Chapter 1 Introduction
1.4 Supramolecular in Organic Devices
One of the major challenges in the field of electronics based on organic molecules is the design of functional, multicomponent architectures possessing long-range ordering. Having an electron-donating as well as an electron-accepting chromophore is a prerequisite to obtain organic photovoltaics. It has also been demonstrated that incorporation of energy- or electron-accepting chromophores into π-conjugated polymer backbones can rigorously alter the electrooptical properties of
the resulting copolymers. The copolymers can be characterized by either almost exclusive emission from the incorporated acceptor moiety or efficient charge transfer.
Recently, an end was put to a long discussion about undesired green emission in polyfluorenes, which appeared to arise from efficient energy transfer to small amounts of oxidized monomer,59 indicating the necessity for high-purity polymers.
The viability of this functional approach has been shown by the successful tuning of electroluminescence in a light-emitting diode (LED) consisting of PPV with dangling porphyrins.60 Also, a photovoltaic device based on a blend of PPV and polyfluorene with dangling perylene proved to yield high external quantum efficiencies in both the perylene and the polyfluorene absorption regions, due to energy transfer from the polyfluorene to the perylene with near unit efficiency.61 Moreover, connecting the electrooptical properties in organic devices have been
established through the supramolecular interactions, e.g. H-bonds, in organic, dendritic, and polymeric H-bonded complex systems. This was illustrated by a recent report on a triple hydrogen-bonded triad consisting of a central perylene that was connected to two C60 chromophores (Figure 1.11).62 Novel monomer and PPV-donor and PPV-acceptor bearing a terminal terpyridine chelating unit were reported (Figure 1.12).63 Three new photoactive supramolecular dyads have been prepared by complexing the ruthenium with the PPV-terpyridine ligands. Studies on the incorporation of such ligands and supramolecular building blocks into polymers were performed through photophysical properties. An efficient energy transfer process from the conjugated polymer block to the metal complex was shown. Moreover, the preparation of several different fullerene-based materials bearing chelating pyridyl groups (PyFs, Figure 1.13)64 was reported, with a comparative investigation of their interactions with ZnPc in solid thin films and evaluation of the performance of these materials in bilayer organic solar cells. To achieve efficient photocurrent generation in a wide spectral region, they merged bulk heterojunction MDMO-PPV/PCBM cells and bilayer ZnPc/PyF cells in a multicomponent device structure. The combination of bilayer fullerene/ZnPc and bulk heterojunction fullerene/polymer photovoltaic devices can be considered a promising approach to achieve a wide spectral response in organic solar cells while retaining the good charge-transfer and transport properties
of established materials.
Figure 1.11 Superstructure of self-assembly of [60]fullerene derivative 1 with perylene bisimide 5 by H-bonding.
Figure 1.12 The incorporation of a ruthenium complex into the donor-acceptor conjugated polymers has the potential to facilitate the charge carrier generation.
Figure 1.13 Pyrrolidinofullerenes bearing chelating pyridyl groups (PyFs) on vacuum-evaporated films of zinc phthalocyanine (ZnPc) in donor-acceptor bilayer heterojunctions formed by deposition of solution-processed. It is shown that coordination complexes are formed at the interface between these donor and acceptor components; such association facilitates photoinduced charge separation and results in improved performance of the photovoltaic devices.
Chapter 2
Study of Supramolecular Side-Chain and
Cross-Linking Polymers by Complexation of Various H-Donor Acids with H-Acceptor Copolymers
Containing Pendent Carbazole and Fluorescent Pyridyl Units
Two H-bonded acceptor (H-acceptor) homopolymers 14 and 17 were
successfully prepared by polymerization of fluorescent pyridyl monomers PBT and
PBOT (12 and 13), which were synthesized via Sonogashira coupling and
Wittig-Horner reactions. In order to increase the glass transition temperatures as well
as reduce the π-π stacking of the photoluminescent (PL) H-acceptor copolymers and
their H-bonded polymer complexes, fluorescent monomers 12 and 13 were
copolymerized with N-vinylcarbazole monomer CAZ (23) to produce H-acceptor
copolymers 15-16 and 18-19. Supramolecular side-chain and cross-linking polymers
(i.e., H-bonded polymer complexes) obtained by complexation of light-emitting
H-acceptor polymers 14-19 with various proton donor (H-donor) acids 20-22 were
further characterized by DSC, POM, FTIR, XRD, and PL measurements. The
mesomorphic properties can be tuned from the nematic phase in H-acceptor
homopolymers (14 and 17) to the tilted smectic C phase in their H-bonded polymer
complexes (14/20-21 and 17/20-22) by the introduction of H-donor acids (20-22).
Moreover, the PL properties of light-emitting H-acceptor polymers can be adjusted
not only by the central structures of the conjugated pyridyl cores but also by their
surrounding non-fluorescent H-donor acids. In general, redder shifts of PL emissions
in H-bonded polymer complexes occurred when the light-emitting H-acceptor
polymers were complexed with H-donors having smaller pKa values.
2.1 Introduction
Supramolecular chemistry is a new and exciting branch of chemistry encompassing systems held together by non-covalent bonds,and such complexes have considerable application potentials in the rapidly developing fields of molecular electronics and optoelectronics.48a,65,66 More recently, the concept of supramolecular chemistry has been applied to the design of liquid crystalline (LC) polymers in the expectation that molecular interactions may be amplified into macroscopically observable phenomena of self-assembled phases, i.e., liquid crystallinity.67 Supramolecular liquid crystals are molecular complexes generated from complexation of molecular species through non-covalent interactions, e.g., hydrogen bonding. Kato and Fréchet first exploited two different and independent components to generate
liquid crystals through intermolecular hetero-hydrogen-bonding interaction, and this concept in turn resulted in numerous findings of such supramolecular liquid crystals.18,19 The mesogenic properties can be easily modified by miscellaneous proton donors and acceptors, and new liquid crystalline properties, which are different from those of their original moieties, can be easily obtained by the introduction of supramolecular structures. Many kinds of H-bonds and building elements have been explored in the H-bonded structures to stabilize liquid crystalline phases.68 Therefore, side-chain liquid crystalline polymers consisting of polymer backbones, flexible spacers, and mesogenic pendants have great potentials in various utilizations as novel technological materials, such as optical switching elements, optical storage devices, and information displays. Among these approaches, intermolecular H-bonding is simply acquired by complexation of H-bonded donor (H-donor) carboxylic (or benzoic) acid groups with H-bonded acceptor (H-acceptor) pyridyl moieties. Several series of H-bonded polymer complexes and side-chain liquid crystalline polymers through intermolecular H-bonding (interaction between benzoic acid and pyridine) have been reported lately.69,70
The advantages of using organic materials to manufacture electroluminescent (EL) devices are their excellent film-forming properties, processing feasibilities of flexible devices, highly efficient EL properties, and low costs of fabrication.71 As we
know, poly(N-vinylcarbazole) (PVK) has attracted attention due to its applications related to polymer light-emitting diodes (PLEDs) in which the hole transporting layer is formed by PVK or it can be blended with other light-emitting materials. Such PLED devices have shown remarkably high luminescence efficiencies and relatively facile color tunabilities.72-74 In contrast to PVK, Romero et al.75 observed an increase in the external quantum efficiency of PLED devices based on the copolymerization of carbazole units with short thiophene segments, so carbazole units were also used to copolymerize with fluorescent pyridyl moieties in our study. Moreover, tuning emission colors in organic light-emitting materials have been established through the supramolecular interactions, e.g. H-bonds, in organic, dendritic, and polymeric H-bonded complex systems.76-78
In this report, fluorescent pyridyl H-acceptors as pendent groups were incorporated into the side-chain polymeric structures rather than as small molecules in our previous studies.76-78 The purpose of the present study for side-chain conjugated pyridyl polymers is to explore the self-assembled utilization of singly and doubly H-bonded structures (as shown in the schematic illustration of Figure 2.1) in preparing for supramolecular side-chain and cross-linking polymers, respectively. As shown in Schemes 2.1 and 2.2, fluorescent H-acceptor monomers PBT and PBOT (12 and 13) and their corresponding H-acceptor homopolymers (14 and 17)
containing three-conjugated aromatic rings (including two lateral substituted methyl and methoxy groups with one pyridyl terminus) were prepared, and both pyridyl H-acceptor monomers 12 and 13 were further reacted with different molar ratios of carbazole monomer CAZ (23) to produce copolymers 15-16 and 18-19, respectively.
Thus, the glass transition temperatures of the H-acceptor polymers can be controlled by the contents of pendent carbazole monomer CAZ (23) in H-acceptor polymers (14-16 and 17-19). In addition to the syntheses of such fluorescent H-acceptor monomers and polymers, two series of different H-acceptor polymers PBT1-PBT3
(14-16) and PBOT1-PBOT3 (17-19) were complexed with asymmetric
mono-functional H-donors OBA (20) and ONA (21) as well as symmetric bi-functional H-donor THDA (22), respectively (as shown in Figure 2.2). By incorporating of H-acceptor polymers to H-donor acids with different pKa values, the light-emitting properties of the supramolecular polymer complexes can be easily adjusted. Singly/doubly H-bonded processes of side-chain/cross-linking H-bonded polymers were confirmed and investigated by means of their liquid crystalline properties, X-ray diffraction (XRD) patterns, and photoluminescent (PL) properties.
Figure 2.1 Schematic illustration of singly/doubly H-bonded processes for H-bonded side-chain/cross-linking polymers.
Figure 2.2 Mono-acid (singly H-bonded) and bis-acid (doubly H-bonded) donors used in supramolecular side-chain/cross-linking polymers, respectively.
COOH C12H25O
C12H25O
COOH
S COOH
HOOC
OBA (20)
ONA (21)
THDA (22)
Scheme 2.1 Synthetic Routes of Monomer PBT (12).
Scheme 2.2 Synthetic Routes of H-Acceptor Polymers.
2.2 Experimental 2.2.1 Materials
N-vinylcarbazole CAZ (23) was purchased from Aldrich Chemical Co. and used
without further purification. Azobisisobutyronitrile (AIBN) was purchased from Kanto Chemical Co. and recrystallized from ethanol at 40 oC followed by drying in a vacuum oven. Proton donors OBA (20) and ONA (21) were identified as the required materials by 1H and 13C NMR spectroscopy and elementary analyses, which were reported in our previous results,78 and proton donors thiophene-2,5-dicarboxylic acid
THDA (22) was purchased from Aldrich Chemical Co. Chemicals and solvents were reagent grades and purchased from Aldrich, Acros, TCI, and Lancaster Chemical Co.
Dichloromathane and THF were distilled to keep anhydrous before use. The other chemicals were used without further purification.
Syntheses of H-Acceptor Monomers PBT (12) and PBOT (13)
The synthetic route of monomer PBT (12) is shown in Scheme 2.1, and its synthetic procedures are described as follows:
4-Bromo-2,5-dimethylbenzaldehyde (2). 2,5-Dibromo-p-xylene 1 (6.9 g, 26.3 mmol) was dissolved in 60 mL of dry THF purged with nitrogen. A solution of n-BuLi (13.7 mL, 34.2 mmol, 2.5 M in hexane) was added dropwise to a rapidly stirred THF at -78 °C. The rate of addition was adjusted to keep the temperature
below -78 °C. After the solution was stirred to react for 2 h at -78 °C, a solution of DMF (4.1 mL, 52.6 mmol) was added dropwise to keep at the same temperature.
After 2 h, the reaction was quenched with water and extracted with ethyl acetate. The organic extracts were dried over Na2SO4 and then evaporated. The crude product was purified and recrystallized from n-hexane to give a white crystal. Yield: 5.0 g (90%).
1H-NMR (ppm, CDCl3): δ 10.19 (s, 1H), 7.63 (s, 1H), 7.47 (s, 1H), 2.60 (s, 3H), 2.43 (s, 3H).
4-Bromo-2,5-dimethylbenzyl alcohol (3). To a stirred solution of compound 2 (5.0 g, 23.7 mmol) in 100 mL of THF/MeOH (1:1), NaBH4 (0.9 g, 23.7 mmol) was added very slowly and reacted at room temperature. After 1 h, the solution was cooled to 0 °C by ice bath, acidified with dilute HCl solution, and extracted with ethyl acetate.
The resulting extracts in organic phase were combined and washed with water. Then, the organic extracts were dried over Na2SO4 and evaporated. The crude product was purified and recrystallized from dichloromethane/2-propanol to give a colorless crystal. Yield: 4.1 g (80%). 1H-NMR (ppm, CDCl3): δ 7.33 (s, 1H), 7.21 (s, 1H), 4.61 (s, 2H), 2.35 (s, 3H), 2.27 (s, 3H).
1-Bromo-4-chloromethyl-2,5-dimethoxybenzene (4). A stirred solution of
compound 3 (4.1 g, 19 mmol) in 1,4-dioxane (150 mL) was added with concentrated HCl (20 mL, 3N), and then the mixture was refluxed for 10 h. After the reaction was
completed, the crude mixture was added with water. The organic layer was extracted with ethyl acetate, dried over Na2SO4 and evaporated. The crude product was purified by flash column chromatography (silica gel, n-hexane/ethyl acetate 40:1) to give a white solid. Yield: 4.0 g (89%). 1H-NMR (ppm, CDCl3): δ 7.36 (s, 1H), 7.15 (s, 1H), 4.51 (s, 2H), 2.36 (s, 6H).
(4-Bromo-2,5-dimethylbenzyl)diethylphosphonate (5). Compound 4 (4.0 g, 17.1 mmol) was mixed with an excess of triethylphosphite (20 mL) and heated to reflux for 12 h under reduced pressure. The excess of triethylphosphite was removed after reaction. The crude product was purified and washed with hot hexane to give a white solid. Yield: 5.1 g (90%). 1H-NMR (ppm, CDCl3): δ 7.28 (s, 1H), 7.07 (s, 1H), 4.08-3.95 (m, 10H), 3.06 (s, 1H), 2.99 (s, 1H), 2.28 (s, 3H), 2.26 (s, 3H).
1-Bromo-2,5-dimethyl-4-[2-(4-pyridyl)ethenyl]benzene (6). Compound 5 (5.1 g, 15.1 mmol) was dissolved in 60 mL of dry THF purged with nitrogen. A solution of lithium diisopropylamide (22.7 mL, 45.3 mmol, 2.5 M in hexane) was added dropwise to a rapidly stirred solution at -78 °C. The rate of addition was adjusted to maintain the temperature below -78 °C. After the solution was stirred to react for 30 min at -78 °C, a solution of pyridine-4-carboxaldehyde (2 mL, 21.1 mmol) was added dropwise and stirred for 30 min to come back to room temperature. After that, the mixture was stirred to react for 18 h at room temperature. The reaction was quenched
with water and extracted with dichloromethane. Subsequently, the organic layer was dried over Na2SO4 and evaporated. The crude product was purified by column chromatography (silica gel, dichloromethane/acetone 20:1) to give a yellow solid.
Yield: 3.7 g (85%). 1H-NMR (ppm, CDCl3): δ 8.56 (d, J = 4.8 Hz, 2H), 7.42 (s, 1H), 7.40 (d, J = 16.2 Hz, 1H), 7.36 (s, 1H), 7.35 (d, J = 4.8 Hz, 2H), 6.88 (d, J = 16.2 Hz, 1H), 2.38 (s, 3H), 2.35 (s, 3H).
10-(4-Bromophenoxy)-decan-1-ol (8). A mixture of 4-bromophenol 7 (4.9 g, 28.5 mmol), potassium carbonate (8.7 g, 62.7 mmol), 10-bromodecanol (7.4 g, 31.4 mmol), and a few amount of potassium iodide in acetone (200 mL) was heated to reflux and stirred under nitrogen for 48 h. After cooling to room temperature, the solvent was removed under reduced pressure. The residue was taken up in water and extracted with ethyl acetate. Then, the organic layer was dried over Na2SO4 and evaporated. The crude product was purified by column chromatography (silica gel, n-hexane/ethyl acetate 3:1) to give a white solid. Yield: 8.3 g (88%). 1H-NMR (ppm, CDCl3): δ 7.33 (d, J = 9.0 Hz, 2H), 6.75 (d, J = 9.0 Hz, 2H), 3.89 (t, J = 6.3 Hz, 2H), 3.62 (t, J = 6.6 Hz, 2H), 1.78-1.69 (m, 2H), 1.59-1.50 (m, 2H), 1.41-1.29 (m, 12H).
4-[4-(10-Hydroxy-decyloxy)-phenyl]-2-methyl-3-butyn-2-ol (9). A solution of
compound 8 (8.3 g, 25.3 mmol), PPh3 (13.1 mg, 0.51 mmol), and CuI (73 mg, 0.38 mmol) in dry triethylamine (80 mL) was degassed with nitrogen for 5 min.
2-Methyl-3-butyn-2-ol (3.7 mL, 38 mmol) and Pd(PPh3)2Cl2 (180 mg, 0.25 mmol) were added to the solution at room temperature and the mixture was stirred to react at 70 oC for 12 h. The mixture was filtered and the solvent was removed in vacuum.
Afterward, the crude mixture was extracted using dichloromethane. The organic solution was washed with water, and then dried over Na2SO4 and evaporated. The crude product was followed by purifying with column chromatography (silica gel, n-hexane/ethyl acetate 2:1) to give a light yellow solid. Yield: 4.7 g (56%). 1H-NMR (ppm, CDCl3): δ 7.31 (d, J = 9.0 Hz, 2H), 6.79 (d, J = 9.0 Hz, 2H), 3.92 (t, J = 6.6 Hz, 2H), 3.62 (t, J = 6.6 Hz, 2H), 1.77-1.70 (m, 2H), 1.60 (s, 6H), 1.58-1.50 (m, 2H), 1.42-1.29 (m, 12H).
4-Ethynyl-1-(10-hydroxydecan-1-yloxy)benzene (10). A solution of compound
9 (4.7 g, 14.2 mmol) and finely powdered KOH (2.39 g, 42.6 mmol) in 1,4-dioxane (80 mL) was refluxed under nitrogen for 3 h. After cooling to room temperature, the solvent was removed under reduced pressure. The residue was taken up in water and extracted with ethyl acetate, and then acidified with 150 mL of HCl (3 N). The organic solution was washed with water, and then dried over Na2SO4 and evaporated.
The crude product was purified by column chromatography (silica gel, n-hexane/ethyl acetate 4:1) to give a light yellow solid. Yield: 3.6 g (92%). 1H-NMR (ppm, CDCl3): δ 7.39 (d, J = 9.0 Hz, 2H), 6.80 (d, J = 9.0 Hz, 2H), 3.92 (t, J = 6.6 Hz, 2H), 3.62 (t, J =
6.6 Hz, 2H), 2.97 (s, 1H), 1.80-1.70 (m, 2H), 1.57-1.50 (m, 2H), 1.42-1.29 (m, 12H).
10-{4-[2,5-Dimethyl-4-(2-pyridin-4-yl-vinyl)-phenylethynyl]-phenoxy}-decan
-1-ol (11). A mixture of compound 6 (3.7 g, 12.7 mmol), PPh3 (170 mg, 0.64 mmol), and CuI (120 mg, 0.64 mmol) in dry triethylamine (80 mL) was degassed with nitrogen for 5 min. Compound 10 (3.6 mL, 13.3 mmol) and Pd(PPh3)2Cl2 (90 mg, 0.13 mmol) were added to the solution at room temperature, and afterward the reaction mixture was stirred to react at 70 oC for 12 h. The mixture was filtered and the solvent was removed in vacuum. Next, the crude mixture was extracted using dichloromethane. The organic solution was washed with water, and then dried over Na2SO4 and evaporated. The crude product was purified by column chromatography (silica gel, dichloromethane) to give a light yellow solid. Yield: 4.4 g (72%). 1H-NMR (ppm, CDCl3): δ 8.61 (d, J = 6.0 Hz, 2H), 7.56 (d, J = 15.9 Hz, 1H), 7.51 (s, 1H), 7.49 (d, J = 8.7 Hz, 2H), 7.44 (d, J = 6.0 Hz, 2H), 7.36 (s, 1H), 6.98 (d, J = 15.9 Hz, 1H), 6.90 (d, J = 8.7 Hz, 2H), 4.00 (t, J = 6.6 Hz, 2H), 3.68 (t, J = 6.6 Hz, 2H), 2.53 (s, 3H), 2.44 (s, 3H), 1.82 (m, 2H), 1.60 (m, 2H), 1.49-1.16 (m, 12H).
2-Methyl-acrylic acid
10-{4-[2,5-dimethyl-4-(2-pyridin-4-yl-vinyl)-phenylethynyl]-phenoxy}-decyl ester
PBT (12). Compound 11 (1.0 g, 2.1 mmol), vinyl methacrylate (1.24 ml, 0.01 mmol), 1,3-dichloro-1,1,3,3-tetrabutyldistannoxane (92 mg, 0.83 mmmol),
2,6-di-tert-butyl-4-methyl phenol (27 mg, 1.3 mmmol), and 2 ml of THF were added to a round-bottom flask. The solution was stirred at 50 oC for 48 h. Finally, the crude product of monomer PBT (12) was purified by column chromatography (aluminium oxide, n-hexane/dichloromethane 4:1) to give a light yellow solid. Yield: 0.54 g (47%).
1H-NMR (ppm, CDCl3): δ 8.57 (d, J = 5.4 Hz, 2H), 7.51 (d, J = 16.2 Hz, 1H), 7.46 (s, 1H), 7.44 (d, J = 8.7 Hz, 2H), 7.39 (d, J = 5.4 Hz, 2H), 7.31 (s, 1H), 6.93 (d, J = 16.2 Hz, 1H), 6.85 (d, J = 8.7 Hz, 2H), 6.08 (s, 1H), 5.53 (s, 1H), 4.12 (t, J = 6.9 Hz, 2H), 3.96 (t, J = 6.9 Hz, 2H), 2.49 (s, 3H), 2.39 (s, 3H), 1.93 (s, 3H), 1.77 (m, 2H), 1.65 (m, 2H), 1.49-1.20 (m, 12H). 13C NMR (ppm, CDCl3): δ 159.30, 149.92, 145.09, 137.62, 134.60, 133.63, 133.60, 132.96, 130.52, 127.20, 126.47, 125.20, 123.72, 121.00, 115.30, 114.59, 94.65, 87.04, 77.52, 77.10, 76.67, 68.09, 64.84, 29.49, 29.46, 29.37, 29.25, 29.21, 28.62, 26.03, 25.99, 20.39, 19.20, 18.37. MS (EI): m/z [M+] 549.3, calcd m/z [M+] 549.32. Anal. Calcd. for C37H43NO3: C 80.84, H 7.88, N 2.55. Found: C 80.56, H 7.95, N 2.77.
1-{[4-(10-Methacryloyloxy-decyloxy)-phenyl]-ethynyl}-2,5-dimethoxy-4-[2-(
4-pyridyl)ethenyl]benzene PBOT (13). The synthetic procedures of monomer
PBOT (13) were described in our previous report.791H NMR (ppm, CDCl3): δ 8.57 (d, J = 4.5 Hz, 2H), 7.66 (d, J = 16.5 Hz, 1H), 7.50 (d, J = 9.0 Hz, 2H), 7.39 (d, J = 4.5
Hz, 2H), 7.11 (s, 1H), 7.04 (d, J = 16.5 Hz, 1H), 7.04 (s, 1H), 6.87 (d, J = 9.0 Hz, 2H),
6.10 (s, 1H), 5.55 (s, 1H), 4.14 (t, J = 6.6 Hz, 2H), 3.97 (t, J = 6.6 Hz, 2H), 3.96 (s, 3H), 3.89 (s, 3H), 3.62 (t, J = 6.6 Hz, 2H), 1.95 (s, 3H), 1.81−1.75 (m, 2H), 1.58−1.53 (m, 2H), 1.42−1.30 (m, 12H). HRMS (EI): calcd for C37H43NO5, 581.3141; found 581.3146. Anal. Calcd for C37H43NO5: C, 76.39; H, 7.45; N, 2.41. Found: C, 76.15; H, 7.37; N, 2.44.
Syntheses of Polymers
The synthetic routes of polymers are shown in Scheme 2.2.
Homopolymers of PBT1 (14) and PBOT1 (17)
Monomers (1.0 g) of PBT (12) and PBOT (13) were dissolved in THF (5 mL), and then AIBN (3 mol%) was added as an initiator. After 24 h of reaction, the polymerization was terminated and the polymers were precipitated by a large amount of ether. The crude products were redissolved several times in THF and reprecipitated into a large amount of ether to afford 0.56 g of polymers. The yields were 65 ~ 49%.
Copolymers PBT2-PBT3 (15-16) and PBOT2-PBOT3 (18-19)
Monomers (total amount 1.2 g) of PBT (12)/CAZ (23) or PBOT (13)/CAZ (23) with the desired molar ratios were dissolved in THF (6 mL), and then AIBN (3 mol%) was added as an initiator. The reaction mixtures were flushed with nitrogen for 5 min and then heated in a water bath at 60 °C to initiate polymerization. After 24 h of reaction, the polymerization was terminated and the copolymers were precipitated by
a large amount of ether. The products were redissolved several times in THF and reprecipited in ether.
PBT1 (14). Yield: 49%. 1H NMR (ppm, d-dioxane): δ 0.89-1.75 (b, 18H), 1.93 (s, 3H), 2.33 (s, 3H), 2.46 (s, 3H), 3.84-4.03 (b, 4H), 6.78-7.61 (m, 10H), 8.51 (s, 2H).
PBT2 (15). Yield: 55%. 1H NMR (ppm, d-dioxane): δ 0.88-1.85 (b, 19H), 1.95 (s, 3H), 2.34 (s, 3H), 2.48 (s, 3H), 3.80-4.03 (b, 4H), 6.81-8.20 (m, 18H), 8.51 (s, 2H).
PBT3 (16). Yield: 50%. 1H NMR (ppm, d-dioxane): δ 0.92-1.88 (b, 19H), 1.96 (s, 3H), 2.36 (s, 3H), 2.49 (s, 3H), 3.80-4.05 (b, 4H), 6.82-8.22 (m, 18H), 8.53 (s, 2H).
PBOT1 (17). Yield: 58%. 1H NMR (ppm, d-dioxane): δ 0.88-1.78 (b, 18H), 2.08 (s, 3H), 3.79-4.02 (m, 10H), 6.79-7.78 (m, 10H), 8.50 (s, 2H).
PBOT2 (18). Yield: 62%. 1H NMR (ppm, d-dioxane): δ 0.90-1.83 (b, 19H), 2.10 (s, 3H), 3.80-4.05 (m, 10H), 6.78-8.19 (m, 18H), 8.50 (s, 2H).
PBOT3 (19). Yield: 65%. 1H NMR (ppm, d-dioxane): δ 0.87-1.85 (b, 19H), 2.16 (s, 3H), 3.83-4.10 (m, 10H), 6.65-8.21 (m, 18H), 8.51 (s, 2H).
2.2.2 Preparation of Supramolecular Complexes
In all cases, all proton donors (as shown in Figure 2.2) and acceptor polymers were dissolved in THF to make a clear solution. After that, most of the solvents were evaporated under ambient conditions, which were followed by drying in a vacuum oven at 60 °C for several hours. The complexation of H-donor acids and H-acceptor
polymers through hydrogen bonding occurred during the solvent evaporation. The complexes of all H-acceptor polymers with H-donor acids OBA (20) and ONA (21) had the equal molar amount of pyridyl H-acceptor and carboxylic acid H-donor groups (in 1:1 molar ratio) to form singly H-bonded supramolecules (H-bonded side-chain polymers), and with THDA (22) had the double amounts of pyridyl H-acceptor groups to those of carboxylic acid H-donor groups (in 2:1 molar ratio) to form doubly H-bonded supramolecules (H-bonded cross-linking polymers).
2.2.3 Measurements and Characterization
1H NMR spectra were recorded on a Varian unity 300 MHz spectrometer using CDCl3 and d-dioxane as solvents. Elemental analyses were performed on a HERAEUS CHN-OS RAPID elemental analyzer. Fourier transform infrared (FT-IR) spectra were performed a Nicolet 360 FT-IR spectrometer. The textures of mesophases were characterized by a polarizing optical microscope (POM, model:
Leica DMLP) equipped with a hot stage. Temperatures and enthalpies of phase transitions were determined by differential scanning calorimetry (DSC, model: Perkin Elmer Pyris 7) at a heating and cooling rate of 10 °C/min under nitrogen. Transition temperatures (°C) and enthalpies (in parentheses, kJ/mol) were determined by DSC second scans. Thermogravimetric analyses (TGA) were conducted on a Du Pont Thermal Analyst 2100 system with a TGA 2950 thermogravimetric analyzer at a
heating rate of 20 oC/min under nitrogen. Gel permeation chromatography (GPC) analyses were conducted with a Water 1515 separations module using polystyrene as a standard and THF as an eluant. UV-visible absorption spectra were recorded in dilute THF solutions (10-6 M) on a HP G1103A spectrophotometer, and photoluminescence (PL) spectra were obtained on a Hitachi F-4500 spectrophotometer. Thin films of UV-vis and PL measurements were spin-coated on quartz substrates from THF solutions with a concentration of 1 wt%. The PL quantum yields (ΦPL) of polymers were measured with 9,10-diphenylanthracene as a reference (in cyclohexane, ΦPL = 0.9).80 Synchrotron powder X-ray diffraction (XRD) measurements were performed at beamline BL17A of the National Synchrotron Radiation Research Center (NSRRC) in Taiwan, where the X-ray wavelength used was 1.32633 Å. X-ray diffraction XRD data were collected using imaging plates (IP, of an area = 20 × 40 cm2 and a pixel resolution of 100) curved with a radius equivalent to the sample-to-image plate distance of 280 mm, and the diffraction signals were accumulated for 3 min. The powder samples were packed into a capillary tube and heated by a heat gun, where the temperature controller was programmable by a PC with a PID feed back system. The scattering angle theta values were calibrated by a mixture of silver behenate and silicon.
2.3 Results and Discussion
2.3.1 Synthesis and Characterization of Polymers
As shown in Scheme 2.1, monomer PBT (12) was successfully synthesized via Sonogashira coupling and Wittig-Horner reactions to obtain three-conjugated aromatic rings. In order to synthesize the designed methacrylate monomer containing end-capping pyridine, it is crucial to avoid H-bonding of the pyridine moiety, and thus no acidic reactants can be used. Therefore, vinyl methacrylate (instead of methacryloyl chloride) was finally used as a reactant according to the literature81 to get a high yield of methacrylate PBT (12), where 1,3-dichloro-1,1,3,3-tetrabutyldistannoxane was required as a catalyst to proceed this reaction and the polymerization of PBT was avoided by using an inhibitor 2,6-di-tert-butyl-4-methyl phenol. Two analogous series side-chain polymers composed of monomers PBT (12) and PBOT (13) with different lateral methyl and methoxy groups in central cores were synthesized. Finally, methacrylate monomers
PBT (12) and PBOT (13) were in conjunction with N-vinylcarbazole CAZ (23) during the conventional synthesis of random free radical copolymerization, where the contents of CAZ units in the copolymers were determined by 1H NMR. All of these polymers were dissolved in high polar organic solvents (such as THF and DMF) to form good transparent films on glass substrates. The average molecular weights obtained from GPC are illustrated in Table 2.1. The number-average molecular
weights (Mn) of polymers are between 8800 and 15000 g/mol with polydispersity
weights (Mn) of polymers are between 8800 and 15000 g/mol with polydispersity