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slow down charge recombination, leading to the generation of a
long lived charge-separated state with a high quantum yield [5–
10]. Taking into account the fact that fullerene and porphyrin tend
to make a supramolecular complex in solutions as well as in the so-
lid state [11–14], and as this type of model system is of great
importance not only in opto-electronic technologies [15], but also
in life science in relation to respiration [16], photosynthesis [17]
and photomedicine [18], it would be a great idea to see whether
any photophysical changes take place in the composite mixture
containing fullerene and porphyrin when silver nanoparticles
(AgNp) are added in such assembly. For the aforesaid reasons, we
have designed a monoporphyrin molecule, namely 5,15-di(para-
methoxyphenyl)porphyrin metal Zn (1) (see Scheme 1 and Scheme
2) to find out its intermolecular interaction with fullerenes C60 and
The ground state absorption spectrum of 1 (1.880 ꢂ 10ꢁ6
mol dmꢁ3, Fig. 1(i)) in toluene recorded against the solvent as ref-
erence displays one broad Soret absorption band (kmax = 413 nm)
corresponding to the transition to the second excited singlet state
S2. As for the Q absorption bands, 1 shows one major absorption
band at 540 nm and one minor band at 503 nm (Fig. 1(i)). Q
absorption bands in metalloporphyrin correspond to the vibronic
sequence of the transition to the lowest excited singlet state S1.
The inset of Fig. 1, i.e., Fig. 1(ii), shows the electronic absorption
spectrum of 0.02 ml AgNp solution in 4 ml toluene measured
against toluene. The distinctive color of AgNp is due to a phenom-
enon known as plasmon absorbance. Incident light creates oscilla-
tions in conduction electrons on the surface of the nanoparticles
and electromagnetic radiation is absorbed. The spectrum of the
clear yellow colloidal silver shows distinct absorption band near
the region of 443 nm due to its surface plasmon band resonance
character [26]. When 0.02 ml solution of AgNp is added to the solu-
tion of 1 (1.880 ꢂ 10ꢁ6 mol dmꢁ3) and the electronic absorption
spectrum of the mixture is recorded against the same concentra-
tion of AgNp in toluene, the intensity of the Soret absorption band
is found to decrease from absorbance value of 0.765–0.678
(Fig. 1(iii)). In our present work, we have made a detailed study
how the surface plasmon band resonance of AgNp is affected in
presence of only fullerene, only porphyrin and fullerene-porphyrin
mixture. Fig. 1S shows the UV–Vis absorption spectrum of AgNp in
toluene measured against the solvent as reference which is shown
in blue color ink. The red spectrum shows the electronic spectrum
of blank C60 in toluene recorded against the solvent as reference.
The sky blue spectrum corresponds to the spectrum of mixture
of C60 and AgNp recorded against the solvent as reference. It is ob-
served that AgNp gets 7 nm red shift in its peak maxima following
the addition of C60. However, in presence of only 1 (magenta color
spectrum) and C60ꢁ1 binary mixture (black colour spectrum),
there is no change observed either in peak maxima or in intensity
of the peak. In both the cases mentioned above, we have not
detected the presence of any sort of additional absorption peak,
which also indicates absence of charge transfer (CT) phenomenon
in our present studies. However, we may observe somewhat shoul-
dering in the absorption spectrum of C60ꢁ1-AgNp composite
around 465 nm. Almost, similar sort of absorption spectral feature
for the surface plasmon band resonance of AgNp is observed in
presence of C70 and C70ꢁ1 mixture recorded in toluene (Fig. 2S).
However, in presence of only C70, the surface plasmon band reso-
nance of AgNp gets 21 nm red shift which is 14 nm larger com-
C70 in absence and presence of AgNp. Metal nanoparticles have size
dependent optical and electrical properties [19]. In this respect, an
important feature of metal nanoparticles is the localized surface
plasmon band resonance [20], which is seen as high extinction
coefficients of metal nanoparticles. As a result of this, smaller sizes
of metal nanoparticles absorb light intensively, whereas scattering
of light becomes an important factor for bigger nanoparticles. The
surface plasmon band resonance causes enhancement of electro-
magnetic field near the metal nanoparticles. Applications utilizing
the surface plasmon resonances of metal nanoparticles include
imaging, sensing, medicine, photonics and optics [21,22]. Although
there are some reports on interaction between fullerene and gold
nanoparticles (AuNp) in presence of porphyrin in recent past
[23,24], there is no such investigation on non-covalent interaction
between fullerene and porphyrin in presence of silver nanoparti-
cles (AgNp). In recent past, a novel two-step bottom-up approach
to construct
a 2-dimensional long-range ordered, covalently
bonded fullerene-porphyrin binary nanostructure is presented in
presence of Ag(110) [25]. However, we anticipate that the combi-
nation of photoactive molecules, like fullerene and porphyrin, into
formation of non-covalent assembly in presence of AgNp may lead
to some new physicochemical aspects. The motivation of the pres-
ent work, therefore, deals with the non-covalent interaction be-
tween fullerenes and monoporphyrin in presence of AgNp.
Binding and selectivity in binding between fullerenes and 1 is
one of the goals of our present studies, other than to envisage var-
ious physicochemical aspects on host–guest chemistry of fullerene
and porphyrin in presence of AgNp.
Materials and methods
pared to C60. The most interesting feature of the UV–Vis
experiment of the C70ꢁ1-AgNp mixture is that the shouldering in
the UV–Vis spectrum that we observe in case of C60ꢁ1 composite,
appears as a distinct peak; the peak maximum is observed at
467 nm. Evidence in favor of ground state electronic interaction
between fullerenes and 1 first comes from the UV–Vis titration
experiment. It is observed that addition of a C60 (1.0 ꢂ 10ꢁ5
mol dmꢁ3) and/C70 solution (1.0 ꢂ 10ꢁ5 mol dmꢁ3) to a toluene
solution of 1 (1.10 ꢂ 10ꢁ5 mol dmꢁ3) decreases the absorbance va-
lue of 1 at its Soret absorption maximum (inset of Fig. 3S and Fig. 2,
respectively) recorded against the pristine acceptor solution as ref-
erence; the extent of decrease is considerably larger in magnitude
compared to AgNp in toluene. However, no additional absorption
peaks are observed in the visible region. The former observation
extends a good support in favor of the non-covalent complexation
between fullerenes and 1 in ground state. The latter observation
indicates that the interaction is not controlled by charge transfer
(CT) transition. Another important feature of the UV–Vis investiga-
tions is the larger extent of decrease in the absorbance value of 1 in
C60 and C70 are purchased from Sigma–Aldrich, USA and used
without further purification. 1 is synthesized in our laboratory
and the detailed synthetic procedures are reported in Supporting
Information. The synthetic schemes are demonstrated as Appendix
A. UV–vis spectroscopic grade toluene (Merck, Germany) is used as
solvent to favor the intermolecular interaction between fullerene
and 1, as well as to provide good solubility and photostability of
the samples. UV–vis spectral measurements have been performed
on a Shimadzu UV-2450 model spectrophotometer using quartz
cell with 1 cm optical path length. Steady state emission spectra
are recorded with a Hitachi F-4500 model fluorescence spectro-
photometer. DLS measurements have been done with Nano S Mal-
vern instrument employing a 4 mW He-Ne laser (k = 413 nm)
equipped with a thermostated sample chamber. All the scattered
photons are collected at 173° scattering angle. SEM measurements
are done in a S-530 model of Hitachi, Japan instrument having IB-2
ion coater with gold coating facility.
presence of C70 in comparison to C60
observation suggests greater amount of interaction between C70
. This spectroscopic
Results and discussions
UV–Vis investigations
and 1. However, measurements of UV–Vis spectrum of the