Spectral investigations of meso -tetraalkylporphyrin-fullerene host-guest complexes

Article abstract of DOI:10.1142/S1088424615500716

Meso-tetraalkylporphyrins and their Zn(II) complexes were synthesized and characterized by various spectroscopic techniques. Single crystal X-ray structure of meso-tetrapropylporphyrin (3) revealed the orientation of alkyl chains and planar conformation of porphyrin macrocycle. Spectroscopic, photophysical and electrochemical redox properties of self-assembled donor-acceptor dyads formed by meso-tetraalkylporphyrins and fullerene C₆₀ were investigated. These studies revealed 1:1 supramolecular dyad formation between the electron donor porphyrins and the electron acceptor, fullerene entities. The determined association constants (K) follow the order: H₂TMeP (1) > H₂TEtP (2) > H₂TPrP (3) > H₂THexP > H₂TPP. The effect of alkyl chain length on porphyrin-fullerene complexation was investigated. The redox behavior of self-assembled dyads was investigated in PhCN containing 0.1 M TBAPF₆ as supporting electrolyte. The oxidation potentials of dyads are positively shifted (20-100 mV) as compared to corresponding meso-tetraalkylporphyrins indicating the supramolecular interactions between the constituents in the ground state. The geometric and electronic structure of 1:C₆₀ was probed by DFT calculations which suggested the possibility of charge transfer from meso-tetraalkylporphyrin to fullerene C₆₀.

Full text of DOI:10.1142/S1088424615500716

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2015; 19: 1–10
DOI: 10.1142/S1088424615500716
Published at http://www.worldscinet.com/jpp/
Spectral investigations of meso-tetraalkylporphyrin-fullerene
host–guestcomplexes
Nitika Grover, Pinki Rathi and Muniappan Sankar*
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India
Received 5 March 2015
Accepted 5 May 2015
ABSTRACT: Meso-tetraalkylporphyrins and their Zn(II) complexes were synthesized and characterized
by various spectroscopic techniques. Single crystal X-ray structure of meso-tetrapropylporphyrin
(3) revealed the orientation of alkyl chains and planar conformation of porphyrin macrocycle.
Spectroscopic, photophysical and electrochemical redox properties of self-assembled donor–acceptor
dyads formed by meso-tetraalkylporphyrins and fullerene C were investigated. These studies revealed
6
0
1
:1 supramolecular dyad formation between the electron donor porphyrins and the electron acceptor,
fullerene entities. The determined association constants (K) follow the order: H TMeP (1) > H TEtP (2)
2
2
>
H TPrP (3) > H THexP > H TPP. The effect of alkyl chain length on porphyrin-fullerene complexation
2
2
2
was investigated. The redox behavior of self-assembled dyads was investigated in PhCN containing
0
1
.1 M TBAPF as supporting electrolyte. The oxidation potentials of dyads are positively shifted (20–
00 mV) as compared to corresponding meso-tetraalkylporphyrins indicating the supramolecular
6
interactions between the constituents in the ground state. The geometric and electronic structure of
:C was probed by DFT calculations which suggested the possibility of charge transfer from meso-
1
6
0
tetraalkylporphyrin to fullerene C .
6
0
KEYWORDS: meso-tetraalkylporphyrins, supramolecular dyad, porphyrin-fullerene host–guest
complexes.
systems [3]. Host molecules encapsulating fullerenes are
INTRODUCTION
of great importance because of their potential application
to the extraction, solubilization and chemical modification
of the fullerenes [4a]. The cyclic oligomers consisting of
electron-rich aromatic components, such as calixarenes,
resorcinarenes and cyclotriveratrylenes, have been
reported as p-hosts for fullerenes [4].One demanding class
of compounds which has caught the awareness of many
research groups and having vast positive aspect as well as
potential is the porphyrin-fullerene conjugates [5–7]. This
consideration results from the fact that a fullerene and a
porphyrin are instinctively attracted each other to form a
host–guest complex both in the solid state and in solution
despite the disparity in external shape between the planar
porphyrin and the curved fullerene. Fullerenes [8] have
been demonstrated to be good candidates for electron
acceptors due to their low reduction potentials [9], three-
dimensional arrangement [10], and low reorganization
energy involved in electron-transfer reactions [11].
The manipulation of weak forces to assemble new
molecular entity is one of the major areas of interest in
modern chemistry [1]. Usually, H-bonding, electrostatics,
labile metal–ligand bonds, and flat p–p interactions have
been used to assemble new structures. The spontaneous
interaction between simple donor–acceptor molecules
leading to isolated nanostructures offers a great potential
for straightforward discoveries and realistic applications
[1c]. Further, non-covalent interactions play a very
significant role in the execution of various molecular
building blocks which can be utilized for the inception
and implementation of advanced functional materials [2].
Such self-assemblies of carefully monitored and designed
building blocks can lead to sophisticated photo-active
*
Correspondence to: Muniappan Sankar, email: sankafcy@iitr.
ac.in, tel: +91 1332-284-753, fax: +91 1332-273-560
Copyright © 2015 World Scientific Publishing Company

2
N. GROVER ET AL.
Porphyrins [12] have been utilized as electron donors due
to their intense absorption in the visible region and due
to the fact that they are easily oxidized in photoinduced
electron transfer. As a result, extensive studies have been
performedoncovalentlylinkedandself-assembleddonor–
acceptor dyads composed of porphyrin and fullerene
as donor and acceptor entities. Sun et al. [13] reported
the first structural characterization of a pyrrolidine-
functionalized C60 species, the crystal packing of the
RESULTS AND DISCUSSION
Synthesis and characterization
Meso-tetraalkylporphyrins (1–3) and their Zn(II)
complexes (1a–3a) were synthesized according to
the modified procedure reported in the literature as
shown in Scheme 1 [17a]. All synthesized porphyrins
1
were characterized by UV-vis, fluorescence, H NMR
dyad revealed an intermolecular interaction of the C60
spectroscopic techniques, mass spectrometry and cyclic
1
ball in remarkably close approach to the porphyrin plane.
voltammetric studies. H NMR spectra of these porphyrins
Later, unique cocrystallites of C and C fullerenes with
60
70
exhibited characteristic resonances arising from b-pyrrole
protons (~9.5 d ppm), and imino protons (for free-base
porphyrins, -2.4 to -2.8 d ppm) as shown in Figs S1 to
S6 (see the Supporting information section). Meso-alkyl
group (methyl/methylene) which is directly attached to
the porphyrin ring has shown considerable downfield shift
various metal octaethylporphyrins (MOEPs) and metal
tetraphenylporphyrins (MTPPs) have been reported and
they have shown distinct physicochemical properties
[6, 7]. The intermolecular fullerene/porphyrin contacts
range from 2.6 to 3.0Å, which are shorter than typical p–p
interactions (3.0–3.5 Å). Structures of supramolecular
(4–5 ppm) due to deshielding effect conjugated porphyrin
complexes featuring
interaction have been characterized in the solid state
in the form of co-crystals) [5, 14]. Nevertheless, these
a
single porphyrin-fullerene
p-system. The integrated intensities of the proton resonances
of these porphyrins and mass spectrometry results (Figs S7
to S11 in Supporting information) are consistent with the
proposed structures of 1–3 and their corresponding Zn(II)
complexes (1a–3a).
(
component of porphyrin-fullerene complexes readily
detach in solution as a result of reduced thermodynamic
stability. In spite of these few covalent macrocyclic
metalloporphyrin dimers [15] and one trimer [16]capable
offormingthermodynamicallystableinclusioncomplexes
with fullerenes in solution have been described. The gain
in stability of these complexes not only derives from the
macrocyclic effect as discussed above but is also due to
the multivalency (several porphyrin units) built into the
receptor’s structure. Meso-tetraalkylporphyrins [17] and
their metal complexes are electron rich porphyrins having
intense absorption and emission. These porphyrins
Crystallographic data of H TPrP (3) is listed in
2
Table S2 (Supporting information). ORTEP views (top
and side) of 3 are shown in Fig. 1. 3 has shown planar
confirmation [17c] as evidenced from the displacement
of 24 core atoms from the mean plane, D24 = 0.031 Å
and displacement of b-carbon from mean plane, DC =
b
0
.04 Å. Two of the adjacent meso-propyl groups are
oriented above the porphyrin plane and rest of the two
are projected below the porphyrin plane. The crystal
structure packing of 3 along the a and b crystallographic
axes were shown in Fig. S12 (Supporting information).
Notably, these porphyrins are held together by weak p–p
interactions with a distance of ~3.72 Å.
formed supramolecular dyads with C due to their planar
60
structure and electron rich nature. As a continuing effort
to build novel supramolecular donor–acceptor systems,
in the present study, we have developed donor–acceptor
dyads using meso-tetraalkylporphyrins (1–3) and their
Zinc(II) complexes (1a–3a) with fullerene C60 and
studied their spectroscopic as well as electrochemical
redox properties.
UV-visible spectral studies
The UV-vis absorption spectra of meso-tetraalkyl-
porphyrins (1–3) and their Zn(II) complexes (1a–3a)
R
R
R
R
NH
N
N
N
N
N
Propionic acid, H2O
2 2
Zn(OAc) ·2H O
+
R
-CHO
R
R
R
Zn
R
Pyridine, 90 °C, 2 h
CHCl3/CH3OH
N
H
N
HN
R
R
R = Me (1)
R = Et (2)
R = Pr (3)
R = Me (1a)
R = Et (2a)
R = Pr (3a)
Scheme 1. Synthesis of meso-tetraalkylporphyrins (1–3) and their corresponding Zn(II) complexes (1a–3a)
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 2–10

SPECTRAL INVESTIGATIONS OF MESO-TETRAALKYLPORPHYRIN-FULLERENE HOST–GUEST COMPLEXES
3
Fig. 1. ORTEP diagrams of H TPrP (3) showing (a) top and (b) side views
2
3
-1 19a
1
0–100 times higher than H TPP (K ~ 10 M ) and
2
Zn-porphyrin dyad [19]. The K values of free-base
porphyrins with C follow the trend
6
0
H TPP < H THexP < 3 < 2 < 1
2
2
H TMeP (1) exhibited highest binding constant
2
among all free-base porphyrins. As we increase the
length of alkyl chain, the association constant decreases
is possibly due to the free rotation of alkyl chains that can
hinder the approach of C60 towards the porphyrin plane
as shown in Fig. 1. Zn(II) porphyrins (1a–3a) exhibited
similar spectral profiles as shown in Figs S15 to S17
(Supporting information). All the plots exhibit straight
lines with greater than 0.96 correlation coefficient,
clearly indicating the 1:1 stoichiometry of C and meso-
6
0
tetraalkylporphyrins in the complex.
Fig. 2. UV-vis spectra of H TEtP (2) and its Zn(II) complex
2
(
2a) in CH Cl at 298 K
2 2
Fluorescence spectral studies
The fluorescence spectra of meso-tetraalkylporphyrins
(1–3) and their Zn(II) complexes (1a–3a) were recorded
in CH Cl at 298 K. Table S1 (Supporting information)
were recorded in CH Cl at 298 K. Table S1 (Supporting
2
2
information) lists the absorption spectral data of 1–3
and 1a–3a in CH Cl . These porphyrins exhibited
2
2
lists the emission spectral data of 1–3 and 1a–3a. These
2
2
characteristic electronic absorption spectral features
Fig. 2) similar to H TPP and ZnTPP [18a]. The
porphyrins exhibited ~10 nm red-shift in their emission
(
spectra as compared to H TPP and ZnTPP. The singlet
2
2
Interaction between C60 and meso-tetraalkylporphyrins
1–3) was studied by UV-visible spectral titrations by
adding C to each of the individual starting porphyrins in
excited state quenching of meso-tetraalkylporphyrin and
C60 was investigated to obtain the quenching behavior
with respect to self-assembled dyads. To this end,
constant concentration of porphyrins (1–3 and 1a–3a)
were titrated with increasing concentrations of fullerene
C60 in toluene at 298 K. By adding the fullerene, for
example, to a solution of 3, distinct quenching of the
porphyrin emission was observed. Figure 4 illustrates
several characteristic changes at 666 nm and 736 nm
occurred as the complex formation take place. There
was an appreciable decrease of the Soret band extinction
is observed which is probably due to host–guest
complexation of meso-tetraalkylporphyrin and fullerene.
Quenching indicated a probable relaxation pathway from
the first singlet excited state of the porphyrin to that of the
fullerene in toluene as solvent, as a result fluorescence
(
6
0
toluene as shown in Fig. 3. The decrement in the intensity
of Soret band (415 nm) and the concomitant increment
in Q-bands (518, 554 and 559 nm) revealed the host–
guest complexation between porphyrin 3 and fullerene.
The spectral intensity changes of the Soret band were
used to construct a Benesi–Hildebrand plot [18b] as
shown in Fig. 3b. The association constant (K) for 3:C
6
0
4
-1
supramolecular complex was found to be 1.83 × 10 M
with 1:1 stoichiometry. The similar results were observed
for 1 and 2 in toluene at 298 K as shown in Figs S13
and S14 (Supporting information). The observed K
values obtained from UV-vis spectral titrations range
4
5
-1
from 10 – 10 M are listed in Table 1. These values are
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 3–10

4
N. GROVER ET AL.
Fig. 3. (a) Spectral changes observed during the titration of fullerene (C ) to the solution containing H TPrP (3) in toluene at 298 K.
6
0
2
(
b) Benesi-Hildebrand plot constructed for evaluating the binding constant as well as stiochiometry for 3:C60 host–guest complex
Table 1. Association constants of porphyrin-C60
supramolecular dyad in toluene at 298 K
deactivation of the photoexcited porphyrin-fullerene
dyad. According to the results obtained in the performed
optical absorption and emission experiments, the
quenching event can be credited to photoinduced energy
transfer from porphyrin moiety to the fullerene in the
supramolecular complexes of 1–3 and 1a–3a with C60.
Figure 4 shows the fluorescence spectral change
during the titration of H TPrP and C . Spectral changes
-
1
Porphyrin
Association constant, M
Log K
a
3
H TPP
1 × 10
3.00
3.23
5.12
4.68
4.26
5.33
4.41
3.73
2
b
3
H THexP
1.7 × 10
2
5
H TMeP
1.33 × 10
2
2
60
4
H TEtP
4.84 × 10
2
are used to calculate the Stern-Volmer equation [23] as;
4
H TPrP
1.83 × 10
2
F0/F = 1 + K [fullerene]
(1)
5
Zn TMeP
Zn TEtP
2.18 × 10
4
3
where F is the fluorescence intensity in the absence of
2.59 × 10
0
C , F is the fluorescence intensity in the presence of C
60
60
ZnTPrP
5.4 × 10
and K is the quenching constant. A plot between (F –F)/F
0
a
b
Data taken from Ref. 19a; taken from Ref. 19c;
and [C ] results into straight line reveals the 1:1 binding
6
0
H THexP = meso-tetrahexylporphyrin
2
between these porphyrins and C possibly due to static
60
quenching. Hence the quenching constant is equal to
association constant (K).
intensity decreases. Another probable explanation is
that charge separation might also occur from the excited
state of the porphyrin to the C in toluene medium [20].
Interestingly, 2–3 and 2a–3a exhibited lower binding
constants as compared to 1 and 1a, respectively which
is due to the steric hindrance offered by meso-tetraalkyl
chains. As we increase the length of the alkyl chain from
C to C , the binding constant decreases considerably. In
6
0
Mutual competition between energy and electron transfer
processes is a common prophecy in porphyrin-fullerene
donor–acceptor dyads [21]. In conformationally flexible
porphyrin-fullerene dyads, the arrangement of p-stacking
interactions are assisted by through-space interactions
between the two chromophores which has been reported
and explained via quenching studies of porphyrin
fluorescence and formation of fullerene excited states
1
6
general, all alkyl substituted porphyrins (from propyl to
methyl) have exhibited ~10–100 times higher binding
constants (Fig. 5) as compared to H TPP is possibly
2
due to electron-rich nature of porphyrin p-system and
decrement in steric hindrance offered by alkyl chains.
(
by energy transfer) as shown with photophysical
1
H NMR studies
experiments in the literature [22]. Similar results were
obtained for other complexes as shown in Figs S18 to
S22 (Supporting information).
The association of tetraalkylporphyrins (1–3) with C
60
1
wasmonitoredby HNMRtitrationsinbenzene-d at298K.
6
The photophysical experiments disclose that energy
transfer route usually dominant over the electron transfer
route in non-polar solvent like toluene attributed to
Addition of 1.1 equivalent C60 in solution of porphyrin
results into upfield shift of b- as well as meso-alkyl
1
protons. Figure 6 shows the comparative H NMR of 1 and
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 4–10

SPECTRAL INVESTIGATIONS OF MESO-TETRAALKYLPORPHYRIN-FULLERENE HOST–GUEST COMPLEXES
5
Fig. 4. (a) Fluorescence spectral changes observed during the titration of fullerene (C ) to the solution containing 3 in toluene at
6
0
2
98 K; (b) Stern-Volmer plot for 3:C60 host–guest complex
Cyclic voltammetric studies
Determination of redox potentials of these host–guest
porphyrin-fullerene complexes is important to explore
the existence of charge-transfer interactions between the
porphyrin donor and fullerene acceptor in the ground
state, andalsotoevaluatetheenergeticofelectron-transfer
reactions. Keeping this in mind, we have performed a
systematic study to calculate the redox activities of the
self-assembled dyads using cyclic voltammetric (CV)
technique. CV studies were performed in benzonitrile
containing 0.1 M TBAPF , as both porphyrins and C
6
60
are nicely soluble in benzonitrile. Table 3 represents
electrochemical redox properties of dyad as compared to
porphyrins. As revealed from redox data, alkylporphyrins
are electron-rich in nature. The cyclic voltammograms of
the dyad formed by meso-tetraalkylporphyrins and C60
show two or three reductions, among them, second is due
Fig. 5. Bar graph represents log K values of differ alkyl
porphyrins and their zinc complexes
1
:C host–guest complex. Figures S23 to S27 (Supporting
to both porphyrin and C . The oxidation potentials of
60
60
1
information) represent the comparative H NMR spectra
of 2–3, 1a–3a and their C60 adduct, respectively. These
experimental results show upfield shift of protons is due
to interaction of porphyrins with C . Table 2 shows the
dyads are positively shifted (20–100 mV) as compared
to meso-tetraalkylporphyrin. The redox potentials of
porphyrins and C60 entities revealed small changes
upon dyad formation suggesting the existence of weak
charge transfer interactions. These clarification are in
concurrence with the earlier value reported for the other
porphyrin-C60 derivatives [19a]. Furthermore, we could
obtain similar association constants (K) for 2 and 3 with
C60 in benzonitrile (Figs S29 and S30 in Supporting
information) indicating the formation of charge transfer
complexes as observed in toluene at 298 K.
60
change in chemical shift of protons by adding 1.1 eq. C to
60
the solution of alkyl porphyrins. The observed upfield shift
follows the order 1 > 2 > 3 and in good accordance with
observed association constant values. Further, we have
1
carried out H NMR titration of 3 with increasing amounts
of C (0 to 2 equiv.) in C D at 298 K. We have observed
6
0
6
6
1
upfield shift in H NMR signals while increasing [C ] and
60
saturated at 1 equivalent of [C ] indicating 1:1 porphyrin
60
C60 complexation. Figure S28 (Supporting information)
Computational studies
shows a plot of [C ] vs. Dd by nonlinear curve-fitting. The
60
association constant (K) was calculated from the slope of
The geometry and electronic structure of the dyad was
probed by DFT calculations using the B3LYP functional
and 3-21G basis set. D’souza et al. have already
reported the advantages of 3-21G basis set in predicting
the plot. The observed association constant (K) is 3.9 ×
4
-1
1
0 M which is close to the value obtained from UV-vis
titration in toluene at 298 K.
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 5–10

6
N. GROVER ET AL.
1
Fig. 6. H NMR spectra of (a) 1:C adduct (b) 1 in C D at 298 K
6
0
6
6
Table 2. Change in chemical shift of protons by adding 1.1 eq.
The edge-to-edge distance and distance between
C60 to the solution of 1–3 and 1a–3a in C D at 298 K
6
6
the porphyrin to the fullerene spheroid were found to
be 10.5 Å and 3.7 Å, respectively. These values were
comparable to the earlier computed and calculated from
Porphyrin
Chemical shift (d in ppm)
b-H meso-CH3 meso-CH2 meso-CH2
NH
X-ray structural studies of ZnTPP-C Im dyad [25]. The
60
B3LYP/3-21G calculated HOMO and LUMO for the
investigated dyad are shown in Figs 7b–7c. The HOMO
was found to be located on the porphyrin entity whereas
LUMO was on the C entity. The absence of HOMOs on
1
9.220
9.113
9.404
9.334
9.330
9.260
9.480
9.310
9.511
9.441
9.380
9.310
4.247
-1.744
-1.851
1
2
2
3
3
1
1
2
2
3
3
:C60
:C60
4.140
2.038 4.929–4.872
1.968 4.859–4.802
1.195 4.765
1.125 4.695
4.588
-2.745
6
0
C60 and LUMOs on the porphyrin macrocycle suggests
-2.815
weak charge transfer-type interactions between the donor
and acceptor entities of the dyad in the ground state.
2.53–2.43 -2.023
2.46–2.36 -2.093
:C60
a
EXPERIMENTAL
a:C60
a
4.418
2.080 4.973–4.916
2.010 4.903–4.846
1.237 4.829
1.167 4.759
Chemicals
a:C60
a
Pyrrole purchased from Alfa Aesar and used as
received.Acetaldehyde, propionaldehyde, butyraldehyde,
pyridine, Zn(OAc) ·2H O, Na SO and NaHCO were
2.497–2.403
2.420–2.330
a:C60
2
2
2
4
3
purchased from HiMedia, India and used as received.
Fullerene C and benzene-d was purchased from Sigma-
Aldrich and used as received. All solvents employed
in this present work were of analytical grade and
distilled or dried before use. Silica gel (100–200 mesh)
was purchased from Thomas Baker, India and used as
the structure of porphyrin-fullerene donor–acceptor
dyad [24]. In our calculations, the starting compounds
6
0
6
(
porphyrin and C ) were fully optimized and allowed
60
to interact. Figure 7 represents the fully optimized 1:C60
Dyad. The geometric parameters of the conjugates were
obtained after complete energy optimization.
received. TBAPF was recrystallised twice with ethanol
6
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 6–10

SPECTRAL INVESTIGATIONS OF MESO-TETRAALKYLPORPHYRIN-FULLERENE HOST–GUEST COMPLEXES
7
a
Table 3. Electrochemical redox data of 1–3 and 1a–3a in presence and absence of C60 in
benzonitrile at 298 K
Porphyrin
Oxidation
Reduction
DE1/2
PI+/II+
P0/I+
0/-
I-/II-
0/-
I-/II-
P
P
C60
C60
H TMeP
0.78
0.80
0.78
0.82
0.78
0.88
0.74
0.70
0.61
0.59
0.65
0.58
-0.98
-0.86
-1.13
-0.97
-0.98
-0.88
-1.25
—
-1.28
-1.49
-1.35
-1.39
-1.33
-1.32
1.46
1.78
1.91
1.79
1.76
1.76
1.99
2
H TMeP+C
2
—
60
H TEtP
2
H TEtP+C
2
-0.48
-0.45
-0.47
-0.47
-0.46
60
H TPrP
2
H TPrP+C
2
1.31
1.08
60
ZnTMeP
ZnTMeP+C60
ZnTEtP
-0.91
-0.92
-0.93
1.05
1.09
1.05
1.01
-1.43
-1.40
-1.53
-1.39
2.04
1.99
2.18
1.97
ZnTEtP+C60
ZnTPrP
ZnTPrP+C60
a
Ag/AgCl taken as reference electrode and 0.1 M TBAPF as supporting electrolyte.Aliquitos
6
of 0.01 M solution of C60 (excess with respect to porphyrins) in PhCN were added.
Fig. 7. (a) B3LYP/3-21G optimized structure of H TMeP(1):C supramolecular dyad (b) HOMO and (c) LUMO orbitals
2
60
1
and dried at 50°C under vacuum for two days. Toluene
length. H NMR spectra were recorded on JEOL ECX
(
for UV-visible spectral studies) was dried and distilled
400 MHz spectrometers in CDCl . ESI mass spectra
3
from sodium-benzophenone mixture. Precoated thin
layered silica gel chromatographic plates were purchased
from E. Merck and used as received.
were recorded on Bruker Daltanics microTOF mass
spectrometerinpositiveionmodeusingCH CNassolvent.
3
The X-ray quality single crystals of 3 were obtained by
vapor diffusion of hexane into the tetrachloroethane
solution of 3. Single-crystal XRD data was collected on
a Bruker Apex-II CCD diffractometer equipped with a
liquid cryostat. The ground state geometry optimisation
in gas phase was carried out by DFT calculations using
B3LYP functional with 3-21G basis set. Electrochemical
measurements were carried out using CH instruments
(CHI 620E). A three electrode assembly was used
Instruments and methods
Optical absorption spectra were recorded on
Agilent Cary 100 spectrophotometer using a pair of
quartz cells of 3.5 mL volume and 10 mm path length.
Fluorescence spectra were recorded on Hitachi F-4600
spectrofluorometer using a quartz cell of 10 mm path
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 7–10

8
N. GROVER ET AL.
consisted of a Platinum working electrode, Ag/AgCl as a
reference electrode and a Pt-wire as a counter electrode.
eluent. Yield 42 mg (85%). UV-vis: lmax, nm 418 (5.08),
1
553 (3.55), 592 (3.13) H NMR (CDCl ): d, ppm 9.59 (s,
3
8
H, b-H), 5.06–5.01 (J = 7.6, 7.6 q, 8H, meso-CH ), 2.17
2
(J = 7.6, t, 12H, meso-CH ). ESI-MS: m/z found [M +
3
Synthesis
+
H + CH OH] 517.5 calcd. 517.1941.
3
Synthesis of 5,10,15,20-tetramethylporphyrin (1).
Synthesis of 5,10,15,20-tetrapropylporphyrin (3).
3
00 mL of propionic acid was taken in 500 mL round
300 mL of propionic acid was taken in 500 mL RB flask.
bottom flask. To this, 2.3 mL of acetaldehyde, 12 mL
To this, 2.3 mL of butyraldehyde, 12 mL of H O and 1 mL
2
of H O and 1 mL of pyridine were added and heated
of pyridine were added and heated to 90°C for 5–10 min.
To this mixture, 4 mL of pyrrole was added and heated
to 80°C for 30 min. Then, 1 mL butyraldehyde was
added to the reaction mixture as supplementary amount
and heated for further 2 h. Reaction mixture was cooled,
washed with hot NaOH solution followed by extraction
2
to 90°C for 5–10 min. To this hot mixture, 4 mL of
pyrrole was added and heated to 80°C for 30 min. Then,
1
mL acetaldehyde was added to the reaction mixture
as supplementary amount and heated for further 2 h.
Reaction mixture was cooled and washed with hot sodium
hydroxide solution followed by extraction with CHCl3.
The crude porphyrin was chromatographed on silica gel
with CHCl . The crude porphyrin was chromatographed
3
on silica column using CHCl as a eluent. Yield was
3
column using CHCl as a eluent. Yield was found to be
found to be 0.4 g (10%). UV-vis: lmax, nm 415 (5.59),
3
1
0
.28 g (8%). UV-vis: lmax, nm 415 (5.07), 519 (3.67), 555
518 (4.13), 554 (3.19), 559 (3.62), 658 (3.76). H NMR
1
(
3.50), 604 (3.13), 661 (3.37). H NMR (CDCl ): d, ppm
(CDCl ): d, ppm 9.47 (s, 8H, b-H), 4.92 (J = 3.2, t, 8H,
3
3
9
.46 (s, 8H, b-H), 4.57 (s, 12H, -CH ), -2.41 (s, 1H, NH).
meso-CH ), 2.48–2.58 (m, 8H, meso-CH ), 1.32 (J =
3
2
2
+
ESI-MS: m/z found [M + H] 367.1902 calcd. 367.1878.
Synthesis of 5,10,15,20-tetramethylporphyrinato
Zinc(II) (1a). 40 mg (0.108 mmol) of 1 was taken in
3.2, t, 12H, meso-CH ), -2.69 (s, 1H, NH). ESI-MS: m/z
3
+
found [M + K] 517.271 calcd. 517.7609.
Synthesis of 5,10,15,20-tetrapropylporphyrinato
2
5 mL of CHCl . To this, 0.239 g (10 equiv., 1.08 mmol)
Zinc(II) (3a). 50 mg (0.104 mmol) of 3 was taken in
3
of Zn(OAc) ·2H O in 5 mL of methanol was added and
25 mL of CHCl . To this, 0.230 g (10 equiv., 1.04 mmol)
2
2
3
refluxed for 30 min and then cooled to room temperature,
washed with water, dried over anhydrous sodium
sulphate. The crude product was purified by column
of Zn(OAc) ·2H O in 10 mL of methanol was added and
2
2
refluxed for 30 min and then cooled to room temperature,
washed with water, dried over anhydrous sodium
sulphate. The crude product was purified by column
chromatography on silica gel column using CHCl as
3
eluent. Yield 36 mg (85%). UV-vis: lmax, nm 418 (5.11),
chromatography on silica gel column using CHCl as
3
1
5
8
55 (3.68), 594 (3.50). H NMR (CDCl ): d, ppm 9.46 (s,
eluent. Yield 39 mg (83%). UV-vis: lmax, nm 418 (5.68),
3
1
H, b-H), 4.57 (s, 12H, -CH3).
554 (4.16), 592 (3.72). H NMR (CDCl ): d, ppm 9.57
3
Synthesis of 5,10,15,20-tetraethylporphyrin (2).
00 mL of propionic acid was taken in 500 mL RB flask.
(s, 8H, b-H), 4.96 (J = 7.6, t, 8H, meso-CH ), 2.63–2.54
2
3
(m, 8H, meso-CH ), 1.36 (J = 7.6, t, 12H, meso-CH ).
2
3
+
To this, 2.1 mL of propionaldehyde, 12 mL of H O and
ESI-MS: m/z found [M] 540.6 calcd. 540.2231.
2
1
1
mL of pyridine were added and heated to 90°C for 5–
0 min. To this mixture, 4 mL of pyrrole was added and
heated to 80°C for 30 min. Then, 1 mL propionaldehyde
was added to the reaction mixture as supplementary
amount and heated for further 2 h. Reaction mixture
was cooled, washed with hot sodium hydroxide solution
CONCLUSION
Meso-tetraalkylporphyrins with varying alkyl chain
length were synthesized and characterized by various
spectroscopic techniques. Crystal structure of meso-
tetrapropylporphyrin exhibited planar confirmation of
porphyrin macrocycle. The binding of C60 with the 1–3
and their zinc complexes was determined by H NMR,
UV-vis and fluorescence spectroscopic analyses. From
UV-vis and fluorescence titrations, the stoichiometry
followed by extraction with CHCl . The crude porphyrin
3
was chromatographed on silica gel column using CHCl3
as a eluent. Yield was found to be 0.38 g (10%). UV-vis:
1
lmax, nm 416 (4.97), 517 (3.60), 551 (3.42), 599 (3.06),
1
6
4
56 (3.26) H NMR (CDCl ): d, ppm 9.46 (s, 8H, b-H),
3
.96–5.01 (J = 7.6, 7.2, q, 8H, meso-CH ), 2.12 (J = 7.6,
2
t, 12H, meso-CH ), -2.65 (s, 1H, -NH). ESI-MS: m/z
of complexation between porphyrin and fullerene (C60)
was found to be 1:1 as shown in Scheme 2. These meso-
tetraalkylporphyrins have shown 10–100 times higher
3
+
found [M + H] 423.2562 calcd. 423.2504.
Synthesis of 5,10,15,20-tetraethylporphyrinato
Zinc(II) (2a). 50 mg (0.118 mmol) of 2 was taken in
association constants than H
increase the alkyl chain length from C
2
TPP and H
to C
6
2
THexP. As we
2
5 mL of CHCl . To this, 0.258 g (10 equiv., 1.18 mmol)
1
, a marked
3
of Zn(OAc) ·2H O in 8 mL of methanol was added and
decrement (100 times) in the association constants was
observed due to enhanced steric hindrance offered by
alkyl chains. The anodic shift in oxidation potentials (20–
100 mV) of porphyrin-fullerene dyads as compared to
meso-tetraalkylporphyrins indicating the supramolecular
2
2
refluxed for 30 min and then cooled to room temperature,
washed with water, dried over anhydrous sodium
sulphate. The crude product was purified by column
chromatography on silica gel column using CHCl as
3
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 8–10

SPECTRAL INVESTIGATIONS OF MESO-TETRAALKYLPORPHYRIN-FULLERENE HOST–GUEST COMPLEXES
9
R
R
R
R
R
N
N
N
N
N
Toluene
N
R
M
R
+
M
N
N
R
R
R
Porphyrin:C60
C60
M = 2H, Zn(II)
Scheme 2. Host–guest interaction of meso-tetraalkylporphyrins and C60 in toluene
interactions between the constituents in the ground state.
The optimized geometry and electronic structure of 1:C60
supported the formation of supramolecular dyad and
the possibility of charge transfer interactions between
porphyrin host and fullerene C guest.
Angew. Chem. 1996; 108: 1242–1286. (c) Fukuzumi
S. Functional Organic Materials, Wiley-VCH:
Weinheim, 2007; pp 465–510. (d) Balzani V, Credi
A and Venturi M. Molecular Devices and Machines,
Wiley-VCH: Weinheim, 2008; pp 171–207.
60
3
. (a) Sanchez L, Martin N and Guldi DM. Angew.
Chem. Int. Ed. 2005; 44: 5374–5382. (b) Balzani V,
CrediA, Silvi S andVenturi M. Chem. Soc. Rev. 2006;
Acknowledgements
This work is supported by the Council of Scientific
and Industrial Research, CSIR (Grant No. 01(2694)/12/
EMR-II) India. NG and PR sincerely thank MHRD and
CSIR, India for fellowship.
3
5: 1135–1149. (c) Figueira-Duarte TM, Gegout A
and Nierengarten JF. Chem. Commun. 2007; 109–
19. (d) NakamuraY, Aratani N and Osuka A. Chem.
1
Soc. Rev. 2007; 36: 831–845. (e) Hizume Y, Tashiro
K, Charvet R, Yamamoto Y, Saeki A, Seki S and
Aida T. J. Am. Chem. Soc. 2010; 132: 6628–6629.
(f) Chitta R and D’Souza F. J. Mater. Chem. 2008;
18: 1440–1471. (g) D’Souza F, Smith PM, Zandler
ME, McCarty AL, Itou M, Araki Y and Ito O. J. Am.
Chem. Soc. 2004; 126: 7898–7907. (h) D’Souza F,
Maligaspe E, Karr PA, Schumacher AL, Ojaimi ME,
Gros CP, Barbe J-M, Ohkubo K and Fukuzumi S.
Chem. Eur. J. 2008; 14: 674–681. (i) Marczak R,
Sgobba V, Kutner W, Gadde S, D’Souza F and Guldi
DM. Langmuir 2007; 23: 1917–1923. (j) Imahori H.
Org. Biomol. Chem. 2004; 2: 1425–1433. (k) Kira A,
Umeyama T, MatanoY,Yoshida K, Isoda S, Park J-K,
Kim D and Imahori H. J. Am. Chem. Soc. 2009; 131:
3198–3200. (l) Imahori H, Ueda M, Kang S, Hayashi
H, Kaji H, Seki S, Saeki A, Tagawa S, Umeyama T,
Matano Y, Yoshida K, Isoda S, Shiro M, Tkachenko
NV and Lemmetyinen H. Chem. Eur. J. 2007;
Supporting information
1
H NMR and mass spectra of 1–3 and 1a–3a, UV-vis,
1
fluorescence and H NMR titrations of 1–2 and 1a–3a with
C and UV-vis and crystallographic data (Figures S1–S30,
60
Tables S1–S2) are given in the supplementary material.
This material is available free of charge via the Internet at
http://www.worldscinet.com/jpp/jpp.shtml.
Crystallographic data have been deposited at the
Cambridge Crystallographic Data Centre (CCDC) under
number CCDC-1051569. Copies can be obtained on
request, free of charge, via www.ccdc.cam.ac.uk/data_
request/cif or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK (fax:
+44 1223-336-033 or email: data_request@ccdc.cam.
ac.uk).
REFERENCES
13: 10182–10193. (m) Kotiaho A, Lahtinen RM,
1
. (a) Lehn JM. Supramolecular Chemistry: Concepts
and Perspectives, VCH: Weinheim, 1995. (b) Vogtle
F. Supramolecular Chemistry, Wiley: Chichester,
Tkachenko NV, Efimov A, Kira A, Imahori H and
Lemmetyinen H. Langmuir 2007; 23: 13117–13125.
4. (a) Diederich F and Gomez-Lopez M. Chem. Soc. Rev.
1999; 28: 263–277. (b) Haino T, Yanase M and Fuka-
zawaY. Angew. Chem., Int. Ed. 1998; 37: 997–998.
5. (a) Moreira L, Calbo J, Illescas BM, Arago J,
Nierengarten I, Delavaux-Nicot B, Orti E, Martin N
and Nierengarten JF. Angew. Chem. Int. Ed. 2015; 54:
1
991. Supramolecular Chemistry of Fullerenes,
Martin N and Nierengarten JF. (Eds.) Tetrahedron
Symposium-in-Print, 2006; 62: 1905–1932.
. (a) Imahori H and Fukuzumi S. Adv. Funct. Mater.
2
2004; 14: 525–536. (b) Philip D and Stoddart JF.
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 9–10

10
N. GROVER ET AL.
1
255–1260. (b) Stranius K, George L, Efimov A,
Ruoko T-P, Pohjola J and Tkachenko NV. Langmuir
015; 31: 944–952. (c) Kamimura T, Komura M,
Komiyama H, Iyoda T and Tani F. Chem. Commun.
015; 51: 1685–1688. (d) Umeyama T, Mihara J,
Press: Burlington, MA, 2000. (b) Smith KM. Por-
phyrins and Metalloporphyrins, Elsevier: NewYork,
1977.
2
13. Sun YP, Drovetskaya T, Bolskar RD, Bau R, Boyd
PDW and Reed CA. J. Org. Chem. 1997; 62:
3642–3649.
14. (a) Grimm B, Schornbaum J, Cardona CM, van
Paauwe JD, Boyd PWD and Guldi DM. Chem.
Sci. 2011; 2: 1530–1537. (b) Lyons DM, Mohan-
raj J, Accorsi G, Armaroli N and Boyd PWD. New
J. Chem. 2011; 35: 632–639. (c) Sun D, Tham FS,
Reed CA and Boyd PWD. Proc. Natl. Acad. Sci.
U.S.A. 2002; 99: 5088–5092.
2
Hayashi H, Kadota N, Chukharev V, Tkachenko
NV, Lemmtyinen H, Yoshida K, Isoda S and Ima-
hori H. Chem. Commun. 2011; 47: 11781–11783.
. (a) Boyd PDW and Reed CA. Acc. Chem. Res. 2005;
6
3
8: 235–242. (b) Drovetskaya T, Reed CA and
Boyd P. Tetrahedron Lett. 1995; 36: 7971–7976. (c)
Mustafizur Rahman AFM, Bhattacharya S, Peng X,
Kimura T and Komatsu N. Chem. Commun. 2008;
1
3
196–1198. (d) Guldi DM. Chem. Soc. Rev. 2002;
1: 22–36. (e) Liao MS, Watts JD and Huang MJ. J.
15. (a) Charvet R,YamamotoY, SasakiT, Kim J, Kato K,
Takata M, Saeki A, Seki S and Aida T. J. Am. Chem.
Soc. 2012; 134: 2524–2527. (b) Hajjaj F, Tashiro
K, Nikawa H, Mizorogi N, Akasaka T, Nagase S,
Furukawa K, Kato T and Aida T. J. Am. Chem. Soc.
2011; 133: 9290–9292. (c) Shoji Y, Tashiro K and
Aida T. Chirality 2008; 20: 420–424. (d) Tashiro
K and Aida T. Chem. Soc. Rev. 2007; 36: 189–197.
(e) Zheng J-Y, Tashiro K, Hirabayashi Y, Kinbara
K, Saigo K, Aida T, Sakamoto S and Yamaguchi
K. Angew. Chem. Int. Ed. 2001; 40: 1857–1861. (f)
Yamaguchi T, Ishii N, Tashiro K and Aida T. J. Am.
Chem. Soc. 2003; 125: 13934–13935.
Phys. Chem. B 2007; 111: 4374–4382. (f) D’Souza
F, Smith PM, Rogers L, Zandler ME, Shafiqul Islam
DM, Araki Y and Ito O. Inorg. Chem. 2006; 45:
5
057–5065. (g) Olmstead MM and Nurco DJ. Cryst.
Growth Des. 2006; 6: 109–113. (h) Sun DY, Tham
FS, Reed CA, Chaker L and Boyd PDW. J. Am.
Chem. Soc. 2002; 124: 6604–6612. (i) Boyd PDW,
Hodgson MC, Rickard CEF, Oliver AG, Chaker L,
Brothers PJ, Bolskar RD, Tham FS and Reed CA.
J. Am. Chem. Soc. 1999; 121: 10487–10495. (j)
Konarev DV, Khasanov SS, Saito G, Lyubovskaya
RN, Yoshida Y and Otsuka A. Chem. Eur. J. 2003;
16. Gil-Ramirez G, Karlen SD, Shundo A, Porfyrakis
K, Ito Y, Briggs GAD, Morton JJL and Anderson
HL. Org. Lett. 2010; 12: 3544–3547.
9
: 3837–3848.
7
. (a) Maligaspe E, SandanayakaASD, Hasobe T, Ito O
and D’Souza F. J. Am. Chem. Soc. 2010; 132: 8158–
17. (a) Neya S and Funasaki N. J. Heterocyclic chem.
1997; 34: 689–690. (b) Ikeue T, Ohgo Y, Uchida
A, Nakamura M, Fujii H and Yokoyama M. Inorg.
Chem. 1999; 38: 1276–1281. (c) Codding PW and
TulinskyA. J. Am. Chem. Soc. 1972; 94: 4151–4157.
18. (a) Meot-Ner M and Adler AD. J. Am. Chem. Soc.
1975; 97: 5107–5110. (b) Benesi HA and Hildebrand
JH. J. Am. Chem. Soc. 1949; 71: 2703–2707.
19. D’Souza F, Deviprasad GR, Zandler ME, Hoang
VT, Arkady K, Van Stipdonk M, Perera A, El-
Khouly ME, Fujitsuka M and Ito O. J. Phys. Chem.
A. 2002; 106: 3243–3252.
8164. (b) D’Souza F and Ito O. In Handbook of Por-
phyrin Science, Vol. 1, Kadish KM, Smith KM and
Guilard R. (Eds.)World Science Publishers: 2010; pp
3
07–437. (c) D’Souza F, Deviprasad GR, El-Khouly
ME, Fujitsuka M and Ito O. J. Am. Chem. Soc. 2001;
23: 5277–5284. (d) Sandanayaka ASD, ArakiY, Ito
1
O, Chitta R, Gadde S and D’Souza F. Chem. Com-
mun. 2006; 4327–4329. (e) D’Souza F, Chitta R,
Gadde S, Zandler ME, McCarty AL, Sandanayaka
ASD, Araki Y and Ito O. J. Phys. Chem. A 2006;
110: 4338–4347. (f) D’Souza F, Smith PM, Rogers
L, Zandler ME, Shafiquil IDM, Araki Y and Ito O.
Inorg. Chem. 2006; 45: 5057–5065.
20. Imahori H and Sakata Y. Eur. J. Org. Chem. 1999;
2445–2457.
8
9
. (a) Kroto HW, Heath JR, O’Brien SC, Curl RF
and Smalley RE. Nature 1985; 318: 162–163. (b)
Kratschmer W, Lamb LD, Fostiropoulos F and
Huffman DR. Nature 1990; 347: 345–358.
. Xie Q, Perez-Cordero E and Echegoyen L. J. Am.
Chem. Soc. 1992; 114: 3978–3980.
21. Martini I, Ma B, Da Ros T, Helgeson R, Wudl F and
Schwartz B. Chem. Phys. Lett. 2000; 327: 253–262
and references cited there in.
22. Gust D, Moore T, Moore A, Kuciauskas D, Lidell
P and Halbert B. J. Photochem. Photobiol. B 1998;
43: 209–216.
1
1
0. Fullerene and Related Structures; Ed Hirsch A
Springer: Berlin, 1999; 199: 173–187.
1. Imahori H, Hagiwara K, Akiyama T, Akoi M,
Taniguchi S, Okada S, Shirakawa M and Sakata Y.
Chem. Phys. Lett. 1996; 263: 545–550.
23. Principles of Fluorescence Spectroscopy, 2nd ed.,
Lakowicz JR. (Ed.) Kluwer Academic/Plenum:
New York, 1999.
24. Zandler ME and D’Souza F. C. R. Chemie 2006; 9:
960–981.
1
2. (a) The Porphyrin Handbook, Vol. 1–10, Kadish
KM, Smith KM and Guilard R. (Eds.) Academic
25. D’Souza F, Rath NP, Deviprasad GR and Zandler
ME. Chem. Commun. 2001; 267–268.
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 10–10