Tuning J-type dimers of non-peripherally substituted zinc tetra-4-tert-butylphenophthalocyanine

Article abstract of DOI:10.1016/j.saa.2008.04.017

It was found, by UV-vis and TOF-MS, that the head-to-tail dimers of non-peripherally substituted zinc tetra-4-tert-butylphenophthalocyanine are inclined to form in non-coordinated solvent, e.g. chloroform and especially in dilute solution under 1.25 × 10^-6 mol/mL. The aforementioned dimers in solution can be tuned by altering concentration or adding coordinated solvent, e.g. methanol, which might be further improved to a practical strategy for preparation of J-aggregates in the future.

Full text of DOI:10.1016/j.saa.2008.04.017

Spectrochimica Acta Part A 71 (2008) 1397–1401
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Tuning J-type dimers of non-peripherally substituted zinc
tetra-4-tert-butylphenophthalocyanine
Fangdi Conga,b, Jianxin Lia, Chunyu Maa, Junshan Gaob, Wenjuan Duana, Xiguang Dua,b,∗
a Faculty of Chemistry, Northeast Normal University, Renmin Road, Changchun 130024, China
b College of Material Science & Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
a r t i c l e i n f o
a b s t r a c t
Article history:
It was found, by UV–vis and TOF-MS, that the head-to-tail dimers of non-peripherally substituted zinc
tetra-4-tert-butylphenophthalocyanine are inclined to form in non-coordinated solvent, e.g. chloroform
and especially in dilute solution under 1.25 × 10−6 mol/mL. The aforementioned dimers in solution can
be tuned by altering concentration or adding coordinated solvent, e.g. methanol, which might be further
improved to a practical strategy for preparation of J-aggregates in the future.
Received 24 December 2007
Received in revised form 29 March 2008
Accepted 22 April 2008
Keywords:
Phthalocyanine
Dimer
© 2008 Elsevier B.V. All rights reserved.
J-aggregate
Equilibrium
Tuning
Spectra
1. Introduction
head-to-tail dimers of non-peripherally substituted zinc tetra-
4-tert-butylphenophthalocyanine (nsztPc) in chloroform, which
Supramolecular aggregations of phthalocyanines (Pcs), dimers
and oligomers, have attracted considerable interest for their
potential application in optoelectronic technologies such as
excitation-energy transfer, charge separation, and hole-transfer
reactions, photosynthetic light-harvesting antenna, etc. [1,2]. A
number of studies have been carried out on the preparation
and property of Pc aggregations [3], especially the structurally
various dimers formed via covalent bond linkage [2–5], dialky-
lammonium cations action [6], intermolecular coordination [1,7,8]
and the like. The head-to-tail dimers, J-type aggregates, usu-
ally showed strong optical properties, e.g. fluorescence whereas
the face-to-face dimers, H-type aggregates, did not [1,2]. The
synthesis of J-aggregates, in contrast to Pc monomers, were
generally more difficult for the rigorous requirement that Pc
substrates must synchronously have unsymmetric structures
and special coordination atoms around Pc ring or between Pc
molecules [1–8]. The ways to obtain the J-type Pc dimers via
straightforwardly intermolecular coordination of tetra-substituted
Pc compounds have not ever been found in literatures by
us to date. Herein, we present a facile protocol to tune the
might be improved to a practical strategy to prepare the J-
aggregates of Pc complexes by intermolecular coordination in the
future.
According to a well-established synthetic route to soluble
tetra-substituted Pcs via the aromatic nucleophilic substitution
reaction between 4-nitrophthalonitrile or 3-nitrophthalonitrile
and a suitable oxygen nucleophile followed by cyclotetramerisa-
tion of the resultant phthalonitrile derivatives [9–11], we prepared
several phenoxy-substituted metal Pcs to study their UV–vis spec-
tral properties. Among them, the non-peripherally substituted
zinc Pcs in non-coordinated organic solvents, e.g. chloroform
and dichloromethane displayed particular spectra, in which Q
bands split to two peaks. The Q band split may be caused by
the isomers with Cs, C2 and C2v symmetry, respectively [12,13]
(Fig. 1). But no Q band split was found for them in coordinated
organic solvent, e.g. methanol, ethanol and acetone, etc. More
importantly, to the best of our knowledge, there are no litera-
tures presently that report the Q band split caused by isomers
of peripherally or non-peripherally tetra-substituted metal Pcs.
Hence there should be other factors that caused the Q band split.
Based on the study on specially coordination-formed J-type Pc
dimers [7,8], it was concluded that there were the J-type dimers
of the above Pc compounds in chloroform, which lead to Q split.
In order to ascertain the split phenomenon, we took nsztPc as
an example to study the equilibrium between the J-type dimers
∗
Corresponding author at: Faculty of Chemistry, Northeast Normal University,
Renmin Road, Changchun 130024, China. Tel.: +86 431 8509 8720.
E-mail address: xgdu@yahoo.cn (X. Du).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.04.017

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F. Cong et al. / Spectrochimica Acta Part A 71 (2008) 1397–1401
Fig. 1. Isomers of non-peripherally substituted metal Pc.
and monomers in chloroform by altering concentration and drop-
ping methanol. The imagined structure for J-type dimers of C4
symmetric nsztPc in chloroform was given in Fig. 2. And the
possible structures of J-dimers formed via intermolecular self-
coordination of other isomers were ignored here for their low ratio
[14].
then poured into 10% NaCl solution (400 mL) and stirred till pre-
cipitate appeared. The product was collected and future purified
by flash column (petroleum ether–ethyl ether 1:1) to afford 3-
tert-butylphenophthalonitrile (9.52 g, 86%). m.p. 104–106 ◦C; 1H
NMR (500 MHz, CDCl3): ( 7.55 (dd, 1H, J = 8 Hz, ArH), 7.45 (d, 2H,
J = 9 Hz, ArH), 7.43 (d, 1H, J = 8 Hz, ArH), 7.09 (d, 1H, J = 8 Hz, ArH),
7.02 (d, 2H, J = 9 Hz, ArH), 1.34 (s, 9H, t-C4H9); TOF-MS—m/z: 299.1
[M+Na+], 314.9 [M+K+]; IR (KBr): 2231 (CN), 1276 ꢀs cm−1 (COC).
Anal. Calcd for C18 H16 N2O: C 78.2, H 5.8, N 10.1; found: C 78.5, H
5.9, N 9.8.
2. Experimental
2.1. Materials and methods
Pentan-1-ol was distilled from Na prior to use. DMSO was
predried over BaO and distilled under reduced pressure. Col-
umn chromatography purifications were preformed on silica gel.
All other reagents and solvents are commercial available and
used without further purification. Petroleum ether used had b.p.
60–90 ◦C.
2.3. The synthesis of nsztPc
3-tert-Butylphenophthalonitrile
Zn(OAc)2·2H2O (0.22 g, 1.0 mmol) were added under stirring
to pentan-1-ol (10 mL) with catalytic amount of 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU) in 25-mL one-neck
(1.04 g,
4.0 mmol)
and
a
a
High-resolution 1H NMR spectra were recorded on a Varian
Unity 500 spectrometer. IR spectra were measured on a Magna
560 FT-IR spectrometer. UV–vis spectra were taken on a Cary 500
UV–VIS–NIR spectrophotometer. MS spectra were obtained on a
Voyager-De STR MALDI-TOF-MS spectrometer. Elemental analyses
were performed on a PerkinElmer 2400 Elemental Analyzer.
round-bottomed flask equipped with an air condenser. The
mixture was stirred and heated at 135 ◦C under N2 for 24 h.
After cooling under N2, the black cyan solution was poured into
methanol, stirred and collected by vacuum filtration to afford
the crude product after dried. It was washed with methanol by
Soxhlet extraction to remove 3-tert-butylphenophthalonitrile and
other remnants. In the end, the collected solid was purified by
column chromatography with chloroform–methanol (10:1) as
the mobile phase to give pure blue-green solid nsztPc (0.64 g,
50%). m.p. >320 ◦C. 1H NMR (500 MHz, CDCl3): ı 7.31–7.39 (m,
12H, ArH), 6.86–7.03 (m, 16H, ArH), 1.29–1.35 (m, 36H, 4t-C4H9),
LDI-1700-TOF-MS—m/z: 1168.6 [M]+; IR (KBr): 1251 ꢀs cm−1 (COC);
Anal. Calcd for C72H64N8O4Zn: C 73.9, H 5.5, N 9.6; found: C 73.6,
H 5.8, N 9.4.
2.2. The synthesis of 3-tert-butylphenophthalonitrile
3-Nitrophthalonitrile (6.92 g, 40 mmol) and 4-tert-butylphenol
(6.08 g, 40 mmol) were added to 100 mL anhydrous DMSO at RT.
The reaction mixture was stirred and 4.2 g LiOH·H2O (100 mmol)
was interfused over a 2-h period and the mixture was then stirred
for 1 day. The reaction was monitored by TLC. The mixture was
Fig. 2. Imagined structure for J-type dimer of nsztPc with C4 symmetry.

F. Cong et al. / Spectrochimica Acta Part A 71 (2008) 1397–1401
1399
Fig. 4. Mass spectra of nsztPc in chloroform.
Fig. 3. The UV–vis spectra of nsztPc in chloroform.
peaks increased with concentration diluted. But above the cc, only
the Q2, B2 and S2 were immobile, whereas the Q1 702 nm, B1 334 nm
and S1 633 nm with the absorbance of monomers and J-dimers,
gradually shifted to the Q1 712 nm, B1 324 nm and S1 645 nm with
the absorbance of J-dimers along with the concentration diluted
till cc. From Fig. 3, it was obviously seen that the absorbance of
Q1 relative to Q2 decreased with concentration diluted. Namely,
the monomers gradually transform to J-dimers with concentration
diluted till cc.
3. Results and discussion
3.1. Tuning J-type nsztPc dimers by altering concentration
As a non-peripherally phenoxy-substituted metal Pc, the nsztPc
could dissolved in some non-coordinated organic solvents such as
chloroform, dichloromethane and chlorobenzene, etc., as well as
some coordinated organic solvents, e.g. methanol, ethanol, ace-
tone, DMF and DMSO, etc. In non-coordinated solvents, it showed
Q-band split phenomenon (Fig. 3), which differed from that with
the other metals and the peripherally phenoxy-substituted metal
Pcs. Based on the analysis in Section 1 the Q split might be for the
existence of J-type nsztPc dimers in non-coordinated solvent, e.g.
chloroform, which usually displayed two peaks in the region of Q-
band absorbance. In our research, it was found that the two split
peaks can be tuned by altering the concentration of znstPc in chlo-
roform (Fig. 3 and Table 1). After the concentration decreases under
a critical value 1.25 × 10−6 mol/mL (cc), the Q absorbance shows
the characters of J-type Pc dimers, which has two immobilized
split peaks Q1 (712 nm) and Q2 (744 nm), and always is the one
right higher than that left for the former from the energy-lower
␲–␲* transition [1–8]. According to the interpretation on exciton
interaction of Qx and Qy transition dipoles [1,12], here Q2 and Q1
correspond to Qx and Qy transition absorbance, respectively (Fig. 2).
Another interesting phenomenon was that the B band and shoulder
absorbance also split two peaks B1 (325 nm) and B2 (416 nm), and
S1 (645 nm) and S2 (667 nm), respectively. Moreover, the log ε of all
3.2. Understanding the forming of J-type nsztPc dimers
The dimer peak could also be directly detected by TOF-MS even
if the dimers were prone to decompose to monomers under detect-
ing condition (Fig. 4). And also it is found that the peak height of
charged dimer ions obviously increased with concentration diluted.
The phenomenon disobeyed the routine that aggregates formed at
high concentration and molecular monomers existed at low con-
centration. The possible reasons that caused J-type nsztPc dimers
to be incline to form at low concentration might be ascribed to two
intermolecular actions: the non-polar action from Pc rings with
18-␲ electron conjugated systems and the polar action from coor-
dination between phenoxy-oxygen atom around one Pc ring and
zinc atom in the center of another Pc ring. As we all knew that
the former was so strong as to cause Pc compounds being insolu-
ble in common organic solvents if no suitable substituents around
Pc ring [9–11]. And the latter was so weak as to be hard found
Table 1
Parameters on UV–vis spectra of nsztPc in chloroform under different concentration
a
␭
(nm)/log ε
Cb
a
b
c
d
e
f
g
h
i
Q1
Q2
702, 5.45
744, 4.79
704, 5.31
744, 5.16
711, 5.17
744, 5.33
712, 5.17
744, 5.36
712, 5.20
744, 5.39
712, 5.25
744, 5.44
712, 5.36
744, 5.50
712, 5.51
744, 5.61
712, 5.69
744, 5.77
B1
B2
334, 4.93
416, 4.57
332, 4.90
416, 4.62
327, 4.86
416, 4.70
325, 4.88
416, 4.75
325, 4.93
416, 4.81
325, 5.04
416, 4.95
325, 5.20
416, 5.13
325, 5.36
416, 5.31
325, 5.55
416, 5.52
S1
S2
633, 4.72
667, 4.74
638, 4.64
667, 4.75
644, 4.69
667, 4.77
645, 4.75
667, 4.81
645, 4.82
667, 4.88
645, 4.98
667, 5.01
645, 5.15
667, 5.17
645, 5.39
–, –c
645, 5.64
–, –
a
Taken on a Cary-500 UV–vis spectrophotometer.
b
c
(a–i) represent 1.0 × 10−5, 5.0 × 10−6, 2.5 × 10−6, 1.25 × 10−6, 6.25 × 10−7, 3.13 × 10−7, 1.56 × 10−7, 7.81 × 10−8 and 3.91 × 10−8 mol/L, respectively.
The peak is not clear.

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F. Cong et al. / Spectrochimica Acta Part A 71 (2008) 1397–1401
Fig. 6. The UV–vis spectra of solution (1.3 × 10−6 mol/L, nsztPc in CHCl3) with 0, 5,
Fig. 5. The UV–vis spectrum of solid nsztPc film on
a piece of quartz glass
10, 15, 20 and 25 drops of CH3OH, respectively).
(10 mm × 10 mm × 0.2 mm), prepared by immerging the glass into 30 mL solution
(1.3 × 10−6 mol/L, nsztPc in CHCl3) in a 50-mL beaker, and enveloping mouth with
filter paper and setting for 3 days.
coordinate with zinc in the center of Pc ring and then decompound
the J-dimers to monomers. The S1 of monomers, like the shoulder
peaks of many other Pc complexes, is ascribed to the absorbance of
n–␲* transition associated with the aza nitrogen lone pairs [15–18],
which has been testified by the disappearance of the S1 after proto-
nation of aza nitrogen [19]. However, the S2 does not give obvious
difference during the course of methanol being dropped in solu-
tion, which needs further investigation. In addition, it seems that
no absorbance of H-type dimers in the above liquid-phase UV–vis
spectra because it should appears between the said S1 (630 nm)
and S2 (667 nm) of monomers according to the previous reports
[20–25], which is proved by the UV–vis spectrum of nsztPc in solid.
H-type dimer and monomer absorbance of nsztPc were at 650 nm
and 700 nm, respectively (Fig. 5).
in coordinated solvents. In terms of nsztPc in chloroform, at high
concentration, the strongly non-polar action covered the weakly
polar action, and easily caused nsztPc molecules to form H-dimers,
instead of J-dimers, after chloroform volatilizing (Fig. 5). Whereas,
at low concentration, the abundant chloroform molecules caused
the intermolecular distances of nsztPcs to increase and weaken the
non-polar action. In the circumstance, the zinc atom in the center
of Pc ring and the phenoxy-oxygen atom around Pc ring just liked
the positive charge and the negative charge to attract each other.
Namely, the coordinated action unfolded and caused the J-dimers
to form. However, the aforementioned understanding to the uncon-
ventional phenomenon was not perfect and needed further studied
by us.
As for as the peripherally phenoxy-substituted metal Pcs, it was
considered by us that the substituents of them could rotate freely
and then disturbed the coordination between phenoxy-oxygen
atom and metal in Pc ring. So no Q-band split phenomenon were
found for them. In another way, the zinc in Pc ring relative to the
other metals was prone to coordinate with oxygen or nitrogen
[1–8]. In our research, the non-peripherally phenoxy-substituted
Pcs with other metals also did not show the Q-band split. The result
was that only the non-peripherally phenoxy-substituted zinc Pcs,
e.g. nsztPc displayed Q-band split phenomenon because their sub-
stituents could not rotate freely due to the steric hindrance from Pc
ring.
4. Conclusion
In summary, J-dimers of nsztPc have a dynamic equilibrium
with its monomers in chloroform and are almost unique bellow
1.25 × 10−6 mol/mL, which can be verified by altering concentration
or dropping methanol. Namely, the preparation of J-type dimers
of Pc like nsztPc must be carried out in dilute solution with non-
coordinated organic liquid as solvent, for example by the way
treating the dilute solution with lyophilization.
Acknowledgements
Authors thank the National Science Foundation of China (NSFC
20472014), the National Science Foundation of China (NSFC
E030905-90505008), the Jiangsu Province Science Foundation of
China (JSSFC BK2005126) and the 41st Postdoctoral Science Foun-
dation of China, for financial support.
3.3. Tuning J-type nsztPc dimers by coordinated solvent
The movement of equilibrium between the J-dimers and
monomers of nsztPc can further be confirmed with the effect of
some coordinated solvents, methanol or ethanol, on the UV–vis
spectra of nsztPc in chloroform. With methanol continuously
dropped into the solution, all peaks changes except for S2. The Q2
as well as B2 decreases obviously and disappears finally, and con-
trarily the Q1 and B1 not only increase but also shift blue to 700 nm
and shift red to 334 nm, respectively, and again the S1 increases and
shifts blue to 630 nm. In the end, the UV–vis spectrum of J-dimers
is converted to that of monomers with one Q band and one B band
(Fig. 6). In other words, the methanol as a coordination reagent
has an oxygen atom to replace the tert-butylpheno-oxygen atom to
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