Browsing by Author "Lee, Tien-Hsin"

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Role of the Comonomeric Units in Reaching Linear Backbone, High Solid-State Order and Charge Mobilities in Heptacyclic Arene-Based Alternating Copolymers
(2013-10-08)
Lee, Tien-Hsin
;
Wu, Kuan-Yi
;
Lin, Tai-Yen
;
Wu, Jhong-Sian
;
Wang, Chien-Lung
Unpredictable trends of charge mobility (mu) in multicyclic heteroarenes-contained polymers remain an obstacle in designing high performance polymers used in polymeric field effect transistors (PFETs). The roles of the comonomeric units in reaching high hole mobility (mu(h)) of copolymers containing a heptacyclic arene unit, dithienocyclopentacarbazole (DTCC) were investigated in this study. A series of four DTCC-based alternating copolymers, PDTCC-1T, PDTCC-3T, PDTCC-BDT, and PDTCC-TT, were synthesized from the Pd-catalyzed copolymerizations between DTCC and comonomeric units including thioene (1T), terthiophene (3T), benzodithiophene (BDT) and thienothiophene (TT) units. Among the four DTCC-based alternating copolymers, highest mobility of 1.36 X 10(-2) cm(2) s(-1) was reached in PDTCC-3T. Optoelectronic and 2D-WAXD studies revealed that strong electronic interaction and highly ordered solid-state structure were only observed in PDTCC-3T. It is attributed to the combination of two axisymmertric units, DTCC and 3T, linearized the polymer backbone, leading to a compact solid-state packing and high mu(h), while centrosymmertic comonomeric units, BDT and TT curved the polymer backbones of PDTCC-BDT and PDTCC-TT, which decreases solid-state order and mu(h). Furthermore, the short axisymmeritric 1T although results in a linear backbone of PDTCC-1T, comparing to 3T, it is too short to effectively reduce interchain steric hindrance caused by the solubilizing octyl chains on DTCC. Thus, effective pi-pi stacking is hindered in PDTCC-1T, resulting in low mu(h). The macroscopic performances of mu(h)s agreed well with the optoelectronic and 2D-WAXD studies. It is concluded that the linear backbone of DTCC copolymers is the prerequisite to reach ordered solid-state packing, which facilitate effective charge transport, and it depends on the prudent choose on the symmetry of the comonomeric unit. In addition, balance between the solubility and adequate crowdedness of lateral side chains is essential for a PFET material to be not only easily processed, but also effectively pi-pi stack.
Synthesis of cyclopentyloxy terphenyl liquid crystals with negative dielectric anisotropy
(2015-01-02)
Lee, Tien-Hsin
;
Chen, Jiun-Tai
;
Hsu, Chain-Shu
;
應用化學系
;
Department of Applied Chemistry
Liquid crystalline materials possessing negative dielectric anisotropy (Delta epsilon) have attracted considerable attention because they can be used to formulate eutectic mixture for several display applications. The negative Delta epsilon can be achieved by introducing a lateral polar substituent onto the mesogen core of a liquid crystalline material, and fluorine atoms are usually used because of the small size and high electronegativity. 2,3-ortho-Difluoro substituent liquid crystals exhibit stable and profound physical properties such as the low viscosity, strong negative Delta epsilon, and high solubility. To avoid the decrease of the mesophase range, 2,3-ortho-difluorophenyl is often placed next to the terminal chain. In this paper, we have synthesised a new series of 2,3-ortho-difluoroterphenyl liquid crystals with a negative dielectric anisotropy. Ether oxygen is introduced to the structure because it can further increase the lateral dipole moment. 3-Alkylcyclopentane end group decreases both the melting point and the viscosity, which makes it an appropriate substituent for negative Delta epsilon 2,3-ortho-difluoroterphenyl liquid crystals. The mesomorphic properties as well as the optical anisotropies of the synthesised liquid crystals are discussed in this paper. All compounds in the series are found to possess highly negative dielectric anisotropy, wide mesophase ranges; therefore, they have a great potential to formulate eutectic mixture for liquid crystal displays.
Synthesis of fluorinated terphenyl liquid crystals with 3-propylcyclopentane end group
(2014-01-01)
Lee, Tien-Hsin
;
Hsu, Chain-Shu
;
應用化學系
;
Department of Applied Chemistry
High performance liquid crystal (LC) displays require nematic mixtures with low rotational viscosity to reduce the response time and large dielectric anisotropy to reduce the threshold voltage. Furthermore, liquid crystals (LCs) with low melting temperature and high clearing temperature are particularly attractive for automobile and outdoor display applications. In this article, we report a series of new fluorinated terphenyl LCs with 3-alkylcyclopentane end group. The terphenyl mesogen is designed for high Delta n value, and the lateral fluorine atom is used to reduce the melting temperature. In comparison with the terphenyl analogue containing a 4-alkylcyclohexyl end group, discussed in previous works, the obtained LCs show wider nematic temperature range and smaller rotational viscosity because 3-alkylcyclopentyl moiety is introduced. The effect of alkyl chain length and the lateral fluoro substituent on the mesomorphic properties of the obtained LC is discussed. The results show that the nematic temperature range increases with the alkyl chain length increase. The position of the lateral fluoro substituent also plays an important role; LC with the fluoro substitution on the central benzene ring provides the widest nematic temperature range. In conclusion, we have synthesised a new series of LCs with low melting point, wider nematic temperature range and high Delta n value, which is promising in formulating eutectic mixture for display application.
Synthesis of fluorinated terphenyl liquid crystals with 3-propylcyclopentane end group
(2014-01-01)
Lee, Tien-Hsin
;
Hsu, Chain-Shu
;
應用化學系
;
Department of Applied Chemistry
High performance liquid crystal (LC) displays require nematic mixtures with low rotational viscosity to reduce the response time and large dielectric anisotropy to reduce the threshold voltage. Furthermore, liquid crystals (LCs) with low melting temperature and high clearing temperature are particularly attractive for automobile and outdoor display applications. In this article, we report a series of new fluorinated terphenyl LCs with 3-alkylcyclopentane end group. The terphenyl mesogen is designed for high Delta n value, and the lateral fluorine atom is used to reduce the melting temperature. In comparison with the terphenyl analogue containing a 4-alkylcyclohexyl end group, discussed in previous works, the obtained LCs show wider nematic temperature range and smaller rotational viscosity because 3-alkylcyclopentyl moiety is introduced. The effect of alkyl chain length and the lateral fluoro substituent on the mesomorphic properties of the obtained LC is discussed. The results show that the nematic temperature range increases with the alkyl chain length increase. The position of the lateral fluoro substituent also plays an important role; LC with the fluoro substitution on the central benzene ring provides the widest nematic temperature range. In conclusion, we have synthesised a new series of LCs with low melting point, wider nematic temperature range and high Delta n value, which is promising in formulating eutectic mixture for display application.
The synthesis of anthradithiophene-based liquid crystals and their applications in organic thin film transistors
(2016)
Liau, Wei-Lung
;
Lee, Tien-Hsin
;
Chen, Jiun-Tai
;
Hsu, Chain-Shu
;
應用化學系
In this communication, we report the development of high mobility organic thin film transistor (OTFT) devices using anthradithiophene-based organic semiconductors. Asymmetric molecular structures are introduced by attaching phenyl groups to the fused rings to obtain a wider temperature range of the liquid crystal phases of the anthradithiophene-based molecules. The rotation of the phenyl groups makes the molecules more flexible, leading to a lower liquid crystal transition temperature and a wider liquid crystal temperature range. An excellent OTFT carrier mobility of 0.68 cm(2) V-1 s(-1) of the devices is achieved, which is good enough for use in the manufacturing processes of current electronic devices such as TFT liquid crystal display (LCD) devices.