Chem. Mater. 1995, 7, 596-598
596
Modular High-T, Second-Order Polymeric Nonlinear Optical Materials. Polyfunctional Epoxide and Diisocyanate Cross-Linked Chromophoric Polyhydroxystyrenes
Scheme 1. Synthesis of
(S)-( +)-N-[p-(4-Nitrostyl)phenyllprolinol &OHN
KzCO,. DMSO
+
I
H
CHO
CHO
Eric T. Crumpler, Jennifer L. Reznichenko, Dequan Li, and Tobin J. Marks*
Department of Chemistry and The Materials Research Center Northwestern University Evanston, Illinois 60208-3113 Weiping Lin, Paul M. Lundquist, and George K. Wong
Department of Physics and Astronomy and The Materials Research Center Northwestern University, Evanston, Illinois 60208 Received November 23, 1994 Revised Manuscript Received February 14, 1995 Key goals in the pursuit of device-applicable poled second-order polymeric NLO materials1 include (i) maximizing chromophore number density, (ii)maximizing and understanding isolated and matrix-bound chromophore second-order response, (iii) maximizing the temporal stability of poling-imposed chromophore/ matrix acentricity, and (iv) maximizing chromophore/ matrix thermdoxidative stability. Considerable progress is being made in all of these areas, with (i) best addressed by covalently appending chromophore moieties to the polymer backbone2 and (ii)by a combination of exploratory synthesis3 and quantum chemical analyIssue (iii) presents a significant challenge to our current understanding of glassy polymer chain dynamics and appears best addressed by strategies which and/or backbone design.2j,6 elevate Tgvia cros~-linking2h~~,5 Issue (iv) has only recently been empha~ized.~ Our approach to goals (iii) and (iv) focuses on modular chromophore cross-linker systems which matrix
+
+
(1) (a) Burland, D. M.; Miller, R. D.; Walsh, C. A. Chem. Reu. 1994, 94, 31-75 and references therein. (b) Marks, T. J.; Ratner, M. A. Angew. Chem., Int. Ed. Engl. 1995,34,155-173and references therein. (2)(a) Ye, C.; Marks, T. J.; Yang, J.;Wong, G. K. Macromolecules 1987,20,2322-2324. (b) Ye, C.; Minami, N.; Marks, T. J.; Yang, J.; 2899-2901. (c) Singer, K.D.; Wong, G. K. Macromolecules 1988,21, Kuzyk, M. G.; Holland, W. R.; Sohn, J. E.; Lalama, S. J.; Commizzoli, R. B.; Katz, H. E.; Schilling, M. L. Appl. Phys. Lett. 1988,53,18001802.(d) Eich, M.; Sen, A,; Looser, H.; BjorMund, G. C.; Swalen, J. D.; Twieg, R.; Yoon, D. Y. J . Appl. Phys. 1989,66, 2559-2567. (e) Jungbauer, D.; Terakoka, I.; Yoon, D. Y .; Reck, B.; Swalen, J. D.; Twieg, R.; Willson, C. G. J . Appl. Phys. 1991,69, 8011-8017. (0 Mortazavi, M. A.; Knoesen, A.; Kowel, S. T.; Henry, R. A.; Hoover, J. M.; Lindsay, G. A. Appl. Phys. B , 1991,287-295. (g) Lindsay, G. A.; Henry, R. A.; Hoover, J . M.; Knoesen, A.; Mortazavi, M. A. Macromolecules, 1992, 25,4888-4894. (h) Xu, C.; Wu, B.; Todorova, 0.; Dalton, L. R.; Shi, Y.; Ranon, P.; Steier, W. H. Macromolecules 1993,26,5303-5309and references therein. (i) Yu, L.; Chan, W.; Dikshit, S.; Bao, Z.; Shi, Y.; Steier, W. H. Appl. Phys. Lett. 1992,60, 1655-1657. (i) Peng, Z.; Yu, L. Macromolecules 1994,27,2638-2640. (k) Wang, H.; Jarnagin, R. C.; Samuelski, E. T. Macromolecules 1994,27,4705-4713. (3)(a) Gilmour, S.;Montgomery, R. A,; Marder, S. R.; Cheng, L.T.; Jen, A. K.-Y.; Yoming, C.; Perry, J. W.; Dalton, L. R. Chem. Muter. 1994,6,1603-1604and references therein. (b) Rao, V. P.; Jen, A. K.Y.; Wong, K. Y.; Drost, K. J. J . Chem. Soc., Chem. Commun. 1993, 1118-1119 and references therein. (4)Kanis, D. R.; Ratner, M. A,; Marks, T. J . I n ref l a , pp 195-242 and references therein.
0897-475619512807-0596$09.00/0
H
CHO
-
I-
offer fundamental probes of structure/processing relationships and employ interchangeable components which can individually evolve with the state of the art. In this regard, the hctionalizability, processability, and favorable thermavchain dynamic/oxidative characteristics (Tg= 155-188 "C; Td = 392 "C; Td = onset temperature of the thermal decomposition exotherm) of poly(phydroxystyrene) (PHSP render it an excellent scaffold with which to evaluate polymer-chromophore functionalization relationships,2b relaxation dynamic^,^ and cross-linking architecture.1° These results lead us to the current investigation of PHS functionalized with a prototypical7 high$ chromophore and cross-linked with reagents anticipated to afford very high Tgmatrices.ll The model donor-acceptor substituted stilbene chroD cm5/esu mophore (SI-(+)-NSP@/3$ = 480 x (0.65 eV), 1050 x D cm5/esu (1.17 eV))12was ( 5 ) (a)Hubbard, M. A.; Minami, N.; Ye, C.; Marks, T. J.; Wong, G. K. SPIE Proc. 1988,971,136-143. (b) Hubbard, M. A.; Marks, T. J.; Yang, J.; Wong, G. K. Chem. Mater. 1989,1,167-169.(c) Jungbauer, D.; Reck, B.; Tweig, R.; Yoon, D. Y.; Willson, C. G.; Swalen, J . D. Appl. Phys. Lett. 1990,56,2610-2612.(d) Jeng, R. J.; Chen, Y. M.; Jain, A. K.; Kumar, J.; Tripathy, S. K. Chem. Mater. 1992,4,1141-1144. (6)(a) Dai, D. R.; Marks, T. J.; Yang, J.; Lundquist, P. M.; Wong, G. K. Macromolecules 1990,23,1891-1894. (b) Hayashi, A.; Goto, Y.; Nakayama, M. Chem. Mater. 1991,3,6-8. (c) Robello, D. R.; Dao, P. T.; Phelan, J.; Revelli, J.; Schildkraut, J. S.; Scozzafava, M.; Ulman, A,; Willand, C. S. Chem. Mater. 1992,4 , 425-435. (d) Hubbard, M. A.; Marks, T. J.; Lin, W.; Wong, G. K. Chem. Mater. 1992,4, 965968. (7)(a) Moylan, C. R.; Twieg, R. J.; Lee, V. Y.; Swanson, S. A.; Betterton, K. M.; Miller, R. D. J . Am. Chem. SOC.1993,115,1259912600 and references therein. (bj Moylan, C. R.; Swanson, S. A.; Walsh, C. A.; Thackara, J . I.; Twieg, R. J.; Miller, R. D.; Lee, V. Y. SPIE Proc. 1993,2025,192-201. (8)(a) Brown, W. E. I n Handbook of Plastic Materials and Technology; Rubin, I. I., Ed.; John Wiley & Sons: New York, 1990;pp 459485.(b) Poly(p-hydroxystyrene) Product Information Bulletin; HoechstCelanese Chemical Intermediates Division, Portsmouth, VA. (9)(a)Firestone. M. A,: Park, J.: Minami, N.: Ratner, M. A.; Marks, T. J.; Lin, W.; Wong, G. K. Macromolecules, in press. (b) Firestone, M. A,; Marks, T. J.;Ratner, M. A,; Lin, W.; Wong, G. K. Macromolecules, in press. (10)(a) Park, J.; Marks, T. J.; Yang, J.; Wong, G. K. Chem. Mater. 1990,2,229-231. (b) Jin, Y.; Cam, S. H.; Marks, T. J.; Lin, W.; Wong, G. K. Chem. Mater. 1992,4 , 963-965. (c) Wang, J.-F.; Hubbard, M. A.; Jin, Y.; Lin, J. T.; Marks, T. J.; Lin, W. P.; Wong, G. K. SPIE Proc. 1993,2025,62-68. (11) Communicated in part: Crumpler, E. T.; Li, D.; Marks, T. J.; Ratner, M. A.; Lin, W.; Wong, G. K. Abstracts, 207th National Meeting of the American Chemical Society, San Diego, CA March 13-17,1994, INOR 521. (12)Computed using the semiempirical ZINDO/SOS f ~ r m a l i s m . ~
0 1995 American Chemical Society
Chem. Mater., Vol. 7, No. 4, 1995 597
Communications Scheme 2. Synthesis of Chromophore-Functionalized Poly@-hydroxystyrenes)
I
TsCI, pyridine ROH
ROTS
ROTE
NaN(T?W2. T W
+
I
I
c)H
OH
O
300
400
500
600
700
800
Wavelength (nm)
synthesized in two straightforward steps (67% overall yield) as shown in Scheme 1 and was characterized using standard analytical techniques.13 The chiral functionality is introduced to provide additional resistance to possible centrosymmetric chromophore aggregation at high chromophore number den~ities.~* Functionalization of PHS (E, = 22 000) was carried out as shown in Scheme 2, where n = 0.42-0.81 (5268% chromophore by weight), and the resulting (5')-(+)NSP-PHS products were purified by dissolution in dry THF, precipitation with cyclohexane, and vacuum drying. Polymer characterization was by standard analfiical techniques.14 In regard to thermal properties, n = 0.81 (5')-(+)-NSP-PHS exhibits a temperature modulated DSC-determined (10 "C/min) Tg = -182 "C and a T d of -290 "C. This can be compared to T d values for (5')-(+)-NSP and PHS of -290 and -392 "C, respectively. Cross-linking experiments were carried out with the difunctional diisocyanate reagent 4,4'-diisocyanato-3,3'dimethoxybiphenyl (DIISO) and the tetrafunctional
DIISO
TPGX
tetraphenylglycidyl ether of p-xylene (TPGX), both of which are known to afford high-T, cross-linked matrices.15J6 DSC-guided curing experiments" established optimum Tgvalues ( n = 0.81; 0.14-0.18 equiv of crosslinking functionality/phenol unit) of245 and 255 "C for (SI-(+I-NSP-PHS-DIISO and (5')-(+I-NSP-PHS-TPGX, respectively. The observed Td in both cases of -290 "C closely parallels those of (5')-(+)-NSPand (5')-(+)-NSPPHS (vide infra), arguing that in this case, the cross-
Figure 1. SHG wavelength dependence of ~ ( (dark ~ 1 points) and the linear absorption spectrum (unbroken line) for a poled, cross-linked (SI-(+)-NSP-PHS-TPGX film. Note that the f 2 ) dispersion is plotted as a function of the output wavelength; thus, the 435 nm resonance in the optical spectrum corresponds to the 870 nm resonance in the x@) dispersion.
linked matrix does not significantly affect the onset of thermal decomposition (which is then predominantly chromophore centered). Thin films of (5')-(+)-NSP-PHS, (5')-(+)-NSP-PHSDIISO, and (5')-(+)-NSP-PHS-TPGX were spin cast onto ITO-coated glass substrates from filtered THF (distilled from NdK)solutions (0.2 pm syringe filter) in a class 100 laminar flow clean hood. The films were then vacuum annealed at 60 "C for 24 h. Film thicknesses were measured using a Tencor Alpha Step 200 profiler and were in the range 1.2-1.4 pm. Corona poling (+4 t o +5 kV potential) was carried out under Nz using the variable-temperature poling, in situ i l o = 1064 nm ( h w = 1.17 eV) SHG monitoring instrumentation described e l ~ e w h e r e . ~The ~ , ~poling sample temperatures were ramped in steps toward the aforementioned T, values, maintained at maximum temperature for 30 min (to allow curing and alignment), and then slowly cooled (-10 "C/min)in the field under Nz to room temperature. There is no visual evidence of sample damage under these poling conditions, and transmission optical spectra exhibit the intensity dimunition and slight blue shift of the principal NSP charge-transfer excitation (445 435 nm)12 typical of poling-aligned chromophoric matrices.18 Initial film x(2)values are 2.4 x esu (100 p d ) , 0.84 x esu (35 p d ) , and esu (36 p d ) for n = 0.81 (5')-(+)-NSP0.85 x PHS, (5')-(+)-NSP-PHS-DIISO,and (5')-(+)-NSP-PHSTPGX, respectively. The degree to which such responses are influenced by resonant effects and the degree to which they can be corrected by a simple two-
-
(15) (a) Lohse, F. Makromol. Chem., Macromol. Symp. 1987, 7, 1-16. (b) Oleinik, E. F. Adv. Polym. Sci. 1986,80, 49-99. (c) Dusek, K.Adv. Polym. Sci. 1986,78, 1-59. (d) Rozenberg, B. A. Adu. Polym. Sci. 1986,75, 113-165. (16)(a) Frisch, K. C.; Klempner, D. In Comprehensive Polymer (13)Mass spectrum: mle = 325.1,324.1,295.1,294.1,293.1,263.1, Science; Allen, G.; Bevington, J. C., Eds.; Pergamon Press: Oxford, 248.1,247.1. 'H NMR (CDCls) 6 8.17(d, J = 8.7Hz, 2 HI, 7.58(d, J = 1989;Vol. 5, Chapter 24. (b) Backus, J. C., et al. Encyclopedia of 8.7Hz, 2 H), 7.43 (d, J = 8.6Hz, 2 H), 7.18 (d, J = 16 Hz, 1 H), 6.95 Polymer Science and Engineering; Wiley: New York, 1988;Vol. 13, (d, J = 16 Hz, 1 H), 6.70(d, J = 8.6Hz, 2 H), 3.94(m, 1 HI, 3.69 (m, pp 243-303. 2 H),3.55 (t, 1 H), 3.25 (m, 1 H), 2.07 (m, 5 H). Anal. Calc for (17)(a) Wang, X.;Gillham, J. K. J . Coatings Technol. 1992,64,37ClSH2,,N203: C, 70.35;H, 6.21;N, 8.64.Found: C, 69.92;H, 6.07;N, 45.(b) Wisanrakkit, G.; Gillham, J . K. J . Coatings Technol. 1990,62, 8.34.UV-vis spectrum: ,I,,= ,= 300 nm, 435 n m (THF). 35-50. (14)Representative data for n = 0.81: 'H NMR (DMSO) 6 8.75(18)(a) Mortazavi, M. A,; Knoesen, A,; Kowel, S. T.; Higgins, B. 9.15(br), 7.9-8.2 (br), 7.55-7.8(br), 6.7-7.0(br), 3.32(d). Anal. Calc G.; Dienes, A. J . Opt. SOC.A m . B 1989,6,733-741. (b) Page, R. H.; Jurich, M. C.; Reck, B.; Sen, A.; Twieg, R. J.; Swalen, J. D.; Bjorklund, for (CsHsO)o.is(Cz~H2~0~N~)o.ai: C, 76.28;H, 6.18;N, 6.16.Found: C, 75.59;H, 6.44;N, 6.16. G. C.; Willson, C. G. J. Opt. SOC.Am. B 1990,7, 1239-1250.
Communications
598 Chem. Mater., Vol. 7, No. 4, 1995
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400
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I200
1600
2000
Time (hours)
0.8
-
--3
0.6
-
-x
0.4 -
o^
!!
1
2x N
0.2
1
0.0
0
200
400
600
800
Time (hours)
I.Oil*
--f
02-
-5-
0.6 -
-X
0.4-
N
-X N
* * .*
*.a
.
e.
.. ;.
1000
for LO = 840-1440 nm with the optical parametric amplification instrumentation described e1se~here.l~ It can be seen in Figure 1 that the x(2' response closely tracks the linear optical response arising from the NSP charge-transfer excitation (verifying the mechanism of the response) with the ~ ( maximum ~ 1 (on resonance) approaching -2.0 x esu (83 pm/V) and falling to -0.28 x esu (12 pm/V) at 10 = 1440 nm (well off resonance). In contrast, the simple two-level mode120 1 pmN which is clearly yields a 10= 1440 nm ~ ( of~ -39 an overestimation and underscores the great value of measuring the complete frequency dependence of the second-order response. ~ ( temporal ~ 1 stability studies were carried out under air in thermostated ovens, with concurrent calibrated SHG and transmission optical spectroscopic measurements. Reproducibility in poled film SHG measurements is estimated to be f 6 % . Figure 2 compares the ~ ( temporal ~ 1 characteristics of a corona-poled un-crosslinked (SI-(+)-NSP-PHSfilm at 25 "C in air with those of the DIISO and TPGX cross-linked specimens at 100 "C in air. It can be seen that cross-linking effects a very ~ 1 stability, with significant enhancement in ~ ( temporal (SI-(+I-NSP-PHS-TPGXexhibiting 290% retention of ~ ( after ~ 1 1600 h in air (295%assuming the first several data points reflect dissipation of initially deposited charge). In accord with these SHG results, the crosslinked film optical spectra exhibit negligible changes in the 435 nm absorption intensity over the course of the decay measurements. In regard t o synthetic strategies for new classes of polymeric second-order NLO materials, this study illustrates, using a readily accessible model chromophore, the versatility and stability possible with poled, modular cross-linked PHS matrices. Although neither poling nor cross-linking processes were likely to be completely ~ 1 stability optimized, the NLO response and ~ ( temporal readily achievable with an appended donor-acceptor stilbene and a polyfunctional epoxide cross-linker are noteworthy. Insertion of other chromophore modules is presently in progress.
0.2 0.0 1
Acknowledgment. We thank the NSF-MRL Program (Grant DMR 9120521) through the Northwestern University Materials Research Center and AFOSR (Contract 93-1-0114)for support of this research. E.T.C. thanks NASA for a Minority Graduate Student Researcher Predoctoral Fellowship. CM9405234 (19) Lundquist, P. M.;Yitzchaik, S.; Zhang,T.; Kanis, D. R.; Ratner, M. A,; Marks, T.J.; Wong, S . K Appl. Phys. Lett. 1994, 64, 21942196. (20) (a) Oudar, J. L. J. C h e n . Phys. 1977,67,446-457. (b) Oudar, J. L.; Chemla, D. S. J. Chem. Phys. 1977, 66,2664-2668.
