Browsing by Author "Chen, Te-Cheng"

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Hydrogen-bonded effects on supramolecular blue phase liquid crystal dimeric complexes
(2015-01-01)
Wei, Chong-Lun
;
Chen, Te-Cheng
;
Raghunath, Putikam
;
Lin, Ming-Chang
;
Lin, Hong-Cheu
In this study, a series of novel asymmetric hydrogen-bonded (H-bonded) dimeric complexes D/P and D/P* (proton donors D = A, A*, AF and AF*) were synthesized and self-assembled by appropriate molar ratios of H-donors (A, A*, AF and AF*) and H-acceptors (P and P*). In addition, the influences of the lateral fluoro-substituent of H-donors, the number (along with the position) of chiral centers and the molar ratio of H-donors and H-acceptors on the mesophasic behaviours (e.g., BPs) of asymmetric H-bonded dimeric complexes are investigated. Interestingly, the blue phase (i.e., BPI) was observed in complexes A*/P, A*/P*, AF*/P and AF*/P* containing at least a chiral center in H-donors (A* and AF*), including the widest BPI ranges of complexes AF*/P* (ca. 6 degrees C and 13 degrees C for 1 : 1 and 3 : 1 mol, respectively). For the first time, the hydrogen-bonded effects on supramolecular blue phase LCs are compared with their analogous covalent diads. Based on our theoretical calculation, we discovered that the bend angle plays an important role in manipulating the existence of the blue phase, which is preferred to appear at the bend angle within 132.1-152.9 degrees. Hence, owing to inappropriate bend angles, both H-bonded dimeric complex A/P* and covalent diad A*-P (with bend angles of 162.0 degrees and 126.5 degrees, respectively) did not possess any blue phase.
Novel asymmetrical single- and double-chiral liquid crystal diads with wide blue phase ranges
(2015-01-01)
Wei, Chong-Lun
;
Chen, Te-Cheng
;
Raghunath, Putikam
;
Lin, Ming-Chang
;
Lin, Hong-Cheu
In this study, two series of novel asymmetrical single- and double-chiral liquid crystal diads using a central linker to link two different mesogenic cores were successfully synthesized. The effects of the position of chiral centers and the number of aromatic rings on the mesomorphic and electro-optical properties were investigated. We found that diads III-N (where N = A, B, C and D) have better mesophasic properties than II-N (where N = A, B, C, D and E). Compared with III-C with a chiral center at the terminal alkoxyl chain, diad III-D exhibited the widest temperature range of BPI (ca. 31 degrees C) as the chiral center was introduced to the central linker. Besides III-D, BPs were also observed in diads II-B and III-B with a chiral center at the central spacer. According to our experimental results and molecular modeling, the mesomorphic properties and temperature ranges of BPs will be affected by the values of biaxiality and dipole moment, along with the bent shape of molecular geometry. Therefore, we demonstrated the first example of asymmetrical single- and double-chiral liquid crystal diads involved chiral centers located at the central linker to exhibit BPs, including the mesophases of BPI and BPIII, which might offer new BP single-components to the future applications of eutectic liquid crystal mixtures with wide BP ranges.
Quenching effects of gold nanoparticles in nanocomposites formed in water-soluble conjugated polymer nanoreactors
(2012-02-17)
Yang, Po-Jen
;
Chu, Hsuan-Chih
;
Lee, Yu-Hsien
;
Kobayashi, Takayoshi
;
Chen, Te-Cheng
In this paper we describe the first example of the in situ synthesis of gold nanoparticles (AuNPs) in the presence of a water-soluble conjugated polyfluorene (NPF) presenting pendent ammonium groups, with the polymer acting as an aqueous surfactant and providing fluorescent nanoreactors. Using this approach, we produced well-dispersed NPF-AuNP nanocomposites without the need for any additional reducing agents. The photoluminescence emission intensity of NPF-AuNP nanocomposite solution was quenched to a greater extent upon increasing the concentration of AuNPs, presumably through energy transfer or electron transfer from the fluorescent polymer to the metal nanoparticles. Through variations in the degrees of protonation and deprotonation of the amino groups of NPF at different values of pH, we found that the extent of quenching of AuNPs in NPF-AuNP nanocomposite solutions was directly related to the adsorption and desorption behavior of NPF on the metal surfaces. Transmission electron microscopy revealed that the greatest aggregation of AuNPs in the nanocomposite solution occurred at pH 3. suggesting that the ammonium groups (RNMe2 at pH 8.5; RNMe2H+ at pH 3) of the polymer side chains adsorbed onto the AuNP surfaces under these conditions. Distinct time-resolved fluorescence signals of the AuNP-quenched NPF polymers at different values of pH confirmed the interactions between these species. (C) 2012 Elsevier Ltd. All rights reserved.
Recoverable fluorescence chemosensors for Ni2+ ions based on hydrogen-bonded side-chain copolymers presenting pendent benzoic acid and pyridyl receptor units
(2012)
Yang, Po-Jen
;
Chu, Hsuan-Chih
;
Chen, Te-Cheng
;
Lin, Hong-Cheu
;
材料科學與工程學系
In this study we synthesized the novel fluorescent conjugated homopolymers P1 and P4 and the copolymers P2 and P3 containing proton-acceptor (pyridyl receptor) M1 monomer units and proton-donor (benzoic acid) M2 monomer units and investigated them as recoverable chemosensors for Ni2+ ions (based on adjusting the fluorescence energy transfer between the M1 and M2 moieties through varying the degree of hydrogen bonding). The levels of available (i.e., non-hydrogen-bonded) pyridyl receptors in the copolymers P2 and P3 were modified using different molar ratios of the pyridyl monomer M1 and the benzoic acid monomer M2. Significant chelation of the Ni2+ ions by the fluorescent homopolymers P1 and P4 and the copolymers P2 and P3 was evident by their distinct fluorescence quenching behaviors; the specific quenching constants (K-SV) decreased in the order P1 > P2 > P3 > P4, following the trend of the molar ratios of pyridyl receptors. When we added a third component, cyclodextrin (CD), to cap the benzoic acid moieties and, thereby, disrupt the hydrogen bonding between the M1 and M2 moieties in the copolymers P2 and P3, the levels of available pyridyl receptors in the recoverable chemosensor copolymers increased, resulting in relatively higher quenching constants for the P2 + CD, P3 + CD and blend (P1/P4) + CD systems. Fluorescence decay experiments revealed that the addition of CD also increased the fluorescence quenching efficiencies of the copolymers P2 and P3 towards Ni2+ ions. Such supramolecular (hydrogen-bonded) side-chain fluorescent copolymers might have practical applicability as recoverable and/or adjustable chemosensors.