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Syntheses, electrical and nonlinear optical properties of PPV derivatives containing alkoxynitrostilbene group
SyntheticMetals 71 (1995) 1719-1720
ELSEVIER
Syntheses, electrical and nonlinear optical properties of PPV derivatives containing alkoxynitrostilbene group Ki-Jeong Moon, Kwang-Sup Lee’ and Hong-Ku Shim’ *Dept. of Chemistry, Korea Advanced Institute of Science and Technology, Taejon 305-701, Korea ‘Dept. of Macromolecular Science, Han Nam University, Taejon 300-791, Korea Abstract Poly[2-(~4-[2-(4-nitrophenyl)vinyl]pheno~~pro~~)phenylene~ylene], poly(NO2STPV), containing nonlinear optical chromophore and its copolymers with PPV were prepared through the Wessli&s precurso r method. These polymers were characterized by using UV-visible and FT-IR sp” troscopy . The electrical conductivities of FeCkdoped poly (NO2!XPV) and its copolymer films were in range of 1O5- 10 S/cm. The copolymer films were readily drawn upto draw ratio of 4.8- 6.4, and their conductivities were - 10s2 S/cm. The third order nonlinear optical susceptibility, xt3’, was measured by using degenerate four-wave mixing(DFWM) technique at 602 run. The measured xc3’value of poly(NO2STPV) was 1.7 x 10 -loesu. 1. INTRODUCTION There has been considerable interest in organic nonlinear optical materials because of their potential application in integrated electrooptical devices.’ Though many secondorder NLO polymers have been developed, their temporal stability after poling has been one of the major problems to be improved for practical applications. Electra-optic responses of the poled polymers decay slowly at elevated temperature because of the relaxation of the dipole alignment induced by electric field. One approach is using very rigid polymersastheb&bone toimpmvethethermalandtempo~ stability.2 PPV derivatives can be used as good materials for thermally stable NLO device applicationsbecause they have highly rigid backbone structure and good thermal
stability up to 300°C. Attaching donor and acceptor groups or NLO chromophores to PPV as either side chaii or directly to the polymer backbone may result in highly stable materials. It was demonstmted that the second-order nonlinear optical properties of poly(2-cyano-5-methoxy-1,4-phenylene vinylene) (PCMPV) and copolymers with PPV were stable up to 100°C when the materials were poled during elimination3 In this article, we report the syntheses and characterizations of new PPV derivatives containing a second-order NLO active pendant group. 2. EXPERIMENTAL
SSDI
0379-6779(94)03020-7
Scheme I
o(cuso~
PHOP~CHO/KOH en, OMF
CH, O(‘WbO
2
The overall pathway of preparation for the bissulfonium salt monomer and the homopolymer outlined in Scheme I, 2,ldimethylphenol was alkylated by the reaction of 3chloropropanol in basic condition. The compound 1 treated with methanesulfonyl chloride produced the mesylated compound 2. The subsequent substitution reaction of the with p-hydroxybenzaldehyde afforded mmpound2 compound 3. In this reaction, mechanical stirring improved By the reaction of diethyl pthe product yield. nitrobenzylphosponate carbanion with aldehyde group of compound3 was obtained compound 4. The bisbromomethyl compound5 was prepared by radical reaction with Nbromosuccinimide. The sulfonium salt monomer 6 was obtained by reacting compound 5 with excess 0379-6779/95/$09.50
tetrahydrothiophene for 5 h in dimethylformamide@. The monomer sulfonium salt in water/DMF cosolvent was polymerized by addition of a 1.0 N NaOH solution at 0 “C. A homogeneous and viscous solution was obtained. For the copolymers, the total moles of the two monomers were kept constant, but their mole ratios were varied. The reaction was quenched by adding of excess acetone. The precipitated precumor polymer redissolved in DMF. The films cast from r polymer solutions were subjected to thermal the=Pr== eliminationin vacua (10q2Torr)at 210 “C for 10 h to tmr&orm them into the final polyconjugated polymer films (thickness lo-20 um). If desired, the precursor polymer films were uniaxially stretched in the temperature range of 110-120 “C using a zone heating apparatus.
0
1995 Elsevier
Science
S.A. All rights reserved
3
6
A
CHO
1720
K.-J. Moon et al. I Synthetic Metals
Table 1. Electrical conductivities
and xt3) value of polymers PV : N02STPV
Polymers’
71 (1995) 1719-1720
in feed (actual)
Draw ratio (ULO)
Conductivity (S/cm) FeC13 doped
poly( N02STPV)
0:100(0:100)
1
8.4x1 0 -4
62-poly( PV-co-N02STPV)
50:50(38:62)
1
3.9x1 0 -3
4.8
2.9x1 0 -2
1
4.5x1 0 3
6.4
7.3x10 -2
65:35(47:53)
53-poly( PV-co-N02STPV)
a. The numerical value
xt3)(esu)
1.7x1 0 -I0
-
for mol % of N02STPV units
3. RESULTS AND DISCUSSION
3.2.
3.1. Characterization of Monomer and Polymers
Table 1 shows draw ratios and the maximum conductivity values of FeCls-doped poly(NO2STPV) and copolymers. The electrical conductivity of the poly(NO2STPV) was 8.4 x 18 ’ S/cm and the copolymer films showed the conductivity values of _ 10 _3 S/cm. The precursor homopolymer of poly(NO2STPV) could not be stretched because of its brittleness.On the contrary, the precursor films of copolymers were stretchable to the draw ratio of 4.8-6.4. The drawn copolymer films showed the enhanced conductivity values of -10 _* S/cm . It is originally expected that the presence of the strong electrondonating group decreases the oxidation potential of the polymer chain resulting in increased dopability and conductivity. However, the conductivity values of poly(NO2STPV) and its copolymers were not high. This result can be explained by the bulkyness of substituent disturbii x-conjugation Third-order nonlinear optical susceptibility of homopolymer, poly(NO2 STPV ), x0) (-0; w,w,--o), was evaluatedby comparing the strength of the conjugated DFWM signal with that of THF at the same incident photon flux. The measured xt3)value for poly(NO2STPV) was 1.7 x 10 ‘O esu . This value is slightly smaller than that of PPV, 4.8~10’~ esuat682nmreportedbySiietal.4
The FT-IR spectra of the poly(N02STPV) and its copolymers are compared with those of corresponding precursor polymer films. A weak but sharp absorption of precursor polymer at 962 cm-’is due to the trans vinylene -C-H out-of-plane bending mode of stilbene double bond. The absorption intensity at this position is increased after elimination, suggesting that the generated double bonds in the main chain are also entirely of trans configuration. Very strong absorptions at 1510 cm-’ and 1335 cm-’ due to asymmetric and symmetric stretching vibration of nitro group, respectively, are not changed after elimination of precursor polymers.
Electrical conductivities properties of polymers
and
3rd-order
NLO
The evaluation of the 2nd-order NLO properties for the polymers are in progress. The authors wish to express their Acknowledgement. appreciation to Prof. P. N. Pmsad for DFWM measurements. 300
400
500
600
700
wavelength
Figure 1. W-visible spectra of polymers and their monomer
Figure 1 shows the UV-visible spectra of poly(NO2STPV), its monomer and two copolymers. Both of poly(NO2STPV) and its monomer show the strong x-x* transition of trans stilbene moiety at about 383nm. However, the absorption maximum was not changed and the absorbance in longer wavelength range was increased about twice in the case of homopoymer compared with that of the monomer due to conjugated polymer backbones. The LTV-visiblespectra of the copolymers showed very similar patterns.
REFERENCES 1. S.R. Marder, J.E. Sohn, and G.D. Stucky(eds), Materials for Nonlinear Optics, ACS symposium series, 455 Washington, lX,1991. 2. Z. Peng and L. Yu, Macromolecules, 27(1994) 2638. 3. J.-J. Kim, D.-H. Hwang, S.-W. Kang and H.-K. Shim, Mat. Res. Sot. Symp. Proc., 277(1992) 229. 4. B.P. Sigh, P.N. Pmsad and F.E. Karasz, Polymer, 29(1988) 1940.
ELSEVIER
Syntheses, electrical and nonlinear optical properties of PPV derivatives containing alkoxynitrostilbene group Ki-Jeong Moon, Kwang-Sup Lee’ and Hong-Ku Shim’ *Dept. of Chemistry, Korea Advanced Institute of Science and Technology, Taejon 305-701, Korea ‘Dept. of Macromolecular Science, Han Nam University, Taejon 300-791, Korea Abstract Poly[2-(~4-[2-(4-nitrophenyl)vinyl]pheno~~pro~~)phenylene~ylene], poly(NO2STPV), containing nonlinear optical chromophore and its copolymers with PPV were prepared through the Wessli&s precurso r method. These polymers were characterized by using UV-visible and FT-IR sp” troscopy . The electrical conductivities of FeCkdoped poly (NO2!XPV) and its copolymer films were in range of 1O5- 10 S/cm. The copolymer films were readily drawn upto draw ratio of 4.8- 6.4, and their conductivities were - 10s2 S/cm. The third order nonlinear optical susceptibility, xt3’, was measured by using degenerate four-wave mixing(DFWM) technique at 602 run. The measured xc3’value of poly(NO2STPV) was 1.7 x 10 -loesu. 1. INTRODUCTION There has been considerable interest in organic nonlinear optical materials because of their potential application in integrated electrooptical devices.’ Though many secondorder NLO polymers have been developed, their temporal stability after poling has been one of the major problems to be improved for practical applications. Electra-optic responses of the poled polymers decay slowly at elevated temperature because of the relaxation of the dipole alignment induced by electric field. One approach is using very rigid polymersastheb&bone toimpmvethethermalandtempo~ stability.2 PPV derivatives can be used as good materials for thermally stable NLO device applicationsbecause they have highly rigid backbone structure and good thermal
stability up to 300°C. Attaching donor and acceptor groups or NLO chromophores to PPV as either side chaii or directly to the polymer backbone may result in highly stable materials. It was demonstmted that the second-order nonlinear optical properties of poly(2-cyano-5-methoxy-1,4-phenylene vinylene) (PCMPV) and copolymers with PPV were stable up to 100°C when the materials were poled during elimination3 In this article, we report the syntheses and characterizations of new PPV derivatives containing a second-order NLO active pendant group. 2. EXPERIMENTAL
SSDI
0379-6779(94)03020-7
Scheme I
o(cuso~
PHOP~CHO/KOH en, OMF
CH, O(‘WbO
2
The overall pathway of preparation for the bissulfonium salt monomer and the homopolymer outlined in Scheme I, 2,ldimethylphenol was alkylated by the reaction of 3chloropropanol in basic condition. The compound 1 treated with methanesulfonyl chloride produced the mesylated compound 2. The subsequent substitution reaction of the with p-hydroxybenzaldehyde afforded mmpound2 compound 3. In this reaction, mechanical stirring improved By the reaction of diethyl pthe product yield. nitrobenzylphosponate carbanion with aldehyde group of compound3 was obtained compound 4. The bisbromomethyl compound5 was prepared by radical reaction with Nbromosuccinimide. The sulfonium salt monomer 6 was obtained by reacting compound 5 with excess 0379-6779/95/$09.50
tetrahydrothiophene for 5 h in dimethylformamide@. The monomer sulfonium salt in water/DMF cosolvent was polymerized by addition of a 1.0 N NaOH solution at 0 “C. A homogeneous and viscous solution was obtained. For the copolymers, the total moles of the two monomers were kept constant, but their mole ratios were varied. The reaction was quenched by adding of excess acetone. The precipitated precumor polymer redissolved in DMF. The films cast from r polymer solutions were subjected to thermal the=Pr== eliminationin vacua (10q2Torr)at 210 “C for 10 h to tmr&orm them into the final polyconjugated polymer films (thickness lo-20 um). If desired, the precursor polymer films were uniaxially stretched in the temperature range of 110-120 “C using a zone heating apparatus.
0
1995 Elsevier
Science
S.A. All rights reserved
3
6
A
CHO
1720
K.-J. Moon et al. I Synthetic Metals
Table 1. Electrical conductivities
and xt3) value of polymers PV : N02STPV
Polymers’
71 (1995) 1719-1720
in feed (actual)
Draw ratio (ULO)
Conductivity (S/cm) FeC13 doped
poly( N02STPV)
0:100(0:100)
1
8.4x1 0 -4
62-poly( PV-co-N02STPV)
50:50(38:62)
1
3.9x1 0 -3
4.8
2.9x1 0 -2
1
4.5x1 0 3
6.4
7.3x10 -2
65:35(47:53)
53-poly( PV-co-N02STPV)
a. The numerical value
xt3)(esu)
1.7x1 0 -I0
-
for mol % of N02STPV units
3. RESULTS AND DISCUSSION
3.2.
3.1. Characterization of Monomer and Polymers
Table 1 shows draw ratios and the maximum conductivity values of FeCls-doped poly(NO2STPV) and copolymers. The electrical conductivity of the poly(NO2STPV) was 8.4 x 18 ’ S/cm and the copolymer films showed the conductivity values of _ 10 _3 S/cm. The precursor homopolymer of poly(NO2STPV) could not be stretched because of its brittleness.On the contrary, the precursor films of copolymers were stretchable to the draw ratio of 4.8-6.4. The drawn copolymer films showed the enhanced conductivity values of -10 _* S/cm . It is originally expected that the presence of the strong electrondonating group decreases the oxidation potential of the polymer chain resulting in increased dopability and conductivity. However, the conductivity values of poly(NO2STPV) and its copolymers were not high. This result can be explained by the bulkyness of substituent disturbii x-conjugation Third-order nonlinear optical susceptibility of homopolymer, poly(NO2 STPV ), x0) (-0; w,w,--o), was evaluatedby comparing the strength of the conjugated DFWM signal with that of THF at the same incident photon flux. The measured xt3)value for poly(NO2STPV) was 1.7 x 10 ‘O esu . This value is slightly smaller than that of PPV, 4.8~10’~ esuat682nmreportedbySiietal.4
The FT-IR spectra of the poly(N02STPV) and its copolymers are compared with those of corresponding precursor polymer films. A weak but sharp absorption of precursor polymer at 962 cm-’is due to the trans vinylene -C-H out-of-plane bending mode of stilbene double bond. The absorption intensity at this position is increased after elimination, suggesting that the generated double bonds in the main chain are also entirely of trans configuration. Very strong absorptions at 1510 cm-’ and 1335 cm-’ due to asymmetric and symmetric stretching vibration of nitro group, respectively, are not changed after elimination of precursor polymers.
Electrical conductivities properties of polymers
and
3rd-order
NLO
The evaluation of the 2nd-order NLO properties for the polymers are in progress. The authors wish to express their Acknowledgement. appreciation to Prof. P. N. Pmsad for DFWM measurements. 300
400
500
600
700
wavelength
Figure 1. W-visible spectra of polymers and their monomer
Figure 1 shows the UV-visible spectra of poly(NO2STPV), its monomer and two copolymers. Both of poly(NO2STPV) and its monomer show the strong x-x* transition of trans stilbene moiety at about 383nm. However, the absorption maximum was not changed and the absorbance in longer wavelength range was increased about twice in the case of homopoymer compared with that of the monomer due to conjugated polymer backbones. The LTV-visiblespectra of the copolymers showed very similar patterns.
REFERENCES 1. S.R. Marder, J.E. Sohn, and G.D. Stucky(eds), Materials for Nonlinear Optics, ACS symposium series, 455 Washington, lX,1991. 2. Z. Peng and L. Yu, Macromolecules, 27(1994) 2638. 3. J.-J. Kim, D.-H. Hwang, S.-W. Kang and H.-K. Shim, Mat. Res. Sot. Symp. Proc., 277(1992) 229. 4. B.P. Sigh, P.N. Pmsad and F.E. Karasz, Polymer, 29(1988) 1940.