Intramolecular aggregation and optical limiting properties of triazine-linked mono-, bis- and tris-phthalocyanines

Article abstract of DOI:10.1016/j.saa.2015.04.093

A series of triazine-linked mono-, bis- and tris-phthalocyanines are synthesized, intramolecular aggregation is found in bis- and tris-phthalocyanines via π-π stacking interaction. Theoretical and experimental studies reveal the formation of the intramole

Full text of DOI:10.1016/j.saa.2015.04.093

Accepted Manuscript
Intramolecular aggregation and optical limiting properties of triazine-linked
mono-, bis- and tris-phthalocyanines
Jun Chen, Tao Zhang, Shuangqing Wang, Rui Hu, Shayu Li, Jin Shi Ma,
Guoqiang Yang
PII:
S1386-1425(15)00565-X
http://dx.doi.org/10.1016/j.saa.2015.04.093
SAA 13644
DOI:
Reference:
To appear in:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
Received Date:
Revised Date:
Accepted Date:
11 December 2014
18 March 2015
20 April 2015
Please cite this article as: J. Chen, T. Zhang, S. Wang, R. Hu, S. Li, J.S. Ma, G. Yang, Intramolecular aggregation
and optical limiting properties of triazine-linked mono-, bis- and tris-phthalocyanines, Spectrochimica Acta Part A:
Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.04.093
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Intramolecular aggregation and optical limiting properties of
triazine-linked mono-, bis- and tris-phthalocyanines
[a] [b]
Jun Chen*
[a]
, Tao Zhang , Shuangqing Wang* , Rui Hu , Shayu Li , Jin Shi Ma , Guoqiang Yang*
[a]
[a]
[a]
[a]
[a]
[
a] Beijing National Laboratory for Molecular Sciences, Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of
Sciences, Beijing 100190, P. R. China.
[
b] School of Materials Science and Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, P. R. China.
Corresponding authors, E-mail: gqyang@iccas.ac.cn (G. Yang), g1704@iccas.ac.cn (S. Wang), chenjun@iccas.ac.cn (J. Chen)
*
Abstract
A series of triazine-linked mono-, bis- and tris-phthalocyanines are synthesized, intramolecular aggregation is
found in bis- and tris-phthalocyanines via π-π stacking interaction. Theoretical and experimental studies reveal the
formation of the intramolecular aggregation. The spectrographic, photophysical and nonlinear optical properties of
these compounds are adjusted for the formation of the intramolecular aggregation. The bis-phthalocyanine dimer pre-
sents smaller fluorescence quantum yield, lower triplet formation yield and the triplet-minus-ground state extinction
coefficient, which causes poorer optical limiting performance. It is interesting that the tris-phthalocyanine is composed
of a mono-phthalocyanine part and a bis-phthalocyanine part, the optical limiting property of the tris-phthalocyanine is
similar to that of mono-phthalocyanine.
Keywords: phthalocyanine; triazine; optical limiting properties; intramolecular aggregation; photophysical properties.
1. Introduction
Phthalocyanines (Pcs) exhibit a remarkable photophysical properties that lead themselves to applications in optical
limiters, solar cells, semiconductor, photodynamic therapy and so on [1]. Aggregation is a well-known phenomenon in Pc
chemistry. Interactions can occur between adjacent phthalocyanine rings both in organic and aqueous phase, resulting in
the coupling between the electronic states of two, or more, phthalocyanine units [2]. The outstanding optical and
photosensitizing properties of Pcs with abroad absorption range and high excitons quantum yields are always restricted in
an aggregated state. The suppression and control of aggregation properties of Pcs is a challenge in material science,
especially for their applications in nonlinear optics [3]. In order to understand the electronic configuration between
chromophores, the study on the photophysical processes of both monomeric and aggregated molecules is important in
designing organic materials for applications in optoelectronic technologies.

Even though the intermolecular aggregation can be reduced by introduction of bulky substituents into peripheral or
axial positions of Pc cores to enlarge the distance between molecules [4], only a few examples of investigations focus on
the intramolecular aggregation of multi-nuclear phthalocyanine-based materials [5]. To get better insight into the
relationship between aggregation and optical properties, especially the photophysical processes of excited states, it is
necessary to design and synthesize new models with high fluorescence quantum yield and well-defined structures. Here
we designed a series of triazine-linked compounds, connected with mono-, bis- and tris-phthalocyanines(Figure 1), to
reveal the formation of the intramolecular dimers and the influence on the excited states and optical limiting behavior.
2. Experimental
2.1 General
All organic solvents were commercially available, dried and distilled by appropriate methods before use [6]. 4-
tert-Butylphenoxyphthalonitrile and 4-hydroxylphenoxyphthalonitrile were prepared using similar methods as de-
1
scribed in the literatures [7]. H NMR spectra were performed on a DPX400 Bruker FT-NMR spectrometer with
3
CDCl as solvent and tetramethylsilane (TMS) as internal standard. The mass spectra were obtained on a Biflex
MALDI-TOF. Elemental analyses were performed on a Carlo Erba-1106 elemental analyzer. UV-vis absorption spec-
tra were recorded on a Hitachi U-3010 spectrophotometer. Fluorescence spectra were recorded on a Hitachi F-4500
fluorescence spectrophotometer. The fluorescence lifetimes were investigated with single-photon counting technique
with Edinburgh FL900 spectrophotometer.
The triplet state formation yields were determined by flash photolysis at nanosecond time scale. The excitation
light was the harmonic of Nd:YAG laser (Continuum Surelite II, 355nm and 7ns FWHM). A pulsed xenon arc lamp
was used to provide the analyzing light. The configuration of the monitoring light with respect with the excitation laser
pulse is right-angle geometry. The liquid samples (1.0cm quartz cell) were settled on the platform at the intersection of
monitoring light and excitation pulse. All the samples are optically dilute at the laser excitation wavelength. The sig-
nals were detected by Edinburgh LP900 and recorded on Tektronix TDS 3012B oscilloscope and computer. The tri-
plet-minus-ground state extinction coefficients (∆ε
The quantum yields of the triplet state (Ф ) were determined by the comparative method[8], using unsubstituted ZnPc
in 1-chloronaphthalene as reference standard (Ф
T
) were calculated by the method of total depletion or saturation [8].
T
T
=0.65). The optical limiting properties were measured by the standard
2

setup of previously reported method [8]. Theoretical molecular simulations were performed using the GROMACS
simulation suite [9].
2.2 Synthesis
2
2,9,16-Tri-tert-butylphenoxy-23-hydroxylphenoxy-phthalocyanine (H Pc-OH)
A mixture of 4-tert-butylphenoxyphthalonitrile (0.236g, 1mmol) and 4-hydroxylphenoxyphthalonitrile (2.48g,
9
mmol) was added to 50mL dry 1-pentanol with 1.5mL 1,8-diazabicyclo[5.4.0]undec-7-ene(DBU) as a catalyst. The
mixture was stirred at 60℃ for 1 hour under a nitrogen atmosphere. The mixture was slowly brought to boiling over 1
hour and then refluxed for 36h, after the reactant was cooled to room temperature, 50mL of methanol/water (1/1) mix-
ture was added, the blue precipitated product was filtered, and washed with hydrochloric acid (5%, 50mL), then 50mL
methanol, the crude product was purified by a silica-gel column chromatography with toluene as first eluent to remove
2 58 8 5
the byproduct, and then using THF as eluent to give 0.78g (yield: 73%) of H Pc-OH (C68H N O ). MALDI-TOF:
1
1
067.8(m/z) (calcd. 1066.45); H NMR (DMSO-d6, 400MHz) δ= 7.78-8.11 (broad, 8H, Pc-H), 7.30-7.48 (dd, 6-H,
Phenyl–H), 7.01-7.30 (m, 10H, Phenyl–H), 6.90-7.08 (broad, 4H, Pc-H), 5.30 (s, 1-H, OH), 5.12 (broad, N-H), 2.18
broad, N-H), 1.26-1.37 (s, 27H, tBu-H) ppm; Anal. Calcd (%) for C68 : C 76.53, H 5.48, N 10.50; found C
(
58 8 5
H N O
76.21, H 5.64, N 10.15.
1,3-Di-tert-butylphenoxy-5-phthalocyanine substituted triazine (Mono-phthalocyanine 1).
4-tert-Butylphenol (75mg, 0.5mmol) and 1,3,5-trichlorotriazine (46mg, 0.25mmol) were added to 5mL dry toluene
o
with 6mg of sodium silk as catalyst. After stirring the reaction mixture at 60 C under argon for 3h, H
2
Pc-OH(0.267g,
o
0
.25mmol) was added and the mixture was stirred at 110 C for 4h, then the toluene was removed under reduced pres-
sure. The crude product was washed with methanol and then purified by a silica-gel column chromatography with di-
83 11 7
chloromethane as first eluent and then THF to give 0.3g (yield: 83%) of the mono-phthalocyanine 1–H (C91H N O ).
1
MALDI-TOF: 1442.8(m/z) (calcd. 1442.65) (Figure 2); H NMR (CDCl
3
, 400MHz): δ=7.82-8.28 (broad, 8H, Pc-H),
7
.53-7.60 (dd, 6H, Phenyl–H), 7.26-7.47 (dd, 12H, Phenyl–H), 7.15-7.25 (dd, 6H, Phenyl–H), 6.99-7.04 (m, 4H, Pc-
H), 5.05 (broad, N-H), 2.10 (broad, N-H), 1.44-1.47 (s, 45-H, t-Bu-H) ppm; Anal. Calcd (%) for C91 : C
5.76, H 5.80, N 10.68; found C 76.11, H 5.95, N 10.35.
83 11 7
H N O
7
3

3
1-H(144mg, 0.1mmol) and anhydrous InCl (25mg, 0.11mmol) was added to 3mL 1-chloronaphthalene and the
o
mixture was stirred at 140 C for 2h, after the reactant was cooled to room temperature, 5mL of n-hexane was added,
the blue precipitated product was filtered, and washed with 5mL methanol, the crude product was purified by a silica-
gel column chromatography with chloroform/THF (5:1) as eluent to obtain 135mg(yield: 85%) of 1-In
+
1
(
C
91
H
83
N
11
O
7
InCl). MALDI-TOF: 1589.6(m/z) (calcd. 1589.5), 1554.1 (M -Cl); H NMR (CDCl
.12 (broad, 4H, Pc-H), 8.68-8.81 (broad, 4H, Pc-H), 7.76-7.83 (dd, 6H, Phenyl–H), 7.53-7.60 (m, 10H, Phenyl–H),
.41-7,45 (dd, 2H, Phenyl–H), 7.29-7.37 (dd, 6H, Phenyl-H), 7.02-7.05 (m, 4H, Pc-H), 1.34-1.37 (s, 45H, tBu-H) ppm;
InCl: C 68.70, H 5.13, N 9.68; found C 69.11, H 5.39, N 9.88.
3
, 400MHz): δ=9.09-
9
7
81 11 7
Anal. Calcd (%) for C91H N O
1-tert-Butylphenoxy-3, 5-diphthalocyanine substituted triazine (Bis-phthalocyanine 2).
4-tert-Butylphenol (37.5mg, 0.25mmol) and 1,3,5-trichlorotriazine (46mg, 0.25mmol) were added to 5mL dry
o
toluene with 6mg of sodium silk as catalyst. After stirring the reaction mixture at 60 C under argon for 3h, H
2
Pc-
o
OH(0.538g, 0.5mmol) was added and the mixture was stirred at 120 C for 12h, then the toluene was removed under
reduced pressure. The crude product was washed with methanol and then purified by a silica-gel column chromatog-
raphy with dichloromethane as first eluent and then THF to give 0.43g (yield: 72%) of the bis-phthalocyanine 2-H
1
(
(
C
149
H
127
N
19
O
11). MALDI-TOF: 2359.0(m/z) (calcd. 2359.0) (Figure 3); H NMR (CDCl
3
, 400MHz): δ=7.88-8.10
broad, 16H, Pc-H), 7.50-7.51 (d, 12H, Phenyl–H), 7.29-7.44 (d, 14H, Phenyl–H), 7.10-7.26 (d, 10H, Phenyl–H), 6.97-
.03 (m, 8H,Pc-H), 5.0 (broad, N-H), 2.25 (broad, N-H), 1.34-1.43 (s, 63H, t-Bu-H) ppm; Anal. Calcd (%) for
11: C 75.84, H 5.42, N 11.28; found C 75.53, H 5.71, N 11.57.
-H (236mg, 0.1mmol) and anhydrous InCl (50mg, 0.23mmol) was added to 3mL 1-chloronaphthalene and the
7
149 127 19
C H N O
2
3
o
mixture was stirred at 150 C for 2h, after the reactant was cooled to room temperature, 5mL of n-hexane was added,
the blue precipitated product was filtered, and washed with 5mL methanol, the crude product was purified by a silica-
gel column chromatography with chloroform/THF (3:1) as eluent to obtain 205mg (yield: 77%) of 2-In
+
1
(
C
149
H
123
N
19
O
11In
2
Cl
δ=9.10 (broad, 8H, Pc-H), 8.69-8.82 (broad, 8H, Pc-H), 7.75-7.85 (dd, 6H, Phenyl–H), 7.57-7.58 (m, 12H, Phenyl–H),
.41-7,45 (dd, 4H, Phenyl–H), 7.29-7.35 (m, 14H, Phenyl-H), 6.94-7.04 (m, 4H, Pc-H), 1.34-1.46 (s, 63H, t-Bu-H)
ppm; Anal. Calcd (%) for C149 Cl : C 67.37, H 4.67, N 10.02; found C 67.76, H 4.95, N 9.92.
2 3
). MALDI-TOF: 2655.7(m/z) (calcd. 2654.71), 2619.2 (M -Cl); H NMR (CDCl , 400MHz):
7
H
123
N
19
O
11In
2
2
1,3,5-Triphthalocyanine substituted triazine (Tris-phthalocyanine 3).
4

2
1,3,5-trichlorotriazine (46mg, 0.25mmol) and H Pc-OH(0.805g, 0.75mmol) of was added to 15mL of toluene and
o
the mixture was stirred at 120 C for 15h, then the toluene was removed under reduced pressure. The crude product was
washed with methanol and then purified by a silica-gel column chromatography with dichloromethane as first eluent
171 27
and then THF to give 0.64g (yield: 78%) of the tris-phthalocyanine 3-H (C207H N O15). MALDI-TOF: 3276.5(m/z)
1
(
calcd. 3276.35) (Figure 4); H NMR (CDCl
3
, 400MHz): δ=7.85-8.10 (broad, 24H, Pc-H), 7.45-7.60 (d, 18H, Phenyl–
H), 7.32-7.42 (dd, 18H, Phenyl–H), 7.12-7.26 (m, 12H, Phenyl–H), 6.88-7.04 (m, 12H, Pc-H), 5.15 (broad, N-H), 2.03
broad, N-H), 1.25-1.43 (s, 81H, tBu-H) ppm; Anal. Calcd (%) for C207 15: C 75.87, H 5.26, N 11.54; found C
5.51, H 5.59, N 11.15.
(
171 27
H N O
7
3
3-H(327mg, 0.1mmol) and anhydrous InCl (75mg, 0.34mmol) was added to 5mL 1-chloronaphthalene and the
o
mixture was stirred at 160 C for 2h, after the reactant was cooled to room temperature, 10mL of n-hexane was added,
the blue precipitated product was filtered, and washed with 10mL methanol, the crude product was purified by a silica-
gel column chromatography with chloroform/THF (2:1) as eluent to obtain 320mg (yield: 86%) of 3-In
+
1
207 165 27 3 3 3
(C H N O15In Cl ). MALDI-TOF: 3720.8(m/z) (calcd. 3719.92), 3685.3 (M -Cl); H NMR (CDCl , 400MHz):
δ=9.07 (broad,12H, Pc-H), 8.60-8.80 (broad, 12H, Pc-H), 7.78-7.80 (dd, 6H, Phenyl–H), 7.51-7.59 (m, 18H, Phenyl–
H), 7.41-7,45 (dd, 6H, Phenyl–H), 7.29-7.35 (m, 18H, Phenyl-H), 6.92-7.07 (m, 12H, Pc-H), 1.26-1.46 (s, 81H, tBu-H)
123 19 2 2
ppm; Anal. Calcd (%) for C149H N O11In Cl :C 66.81, H 4.47, N 10.16; found C 66.30, H 4.88, N 9.88.
3
Results and disscussion
.1 Synthesis and characterization
A series of triazine-linked compounds, connected with mono-, bis- and tris-phthalocyanines were synthesized (shown
3
in Figure 1). 4-tert-Butylphenoxyphthalonitrile and 4-hydroxylphenoxyphthalonitrile were prepared using similar
methods as described in the literatures [7]. After alkyloxylation of 3-Nitrophthalonitrile (a) by 4-tert-butylphenol and 4-
hydroxylphenol respectively, the precursor of substituted 4-tert butylphenoxyphthalonitrile (b) and 4-
hydroxylphenoxyphthalonitrile(c) were obtained. The cyclization of (b) with (c) in the molar ratio of 1/3 resulted in the
asymmetrical single hydroxyl substituted phthalocyanine (d) (H
as catalyst under N atmosphere.
2
Pc-OH) (Scheme 1) in 1-pentanol at 140℃ using DBU
2
5

The target compounds, including monomer 1, dimer 2 and trimer 3, were prepared by mixing H
trichlorotriazine in corresponding molar ratios. After alkyloxylation of 1,3,5-trichlorotriazine (e) by 1 equiv and 2 equiv of
-tert-butylphenol respectively, the 1,3-di-(4-tert-butylphenol)-5-chloro-triazine (f) and 1-di-(4-tert-butylphenol)-3,5-
chloro-triazine (g) were obtained. Compounds (f) and (g) were successively reacted with 1 equiv and 2 equiv of (H Pc-
OH), to give the mono-phthalocyanine 1–H and bis-phthalocyanine 2-H, respectively. And the tris-phthalocyanine 3-H
2
Pc-OH with 1,3,5-
4
2
(
Scheme 2) was obtained by the reactant of 1,3,5-trichlorotriazine with 3 equiv of (H
2
Pc-OH). Then the mono-, bis- and
o
tris-phthalocyanines (1-H, 2-H and 3-H) and InCl
3
were added to 1-chloronaphthalene respectively, reacting at 160 C to
give the mono-, bis- and tris-metalophthalocyanines (1-In, 2-In and 3-In).
The mono-, bis- and tris-phthalocyanines(1-H, 2-H and 3-H) and metalophthalocyanines(1-In, 2-In and 3-In)
were purified by silica-gel column and then sublimated under vacuum to remove all the residual impurities. All
1
phthalocyanines were characterized by elemental analysis and spectroscopic methods including UV-vis, H NMR and
MALDI-TOF-MS, which were consistent with the proposed structures. It is worth to point out that these
phthalocyanines exhibit excellent solubility in many organic solvents such as THF, chloroform, DMF and DMSO,
which is suitable for the investigation of photophysical and optical limiting properties.
3.2 Simulated molecular conformation
For a deeper insight into the intramolecular interaction between the Pc macrocycles of the bis- and tris-
phthalocyanines, molecular dynamics simulations are performed, using the GROMACS simulation suite [9]. Figure 5
depicts the chain structures after conformation optimization and energy minimization. It can be seen that the two Pc
rings in bis-phthalocyanine molecule face each other in a parallel fashion. This face-to-face conformation favors the
formation of intramolecular dimer via π-π stacking interaction. While in tris-phthalocyanine molecule, two of Pc rings
act as intramolecular dimer, leaving one Pc ring unpaired and stood alone as monomer.
Even for the axially metallic chloride substituted Pcs, the intramolecular dimer is observed for 2 and 3. The distances
between the two Pc planes of the dimers are calculated to be about 3.3 Å, which is much smaller than that of
-6
intermolecular distance (calcd. to be about 1300 Å at concentration of 4×10 M) between monomers in dilute solution.
Despite of the high concentration of Pc solution or the solid powder Pc samples, the intermolecular distance of Pc units is
about 35 Å [10], which is also more than 10 times larger than such intramolecular distance in dilute solution.
6

3.3 Ground state absorption and fluorescence emission
The UV-vis spectra of phthalocyanine species can provide a sensitive information for the presence or absence of
interaction between phthalocyanine units. As shown in Figure 6, metal-free of monomer 1-H shows two strong sharp
bands in the 660-700nm region, and two weaker vibrational absorption bands in 610-640nm. A fully uncoupled species
will display an electronic spectrum identical with that of mono-phthalocyanine unit, the spectroscopic profiles of bis- and
tris-phthalocyanines are determined by the extent of coupling between the two Pc units. Apparently for 2-H and 3-H, the
broad and intensity enhanced absorption in the 610-640nm region with weaker sharp peaks in the 660-700nm region are
observed, the relative peak-intensity around 610nm and 640nm are increased and the peaks are almost reversed from that
of monomer 1-H. The peak-intensity change can be attributed to the strong π-π interaction of the face-to-face stacked Pc
-6
-4
dimer. Moreover, the absorption spectrum of 2-H is observed essentially unchanged in the range of 10 -10 M (Figure 7),
suggesting that the change of peak-intensity around 610 and 640nm is not due to the intermolecular aggregation, but an
intramolecular aggregation instead [11]. The aggregation peak is also observed in the spectra of 2-In and 3-In, which is
located at about 650nm, especially for compound 2-In. For indium substituted Pcs, the spectrum of 3-In is almost
identical to the sum of 1-In and 2-In, further suggesting that compound 3-In is composed of a monomer part and a dimer
part as expected.
The emission of monomer 1-In is observed at 711nm, while the dimer 2-In shows a little hypsochromic shift at
707nm with a much weaker intensity, and compound 3-In exhibits its main emission band at 713nm with a bit smaller
intensity compared with that of monomer 1-In (Figure 8, excited at 610nm). Small Stokes shift for 2-In relative to the
monomer 1-In and trimer 3-In is probably due to the strong π-π interaction of intramolecular aggregation [12]. As
compared to the monomer 1-In, the relative fluorescence quantum yield has decreased to 37% and 80% for the dimer
2
-In and trimer 3-In, respectively. The weaker intensity of the emission for the dimer 2-In and trimer 3-In is attributed
to the fluorescence self-quenching of the two adjacent Pc units caused by intramolecular aggregation.
The monomer 1-In shows a fast decay process with a lifetime of τ =0.37ns (98.8%), while two different decay
processes are observed obviously for 2-In and 3-In. A fast process caused by the monomer and a slow one resulted
from the dimer as shown in Figure 8 and Table 1. Apparently for the dimer 2-In, a short lifetime of τ , about 0.36ns,
with a decreased proportion (58.5%) and a long lifetime of τ , about 5.39ns, with an increased proportion (41.5%) are
1
1
2
7

observed. The trimer 3-In exhibits lifetimes of 0.36ns and 5.38ns with proportion of 81.8% and 18.2%, respectively.
The shorter lifetime τ belongs to monomer and the longer one τ is attributed to the decay of the intramolecular dimer.
Two decay modes of both τ and τ are observed although the two Pc planes act as dimer in 2-In, which suggest that
the excited state of the Pc dimer deactivate in the form of both monomer and dimer simultaneously, and that is why in
compound 3 the value of A % is even much higher than A %.
1
2
1
2
1
2
3.4 Optical limiting performence
Pcs with heavy central metal show strong optical limiting performance because of strong reverse saturable absorp-
tion (RSA) [13]. To obtain a thorough understanding of the effect of intramolecular aggregation on nonlinear behav-
iour, optical limiting properties were investigated (Figure 9). It is clear that the monomer 1-In shows the best optical
limiting performance, and the trimer 3-In displays almost equivalent optical limiting behaviour to 1-In. While for the
dimer 2-In, the optical limiting behaviour is much worse than that of compound 1 and 3, in which the samples have the
same linear transmittance (Tlin) of 70%. The values of nonlinear attenuation factor (NAF) [8,14] for 1-In、2-In and 3-
In are 20.3, 12.9 and 18.9, respectively, in which the NAF is the ratio of Tlin and Tlim, the Tlim is limiting saturated
transmittance at high fluence. In addition, the optical limiting thresholds for 1-In、2-In and 3-In were 0.29, 0.49 and
-2
0
.32 (J·cm ), the optical limiting threshold is defined as the input fluence at which the transmittance is 50% of the ini-
T
tial linear transmittance (Tlin). The ratios σ ex/σ
0
of 1-In、2-In and 3-In were estimated as summarized in Table 2 [15].
, suggesting a higher cross section of ground state absorption (σ ) and
T
The dimer 2-In shows the lowest value of σ ex/σ
0
0
T
lower triplet absorption cross section (σ ex) which result in lower probability of reverse saturable absorption (RSA)
[
16].
It’s well known that optical limiting performance is mainly produced by reverse saturable absorption (RSA) resulted
from excited state absorption in Pc compounds [17]. Thus, the triplet parameters such as kisc, Ф and ∆ε are important
T
T
parameters to affect the optical limiting performance [18]. Aggregation is undesirable in optical limiting material since
strong intermolecular interactions usually increase relaxation pathways, shorten the excited state lifetime, and reduce
formation of excited state and the effective nonlinear absorption. As listed in Table 2, monomer 1-In have a high inter-
T
system crossing rate (kisc) and a high triplet quantum yield (Ф ) [18].
8

As a result of intensive intramolecular aggregation, the linear transmittance of dimer 2-In and trimer 3-In are
T
found to be lower than that of monomer 1-In. Then result in lower values of σ ex/σ
0
, even though all solutions have the
same concentration. Moreover, aggregation and intermolecular interactions could also modify the geometry of the de-
localized π-electron clouds and therefore reduce the electronic nonlinear optical response. So, as a result of
intramolecular aggregation, the poorer optical limiting performance of 2-In can be attributed to a lower quantum yield
for the intersystem crossing of Pc from its excited singlet to triplet state, lower linear transmittance as well as lower
T
values of the triplet-minus-ground state extinction coefficients ∆ε .
4
Conclusions
A series of triazine-linked mono-, bis- and tris-phthalocyanines were synthesized, two of the Pc rings in bis- and
tris-phthalocyanine molecules face each other in a parallel fashion to form intramolecular dimer via π-π stacking inter-
action. Simulated conformations clearly depict the formation of the intramolecular aggregate, and both the ground state
absorption and the decay mode of fluorescence emission support this fact. The bis-phthalocyanine dimer presents
smaller fluorescence quantum yield, lower triplet formation yield and the triplet-minus-ground state extinction coeffi-
cient, which causes poorer optical limiting performance. The results will provide useful information for the design and
application of phthalocyanine-based materials.
Acknowledgements
We thank the financial support from the National Basic Research Program of China (Nos. 2011CBA00905,
2
9
013CB834703 and 2013CB834505) and the National Natural Science Foundation of China (Nos. 21233011,
1123033, 21373240, 21273252 and 21205122). The authors also thank two anonymous reviewers for their valuable
comments on improvements to the manuscript.
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1

Captions
Scheme 1. Synthetic route of the phthalocyanines H
2
Pc-OH (d)
Scheme 2. Synthetic route of mono-, bis- and tris-phthalocyanines(1-H, 2-H and 3-H)
Figure 1. Structures of mono-, bis- and tris-phthalocyanines
Figure 2. MALDI-TOF spectra of 1-H
Figure 3. MALDI-TOF spectra of 2-H
Figure 4. MALDI-TOF spectra of 3-H
Figure 5. Simulated conformations of bis-phthalocyanine (2-In, left) and tris-phthalocyanine (3-In, right)
Figure 6. UV-vis absorption of metal-free and indium phthalocyanines monomer 1, dimer 2 and trimer 3 in THF with
-6
concentration of 4×10 M
Figure 7. UV-Vis spectra of 2-H at different concentrations in THF
Figure 8. Fluorescence spectra (excited at 610nm) and decay profiles (excited at 370nm) of mono-phthalocyanine 1-In
-
6
-6
(
(
6×10 M, detected at 711nm),bis-phthalocyanine 2-In (3×10 M, detected at 707nm), and tris-phthalocyanine 3-In
-6
2×10 M, detected at 713nm) in THF
Figure 9. Optical limiting behaviours of 1-In, 2-In and 3-In with linear transmittance of 70% in THF
Table 1. Photophysical properties of monomer 1-In, dimer 2-In and trimer 3-In (excited at 370nm) in THF
Table 2. Parameters for optical limiting properties of 1-In, 2-In and 3-In in THF
1
2

CN
CN
OH
HO
NO2
CN
CN
HO
C(CH3)3
CN
CN
(a)
O
O
3mol
1mol
C(CH3)3
OH
DBU 1-pentanol
OH
(c)
(b)
O
N
(H3C)3C
O
NH
N
N
N
N
HN
C(CH3)3
O
N
O
H2Pc-OH (d)
(H3C)3C
Scheme 1. Synthetic route of the phthalocyanines H Pc-OH (d)
2
1
3

Cl
N
OH
OH
(
e)
N
N
(2 mol)
(1 mol)
Cl
Cl
C(CH3)3
C(CH3)3
RO
N
OR
OR
toluene/sodium H Pc-OH
2
(
f)
N
N
N
N
(
g)
Cl
N
Cl
Cl
toluene/sodium H2Pc-OH
PcH2
H Pc-OH toluene,sodium
2
O
N
N
RO
OR
N
OR
N
O
O
N
N
N
N
(
1-H)
H2Pc
PcH2
(
3-H)
(2-H)
O
N
O
O
PcH2
H Pc
2
PcH2
R=
O
C(CH3)3
Scheme 2. Synthetic route of mono-, bis- and tris-phthalocyanines(1-H, 2-H and 3-H)
1
4

Figure 1. Structures of mono-, bis- and tris-phthalocyanines
1
5

O
N
O
N
N
N
M
N
N
N
O
N
O
1-H: M=2H
O
N
N
N
O
O
Figure 2. MALDI-TOF spectra of 1-H
1
6

Figure 3. MALDI-TOF spectra of 2-H
1
7

Figure 4. MALDI-TOF spectra of 3-H
1
8

Figure 5. Simulated conformations of bis-phthalocyanine (2-In, left) and tris-phthalocyanine (3-In, right)
1
9

0
0
0
0
0
0
0
0
0
.8
.7
.6
.5
.4
.3
.2
.1
.0
1.4
1
1
0
0
0
.2
.0
.8
.6
.4
1
-H
2-H
-H
1
2-In
3-In
-In
3
0.2
0.0
3
00
400
500
600
700
800
300
400
500
600
700
800
Wavelength/nm
Wavelength/nm
Figure 6. UV-vis absorption of metal-free and indium phthalocyanines monomer 1, dimer 2 and trimer 3 in THF with
-6
concentration of 4×10 M
2
0

2
1
1
0 0 0 0
5 0 0 0
0 0 0 0
1.2
.0
-
6
1
x 10 M
1
-
6
5x 10 M
-
5
0.8
0.6
1
1
x 10 M
-
4
x 10 M
0.4
0.2
0.0
5
0 0 0
0
-
5
-5
-5
-5
-4
3
0 0
4 0 0
5 0 0
6 0 0
7 0 0
8 0 0
0.0 2.0x10 4.0x10 6.0x10 8.0x10 1.0x10
C / M
W av elen g th / n m
Figure 7. UV-Vis spectra of 2-H at different concentrations in THF
2
1

4
3
2
1
0
3
2
2
1
1
00
50
00
50
00
Instrument Response
-In
2-In
3-In
1
2
3
-In
-In
-In
1
5
0
0
6
50
700
750
800
850
0
10
20
Time / ns
30
40
Wavelength / nm
Figure 8. Fluorescence spectra (excited at 610nm) and decay profiles (excited at 370nm) of mono-phthalocyanine 1-In
-6
-6
-
(
6×10 M, detected at 711nm),bis-phthalocyanine 2-In (3×10 M, detected at 707nm), and tris-phthalocyanine 3-In (2×10
6
M, detected at 713nm) in THF
2
2

0
0
0
0
.6
.4
.2
.0
Tlin=70%
1
2
3
-In
-In
-In
0
10
20
30
-
2
Input Fluence /J cm
Figure 9. Optical limiting behaviours of 1-In, 2-In and 3-In with linear transmittance of 70% in THF
2
3

Table 1. Photophysical properties of monomer 1-In, dimer 2-In and trimer 3-In (excited at 370nm) in THF
Compds
λF/nm
τ1/ns
A %
τ2/ns
A %
A /A2
Ф (relative)
F
1
2
1
1
.0
1
2
3
-In
-In
-In
711
0.37
98.8
58.5
81.8
5.00
1.20
41.5
18.2
82.3
1.41
4.49
0
0
.37
.80
707
713
0.36
0.36
5.39
5.38
Note: Ф (relative) is determined as the ratio of fluorescence quantum yield of 2 and 3 to 1.
F
2
4

Table 2. Parameters for optical limiting properties of 1-In, 2-In and 3-In in THF
Compds
1-In
2.45×10
70.4%
3.47%
20.3
2-In
3-In
7.15×10
70.9%
3.75%
18.9
-4
-5
-5
C/M
6.40×10
T
Lin
69.7%
5.40%
12.9
T
Lim
NAF
2
-18
-18
-18
σ
0
/cm
2.36×10
2.27×10
9.6
9.37×10
7.58×10
8.1
8.06×10
7.68×10
9.5
T
2
-17
-17
-17
σ
ex /cm
T
ex/
σ
σ
0
8
-1
k
isc/10 s
14.7
6.61
11.0
Ф
T
0.85
0.39
0.69
-1
-1
4
4
4
∆ε
T
/M cm
3.49×10
3.27×10
3.78×10
2
5

Graphical abstract
Intramolecular aggregation and optical limiting properties of
triazine-linked mono-, bis- and tris-phthalocyanines
Jun Chen, Tao Zhang, Shuangqing Wang, Rui Hu, Shayu Li, Jin Shi Ma, Guoqiang Yang
A series of triazine-linked mono-, bis- and tris-phthalocyanines are synthesized, intramolecular aggrega-
tion is found in bis- and tris-phthalocyanines via π-π stacking interaction. Theoretical and experimental
studies reveal the formation of the intramolecular aggregation. The spectrographic, photophysical and
nonlinear optical properties of these compounds are adjusted for the formation of the intramolecular ag-
gregation. The bis-phthalocyanine dimer presents smaller fluorescence quantum yield, lower triplet
formation yield and the triplet-minus-ground state extinction coefficient, which causes poorer optical
limiting performance. It is interesting that the tris-phthalocyanine is composed of a mono-
phthalocyanine part and a bis-phthalocyanine part, the optical limiting property of the tris-
phthalocyanine is similar to that of mono-phthalocyanine.
2
6

HIGHLIGHTS
►
►
►
A series of triazine-linked mono-, bis- and tris-phthalocyanines are synthesized.
Intramolecular aggregation is found in bis- and tris-phthalocyanines via π-π stacking interaction.
The dimers cause poorer optical limiting performance for the intramolecular aggregation.
2
7