High E-O Coefficient Polymers Based on a Chromophore Containing Isophorone Moiety for Second-Order Nonlinear Optics
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Mat. Res. Soc. Symp. Proc. Vol. 488 ©1998 Materials Research Society
length. 5 These favorable features make this isoxazolone chromophore worthy of further exploration. However, the unsubstituted polyene segment of such chromophores render them thermally, photochemically, and chemically unstable.6 In this paper, we demonstrate the improvement of the above mentioned literature chromophore by introducing a six-membered aliphatic ring (isophorone moiety) into the polyene bridge unit. Both unfunctionalized and hydroxyl-flunctionalized chromophores have been synthesized and incorporated into PMMA composite and rigid three dimensional polyurethane thermosetting network respectively. EXPERIMENT Synthesis of Chromophores The synthesis and the chemical structures of the unfunctionalized chromophore E,E,E 1-(4-diethylaminophenyl)-1,3-(2,2-dimethylpropane-3,5-diyl)pentadien-5-ylidene 3-phenyl-5isoxazolone (denoted APII-1) and dihydroxyl-functionalized chromophore (denoted APII-2) are shown in scheme 1.7 Pure trans isomer of the key intermediate 7 was used in the last step of APII-2 synthesis, and different amount of base was used to manipulate the ratio of trans/cis isomers which has significant impact on the bulk nonlinearity. 'H and 13C spectra were taken using a Bruker-250 FT-NMR spectrometer operating at 250 MHz. Elemental analysis were performed by Atlantic Microlab Inc. FT-IR spectra were obtained using a Perkin-Elmer 1760 FTIR spectrophotometer. Absorption maxima were determined by a Perkin-Elmer Lambda-4C UV/Vis spectrophotometer. The chromophore thermostability was measured by Perkin-Elmer DSC7 at a scan rate of 5 *C/min, under nitrogen atmosphere. HPLC has been used to determine the trans/cis isomer ratio. Scheme I. Synthetic Scheme of APII HO OH
Ac>rA
AcO>rAc
HO HAc2OJ~ CO 98%L
APOC /DP 90/
)
K2CO3, H20, CH3OH
CO i
F
HO.VOH
S85%
4
CHO
HO
PNH4Ac '6 0PN 6
HOLc 60%
Pi pridine
7
M
M
M
=N
9-
EtOH 30-40%
"
APII M
~M=H, APII-I1
M=OH,APII-2 4 CHO
Synthesis of Polymers Polymer composites of this chromophore were prepared by co-dissolving with PMMA in dioxane. Loading densities were 10, 20, 25, 30, 45, 55, and 75 percent by weight. After filtered through a 0.2 Wmmicrofilter, excellent-quality thin films were spin cast onto ITOcoated glass substrates. In all cases, there was no observable phase separation, as determined by microscopy and DSC. After drying of the films in vacuo for two days, noncentrosymmetry was induced in the films by corona poling at the temperature which corresponded to the largest thermally-dependent second-harmonic signal. Electro-optic coefficients, refractive indices, and film thicknesses were determined by the attenuated total reflectance (ATR) technique at
152
1.064 ýtm.8 Film thicknesses (ca. 3 mm) were confirmed by a Sloan Dektak IIA surface 9 profilometer. Optical loss data were acquired by a dipping technique. There are two steps in the synthesis of thermosetting polyurethane (Scheme II). Anhydrous dioxane, tolylenediisocyanate (TDI), triethanolamine (TEA) were pur
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