Both of dianhydride and diamines are made to synthesize second-order nonlinear optical polyimides containing side-chained benzobisthiazole based chromophores by method of chemical cycle. Then, this study regarded high Tg and high thermal stability of polyimides as main-chain of polymers and this study regarded high dipolemoment of chromophores as side-chain of polymers Finally, combine two parts into two kind of nonlinear optical polyimides. By changing the structure of main-chain and side-chain, chromophore poled can reduce space-hinder and enhance the electrooptical coefficient r33. This study can identify functional group, the larger absorption wavelength and dissocation temperature of structure of nonlinear optical polyimides by instruments of IR, UV, TGA,¡Ketc. In the measurement of nonlinear optics, polymers owning both of larger dipoleminents and -ether group are regularly poled in characterisitc orientation. Therefore, these polymers have a higher electrooptical coefficient r33. In this results, the r33 of NLO-PIB film is 7.70 pm/V and the r33 of NLO-PIB film is 7.64 pm/V at room temperature.

In this study, we extend the rigidity and resonance of benzobisthiazole for the application as second-order nonlinear optics. A novel nonlinear optical polyimide (NLO-PI) containing side-chained benzobisthiazole- based chromophore has been synthesized. A hydroxyl- containing PI (W2) was prepared using direct thermal imidization of 4,4'-diamino-4"- hydroxytriphenylmethane(DHTM) and 4,4¡¦-(hexafluoroisopropylidene) diphthalic anhydride; the benzobisthiazole-based chromophore was then prepared using 2,5-diamino-1,4- benzenedithiol dihydrochloride as the starting monomer. The final NLO-PI was obtained by the Mitsunobu reaction via ether linkage between W2 and the chromophores. This ether linkage is expected to provide chain flexibility for better orientation under electric field during poling. The C=C bonds inside the chromophores also provide more orientation probabilities and conjugation length. Formation of benzobisthiazole-based chromophore and the corresponding NLO-PI was evidenced by FTIR and UV-vis spectra. TGA reveal a thermal decomposition temperature as high as 350oC, respectively. The electrooptic coefficient of the NLO-PI at a wavelength of 830nm was found to be r33=9.75 pm/V.

Based on a series of study to improve the electrooptic coefficient (r33) of nonlinear optical polyimides (NLO-PI) containing benzobisthiazole- based chromophores in our lab, this work concentrated on the modification of the benzobisthiazole-based chromophore VIII (r33 = 6.62 pm/V). At first, a hydroxyl-containing polyimide was first synthesized by using dianhydride and diamine as reactants via thermal imidization and the benzobisthiazole-based chromophores were synthesized by using DABDT as the starting monomer. The NLO precursors were obtained by the Mitsunobu reaction via ether linkage between PI and chromophore; it was then cured at 300¢J to result in the final NLO-PI. The benzobisthiazole-based chromophore of VIII was modified with an insertion of the ethoxy group between the NLO moiety and the main PI backbone to get the NLO-V-1. This method makes the chromophore easier to orient under the electric field during poling; thus a higher r33 (7.4 pm/V) is ensured. NLO-V-2 is another modified sample which had a phenyldiazene group inserted into the chromophore of VIII to increase the conjugated length; this results in a red shifts from 390 nm (VIII) to 484 nm in UV-abs spectrum but the r33 (5.8 pm/V) has only a slight improvement.

A computational analysis on the first hyperpolarizability (£]) of 5-6-5 heterocyclic rigid-rod benzobisthiazole-based chromophores and their derivatives has been systematically investigated in this study by the software Gaussian03, in an effort to provide a molecular design criterion for better opto-electonic properties. The specific objectives of this study have been focused on (1) understanding of 5-6-5 heterocyclic rigid-rod chromophores and other similar compounds in nonlinear optical property, (2) control on the nonlinear optical properties through the manipulation of the conjugated composition of the chromophores, (3) understanding the effect of the donor and acceptor of chromophore on the nonlinear optical property. The results show that £] value of a chromophore with its 5-6-5 heterocyclic rigid-rod structure near the acceptor is 30 % higher than the one with the same structure near the donor; this reflects a unique property of 5-6-5 heterocyclic rigid-rod structure quite different from other chromophores. In conjugated chromophores, those having double bonds or thiophenes, which have soft structures or heteroatoms, would offer higher £] values. For example, a 5-6-5 heterocyclic rigid-rod chromophore with 15 double bonds has a £] value up to 1.44 x 10-26esu. In the study of multi-donors and acceptors, from 1 donor- 1 acceptor to 2 donors- 2 acceptors, the difference in £] could be up to 116%; however, this difference reduces to only 5% if the chromophere structure becomes unstable. From the band-resolved analysis, it is found that £] values of chromophores are affected by the electronic donor via its HOMO part, the electronic acceptor via its LUMO part, while the conjugated bridge via its molecular orbital exclusive of HOMO and LUMO, depending on the type and degree of conjugation, i.e., HOMO-2 and LUMO+1 for double bonds and HOMO-2, HOMO-1, and LUMO+1 for phenyl moieties. For the 5-6-5 heterocyclic rigid-rod structure, £] value is mainly affected by those molecular orbital below HOMO, i.e., HOMO-2 for those containing double bonds. Further detailed elucidation on the relation between molecular orbital and molecular structure of chromophores can be ambiguously depicted through analyses of electronic distribution on the molecular orbital.

In this study, two series of polymers based on benzobisthiazole were synthesized. The poly(benzobisthiazoles) (PBTs) have been synthesized by the solution polycondensation of 2,5-diamino-1,4-benzenedithiol in poly(phosphoric acid)s (PPA). The diacids used were systematically varied to find the best for the solubilization of the aromatic heterocyclic rigid-rod polymers. The role of PPA is identified and the effects of phosphorous pentoxide and water on PBT during polycondensation are discussed. Polymer properties such as the inherent viscosity, decomposition temperature are correlated to systematically varied diacids. Finally, the effect of diacid architecture on the synthesis and microstructure of PBT is studied. The results are further discussed in terms of resonance, symmetry, and solubilization of the diacids. Next, we extend the rigidity and resonance of benzobisthiazole for the application as second-order nonlinear optics. Novel nonlinear optical (NLO) polyimides containing benzobisthiazole chromophores have been synthesized. The soluble polyimides containing different ratios of carboxylic acids (COOH) were first prepared and the precursors of NLO chromophores reacted with those carboxylic acids, followed by the benzobisthiazole derived chromophores synthesized at 300 oC under vaccum. The formation of benzobisthiazole was evidenced by FTIR and UV-vis spectra in combination with the analysis of model polyimides. The excellent thermal properties of those NLO polyimides were examined by TGA and TMA. PI-1 shows thermal decomposition temperature as high as 554 oC at 10 wt % loss and a Tg of 324 oC. The amorphous morphology of those polyimides was verified by XRD traces and some ordered alignments were found, due to the rigidity of the benzobisthiazole derivatize chromophores. The electrooptic coefficient of PI-1 (r33 = 5.3 pm/V) was obtained.