Design, Synthesis And Properties Of Novel Functionalized Polyacetylenes

In the past half century, there have been great improvements in the structural design, syntheses and properties of functionalized polyacetylenes (PA). They were endowed with many new properties by attaching functional pendants to the polyene backbone. Functional polyacetylenes have been widely used in material fields, especially as opto-electronic materials. This thesis mainly focuses on two topics:(1) the syntheses and sensing behavior of light-emitting polyacetylenes; (2) the syntheses and properties of second-order nonlinear optical polyacetylenes. The main content of each chapter is described as follews:Chapter 1 introduced the structures, syntheses and main catalyst systems of polyacetylenes, discussed the relationship between the property and structure, and reviewed the progress of polyacetylenes in the past decades. Also, the research projects and main contents in this thesis were outlined.In Chapter 2, a new light-emitting polyacetylene (P1) bearing imidazole moieties in the side chain was conveniently prepared through a post-functional strategy. This route avoided the problems encountered in the direct polymerization process of the corresponding monomer. P1 could selectively report the presence of Cu2+(with a detection limit of 1.48 ppm) based on the fluorescence "turn-off’. Interestingly, the quenched luminescence of P1 by Cu2+could be turned on upon the addition of CN" and a-amino acids, making P1 a novel, sensitive, and selective cyanide and a-amino acids probe. The Pl/Cu+complex demonstrated much higher sensitivity towards histidine than other a-amino acids, with the detection limit of 1.3×10-5 mol/L (2.1 ppm). Besides, P1 could give different response to three isomers of amino acids,α-,β-andγ-amino acids, with the highest sensitivity to a-amino acids.In Chapter 3, a new imidazole-containing disubstituted polyacetylene (P3) with strong green fluorescence was successfully prepared through the polymer reaction. The obtained results demonstrated that the halogen atoms could be converted to imidazole groups completely through the nucleopholic substitution reaction by changing the chlorine atoms to bromine ones. Also, P3 was a good chemosensor for metal ions and could be utilized to sense cyanide and a-amino acids, through an indirect approach. P3 exhibited strong green fluorescence and higher fluorescence intensity than P1, which should benefit to observe by naked eye. Although both of P3 and P1 were disubstituted PAs with same imidazole moieties as acceptor, they exhibited much different chemosensing behavior, indicating the possibility to adjust the sensing properties of the resultant chemosensors by modifying their structure at the molecular level.In Chapter 4, for the first time, the "click" chemistry was applied to realize the attachment of highly polar azo chromophores to disubstituted PAs (P5-P14) conveniently. Polymers P5-P14 contained different isolation groups, and the linkage models between the polymer backbone and the side chain are not the same. Our preliminary results demonstrated that the introduction of the isolation groups to the chromophore moieties did not always improve the NLO effect of the resultant materials. For a given chromophore moiety and linkage position in a given polymer system, there is a suitable isolation group present for a chromophore to boost its microscopicβvalue to possibly higher macroscopic NLO property in polymers efficiently.In order to improve the optical transparency of second-order nonlinear optical (NLO) polyacetylenes, the indole groups were used as electron donor instead of aniline moieties. In Chapter 5, the indole-based chromophores were introduced to the side chains of disubstituted polyacetyleces through the "Click" reaction. Different isolation groups were attached to the acceptor part of chromophore moieties through the esterification reaction to further investigate the effect of isolation groups on macroscopic NLO properties. The resultant NLO polyacetylenes exhibited good transparency, with their maximum absorption blue-shifted about 50 nm.As promising candidates for NLO polymeric materials, polyphosphazenes offer many advantages, such as high thermo-oxidative and photochemical stability, and transparency of the backbone in the range of 200 nm to near-IR, etc. In Chapter 6, different isolation groups in different size were introduced to the side chain of NLO polyphosphazenes (P20-P22) through the post-functional strategy. The loading density of NLO chromophore moieties in the polymers was as high as 0.60 per unit, which could not be easily achieved using the conventional direct approach for the preparation of functionalized polyphosphazenes. The NLO effects for P20-P22 increased with increasing the size of the isolation groups, from 33.2 pm/V for P20 to 67.3 pm/V for P22. In Chapter 7, a new series of AIE-(F1-F3) and AIEE-(F4-F6) benzene-cored luminophors were successfully synthesized, which were "pure" aromatic compounds without olefinic functionality. Increasing viscosity or decreasing temperatures of their solutions leaded to enhanced emissions, confirming that the restriction of intramolecular rotations (RIR) process played a critical role in both AIE and AIEE systems.