Processable Cross-Linked Polymers for Nonlinear Optical Applications
- PDF / 277,744 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 51 Downloads / 198 Views
ABSTRACT Novel difunctional barbituric acid methine dyes have been synthesized for nonlinear optical applications. These molecules have been reacted with multi-functional isocyanates resulting in cross-linked polyurethanes. The thermal stability of the dye in crystalline form as well as dissolved in poly(methylmethacrylate) was studied. Results suggest that although the dye crystals were thermally stable to 300 o(, when dissolved in a polymer the stability was markedly lower.
INTRODUCTION Many researchers have focused on organic materials for nonlinear optical (NLO) applications because the inherent delocalization and intramolecular charge-transfer gives rise to large and fast non-linear optical responses. 1 Polymers may offer advantages over crystalline materials in the area of device fabrication due to properties such as processability, toughness, and chemical resistance. 2 In such systems, however, dipolar orientation and thermal stability at elevated temperatures for extended periods of time are emerging as critical issues for use in devices. Barbituric acids and barbituric acid methine dyes have been examined for NLO activity. 3 ,4,5, 6 Kondo used differential thermogravimetric analysis (DTA) to study the thermal stability of barbituric acid methine dyes and attributed the high thermal stability to crystal packing based on hydrogen bonding. 7 Although germane to the issue of polymeric device feasibility, there has been little discussion on thermal 637 Mat. Res. Soc. Symp. Proc. Vol. 328. @1994 Materials Research Society
stability of the barbituric acid methine dyes as components within a 8 polymer system. In the present paper we report the synthesis of several novel barbituric acid dyes for NLO applications. We have also compared thermal stability of these dyes in crystalline form, using thermogravimetric analysis (TGA) and UV-Vis spectroscopy, with stability when dissolved in films of poly(methylmethacrylate). These molecules were reacted with multi-functional isocyanates and poled to yield cross-linked NLO-active polyurethanes.
DISCUSSION Semi-empirical 9 and ab initio quantum mechanics 10 were used to predict the magnitude of g and J0for the designed barbituric acid methine dyes. The dyes displaying the larger calculated ip3 values were synthesized (table I). For the purpose of discussion, 1-(4-nitrophenyl)3-(2"-hydroxy-ethyl)-5-[4"'-N-ethyl-N-2""-hydroxyethyl)aminobenzylidene]barbituric acid, (NPBA, fig. 1) will be highlighted. OH
0
R_ NN
R
=
N-
CH2 CH
0
R'= CICHOH, R"
CI-WH(OH)CII R" = Ph-NQ
Figure 1. NPBA Our synthesis of NPBA yielded both E and Z isomers in a 1:1 ratio as determined from NMR. The g43 value measured from EFISH experiments was 9 times larger than the go13 measured for p-nitroaniline (gPpNA), considerably lower than the predicted value of 13 x (PIgpNA). The calculations were repeated using the NMR isomeric ratio and a good agreement was observed between experiment and calculated values as shown in table I. Calculated values in the table, therefore represent an upper limit as
Data Loading...
