, L ,
4


and L exhibit new diffraction patterns at 2 9.5 and which furnish solid [60]Fullerene
3
4
moiety of L , and L in various packing lattices.
The structures of L and L were also monitored by H and C NMR spectra in CDCl (Fig. 4S).
3
4
1
13
3
3
4
In The next step, selected proton and carbon chemical shifts (of L and L (shown in Fig. 5S)
were collected in Table 3 and compared with the corresponding chemical shifts found for free
macrocyclic ligands 3 and 4 .
3
4
Table 3. The proton and carbon chemical shift changes () recorded for L and L versus 3 and
4
in CDCl3
Chemical shift of the hydrogen and carbon atoms
Compound
ArCH N ArCH N ArCH NCH2 ArCH NCH2 ArCH NCH CH N
ArCH NCH CH N
2
2
2
2
2
2
2
2
2
2
3
L
3.82
5ꢀ.68
2.73
48.9ꢀ*
2.63
48.54
3
3.83
51.1
2.71
49.3
2.60
49.0

(ppm)
-0.01
-0.42
0.02
-0.4
0.03
-0.82
obs (4Hz)
-4
3.80
-168
51.14
8
2.79
-160
49.82
12
2.75
328
49.48
L

ACCEPTED MANUSCRIPT
4
3.82
-0.02
-8
51.50
-0.36
-144
2.80
-0.01
-4
50.20
-0.18
-72
2.76
-0.01
-4
49.82*
-0.32
-128

(ppm)
obs (Hz)
1
3
3
*
the least chemical shift value was considered (see the C NMR spectral assignment for L ).
As it is evident from the data in Table 3, the maximum value of obs recorded for proton and
carbon atoms of -CH - groups near by the nitrogen groups were 12 and 328 Hz, respectively.
2
Such values are much greater than that expected for the solvation effect. In conclusion, these obs
were increased as the result of the covalent bonding of the nitrogen donor groups with
[
[
60]Fullerene. Similar features have previously been reported for some complexes of
60]Fullerene with a series of aromatic hydrocarbons and methylpyridines [43,44].
3
.2. UV–vis and fluorescence investigations
1
4
n
In the following experiments the interaction of L -L (L ) with ZnPc was studied in NMP since
we found NMP as the good solvent for dissolution of L . Besides, previous spectroscopic reports
n
[
45] have presented that the aggregation of [60]Fullerene in their NMP solutions proceeds at the
−
2
−3
concentration range >0.05×10 g cm which was fairly higher than the selected concentrations
in our experiments. The first evidence on the interaction of L with [60]Fullerene in NMP was
n
observed employing UV-vis spectrophotometry shown in Fig. 2.
2
2
2
1
1
0
0
0
.8
.4
.0
.6
.2
.8
.4
.0
(
a)
1
ZnPc / L
ZnPc
3
00 400 500 600 700 800 900 1000
Wavalenght(nm.)

ACCEPTED MANUSCRIPT
1
1
1
1
0
0
0
0
0
.6
.4
.2
.0
.8
.6
.4
.2
.0
(
b)
2
ZnPc / L
ZnPc
3
00
400
500
600
700
800
Wavalenght(nm.)
2
2
2
1
1
1
1
1
0
0
0
0
0
.4
(
c)
.2
.0
.8
.6
.4
.2
.0
.8
.6
.4
.2
.0
3
ZnPc + L
ZnPc
3
00
400
500
600
700
800
Wavalenght(nm.)

ACCEPTED MANUSCRIPT
2
1
1
1
1
1
0
0
0
0
0
.0
.8
.6
.4
.2
.0
.8
.6
.4
.2
.0
(
d)
4
ZnPc / L
ZnPc
300
400
500
600
700
800
Wavalenght(nm.)
1
4
Fig. 2. The UV–vis titration of L -L with ZnPc in NMP as solvent, keeping the concentration of
-
6
-3
n
1
ZnPc fixed at 7x10 mol dm ; the concentration of L increased (from bottom to top) for: L
-5
-5
-5
-5
-5
-4
-3
2
3
-5
-5
1
.8x10 , 3.6x10 , 5.4x10 , 7.2x10 , 9x10 , 1.1x10 mol dm ; L and L 1.25x10 , 2.5x10 ,
-5
-5
-5
-5
-5
-3
4
-4
-4
-4
-
3
.7x10 , 5.0x10 , 6.2x10 , 7.5x10 , 8.7x10 mol dm , L 0.9x10 , 1.9x10 , 2.8x10 , 3.7x10
4
-4
-4
-3
,
4.6x10 , 5.6x10 mol dm .
n
Although not very inclusive, but the most prominent spectral change in the spectra of L /ZnPc
n
was typically due to an insignificant spectral change in the UV region of the L spectrum. For
n
instance, a red shift in 335-nm band of L was perceived in Fig. 2.
Since ZnPc is a well-known fluorophore towards [60]Fullerene [46], fluorescence spectroscopy
was hired to study these interactions. The large molar extinction coefficients found for ZnPc with
respect to [60]Fullerene in the visible UV-vis spectral region allowed us to excite preferentially
the ZnPc, although the ZnPc concentration was much lower than [60]Fullerene. It was observed
that fluorescence of ZnPc at 679 nm, upon excitation at 340 nm (i.e., Soret absorption band), was
1
4
diminished gradually by addition of various concentration of L –L in NMP medium. Typically,
n
the fluorescence spectral changes for ZnPc upon addition of L solution are shown in Fig. 3.

ACCEPTED MANUSCRIPT
3
2
1
0
0
0
0
ZnPc
400
300
200
100
0
3
90
420
450
480
510
540
570
600
wavelenght (nm)
1
ZnPc / L
400
500
600
700
800
Wavelenght (nm)
2
2
1
1
5
0
5
0
5
0
ZnPc
4
3
2
1
00
00
00
00
0
3
90
420
450
480
510
540
570
600
wave lenght (nm)
2
ZnPc / L
400
500
600
700
800
Wavelenght (nm)

ACCEPTED MANUSCRIPT
30
25
20
15
10
5
0
ZnPc
4
3
2
1
00
00
00
00
0
390
420
450
480
510
540
570
600
wavelenght (nm)
3
ZnPc /L
4
00
500
600
700
800
Wavelenght (nm)
30
2
5
4
00
00
00
00
0
20
ZnPc
15
10
3
5
0
420
450
480
510
540
570
600
wavelenght (nm)
4
2
1
ZnPc / L
4
00
500
600
700
800
Wavelenght (nm)
-6
-3
Fig. 3. The steady state fluorescence spectral variation of ZnPc (7x10 mol dm ) in the presence
n
n
of L in NMP medium; the applied concentrations of L were described in the caption of Fig. 2.
The emission peak of the phthalocyanines at 679 nm agreed fairly well with the reported values
in the literature for other phthalocyanines [47]. Employing the method of continuous variation,

ACCEPTED MANUSCRIPT
1
4
Job’s plots (Fig. 4) for L –L were fundamentally established 1:1 stoichiometry for these
interactions.
1
4
Fig. 4. The fluorescence Job’s plots for L –L /ZnPc in NMP
In the next step, the binding constants for these complexes (K ) were estimated according to a
BH
modified Benesi-Hildebrand equation Eq (1) [48]:
Eq. (1)
n
In Eq (1), F and F denote on the fluorescence intensity of ZnPc without and with L (Fig. 3); A
0
is a constant associated with the difference in the emission quantum yield of the complexed and
n
uncomplexed ZnPc. Four typical BH fluorescence plots of L /ZnPc systems were shown in Fig.
5
.

ACCEPTED MANUSCRIPT
1
4
Fig. 5. The Benesi-Hildebrand fluorescence plots of L –L /ZnPc
n
By plotting F /(F -F) (relative fluorescence intensity) versus 1/[L ], K values were obtained
for various L –L /ZnPc complexes shown in Table 4.
0
0
BH
1
4
1
4
Table 4. The calculated KBH values and the respective quantum yield of L –L /ZnPc by
fluorescence spectrophotometry
3
-1
system
K , dm mol
quantum yield (
)
BH
1
L /ZnPc
16925 (±349)
15153 (±662)
11249 (±377)
2714 (±221)
33880 (±933)
0.12
0.14
0.13
0.16
0.10
2
L /ZnPc
3
L /ZnPc
4
L /ZnPc
[
60]Fullerene/ZnPc
KBH values calculated in Table 4 revealed that the rise in the fluorescence quenching efficiency
1
4
observed for L –L , subsequently led to increase in the magnitude of K . This can be attributed
BH
1
4
to the fact that the rigidity of the phthalocyanine molecule results in tight binding of L –L to
60]Fullerene in L –L /ZnPc.
The calculated quantum yields of L –L /ZnPc in NMP are also presented in Table 4. As evident
from Table 4, the calculated quantum yields found for L –L /ZnPc were typically ~0.1 which
1
4
[
1
4
1
4
were not significantly different from the measured quantum yields found for [60]Fullerene/ZnPc.
Basically, the quantum yield can change due to variation in the rate of nonradiative decay and/or
due to conformational transformations in the fluorophore [49]. Evidently, it has already been
reported that light induced energy or electron transfer reactions occurred in self-assembled
supramolecular ZnPc/[60]Fullerene as donor-acceptor systems [49]. As a general phenomenon,
the competition between the energy and electron transfer processes is characteristically a solvent-
dependent photophysical behavior occurred for donor-[60]Fullerene molecular complex [50].

ACCEPTED MANUSCRIPT
Therefore, in the present investigation the quenching phenomenon can be ascribed to the
photoinduced energy transfer from ZnPc to [60]Fullerene.
3
.2.1. Mechanistic Studies
n
As it was seen in Fig. 3, the emission intensity of ZnPc was reduced as the concentration of L
was increased. The spectral changes finally reached a plateau, indicating that the fluorescence
n
quenching was evidently induced by the interaction of L with ZnPc. For this reason, in our
n
fluorescence experiment for L /ZnPc interactions, the Soret absorption band of ZnPc was
employed as the source of excitation wavelength. Applying similar experiments for particular
designed supramolecules containing [60]Fullerene, Yin [51] and Guldi [52] showed that the
second excited singlet state of the ZnPc was deactivated by the following mechanism [52]:
0
2
*
internal conversion
phthalocyanine + h→ phthalocyanine
1
*
energy transfer to [60]Fullerene
0
3
*
phthalocyanine
phthalocyanine/ [60]Fullerene
Fluorescence quenching processes are fundamentally divided into two categories: static and
dynamic quenching [49]. Since the quencher should diffuse to the fluorophore during the lifetime
of the excited state, the rate of a dynamic quenching process is practically controlled by the
diffusion rate of these two chemical species. However, the formation of a ground-state non-
fluorescent complex or the presence of a sphere of effective quenching is crucial for a typical
quenching process with static quenching mechanism. Whilst, dynamic quenching processes
occur as a result of the collision between a ground-state and an excited-state fluorophore
quencher follow by the formation of a transient complex [49].
In this work, both of the steady-state and time resolved fluorescence quenching data were studied
following Stern–Volmer (SV) Eqs. (2) and (3) [49]:
SS
Fo /F = 1 + kq  [Q] = 1 + K [Q]
Eq. (2)
Eq. (3)
· o
sv
TR
o/ = 1 + kq  [Q] = 1 + K [Q]
· o
sv
In Eqs. (2) and (3), F and F denoted on the fluorescence intensities in the absence and presence
o
of the quencher, respectively, k was the bimolecular quenching rate constant, K defined as the
q
sv
Stern-Volmer quenching constant and [Q] was the concentration of the quencher.  and  were
o
the average fluorescence lifetimes of the fluorophore ZnPc in the absence and presence of the
quencher Q, respectively. The superscripts SS and TR on k defined the quenching constants for
q
the steady state and time-resolved experiments, correspondingly.
In our experiments, the fluorescence emission of ZnPc was reduced from F to F in the presence
o
n
of different concentrations of quencher, e.g. L . Fig. 6 displays the Stern-Volmer plots of the
n
quenching processes of ZnPc by L .

ACCEPTED MANUSCRIPT
4
3
3
2
.0
.5
.0
.5
.0
1
L
2
L
4
.0
3.5
3.0
2.5
F /F
F /F
0
0
2
2.0
1
.5
1.5
1.0
1.0
0.00000
0.00002
0.00004
0.00006
0.00008
0.00010
0.00000
0.00002
0.00004
0.00006
0.00008
0.00010
[L], M
[L], M
3
.0
.5
.0
3.5
3
4
L
L
3
2
2
.0
.5
.0
2
2
F /F
0
F /F
0
1
.5
1
.5
1
.0
1
.0
0
.0000 0.0001 0.0002 0.0003 0.0004 0.0005 0.0006 0.0007
L], M
0
.00002
0.00004
0.00006
0.00008
0.00010
[
[
L], M
Fig. 6. The Stern-Volmer (SV) plots from steady state fluorescence emission intensity for ZnPc
1
4
o
in the presence of L -L in NMP at 25 C
n
The plots in Fig. 6 demonstrate the linearity of F /F curves to the quencher concentration L .
o
Basically, it is important to note that observation of a linear Stern-Volmer plot does not
necessarily verify that collisional quenching of fluorescence was occurred since the static
quenching also gave rise to linear Stern-Volmer plots [49]. The static and dynamic quenching
could be recognized by their different reliance on and/or viscosity, temperature or rather by
lifetime measurements.
In the course of lifetime measurements for these interactions, it was establish that the emission
1
4
decay of L -L at 340 nm (Fig. 7) was conveniently fitted to the first order reaction rate.

ACCEPTED MANUSCRIPT
20
20
L1
ZnPc
18
18
L2
ZnPc
16
16
14
14
12
12
10
10
8
6
4
2
0
8
6
4
2
0
5
10
15
20
25
30
35
5
10
15
20
25
30
35
time (s)
time (s)
L3
ZnPc
4
3
2
1
0
0
0
0
0
40
L4
ZnPc
3
2
1
0
0
0
0
5
10
15
20
25
30
35
5
10
15
20
25
30
35
time (s)
time (s)
1
4
Fig. 7. The time profile for the emission of ZnPc, L -L /ZnPc systems at 340 nm.
SS
TR
1
4
The Stern-Volmer (K ) and quenching rate constants (k , and k ) found for L -L /ZnPc were
SV
q
q
presented in Table 5.
SS
TR
Table 5. The calculated values of k , k
and KSV using steady-state and time-resolved
q
q
n
fluorescence experiments for the interactions of various L /ZnPc systems estimated in NMP at
98 K.
2
3
-1
3
-1 -1
K *, dm mol calculated in
k ,dm mol s
SV
q
system
steady-state
experiments
time-resolved
experiments
SS
TR
kq
kq
1
8
8
L /ZnPc
28297(±6854) 26270(±6516)
29406(±1973) 27334(±8587)
24727(±2765) 23590(±3273)
5.8x108
6.1x108
5.1x10
5.4x108
5.6x108
4.9x10
2
L /ZnPc
3
L /ZnPc

ACCEPTED MANUSCRIPT
4
7
8
L /ZnPc
3750(±724)
27338(±2024)
-
7.7x109
1.5x10
5.6x10
-
[
60]Fullerene/ZnPc 73681(±7567)

The calculated value of  for ZnPc was 48.5 s.
0
The results in Table 5 together with the observation of a parallel decrease in both fluorescence
intensity and lifetime parameters (i.e., F /F =  /) pointed out the occurrence of static quenching
0
0
n
for the fluorescence emission of ZnPc in the presence of L . The aforementioned fluorescence
quenching phenomenon is primarily attributed to involvement of a static charge transfer
process considering a static quenching mechanism. Conversely, the incompatibility of K values
SV
4
found for L (comparing the steady-state and time-resolved results in Table 4) waived the static
fluorescence quenching mechanism.
3
.3. Theoretical Calculations
4
In order to collect structural data to evaluate poor K value found for L /ZnPc (Table 4), the
geometry of L was typically explored by DFT calculations using the B3LYP functional and 6-
SV
4
3
1G* basis set [53,54]. In order to find the most stable connection mode through O N -donor
2 3
groups of 3, and 4 to [60]Fullerene backbone, the number of connecting atoms were altered and
the optimized systems were shown in Fig. 6S.
Fig. 5S revealed that major electronic difference expected from these structural modes could be
originated from their total electron withdrawing effect of the nitrogen groups.
Table 6 displays the relative energies (calculated by B3LYP/6-31G* method) as well as the
enthalpy values (calculated by HF/3-21G method) for a-d linking modes (in Fig. 6S) of 3 and 4
3
4
to [60]Fullerene in L and L .
Table 6. The B3LYP/6-31G* optimized relative energies for various modes of linking of 3 and 4
3
4
to [60]Fullerene in L and L .
The connection mode to
Relative Energy calculated
by B3LYP/6-31G* method
Enthalpy of reaction calculated
by HF/3-21G method
name
[
60]Fullerene
-
1
-1
(
kcal mol )
(kcal mol )
a
b
c
d
a
b
c
d
A
B
-35.8
-34.3
771.9
109.8
-1.8
-
21.0
17.1
7.6
-
3
L
A,B
A,B,C
A
-
0
-
122.3
119.3
113.0
B
13.5
-
4
L
A,B
A,B,C
831.1
105.8
-
0
The data in Table 6 demonstrates that although the best chance for linking of O N -donor
2
3
azacrown 3 and 4 to [60]Fullerene is connection through one nitrogen, but the calculated relative
4
energy differences among b-c modes were not very significant for L . Table 6 also showed that

ACCEPTED MANUSCRIPT
3
there could be different linking modes of types a or b modes available to L while linking
4
through c mode for L might be the decisive reason for the observed reduced K value found for
SV
4
L /ZnPc (Tables 4 and 5). In conclusion, having higher number of electron withdrawing nitrogen
groups on 4 linked to [60]Fullerene (by accepting a mode) could resulted in lower K value for
SV
4
3
L with respect to L .
3
4
In order to visualize the geometry and the electronic structures of L and/or L /ZnPc dyads, their
ground states were optimized by B3LYP/6-31G* level with Gaussian 03. As shown in Fig. 8
(panels a-f), all of the dyads revealed stable structures on the Born-Oppenheimer potential
energy surface with no steric constraints between the donor and acceptor entities.
n
3
Fig. 8. HOMOs and LUMOs of L /ZnPc dyads at various electronic states: (a) L /ZnPc, (b)
3
3
4
4
HOMO of L /ZnPc, (c) LUMO of L /ZnPc, (d) L /ZnPc, (e) HOMO of L /ZnPc, (f) LUMO of
4
L /ZnPc done by B3LYP/6-31G* calculations.
3
4
As shown in Fig. 8b,c,e, and f , the calculated HOMOs for L and L /ZnPc were fundamentally
3
4
located on ZnPc entity, while the LUMOs were fundamentally located on L and L entities.
1
3
The so-called interactions recommended L -L /ZnPc as potent fluorophore candidates for
detection of metal ions by fluorescence spectrophotometry through their appended macrocycle
rings which were of our ongoing research theme.

ACCEPTED MANUSCRIPT
Conclusions
Fluorescence spectrophotometry was applied as an efficient method to detect non-covalent
1
4
interaction of ZnPc with [60]Fullerene derivatives bearing aza-crown macrocycles, L -L . The
existence of an efficient quenching mechanism by reducing excited singlet state of ZnPc in the
1
4
presence of L -L in NMP was observed. Comparing the steady state and time resolved
fluorescence results, a notable correlation between decrease in the fluorescence intensity and the
lifetime parameters which confirmed on the occurrence of a static mechanism for the
1
3
fluorescence quenching of ZnPc in the presence of L -L . Meanwhile, the poor Stern-Volmer
4
constant (K ) measured for L was also described according to a structural feature using DFT
SV
calculations.
Acknowledgment
Financial supports from Research Office of Sharif University of Technology and Iran National
Science Foundation are appreciated.
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ACCEPTED MANUSCRIPT
Graphical abstract

ACCEPTED MANUSCRIPT
Highlights
Two new O N -donor aza-crowns anchored to [60]Fullerene were synthesized.
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The steady-state and time resolved fluorescence quenching properties of L -L were studied.
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The correlated decrease in both F /F and  /suggested a static quenching for L -L /ZnPc.
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The quenching was attributed to involvement of a static charge transfer process.
DFT calculations showed the relation between structural features and the observed K values.
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