Synthesis And Properties Of Liquid Crystalline Polyacetylenes Containing Chiral Terphenyl Pendants

π-Conjugated polymers are not only electroactive but also opticalactive. Compared to the inorganic materials, the organic conjugated polymers are light, thin, flexible, easily processed in solutions, controllable electrical and optical properties (by introducing specific functional groups into the polymeric structure for chemical modification or copolymerization) and other superiorities. The conjugated polymers have potential applications in the fields of polymer light-emitting diodes (PLEDs), polymer solar cells (PSCs) and other optical and electronic fields. Side-on-fixed liquid crystalline conjugated polymers is a kind of polymer with mesogenic unit laterally attached to the polymer backbone, the bulk mesogen will make full use of the space around the backbone and form a cylindric "shell" or "jacket". This structure can not only protect the conjugated main-chain from perturbations, but also enhance the main-chain coplanarity, resulting in excellent thermal stability and photoluminescence. Compared to side-end-fixed side-chain liquid crystalline polyacetylenes (SCLCPAs), the side-on-fixed SCLCPAs bear better thermal stability and photoluminescence.The terphenyl is not only a good mesogenic core but also a excellent chromophore. Introducing the terphenyl as pendant into the polyacetylene main chain will result in greatly improved solubility, enhanced thermal stability, unique optical and electronic properties owing to the spontaneous orientation of the mesogenic terphenyl group under the external fields (temperature, electricfield, magnetic field, etc). Meanwhile, if chiral groups are melted into the liquid crystalline conjugated polymers will induce, firstly, the materials exhibits circularly polarized emissions, secondly, the materials may generate chiral smectic C phases (SmC*) responsible for ferroelectric liquid crystallinity which can form ferroelectric liquid crystalline conjugated polymers (FLCCPs) responding to electric field quickly.A side-end-fixed liquid crystalline polyacetylene{-[(CH=C(CH2)6-O-terphenyl-OR*]n-, R* = (S)-2-methylbutyl, PAM6OTPhOR*} containing chiral terphenyl mesogen and a side-on-fixed liquid crystalline polyacetylene {-[(CH=C(CH2)3-OCO-terphenyl-(OR*)]n-, R* = (S)-2-methylbutyl, PAM3OCO(TPh)OR*} containing asymmetric chiral end groups and terphenyl mesogen were synthesized. The mesomorphism, electronic absorption and photoluminescene (PL) induced by the terphenyls were studied systematically, also the special attention was paid to the effects of chiroptical end groups on the forming of chiral liquid crystalline phases and the secondary helix structure of PAM3OCO(TPh)OR*. The Td of PAM3OCO(TPh)OR* (328℃) is higher than PAM6OTPhOR* (300℃) owing to the stronger "jacket effect". PAM6OTPhOR* exhibits enantiotropic SmC* responsible for ferroelectric liquid crystallity while PAM3OCO(TPh)OR* shows enantiotropic chiral smectic A phases (SmA*). The light-emitting bands of the both polymers in the liquid crystalline states are stronger and red-shifted to the long wavelength regions compared to those of states at room temperature. The CD spectra reveal that PAM3OCO(TPh)OR* not only maintain the chiroptical property of the monomer, but also takes one-handed helical structure of the backbone.A side-on-fixed liquid crystalline polyacetylene{-[(CH=C(CH2)3-OCO-terphenyl-(OR*)2]n-, R* = (S)-2-methylbutyl, PAM3OCO(TPh)(OR*)2} containing symmetric chiral end groups and terphenyl mesogen was designed and synthesized. The special attention was paid to the effects of terphenyl mesogen and its "jacket effect" on the thermal stability and photoluminescence, also the effects of chiroptical end groups on the forming of chiral liquid crystalline phases of the monomer and polymer were studied. The monomer exhibits enantiotropic SmC* while its polymer shows enantiotropic SmA*。The "jacket effect" induced by the terphenyl mesogen linked at mass center position endows the polymer with high thermal stability (356℃), high photoluminescence and aggregation-induced emission enhancement (AIEE). The light-emitting property of the liquid crystalline state of the polymer is obviously stronger and red-shifted than those of the solution and thin film states.