www.elsevier.com/locate/tsfThin Solid Films 471 (2005) 96–99

Preparation of a novel class of phthalocyanine containing cross-linked

polymers and their thin films

Ling Qiua,*, Jianfeng Zhaia, Yuquan Shena, Lijun Guob, Guohong Mab, Ye Liub,Jun Mib, Shixiong Qianb

aTechnical Institute of Physics and Chemistry, Chinese Academy of Sciences, Chao Yang Qu, Da Tun Lu Jia3, Beijing 100101, PR ChinabPhysics Department, Fudan University, Shanghai 200433, China

Received 18 April 2003; received in revised form 20 February 2004; accepted 21 April 2004

Available online 1 June 2004

Abstract

Prepolymers containing vanadyl phthalocyanines, prepared by the reaction of amino-substituted vanadyl phthalocyanines and diglycidyl

ether of biphenol A, can be cured to give transparent network polymeric films, which show absorptions at 780 nm and 820 nm, respectively.

The films are stable to organic solvents, inorganic bases and acids. Ultrafast optical responses were observed for both polymers with typical

decay time of about 240 fs.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Cross-linked phthalocyanine polymer; Vanadyl phthalocyanine; Ultrafast optical Kerr effect; Third-order nonlinear optical

1. Introduction

Phthalocyanines have been widely used as dyes and

pigments due to their high thermal stability and chemical

stability. They now draw interest as materials for optical

recording media, nonlinear optical application, light ab-

sorption, electric conduction, photoconduction, energy

conversion, electrode and catalyst. Synthesis of phthalo-

cyanines able to be fabricated into thin films has received

much attention for practical reason. Phthalocyanine com-

pounds with varied substituted groups have been synthe-

sized [1]. They are soluble in organic solvent and thus

can be doped into suitable polymers to form functional

films. Soluble phthalocyanine polymers were also

reported, in which phthalocyanine or metallophthalocya-

nine ring is chemical bonded to the polymer main chains

[2] or side chains [3]. Network phthalocyanine polymers

usually possess high thermal stability [4], but they are

difficult to process due to poor solubility in organic

solvents. Here, we report a novel class of phthalocya-

nine-containing cross-linked polymers. Thin solid films

with good optical quality can be fabricated. The poly-

0040-6090/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.tsf.2004.04.034

* Corresponding author. Tel.: +86-10-64888153; fax: +86-10-

62029375.

E-mail address: chiuling@21cn.com (L. Qiu).

mers are stable to acids, bases and organic solvents.

Ultrafast optical Kerr effects (OKE) were observed from

their thin films. Their thermal stability, chemical stability

and near IR absorption characteristics make them inter-

esting materials for potential application in many research

fields.

2. Experimental details

2,9,16,23-tetraamino vanadyl phthalocyanine (1) and

1,8,15,22-tetraamino vanadyl phthalocyanine (2) were pre-

pared by the procedure described in our previous work [5].

2.1. Prepolymers 1 and 2

2,9,16,23-tetraamino vanadyl phthalocyanine (1) (0.021

g, 3.1�10� 5 mol) and diglycidyl ether of bisphenol A

(DGEBPA; 0.34 g, 1.0� 10� 3 mol) were mixed. The

mixture was stirred at 180 jC under nitrogen for 24 h.

Chloroform was added to dissolve the product. After filtra-

tion and concentration, the solid obtained was dried at 30 jCunder vacuum for 24 h to give dark purple prepolymer 1,

with yield 45% (vanadyl phthalocyanine content: 6.5 wt.%).

Prepolymer 2 can be prepared by similar procedure (vanadyl

phthalocyanine content: 1.3 wt.%).

Scheme 1. The synthetic route of the polymers. Reagents and conditions: (i)

DGEBPA, N2, 180 jC; (ii) catalyst, heating.

Fig. 1. IR spectra of prepolymers 1 and 2.

Fig. 2. Absorption spectra for (a) prepolymer 1; (b) polymer 1, obtained by

quickly curing; and (c) polymer 1, obtained by slowly curing.

L. Qiu et al. / Thin Solid Films 471 (2005) 96–99 97

2.2. Preparation and curing of the films

Twenty milligrams of prepolymer 1 or 2 and catalyst (1%

in weight) were dissolved in 1 ml of dimethylacetamide

(DMAC). Films were prepared by spin coating the solution

on glass substrates. The thickness of the films is 1–5 Am.

After drying under vacuum at 30 jC for 24 h, the films were

heated at curing temperature to give cross-linked polymer

samples.

UV/Vis spectra were taken on a Hitachi 340 UV/Vis

spectrophotometer.

In femtosecond OKE measurements, a Ti/sapphire laser

system was employed as the pulse source, and the output

pulses were centered at 800 nm with 120 fs pulse duration.

The pulse was divided into two parts by a beam splitter, and

the ratio of pump and probe intensity was set to 10:1. The

pump beam was chopped at a frequency of 1.6 kHz and

passed through a computer-controlled optical delay line,

then focused together with probe beam onto the sample. The

polarization of the probe pulse was set at 45j with respect to

that of the pump pulse, and an analyzer with orthogonal

polarization to probe beam was used to detect OKE signal.

Femtosecond pump–probe technique was employed to

measure the ultrafast dynamics of excited molecules, and

the setup arrangement was similar to that of OKE, except

that the polarization of probe beam is set parallel to that of

pump pulses, and no analyzer was in the probe path.

3. Results and discussion

The synthetic route to the network phthalocyanine-con-

taining polymers is given in Scheme I.

Tetraaminophthalocynines 1 and 2 were prepared by

reducing the corresponding tetranitro phthalocyanines. The

reaction between tetraamino phthalocyanine and DGEBPA

was carried out under a nitrogen atmosphere in order to

avoid the oxidation of amino. Prepolymers with varied

Fig. 5. IR spectra for prepolymer 2 before curing reaction (a) and after

curing reaction (b). The curing condition is 110 jC for 5 h; low molecular

weight polyamide as catalyst.

Fig. 3. Absorption spectra for (a) prepolymer 2, (b) polymer 2.

L. Qiu et al. / Thin Solid Films 471 (2005) 96–9998

content of phthalocyanine can be obtained by changing the

molar ratio of the reactants. Fig. 1 shows the IR spectra of

prepolymers 1 and 2. Amino peak was not observed in the

IR spectra of the prepolymers (around 3300–3500 cm� 1,

sharp peak), indicating all amino groups on the phthalocy-

anine ring have been reacted and converted into tertiary

amine. The absorption spectra of prepolymers 1 and 2 in the

visible and near IR region are shown in Figs. 2(a) and 3(a).

Prepolymers 1 and 2 are soluble in many organic solvents

such as acetone, chloroform, tetrahydrofuran, cyclohexane

and N,N-dimethylformamide, etc. Using these solvents,

films of prepolymers 1 and 2 can be obtained by spin

coating.

Network polymers 1 and 2 were obtained by curing

prepolymers 1 and 2 in the presence of catalyst. Figs. 4

and 5 show the IR spectra before and after curing reaction.

Formation of network structure is based on the epoxy group

exiting in the prepolymers. During the curing process,

catalyst initiated the reaction by attacking the carbon atom

of CH2 in the epoxy group, and the formed –O� attacked

another epoxy group. The characteristic peak of epoxy

group at 915 cm� 1 in the IR spectra will disappear after

curing reaction. Hence, the extent of the reaction can be

determined by monitoring this peak. Table 1 lists some

experimental conditions for the completed curing of the

prepolymers.

Fig. 4. IR spectra for prepolymer 1 before curing reaction (a) and after

curing reaction (b). The curing condition is 150 jC for 2 h; 2-Ethyl-4-

methylimidazole as catalyst.

The cross-linked polymers 1 and 2 are stable to acids and

bases, and insoluble in all kinds of organic solvents we have

tested [6].

Figs. 2(b) and 3(b) give the absorption spectra of

polymers 1 and 2 in the solid film state. The films were

prepared by quickly heating prepolymer 1 or 2 to the curing

temperature in the presence of catalyst. Either polymer 1 or

2 has two Q-bands originating from phthalocyanine unit

(maximum absorption peak) and aggregation of the cofacial

interactive phthalocyanine rings (shoulder peak with shorter

wavelength). Q-bands of both polymers 1 and 2 show small

hypsochromic shift to that of their corresponding prepoly-

mers (8 nm for polymer 1, and 4 nm for polymer 2). From

the absorption intensity of the phthalocyanine unit and

aggregation, we see that only a small amount of aggregation

exists in polymers 1 and 2. Usually, phthalocyanine com-

pounds or polymers associate easily in their solid state

because of the strong cofacial interaction between Pc

molecules. Less aggregation in polymers 1 and 2 may be

due to the restriction of cross-chains. In spite of this, we

notice that the cofacial interactions between Pc units are

strong, because the split of Q-band is as large as about 80

nm for both polymers 1 and 2.

In prepolymer 1, there is an absorption peak at about

910 nm in the near IR region, which is caused by J-

aggregation originating from dipole–dipole interaction

between Pc units [7]. It disappeared when the prepolymer

Table 1

Curing condition of the prepolymers

Prepolymer Catalyst Curing

temperature

(jC)

Curing

time

(h)

1 or 2 2-Ethyl-4-methylimidazole 150 2

1 or 2 2-Ethyl-4-methylimidazole 140 5

1 or 2 Low molecular weight

polyamide

120 2

1 or 2 Low molecular weight

polyamide

110 5

Fig. 6. OKE signals of polymer 1 and polymer 2.

L. Qiu et al. / Thin Solid Films 471 (2005) 96–99 99

was cured quickly (Figs. 2(b)). But when slowly heating

the prepolymer to the curing temperature [8], this peak can

remain (Figs. 2(c)).

The substituted position at the Pc ring also affects Q-

band. There is a 40 nm of bathochromic shift when the

substituted position is changed from 2,9,16,23-(polymer 1)

to 1,8,15,22-(polymer 2).

Because of 2-D p electron structure, Pcs have third-

order nonlinear optical properties [9,10]. Large ultrafast

OKE were observed from the films of both polymers 1 and

2 by using femtosecond laser. Fig. 6 shows OKE signals of

them. The decay time of ultrafast response is about 240 fs,

due to exiton–photon coupling of VOPc. This value is

near to the result reported by Wada et al. [11], who

observed that the decay time of ultrafast response was

hundreds of femtoseconds from a similar vanadyl phtha-

locyanine compound.

4. Conclusions

We have synthesized two cross-linked VOPc polymers

and fabricated their thin films by the curing reaction of

prepolymer in the film state. They possess good optical

quality, readily processing properties, thermal stability and

high stability to acids, bases and organic solvents. Less

aggregation occurs in the cross-linked polymers because of

restrain of the network structure. Ultrafast optical Kerr

effect, with decay time of about 240 fs, was observed for

both polymers. The network polymers are promising func-

tional materials as ultrafast optical switch, optical recording

media and other optical applications.

Acknowledgements

The authors thank the National Natural Science Founda-

tion and the National 863 Program Committee of China for

financial support.

References

[1] L. Qiu, Y.Q. Shen, H.J. Xu, J.F. Shen, X.F. Fu, Chin. J. Org. Chem.

13 (1993) 490.

[2] G.C. Bryant, M.J. Cook, Y.G. Ryan, A.J. Thorne, J. Chem. Soc.,

Chem. Commun. 4 (1995) 467.

[3] S. Makhseed, A. Cook, N.B. Mckeown, Chem. Commun. (1999)

419.

[4] D. Wohrle, U. Marose, R. Knoop, Makromol. Chem. 186 (1985)

2249.

[5] L. Qiu, J.F. Zhai, J.Y. Zhou, Y.X. Zhao, Y.Q. Shen, Chinese Patent,

CN 1320651 (2000 Nov.).

[6] The films of polymers 1 and 2 were boiled in 6 N sulfuric acid, 6 N

sodium hydroxide solution, acetone, chloroform, tetrahydrofuran,

N,N-dimethyl formamide, DMAC and cyclohexanone for half an

hour, respectively. No change was observed.

[7] M. Kasha, in: B. Dibartole (Ed.), Spectroscopy of the Excited State,

Plenum, New York, 1976. p. 345.

[8] A typical curing condition is: the prepolymer is maintained at 80 jCfor 0.5 h, 90 jC 0.5 h, 100 jC 0.5 h, 110 jC 1 h, 120 jC 1 h, 130 jC1 h, 140 jC 1 h and 150 jC 2 h with 2-Ethyl-4-methylimidazole as

catalyst.

[9] Z.Z. Ho, C.Y. Ju, W.M. Hethering III, J. Appl. Phys. 62 (1987) 716.

[10] L. Qiu, Y.Q. Shen, H.J. Xu, Z.X. Zhang, P.X. Yie, P. Yuan, Z.J. Xia,

Y.H. Zou, Acta Chimi. Sin. 55 (1997) 37.

[11] T. Wada, M. Hosoda, A.F. Garito, H. Sasabe, A.T. Erasaki, T.

Kobayashi, H. Tada, A. Koma, Proc. SPIE 1560 (1991) 162.