Photophysical and photochemical properties and aggregation behavior of phthalocyanine and naphthalocyanine derivatives

Article abstract of DOI:10.21577/0103-5053.20170215

The photophysical and photochemical properties of phthalocyanine and naphthalocyanine with similar structures were studied in solution and with density-functional theory (DFT) computational method. The extended π-conjugated system in naphthalocyanines causes a bathochromic shift in UV-Vis, emission and excitation bands, and promotes lesser generation of singlet oxygen in solution when compared to phthalocyanines. Time dependent DFT (TD-DFT) calculations point out the molecular orbitals involved in Q-band transition, corresponding to highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) transition with a concentration of charge along x-axis, while the transition to LUMO+1 is in y-axis direction. The presence of tert-butyl substituents does not affect the molecular orbitals shape, but affect their energies. Aggregation studies in dimethyl sulfoxide (DMSO):water solutions showed that naphthalocyanines studied have more aggregation tendency than the phthalocyanines. DFT studies indicated that stacked-dimers are preferred to rotated-stacked conformation due the interaction between Zn^II and nitrogen atom from different monomers.

Full text of DOI:10.21577/0103-5053.20170215

http://dx.doi.org/10.21577/0103-5053.20170215
J. Braz. Chem. Soc., Vol. 29, No. 6, 1199-1209, 2018
Printed in Brazil - ©2018 Sociedade Brasileira de Química
Article
Photophysical and Photochemical Properties and Aggregation Behavior of
Phthalocyanine and Naphthalocyanine Derivatives
Thalita F. M. de Souza, Felipe C. T. Antonio, Mateus Zanotto, Paula Homem-de-Mello
and Anderson O. Ribeiro*
Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC),
Avenida dos Estados, 5001, Bloco B, 09210-170 Santo André-SP, Brazil
The photophysical and photochemical properties of phthalocyanine and naphthalocyanine with
similar structures were studied in solution and with density-functional theory (DFT) computational
method. The extended π-conjugated system in naphthalocyanines causes a bathochromic shift in
UV-Vis, emission and excitation bands, and promotes lesser generation of singlet oxygen in solution
when compared to phthalocyanines. Time dependent DFT (TD-DFT) calculations point out the
molecular orbitals involved in Q-band transition, corresponding to highest occupied molecular
orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) transition with a concentration
of charge along x-axis, while the transition to LUMO+1 is in y-axis direction. The presence
of tert-butyl substituents does not affect the molecular orbitals shape, but affect their energies.
Aggregation studies in dimethyl sulfoxide (DMSO):water solutions showed that naphthalocyanines
studied have more aggregation tendency than the phthalocyanines. DFT studies indicated that
stacked-dimers are preferred to rotated-stacked conformation due the interaction between ZnII
and nitrogen atom from different monomers.
Keywords: phthalocyanine, naphthalocyanine, aggregation, photophysical, computational
studies
Introduction
detailed studies comparing Pc and Nc aggregation in
solution are lacking.12,13
Naphthalocyanines (Nc) are phthalocyanines
derivatives with extended π-conjugated system, which
promotes a bathochromic shift in their absorption bands
(750-900 nm).1,2 Both macrocycles are widely applied
as industrial dyes, in solar cells,3 nonlinear optics,4
electrochromic devices,5 photodynamic therapy (PDT)6
and chemical sensors.7
In the current study, we investigate the impact of
the extended π-conjugation in macrocycles with same
peripheral substituents (Figure 1). We evaluated the
photophysical and photochemical properties in DMSO
solution, and their aggregation in DMSO:water mixtures.
Experimental
Phthalocyanines (Pc) and naphtalocyanines have a
high tendency to aggregate, especially in aqueous solution.
This aggregation influences their photophysical and
photochemical properties leading to disadvantages such as
fluorescence quenching, lesser generation of singlet oxygen
and loss of catalytic activity.8,9
Several works demonstrated that the aggregation
behavior is influenced by many factors, e.g. strong π-π
electron interactions, coulombic forces, central metal,
position and size of the substituents, axial substituents on
the central metal, temperature and solvent.10,11 However,
Materials
All reagents and solvents were used as received.
Zinc phthalocyanine (ZnPc) and zinc-tert-butyl-
phthalocyanine (1) were purchased from Sigma-Aldrich.
The zinc-naphthalocyanine (ZnNc)14 and zinc-tert-butyl-
naphthalocyanine (2) were synthesized15,16 as described.
Equipment
Fourier transform infrared (FTIR) spectra were obtained
on a Varian FTIR-660 spectrophotometer with the sample
*e-mail: anderson.ribeiro@ufabc.edu.br

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Photophysical and Photochemical Properties and Aggregation Behavior of Phthalocyanine and Naphthalocyanine
J. Braz. Chem. Soc.
Figure 1. Structure of phthalocyanines and naphthalocyanines investigated in this study.
1
prepared as KBr pellet. H nuclear magnetic resonance
(NMR) spectra were performed with CDCl3 or DMSO-d6
as solvent and tetramethylsilane (TMS) as internal standard.
All absorption spectra were taken on a Varian Cary
50 UV-Vis spectrometer and fluorescence emission and
excitation spectra using a Varian Eclipse fluorescence
spectrophotometer.
stirred solution was kept for 12 h at 70-80 °C. The dark
reaction mixture was added dropwise to a stirred solution
of 20 mmol of sodium thiosulfate in 300 mL of water.
The yellow precipitate was filtered off, washed with water
and acetone, and then purified by a silica-gel column with
hexane:ethyl acetate (2:1) as eluent.
Fluorescence decay profiles and singlet oxygen quantum
yield were measured using a time-correlated single photon
count (TCSPC) spectrometer (Fluotime 300, PicoQuant)
with a laser diode emitting 634 nm (LDH-D-C-634,
PicoQuant). The data was analyzed with the program
Fluofit, PicoQuant. All measurements were performed at
room temperature.
2,3-Dicyanonaphthalene (3)
Yield 57%; IR (KBr pellet) ν / cm-1 3097-3031 (Ar–H),
2971-2867 (aliph. C–H), 2227 (C≡N), 1716, 1618, 1361,
1274, 1082; 1H NMR (400 MHz, CDCl3) d 8.37 (s, 2H),
8.00 (m, 2H), 7.81 (m, 2H).
6-tert-Butyl-2,3-dicyanonaphthalene (4)
Yield 33%; IR (KBr pellet) ν / cm-1 3099-3000 (Ar–H),
2990-2800 (aliph. C–H), 2229 (C≡N), 1703, 1622, 1363,
Synthesis
1
1261, 1097; H NMR (400 MHz, CDCl3) d 8.32-8.31
Scheme 1 presents the experimental conditions and the
compounds synthesized to obtain the naphthalocyanines
applied in this study.
(d, J 6.82 Hz, 2H), 7.94-7.87 (m, 3H), 1.44 (s, 9H).
General procedure for naphthalocyanines synthesis
General procedure for precursor synthesis
0.43 mmol of 3 or 4 and 0.21 mmol of zinc(II) acetate
were suspended in 1 mL dry pentanol at 150 °C, under inert
gas. Then, 0.43 mmol of 1,8-diazabicyclo[5.4.0]undec-
7-ene (DBU) was added and the solution was stirred for
12 h at 150 °C. After cooling, methanol was added and the
resulted precipitate was centrifuged.
To a solution of 4 mmol of o-xylene or tert-butyl-
o-xylene in 12.0 mL of dry CH2Cl2, 14 mmol of
N-bromosuccinimide were added. The reaction mixture
was refluxed and irradiated with a 125 W mercury vapor
lamp for 6 h. The mixture was filtered while hot and
the filtrate was evaporated to obtain a yellowish solid.
The crude product was dissolved in 12.0 mL of dry
dimethylformamide (DMF), and 4 mmol of fumaronitrile
and 20 mmol of dry NaI were added to the solution. The
Zinc-naphthalocyanine (ZnNc)
The crude product was purified by a silica-gel
column with tetrahydrofuran (THF)/DMF (7:3) as eluent.
Yield 15%; IR (KBr pellet) ν / cm-1 3100-3000 (Ar–H),

Vol. 29, No. 6, 2018
de Souza et al.
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Scheme 1. Synthesis of zinc-naphthalocyanine (ZnNc) and zinc-tert-butyl-naphthalocyanine (2).
2990-2800 (aliph. C–H), 1716, 1653, 1433, 1354, 1149,
1088; 1H NMR (400 MHz, THF-d4) d 8.49-8.40 (m, 8H),
8.11-8.02 (m, 8H), 7.90-7.80 (m, 8H).
the samples and standard at the excitation wavelength,
respectively; n2 and nS2td are the refractive indices of solvents
for the sample and standard, respectively. Unsubstituted
ZnPc (in DMSO) (ΦF = 0.20)17,18 was employed as the
standard. Both the sample and standard were excited at
350 nm. The absorbance of the solutions ranged between
0.06 and 0.09 at the excitation wavelength.
The fluorescence lifetime (τF) values were directly
determined in DMSO by TCSPC method. Both the sample
and standard were excited at 634 nm.
Zinc-tert-butyl-naphthalocyanine (2)
The crude product was purified by a silica-gel column
with toluene/THF (10-30%) as eluent.Yield 18%; IR (KBr
pellet) ν / cm-1 3090-3000 (Ar–H), 2990-2820 (aliph. C–H),
1714, 1460, 1357, 1101; 1H NMR (400 MHz, DMSO-d6)
d 8.43-8.40 (d, J 9.14 Hz, 8H), 8.21-8.18 (d, J 9.60 Hz,
8H), 7.91-7.89 (d, J 1.83 Hz, 2H), 7.88-7.87 (d, J 2.06 Hz,
2H), 1.41 (s, 36H).
Singlet oxygen quantum yields
Fluorescence quantum yields and lifetimes
Singlet oxygen quantum yield (ΦD) values were
determined in air by direct detection of the singlet oxygen
phosphorescence at 1270 nm. The ΦD were determined in
THF by the comparative method using equation 2.19
Fluorescence quantum yields (ΦF) were determined in
DMSO by the comparative method using equation 1.17,18
(1)
(2)
where F and FStd are the areas under the fluorescence
emission curves of the samples and the standard,
respectively; A and AStd are the relative absorbance of
where I and IStd are the phosphorescence intensity of
singlet oxygen at 1270 nm of the samples and the standard,
respectively. Unsubstituted ZnPc (in THF) (ΦD = 0.53)20

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Photophysical and Photochemical Properties and Aggregation Behavior of Phthalocyanine and Naphthalocyanine
J. Braz. Chem. Soc.
was employed as the standard. Both the sample and
standard were excited at 634 nm. The concentration of the
compounds was 5 μM.
found using the same methodology employed for monomer
calculations.
Results and Discussion
Computational studies
Synthesis and characterization
Density-functional theory (DFT) approach was
employed to obtain the geometry of the compounds in
a minimum in the potential energy surface by using the
B3LYP functional and the 6-311G(d,p) basis set. Time
dependent DFT (TD-DFT) was performed for 80 states
in order to obtain the electronic spectra of the compounds
by using the same methodology. Intramolecular vibrations
were not included since they are negligible for rigid
molecules as those studied here.21 Solvent effects were
included by means of the IEFPCM continuum model.22
These calculations were carried out with Gaussian09
package.23
In order to give insight on how absorption spectrum
at low concentrations of phthalocyanine is affected by the
presence of aggregates, we performed DFT calculations by
means of BLYP functional and 6-311G(d) basis set with
Grimme’s correction for dispersion interactions (D3-BJ)24,25
as implemented in ORCA software26 for dimers of ZnPc
and ZnNc. We started geometry optimization with different
stacking conformations, by changing the rotation angle of
one monomer in relation to the other. This methodology was
evaluated for free phthalocyanine previously.27 Absorption
spectra were obtained for the different dimer conformations
The synthesis of naphthalonitriles was realized by a
multistep procedure14-16 starting from o-xylene or tert-butyl-
o-xylene by bromation with N-bromosuccinimide
(NBS) following by a cyclisation with fumarodinitrile.
Naphthalocyanines were synthesized in 1-pentanol, at
150 °C, using DBU as catalyst, under N2 atmosphere. All
compounds were characterized by spectroscopic methods
1
including UV-Vis, IR and H NMR. The results are
consistent with the proposed structures.
In the IR absorption spectra, the formation of
phthalocyanine was confirmed by disappearance of
phthalonitrile C≡N band at 2226 cm-1. The 1H NMR spectra
of 2 exhibited aromatic ring protons with d ranging from 7.88
to 8.43 ppm and aliphatic protons at 1.41 ppm (Figure 2).
The UV-Vis spectra of macrocyclic compounds were
recorded in DMSO (Figure 3). The complexes exhibited
a very intense Q(0, 0) band in the 600-800 nm region and
a Soret band between 300-400 nm. Table 1 summarizes
the wavelengths and associated extinction coefficients
in Q-band. Due to the extended conjugation, the Q-band
maximum was red-shifted around 100 nm for 2 and ZnNc
compared to the phthalocyanine band.
Figure 2. 1H NMR spectrum (500 MHz, DMSO-d6) of compound 2.

Vol. 29, No. 6, 2018
de Souza et al.
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Figure 3. Normalized absorption spectra of ZnPc, 1, ZnNc and 2 in
DMSO.
TD-DFT calculations point out the molecular orbitals
involved in Q-band transition. This band is composed by
two transitions: HOMO →LUMO and HOMO →LUMO+1
(HOMO: highest occupied molecular orbital; LUMO:
lowest unoccupied molecular orbital). Figure 4 presents the
molecular orbitals for ZnPc and ZnNc which correspond to
the already known behavior: HOMO to LUMO transition
consists in a concentration of charge along x-axis, while
the transition to LUMO+1 is in y-axis direction. The same
occurs for ZnNc, but as the conjugated system is larger, the
concentration of charge is more extended along each axis.
Substitutions with tert-butyl groups do not affect expressively
this behavior (molecular orbitals for 1 and 2 are presented
in Figure S1, Supplementary Information (SI) section), and
affect slightly molecular orbitals energies (Table 1).
In region between 300 and 400 nm, there are degenerated
transitions from HOMO-1 to LUMO/LUMO+1. For
naphthalocyanines, besides those transitions, there are
also transitions from HOMO to higher LUMOs, and for
compound 2, those transitions are not degenerated due to
tert-butyl substitutions (Table S1, SI section).
These molecular orbitals are in good agreement with
previous simulations (see Ueno et al.28 for example), but it is
interesting to note that HOMO-1 for ZnPc does not include
the nitrogen in meso positions (N-meso), while metal-free
phthalocyanine does, those nitrogen atoms participation
Figure 4. Molecular orbitals (HOMO-1, HOMO, LUMO and LUMO+1)
involved in transitions that occur in Q-band region for ZnPc and ZnNc.
Hydrogen atoms are represented by yellow spheres, nitrogen in blue,
carbon in dark grey and zinc in light grey (molecular orbitals for
substituted compounds are presented in Supplementary Information
section).
on HOMO-1 causes a well-known stabilization of the
energy of the level. This phenomena is also observed
for other metallophthalocyanines (particularly for NiPc;
for some other metallic cations, HOMO-1 correspond to
3d-like orbitals).29,30 For naphthalocyanines, N-meso atoms
participate in HOMO-1, but its contribution is small.
For all compounds, a small band appears next to
Q-band. In TD-DFT calculated spectra (data presented in
Table 1. Experimental absorption, excitation and emission data for compounds in DMSO and TD-DFT molecular orbital energies
Abs
exc
ems
Compound
Q-band lmax / nm
log ε
5.2
EHOMO / a.u. ELUMO / a.u.
gapHOMO-LUMO / a.u.
0.0801
Excitation lmax / nm
Emission lmax / nm
ZnPc
1
675
678
766
770
–0.1897
–0.1825
–0.1746
–0.1700
–0.1096
–0.1036
–0.1058
–0.1017
607
612
686
688
681
686
778
783
4.5
0.0789
ZnNc
2
5.0
0.0688
5.1
0.0683

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Photophysical and Photochemical Properties and Aggregation Behavior of Phthalocyanine and Naphthalocyanine
J. Braz. Chem. Soc.
Table 2. Photophysical data of compounds in DMSO
Supplementary Information), there are no transitions in this
region, so those bands may not be due to purely electronic
transition of monomeric species.
a
Compound
ZnPc
1
ΦF
τF / ns
3.3
ΦD
0.20
0.18
0.07
0.08
0.53
0.34
0.41
0.29
Fluorescence spectra, quantum yields and lifetimes
3.2
ZnNc
2
2.5
Fluorescence measurements of the compounds were
recorded in DMSO (Table 1). The excitation spectra
were similar to absorption spectra and both were mirror
images of the emission spectra (Figure 5). The proximity
of the wavelength of Q-band maxima of the absorption
and excitation spectra for all compounds suggests that the
nuclear configurations of the ground and excited states
are similar and not affected by excitation.10 Due to the
extended conjugation, the Q-band maxima of the excitation
spectra and emission was red-shifted in the same order of
absorption spectra.
2.4
aIn THF.
naphthalocyanine results in lower values for singlet oxygen
generation.
Aggregation studies
The UV-Vis spectra of compounds were obtained
in DMSO, DMF, toluene, dichloromethane (DCM) and
chloroform, both experimentally (Figure 6 for 2) and
computationally (see Table S2, SI section). These results
are in good agreement and show that the solvent influence
in the absorption spectra is related only to small changes
in bands intensity, due to the different dielectric constants
and van der Waals radii (both affect the transition dipole
moment and, consequently, the oscillator strength).
The compounds showed monomeric behavior in these
solvents, in the concentration range studied (from 1 × 10-6
to 1 × 10-5 mol L-1), as it is possible to see in DMSO in
Figure 7b.
Figure 5.Absorption, excitation and emission spectra of ZnNc in DMSO.
Concentration = 1.0 × 10-6 mol L-1. Excitation wavelength = 350 nm.
The fluorescence quantum yields (ΦF) of the compounds
were determined by comparative method (Table 2).
The values for phthalocyanines were higher than for
naphthalocyanine. The fluorescence lifetime (τF) of the
compounds were determined by using TCSPC and,
again, the values were lower for naphthalocyanines than
phthalocyanines. These results suggest that the addition
of benzene rings to the periphery of phthalocyanine
macrocycle increases the non-radiative losses from excited
states and decreases the efficiency of fluorescence process.
Figure 6.Absorption spectra of 2 in different solvents at 5.0 × 10-6 mol L-1.
Singlet oxygen quantum yields (ΦD)
The aggregation was investigated in DMSO:water
solutions. The absorption spectra of 2 in solution of
DMSO:water for different water volume percentage
are shown in Figure 8. The increase of the amounts of
water in the DMSO:water mixtures leads to a decrease
in the Q-band maximum intensity, demonstrating the
formation of aggregated species. By plotting the intensity
The quantum yield of singlet oxygen generation was
determined using the equation 2 by directed method
measuring phosphorescence intensity of singlet oxygen.
The ΦD values of ZnPc are higher than for other compounds
(Table 2). Once more, higher extended π-conjugation in

Vol. 29, No. 6, 2018
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Figure 7. (a) Absorption spectra of 2 in DMSO from 8.4 × 10-7 to
9.4 × 10-6 mol L-1; (b) intensity at maximum absorption wavelength versus
concentration for all studied compounds, in DMSO.
Figure 8. (a) Absorption spectra of 2 in DMSO/water solutions, water
volume percentage as a parameter; (b) intensity at maximum absorption
wavelength versus water percentage for all studied compounds.
at maximum absorption wavelength versus water content,
a bleaching of 50% in absorbance was observed at 35, 30,
20 and 15% of water for ZnPc, 1, ZnNc and 2, respectively
(Figure 8b). The Q-band has a suddenly decrease in their
maximum intensity when the water volume percentage was
higher than 60, 40, 30 and 40% for ZnPc, 1, ZnNc and 2,
respectively (Figure 8a).
The fluorescence spectra of 2in solution of DMSO:water
for different water volume percentage are shown in Figure 9.
The increase of the amounts of water in the DMSO:water
mixtures causes a bathochromic shift in fluorescence
emission spectra for all compounds. In addition, we
observed a decrease in the fluorescence intensity, probably
due to the aggregation of macrocycles. By plotting the
fluorescence intensity at maximum emission wavelength
versus water content, a bleaching of 50% in fluorescence
intensity was observed at 35, 35, 20 and 15% of water for
ZnPc, 1, ZnNc and 2, respectively. The results were similar
to that obtained in absorbance experiment.
DFT calculations with dispersion corrections for ZnPc
and ZnNc dimers. Table 3 presents the energy for different
conformations of dimers. The geometry optimization
conducted for both compounds, ZnPc and ZnNc, resulted
in two conformations. In the first one, monomers are in
the same orientation for both compounds (0° of rotation),
slightly displaced in the xy plane by 2 Å, and at 2.7 Å
distance between monomers, in good agreement with
previous work31 and the interaction energy for ZnNc is
even larger.
In the second conformation, monomers are
superimposed, but rotated about 45° and the distance
between monomers for ZnNc is 0.7Å larger than for ZnPc,
what results in a smaller interaction. Structures with 0° of
rotation are probably the most stable because the relative
position of each monomer allows the zinc atom to interact
with nitrogen of the other monomer (Figure S3, SI section).
Moreover, in crystals of phthalocyanines and
naphthalocyanines, there are only 0° of rotation aggregates,
and the structures that allow the interaction between Zn
and N-meso are known as β-polymorphs. Electrostatic
In order to quantify the impact of the π-conjugated
system interaction on absorption spectra, we performed

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Photophysical and Photochemical Properties and Aggregation Behavior of Phthalocyanine and Naphthalocyanine
J. Braz. Chem. Soc.
interaction energies can vary, depending on the methodology
employed32 it was found 9.21 kJ mol-1 (2.2 kcal mol-1) with
B3LYP/6-31G(d) and 32.55 kJ mol-1 (7.8 kcal mol-1) with
B3LYP/LanL2MB, both without basis set superposition
error (BSSE) correction. On the other hand, Gantchev et al.35
obtained 155 kJ mol-1 (37.1 kcal mol-1) using molecular
mechanics. The higher interaction energies obtained here
and the smaller distance between monomers may be due to
the slightly larger basis set and, mainly, to the inclusion of
dispersion corrections. These corrections are quite important
since the energy obtained for larger distances of interaction
(dimer 45°) is closer to the results derived from molecular
mechanics simulations.
In brief, here we have found conformations that
correspond to lower (dimer 0°) and higher (dimer 45°)
bound estimate in relation to the dimer inner distance.
Further studies, mainly using calorimetric experiments and
molecular dynamics simulations,36 are needed to propose
other dimer conformations and include explicitly solvent
molecules, to better evaluate energetics and conformations
of dimers and higher aggregates. However, these bound
estimates are already useful to evaluate tendencies of the
effect of interacting molecules on absorption spectra.
TD-DFT spectra for those conformations are presented
in Figure 10 along with experimental spectrum for
8.4 × 10-7 mol L-1 ZnPc and ZnNc solutions and with
monomer theoretical lines (same adjustments for monomer
and dimer theoretical spectra to fit experimental data).
As can be seen, dimer main transitions are quite closer
to the monomer main transition, almost all together
under the experimental Q-band, especially the 0° dimer,
the most stable one. It is worth noting that this dimer
Q-band transition is no more degenerated, since it involves
molecular orbitals from the two monomers that are not
perfectly superimposed (see Table S3 and Figures S4 to
S7, SI section).
Other evidence of dimer presence is the smaller bands
in experimental spectra (between 600 and 650 nm for ZnPc
and 650 and 750 nm for ZnNc): theoretical monomer spectra
do not present transitions in those regions, only dimers do.
The transition closer to Q-band can be attributed to the main
transition of dimer 45°. As this is a less stable dimer, its
concentration in experimental system may be smaller than
the monomer and dimer 0° concentrations, resulting in this
Q-band shoulder. The other band (around 620 nm for ZnPc
and 680 nm for ZnNc) seems to correspond to the highest
energy transitions of dimer 0°. These transitions involve
inner molecular orbitals, as HOMO-2 and HOMO-3,
especially for ZnPc. These orbitals are located on only one
monomer, so the transitions correspond to a charge transfer
from one monomer to the whole dimer. The inclusion of
Figure 9. (a) Emission spectra of 2 in DMSO/water solution, water
volume percentage as a parameter; (b) fluorescence intensity at maximum
emission wavelength versus water percentage for all studied compounds.
Table 3. Aggregation energy (Edim) and structural parameters for dimers
found for ZnPc and ZnNc: approximate rotation angle of one monomer
in relation to the other and distance between monomers
Rotation angle /
degree
Edim /
Compound
ZnPc
Distance / Å
(kcal mol-1)
0
45
0
2.68
3.35
2.71
4.09
–60.00
–49.94
–78.40
ZnNc
45
–31.42
potential surface is a quite useful tool to evaluate the
interaction between compounds32 (Figure S2, SI section),
N-meso correspond to negatively charged regions, which
may allow stronger interaction with the cation ZnII from
the other monomer. The distance between molecules in
crystals is about 3.23 Å for ZnPc33 and 3.29 Å for ZnNc.34
Previous computational simulations furnished the same
conformation we have obtained for dimer 0°, but dimer inner
distance is greater than that we have found. Besides that,

Vol. 29, No. 6, 2018
de Souza et al.
1207
Figure 10. Theoretical absorption spectra calculated with TD-DFT/B3LYP/6-311G(d,p) in DMSO for (a) ZnPc and (b) ZnNc.
thermal effects, as performed by Cabral et al.36 for free
phthalocyanines, could be conducted to complement the
analysis of the influence of aggregation on absorption
spectrum.
Experimental absorption spectra for all compounds
did not show any aggregation behavior in the different
solvents employed. Aggregation tendency is observed as
the water proportion in DMSO:water solution increment.
Naphthalocyanines have more aggregation tendency in
DMSO:water solution due to extended π-conjugated system.
The geometry optimization conducted for ZnPc and
ZnNc stacking dimers resulted in two conformations. In
the first one, monomers are in the same orientation for both
compounds (0° of rotation), but the interaction energy for
ZnNc is quite larger. In the second conformation, monomers
are superimposed, but rotated about 45°, and the distance
between monomers for ZnNc is 0.7Å larger than for ZnPc,
which results in a smaller interaction. Further studies
involving molecular dynamics simulations are needed to
verify other dimer conformations and the relative stability,
including substituted compounds.
Conclusions
In our study we describe the photophysical
and photochemical properties phthalocyanine and
naphthalocyanines with similar structures to understand the
effects of extended π-conjugation on compounds. Q-band
was found to be composed by transitions between HOMO
to the degenerated virtual orbitals LUMO and LUMO+1.
The extended π-conjugated system in naphthalocyanine
diminishes the energy difference between HOMO and
LUMOs and, consequently, causes a bathochromic shift in
UV-Vis absorption, emission and excitation bands.

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Photophysical and Photochemical Properties and Aggregation Behavior of Phthalocyanine and Naphthalocyanine
J. Braz. Chem. Soc.
Theoretical absorption spectra indicate that main
transition of dimers are quite close to the monomer
transition, so the dimeric species, even in diluted solutions,
are possibly present. Furthermore, other smaller bands
present in experimental spectra may correspond to dimer
with 45° of rotation and to higher energy transitions that
involve charge transfer from one monomer to the whole
dimer.
14. Haris, S. P.; Zhang, Y.; Bourdonnec, B. L.; McCurdy, C. R.;
Portoghese, P. S.; J. Med. Chem. 2007, 50, 3392.
15. Pelisson, M. M. M.; Tomé, F. M.; Beltrame, M.; Simioni,A. R.;
Tedesco, A. C.; J. Porphyrins Phthalocyanines 2003, 7, 630.
16. Kliesch, H.; Weitemeyer,A.; Müller, S.; Wörle, D.; Liebigs Ann.
1995, 1269.
17. Gurel, E.; Piskin, M.; Altun, S.; Odabas, Z.; Durmus, M.;
J. Photochem. Photobiol. 2016, 315, 42.
18. Acar, I.; Biyiklioglu, Z.; Durmus, M.; Katenkin, H.;
J. Organomet. Chem. 2012, 708, 65.
Supplementary Information
19. Staicu, A.; Pascu, A.; Boni, M.; Pascu, M. L.; Enescu, M.;
J. Mol. Struct. 2013, 1044, 188.
Data obtained with TD-DFT about the Q-band in
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This work was supported by CEM-UFABC,
FAPESP (2014/18527-8 and 2012/50680-5) and CNPq
(306177/2016-1 and 448125/2014-5).
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