Structures, properties, and applications of soluble polyazulene and azulene containing copolymers 3

Chapter Crystal Structures of Monomers and Oligomers Containing Azulene Unit – Model Compounds for the Corresponding Polymers Introduction In chapter 3, we have described the interesting properties of conjugated copolymers containing azulene units in the main chain, such as stimuli-response upon protonation, stability of the radicals cations, high conductivity upon doping or protonation. All these interesting properties come from their unique electronic structures. However, structural studies of these copolymers have been limited by the defects of these copolymers. For example, due to statistical chain length distribution and interruption of the conjugated chain by mislinkages and other defects, the obtained polymers, lack a rigidly defined structural principle and conjugation is severely disturbed.1 The structure at the chain segment level is also hard to characterize.2 These inaccessibility of the copolymer solids is one of the reasons why model compounds, well-defined oligomeric analogues of the copolymer, have met increasing interest in the filed of conjugated organics.3 Because of the chemical purity and relatively low molecular mass, these model compounds are usually sufficiently crystalline to allow structural resolution by means of diffraction methods. Although X-ray data of oligomers are scarce, X-ray data of model compounds, such as inter-ring bond lengths, torsional angles between the moieties planes, and positioning of the alkyl chains, can give valuable information on polymer properties.4-6 It also provides information to study the solid-state polymer properties.7,8 119 Furthermore, the physical properties of these monomers and oligomers, may be extrapolated to those of their corresponding polymers. Additionally, it has been well demonstrated that oligomers themselves represent excellent candidates for electronic materials.9-12 Thus, to have a better understanding of the polymer structure and properties, we prepared the single-crystals of a series of monomers and oligomers containing azulene unit. To further investigate the side chain effect on solid-state polymer properties, model compound bearing long side chains was synthesized and its single crystal structure was studied. These compounds are analog of the copolymers and their solid state structures, optical and electrical properties were studied as model compounds for the corresponding polymers. Results and Discussion Model compounds design and synthesis Synthesis and characterization of Monoa and Monob are reported in Chapter 3. Palladium-catalyzed Stille coupling reaction13 was employed to prepare the oligomers as described in Scheme 4-1. The common intermediate for synthesis of Oligoa and Oligob, 4’,4’’-Dibromo(1,3-(3’-methyl-thienyl))-azulene, was obtained by bromination of Monob with NBS in chloroform and acetic acid (1:1). Because Monob is less reactive with respect to the corresponding thiophene derivatives, bromination of Monob needed longer reaction time. 3-Methyl-2-phenyl-thiophene was prepared by Grignard coupling reaction between 2-bromo-3-methyl-thiophene and bromobenzene, it was then brominated with NBS in chloroform and acetic acid (1:1) as discussed previously. The Stille reagents for synthesis of Oligoa and Oligob were obtained in high yield by reacting the corresponding Grignard reagent with tributylstannyl chloride in ether. The obtained 120 Stille reagents are enough stable to store at room temperature for more than one week without significant change (detected by 1HNMR). Stille coupling reaction of 4’,4’’-Dibromo(1,3-(3’-methyl-thienyl))-azulene with corresponding Stille reagents catalyzed by Pd(PPh3)4 in refluxing toluene, yielded Oligoa and Oligob as green and yellowish-green solid, respectively. Their single crystals were obtained by evaporating of their dilute solution in hexane and CH2Cl2 at room temperature. Me Br S S Me i Br S i iv Me Monob Me MgBr S iii iii ii Me SnBu3 Br S S Me Br S Me v v Me S Me S S S S Me Me Oligoa SnBu3 S Me Me Oligob Scheme 4-1. Synthesis of Oligoa and Oligob. Reagents and conditions: (i), Mg/Et2O, (ii), Bu3SnCl/Et2O, (iii), NBS/CHCl3/AcOH, (iv), Bromobenzene, (v), AsPh, LiCl, Pd(Ph3)4, 1,4dioxane. To study the long side chain effect on the solid structure of the polymers, monomers with short alkyl-substitutent (less than four carbons) had been prepared but they were found to have difficulty in crystallization. We then turned to monomers with alkoxy side group, 121 which may crystallize easily because of the electro-negative oxygen. MonoO6 was thus designed and synthesized by Grignard coupling of 1,3-dibromo-azulene and 2-bromo-3hexyloxy-thiophene, catalyzed by Ni(dppp)Cl2 in anhydrous THF. During the preparation of MonoO6, two methods were used to prepare 3-alkoxyl-thiophene: The first attempt was made using Ullmann synthesis with copper (I) halide catalysis.14 This method suffered from its low yields, long reaction time, and difficulty in purification. In the second attempt, 3-alkoxyl-thiophene was prepared from 3-methoxyl-thiophene as shown in Scheme 4-2.15,16 In this method, 3-bromo-thiophene was first converted to 3-methoxythiophene by reaction of 3-bromothiophene with MeONa in toluene. 3-Hexoxylthiophene was then afforded by reaction of 3-methoxythiophene with 1-hexanol and NaHSO4 in toluene. The second method showed advantages in high yields and simple purification. Although alkoxyl-thiophene are unstable at r.t., the obtained monomers, MonoO6, however, is quite stable at r.t. This is may be due to the increasing of oxidation potentials of the product. Br S OMe i S OC6H13 OC6H13 iii ii S S Br v O O iv Br Br S S MonoO6 Scheme 4-2. Synthesis of MonoO6. Reagents and conditions: (i), MeONa/MeOH, (ii), hexanol, toluene, (iii), NBS, CHCl3/AcOH, (iv), NBS, benzene, (v), Mg/Et2O, Ni(dppp)Cl2. Characterization HNMR. Structural characterization of the synthesized oligomers was performed using HNMR and 13 CNMR spectra as shown in Figure 4-1a and Figure 4-2a with the assignment of the peaks for Oligoa and Oligob. Comparison of the 1HNMR of Oligoa 122 and Oligob, we found there is less changes of azulene protons even two more thiophenes were inserted into Oligob than in Oligoa. To illustrate, H4,8, and H2 of azulene in Oligob, negatively shifted approximately -0.02 ppm compared to that of in Oligoa. In case of H6 of azulene in Oligoa, there is about 0.04 ppm shift to the low field in Oligob. However, extension of the conjugation by inserting two more aromatic units can be seen from the β-H of thiophene. For instance, two β-H on thiophene in Oligoa was found at 7.30 ppm as a single peak, and shifted to 7.14 ppm in Oligob. Another two β-H on thiophene was found at 7.05 ppm in Oligob. The high field shift of the β-H on thiophene ring in Oligob was attributed to the increase of conjugation. (a) (b) Figure 4-1. (a), HNMR spectrum of Oligoa and (b), its HMQC spectrum. 123 For the purpose to assign the carbons in these oligomers, 2-D HMQC experiments were carried out and the results are displayed in Figure 4-1b and Figure 4-2b. These results also confirmed the expected oligomers structure and revealed that the extension of conjugation has little effect on azulene’s carbons. For instance, C4,8 of azulene was found at 138 and 136 ppm in Oligoa and Oligob, respectively. (a) (b) Figure 4-2. (a), HNMR spectrum of Oligob and (b), its HMQC spectrum. HMR spectrum of MonoO6 is displayed in Figure 4-3. Because of the electron-donating property of oxygen, a large shift of the protons on azulene in MonoO6 comparing to that in the alkyl-substituted monomers such as Monob was found in its 1HMR spectrum. In Figure 4-3, H4,8 of azulene appeared at 8.58 ppm in MonoO6, while H4,8 in Monob were found at 8.38 ppm (Chapter 3). They shifted approximately 0.2 ppm to higher filed. 124 Similarly, H2 in MonoO6 positively shifted around 0.37 ppm when compared to that of in Monob. However, H6 and H5,7 did not show significant shifts as we observed for H4,8 and H2, which may be due to the bond-alternation properties of azulene. Figure 4-3. HNMR spectrum of MonoO6 FT-IR. FT-IR spectra showed that methyl substituted oligomers resemble those copolymers. These compounds showed characteristic frequencies at 3015 cm-1 that was assigned to the aromatic C-H stretching mode, and 2910-2850 cm-1 to the aliphatic C-H stretching. There were no γα-C-H stretching at 3080 cm-1 in these oligomers as we observed in MonoO6, which indicated that all the α position of thiophene was linked in the conjugated oligomers. Absorption at the region 1930-1659 cm-1 was attributed to characteristic absorption of the benzene ring. Absorption at 1560, 1430, and 830 cm-1 characterized the tri-substituted thiophene. Absorption at 1591 (γC=C of azulene) and 734 cm-1(δ=C-H of azulene) characterized existence of azulene in the conjugated systems. Peaks at 1170 cm-1 was attributed to the in-plane C-H deformation, 1070-1000 cm-1 was attributed to the in-plane C-H deformation, and 830-756 cm-1 was attributed to the outplane C-H deformation. 125 1.5 Oligob 1.0 Oligoa 0.5 MonoO6 0.0 4000 3000 2000 1000 -1 Wavenumber (cm ) Figure 4-3. FT-IR spectrum of Oligoa, Oligob, and MonoO6. Structural Analysis Structure of Monoa and Monob. Single crystal of 1,3-dithienyl-azulene (Monoa) and 1,3-di(3-methylthienyl)-azulene (Monob) were obtained and Figure 4-4 illustrates the atomic numbering scheme employed for Monoa and Monob respectively. The crystallographic parameters for these structures are listed in Table 4-1. Both crystals are orthorhombic system but a slight difference in density is observed with Monoa at 1.406g/cm3, and Monob at 1.343g/cm3. The major observation was the large torsion angle between the thiophene ring and azulene ring. In Monoa, the thiophene ring and the five-membered ring of azulene are all nearly planar themselves. But one torsion angle between the thiophene and the fivemembered ring of azulene was found to be 43.20 (C10-C3-C1’-S2) and the other is 34.40 (C9-C1-C1’’-S1). These data are very close to the theory calculation. PM3 calculation has been carried out on Monoa and the calculated dihedral angle between the thiophene ring and azulene ring are 48.50 and 520 at the lowest energy of 619.52 kJ/mol. As 126 expected, larger steric effect of the methyl group increases the torsion angle in between thiophene and azulene ring. In Monob, one torsion angle between thiophene and the fivemembered ring of azulene ring is 44.70 (C10-C3-C1’-S2) and the other is 45.00 (C9-C1C1’’-S1). The large torsion angles arises from steric hindrance between the sevenmembered ring of azulene and the thiophene ring, that is, the repulsion between H4, H8 of azulene and the H or substituted group at 3-position of the thiophene ring. The large torsion angles between azulene and thiophene ring, especially the substituted one (Monob), means that the wave functions of the HOMO for these compounds are at least somewhat less localized than for the reported coplanar oligothiophenes.5,17 Monoa Monob Figure 4-4. Perspective view and atom labeling of the crystal structure of Monoa and Monob. Bonds lengths for Monoa and Monob are displayed in Figure 4-5. For example, the bond-lengths between the azulene and the thiophene ring were found to be 1.459Å (C3- 127 C1’), 1.456 Å (C1-C1’’) in crystal Monoa, and to be 1.465 Å (C3-C1’), 1.461 Å (C1C1’’) in Monob. While the corresponding bond-length in the oligothiophene was found to be 1.451 Å.18 The large steric hindrance effect on conjugation of Monob than Monoa can also be seen from bond-length of β-β single bonds in thiophene. The β-β single bond (C2’-C3’ or C2’’-C3’’) length were found to be 1.415 – 1.416 Å in Monoa and 1.4231.428 Å in Monob. The large torsion angle effect on the physical, optical and electrochemical properties of corresponding polymers was found in their corresponding polymers studies. To illustrate it, the conductivity of Polyb was found to decrease one-tenth of the conductivity of Polya. But to our surprise, although large torsion occurred in the thiophene-azulene copolymer systems, these polymers still showed high conductivities in the range of 1100S/cm. 1. 38 1.415 1.393 1.387 1.3 42 1.41 1.489 38 1. 42 1.40 1.373 1.3 1.416 1.37 1. 38 72 S .70 40 S .727 1.459 1. 1. 71 1.456 . 78 1.3 Monoa 1.3 80 1.41 1.3 47 1.423 1.391 88 .3 1.390 .38 1.484 38 1. 53 15 1.4 1.375 1.3 1.428 1.37 1 .7 04 1.40 73 S .70 1.465 1. 09 S 35 1.461 1.4 1. Monob 1.3 85 Figure 4-5. Bond distance in (a), Monoa; and (b), Monob. 128 Figure 6-10. The HNMR spectra of polymers PB and its corresponding ruthenium carbonyl hybrids. In the FT-IR spectra, all polymers exhibit strong γC-H stretching bands at 2910 - 2850 cm1 , correspond to the alkyl side chain. After coordination of the ruthenium carbonyl cluster, strong bands are found at 2050-1900 cm-1, corresponding to the CO stretching of ruthenium carbonyl group. This is strong evidence to suggest the presence of the ruthenium carbonyl clusters on the polymer backbone. Comparing the relative intensities of the ruthenium carbonyl group absorption with the γC-H stretching of the side chains, the hybrid compositions can also be estimated. As shown in Figure 7, the relative intensities of the ruthenium carbonyl groups to that of the side chain stretching in the resulting hybrids increase with an increasing ratio of Ru3(CO)12 during the thermolysis. 204 (a) (b) Figure 6-11. Comparison of transmission FT-IR spectra of metal free polymers with theirs corresponding hybrids: (a) polymers PA and its ruthenium cluster hybrids, (b), polymer PB and its ruthenium cluster hybrids. Morphologies Studies. We have investigated the morphologies of the polymers and their hybrids by scanning electron microscopy (SEM). Polymer PB and its corresponding hybrids are used as an example. As shown in Figure 6-12a, PB shows a relatively smooth film surface. However, the polymeric surface structure was changed significantly after coordination with the ruthenium carbonyl cluster. In the SEM micrographs, the hybrids show fibrous structures. The morphologies of the hybrids are also influenced by the density of ruthenium carbonyl clusters. For example, cauliflower-structure growth can be seen on 205 the smooth surface freshly prepared hybrid (PB-1), with a low content of ruthenium carbonyl cluster (Figure 6-12b). However, the whole polymer structure was changed to a sponge-like structure for freshly prepared hybrid (PB-2), with a high content of ruthenium carbonyl clusters (Figure 6-12c). It is also interesting to note the morphology change of the hybrids after a long-term annealing at room temperature. These small particles annealed into globular spheres with diameters between 100nm and µm. The more ruthenium carbonyl clusters contained in the hybrids, the smaller the average sphere diameter. Figure 6-12d shows the morphology of the annealed hybrids at room temperature for one month. The observed spheres may have resulted from the strong selfassembling ability of the hybrids with coordination transitional metal clusters and πconjugated polymers. These hybrids have a tendency to anneal together to form a sphere structure with high surface area. Additionally, this self-assembling process very slow, as can be seen from the quasi-continuous phase structure for the annealed hybrid (Figure 612d). The greatly enhanced surface-to-volume ratio of these hybrid materials is predicted to yield an enhanced sensitivity, compared with that of metal-free polymeric films. a b 206 c d e f Figure 6-12. SEM micrographs of (a), P4, (b), PB-2, (c), freshly prepared PB-1, (d), freshly prepared PB-2, (e), PB-1 annealed at r.t. for month, (f), PB-2 annealed at r.t. for month. Thermal analysis The TGA thermogram for the polymers and their hybrids clearly showed a distinct difference; the hybrids are less thermally stable than their corresponding polymers, as shown Figure 6-13. Furthermore, it was found that the decomposition temperature of the hybrids decreases as the density of ruthenium clusters increases. The TGA thermogram for polymer PA exhibited an onset of decomposition temperature (Td) at 4000C, with a relative residual weight of 44% at 8000C, reflecting its relatively high thermal stability. In 207 contrast, the TGA curve for its corresponding hybrids (PA-1 and PA-2), shows a much lower onset of decomposition temperature and a relatively high residual weight. As shown in Figure 6-13, PA-1 exhibited its onset of decomposition at 1760C, with a relative residual weight of 68% at 8000C. Likewise, PA-2 showed an onset of decomposition at 1500C, with a relative residual weight of 70% at 8000C. The lower of the two decomposition temperatures may be due to the decomposition of the CO group in the complex. This was confirmed by the multi-step decomposition and relatively high second onset of decomposition of the hybrids. This conclusion is supported as well by FT-IR spectrum analysis of the hybrids’ residue in TGA measurement. A complete loss of CO stretching frequencies in the IR spectrum was found after heating to ca. 2600C. Hybrids, PB-1 and PB-2, have similar values of decomposition temperature (Td), but the residue weights of the hybrids changed less, when compared with the residue weight of metalfree polymer PB. Differential scanning calorimetry showed endothermeric peaks at 1502000C, which was due to the loss of carbonyl group. No evidence of a glass transition temperature was observed for the polymers. 20 P3 Weight (mg) PA-1 PA-2 15 10 200 400 600 800 Temperature ( C) (a) 208 PB-1 P4 Weight (mg) 7.5 PB-2 5.0 2.5 200 400 600 800 1000 Tempeature ( C) (b) Figure 6-13. Thermogram of (a), P3 and its hybrids, (b), P4 and its hybrids. Optical and electrical properties studies The UV/vis absorption spectra of our polymers and hybrids are shown in Figure 6-14. The maximum absorption for the π-π* transition of the polymer backbone was blueshifted in hybrids, compared to that of the metal-free polymers, just as we observed in the monomers-ruthenium carbonyl cluster complex. The shift (∆λ) depends on the amount of ruthenium carbonyl cluster attached to the conjugated polymer backbone. The absorption of the free polymer, PA, is dominated by an intense band at λmax ≈ 380 nm, arising from the π-π* transition of the conjugated polymer backbone. Coordination of ruthenium cluster to the polymer backbone led to blue shift of the π-π* transition. As shown in Figure 6-14a, PA-1 is blue-shifted ≈ 15 nm and PA-2 showed a ca. 30 nm blue shift. The obvious blue shift of the conjugated polymer’s π-π* transition, after coordination with ruthenium carbonyl cluster, is believed to arise from the disruption of the ruthenium cluster on the aromaticity of azulene, and thus, increasing the HOMO-LUMO gap within the polymers. The PB hybrids displayed similar tunable properties after coordination with ruthenium carbonyl clusters (Figure 6-14b). PB-1 was blue-shifted ca. 16 nm and PB-2 was blue-shifted ca. 26 nm, compared with the metal-free polymers, PB. Importantly, all 209 these hybrids exhibit a characteristic MLCT transition. The MLCT transition appeared as a shoulder at ca. 460-600 nm and 520-610 nm for the PA and PB series, respectively. For the ruthenium-containing polymers, those with low ruthenium content (PA-1 and PB-1) exhibited a less intense MLCT transition absorption, while PA-2 and PB-2, which contained a high ruthenium content, showed an increase of the MLCT transition absorption. These MLCT absorptions are attributed to a reduction in the HOMO-LUMO gap that is caused by the interaction of d(π) electrons, of ruthenium carbonyl clusters, with π electrons of the HOMO of the conjugated polymer backbones.38 The weak MLCT transition may be due to the localization of π electrons on the azulene ring, induced by the coordination with ruthenium carbonyl clusters. UV/vis spectra of the hybrids reveal that the absorption strength of the polymers at longer wavelengths can be adjusted by controlling the content of the ruthenium carbonyl cluster in the hybrids, as clearly shown by the comparison of the spectra of metal-free polymers to their corresponding hybrids. This is a useful feature for controlling the optical properties of the polymers. (a ) A b s o rb a n c e P A -1 P A -2 A b s o rb a n c e .4 .2 P A -1 P A -2 PA .0 450 500 550 600 W a v e le n g th (n m ) PA 300 400 500 600 700 W a v e le n g th (n m ) 210 1.0 (b) Absorbance 3.0 Absorbance 2.5 2.0 0.5 PB-2 PB PB-2 PB-1 0.0 500 1.5 550 600 W avelength (nm) PB 1.0 PB-1 0.5 0.0 300 400 500 600 700 W avelength (nm) Figure 6-14. The UV/vis spectra of polymer P3 and their corresponding hybrids. Electrical chemistry study The effects of ruthenium complex content on the properties of hybrids are also characterized by in their electrochemical behavior. The cyclic voltammograms of the metal free polymers and their corresponding hybrids are shown in Figure 6-15. Comparison of the redox potential of the hybrids to that of metal-free polymers revealed that the oxidation onsets and oxidation potentials corresponding to the conjugated backbone shifted cathodically (i.e., towards more negative potentials) after coordination with ruthenium carbonyl clusters. The shift is greater for the hybrid with a higher ruthenium carbonyl cluster content, as show in Figure 6-15. This indicates that the tunable electronic properties of the hybrids are affected by MLCT interaction between the ruthenium carbonyl cluster and the π-conjugated polymer backbone. Results show that the polymer PA has a reversible, one-electron oxidation process with an oxidation potential at ca. 0.93 V (vs. SCE) and a reversible reductive peak at ca. 0.66 V (vs. SCE), which corresponds to the p-type doping and undoping of the polymer backbone. After coordination with a ruthenium carbonyl cluster, the onset oxidation potential shifted 211 cathodically and the redox process becomes irreversible. For PA-1, a 0.05 V cathodical shift of the on-set potential with a reverse scanning peak at 0.72 V, was found. While for PA-2, the onset potential had a cathodic shift of ca. 0.2 V with a reverse peak at 0.77 V. The cathodical shift of the oxidation potential can also be seen clearly for the polymer PB and its hybrids (Figure 6-15b). This is in agreement with the MLCT absorption in our UV/vis studies. The irreversibility of the oxidation process for these hybrids may be due to charge trapping, which was also observed in other metal containing conjugated polymers.39 The dc conductivities of the polymers and their corresponding hybrids were studied by the conventional four-probe method. These conductivities were measured at different doping times. Measurements showed that the conductivities of these hybrids are in the range of 10-3-10-2 S/cm. This is about a 103 decrease compared with that of iodine-doped metal-free conjugated polymers (σ = 0.1-10 S/cm). Consequently, this may be due to the localization of the π-electrons, and thus, hindrance of the electron mobility along the polymer backbone. (a) Anodic 0.1 mA PA-1 PA Cathodic PA-3 0.4 0.8 1.2 Potential /V vs. SCE 212 (b) 0.1 mA PB-1 PB PB-2 Anodic Cathodic 0.4 0.8 Potential /V vs. SCE 1.2 Figure 6-15. Cyclic voltammogram of (a), polymers P3 and its hybris, (b), polymer P4 and its hybrids in 0.1M tetrabutylammonium hexylfluorophosphate (n-Bu4NPF6) at 80 mV/s. Sensitivities of the hybrids to iodine and TFA The Electrochemical Quartz Crystal Microbalance (QCM) is a good method to investigate the sensitivities of the hybrids to iodine vapor and TFA vapor. As a mass sensor, piezoelectric quartz found early applications as monitors during thin film formation by physical vapor deposition processes. The use of the quartz crystal as a microbalance can be traced to the work of Strutt,40 Onoe,41 and Sauerbrey.42 The extraordinary sensitivity was exploited by the development of QCM to monitor the thickness of micron- and submicron-thick films. At present times, the QCM has become standard equipment in thin-film laboratories. Soon after the development of QCMs, other applications followed, whereby a deposited film responded to chemical or physical interactions to give mass responses. Thus, humidity sensors and other chemical sensors were developed in an explosive growth that still continues. The major advantage of QCM is that it is very sensitive, it is simple to construct and operate, and it can be utilized in a wide variety of circumstances. 213 Early investigations indicated that, for small mass changes, a decrease in the vibration mode frequency of a crystal, upon which a thin film is deposited, is linearly proportional to the deposited mass. The unloaded resonant frequency, fQ, is found from the condition that the bulk material thickness, d, is an integral multiple of half-wavelength λQ (i.e., d = n λQ/2 = nVQ/2fQ), where VQ is the shear wave velocity in quartz. Therefore,43 fQ = nVQ/2d (6.1) if one assumes a fundamental frequency (n = 1), then NAT = dfQ, which is the frequency constant of the commonly used AT-cut crystal. The density, mass, and thickness of the quartz are related by: d = MQ/Aρ, where A is the surface area. This yields ∆f/fQ = -∆MQ/dAρ (6.2) The change is frequency resulting from the decomposition of a thin, uniform film of any foreign substance would be equal to that resulting from a layer of quartz of the same mass. Using the relationship between the thickness and NAT, one obtains ∆f = -∆Mf2Q/AρnAT (6.3) where ∆M is the mass of film of any substance added to quartz plate. From equation 6.3, we can also obtain the following: ∆M = - (AρnAT/f2Q)∆f (6.4) Equation 6.4 is the fundamental relationship that relates the frequency decrease to the increase of mass loading on the quartz crystal, and it reveals that the mass sensitivity can be calculated from the following principle: -∆f / Hz to Times (mins) In our experiments, the QCM was used to measure the iodine mass absorbed by the polymer films coated on the QCM surface. Our QCM was coated with the polymers PA, PA-1, and PA-2 toluene solution, and then dried in an oven. During the measurements, 214 the coated QCM was put into the chamber with one particle of iodine. Their frequency changes were then recorded according to the time and the curve drawn in Figure 6-16. Form the figure we can see that the frequency changes are faster for our hybrids (PA-1 and PA-2) than for metal-free polymer PA. As demonstrated, the frequency change for PA is about 3,470 Hz in the first 10 minutes, while the frequency changes for PA-1 and PA-2 are 8,644 and 14,565 Hz, respectively. Compared with the frequency change for these hybrids, with more ruthenium carbonyl clusters attached to the polymer, we found a faster frequency change of the sample. That is, our substrates absorbed more iodine vapor in the same time span. Ru10-PBTAzOC12 fi-f0 (Hz) 60.0k Ru05-PBTAzOC12 40.0k 20.0k PBTAzOC12 0.0 10 20 Time (Mintues) 30 40 Figure 6-16. QCM measurement of the mass increase caused by iodine absorption by the polymers film. Conductivity measurements also revealed that these hybrids show a faster response time to the iodine vapor than the metal free conjugated polymers. For instance, PA can reach its highest conductivity (σ = 1.64 S/cm) after 72 hours exposure to iodine vapor, while its hybrids reached their highest conductivity (PA-1, σ = 0.04 S/cm; PA-2, σ = 0.007 S/cm) in about 2- hours. The high doping speed of the hybrids may be due to 215 their higher surface area and the multinuclear transitional metal centers. As discussed previously, following coordination with ruthenium, the amorphous polymer films increased their surface area greatly by formation of spheres with diameters of 100 nm to µm. Also, the multinuclear transitional metal clusters make the resulting hybrids more sensitive to iodine vapor.3 The morphology studies of the iodine exposed hybrids by SEM confirm our conclusions. Figure 6-17 displays the hybrid surface changes after exposure to iodine vapor. It clearly shows that the iodine doping mainly occurs at these sphere areas. This is probably because of the large surface area of these regions and the richness of the ruthenium cluster. Figure 6-17. The surface change of the hybrids after exposed to iodine for 40 mins. Conclusions We have shown the first example of the coordination of multinuclear transitional metal clusters into the π-conducting polymer backbone by refluxing the conjugated polymers with the transitional metal cluster in xylene. Analysis of single crystallography data of our model compounds, and comparisons of spectra from our hybrids with that of the model compounds, reveal the coordination mode of the transitional metal cluster with the 216 π-conjugated polymer backbone. As expected, the hybrids displayed tunable optical and electrical properties with different transitional metal cluster contents. NMR, FT-IR, and SEM studies monitored controllable coordination of the transitional metal cluster to the π-conjugated polymer backbone. Importantly, the hybrids showed high sensitivity to iodine vapor during doping, which was realized by the high surface structure of the hybrids. SEM and the presence of multinuclear transitional centers confirmed this. 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Lett., 1989, 54, 1976. 219 [...]... electron-donating properties of the fivemembered ring of azulene and the large torsion angle between the thiophene ring and the benzene ring 134 1 36 1 1.419 8 1 .35 1 39 8 1.465 5 27 S 1 72 7 1 1.41 1 1 .3 7 1.467 9 1 3 9 0 85 1 .3 Ph 6 1 .3 5 1 S 1. 73 S 1 .35 4 28 1.7 1.4 01 1.457 4 72 1 8 72 1 1.471 86 1 .3 1.489 1.417 1 .35 3 9 36 1 1 .3 97 (a) 1.420 1 .37 9 79 1 .3 (b) Figure 4-9 Bond distance in (a), Oligoa; and (b), Oligob... 236 2.5 (3) 1650.2(2) 5626.4( 13) Å cell dimens 137 4 2 8 Dc (g cm -3) 1 .32 9 1 .33 8 1.1 63 abs coeff, mm-1 0.245 0 .31 9 0.2 13 F(000) 992 696 2112 θ range (deg) 1.98 -30 .04 1.96-25.00 1.44-25.00 no of reflcns measd 97 53 17761 30 337 R1 a 0.0 438 0.04 73 0.0 836 wR2a 0.1181 0.1050 0.1995 0 .33 2, -0.211 0 .37 1, -0.244 0.290, -0.266 Z final R indices [ I>2σ(I)] largest difference -3 peak, hole (e Å ) a R1 = Σ||F0| - |Fc||/Σ|F0|;... 2761.9 (3) 31 69.4(2) 8 8 1.406 1 .34 3 abs coeff, mm 0 .37 0 0 .32 9 F(000) 1216 134 4 θ range (deg) 1.86-29.99 2.12 -30 .00 no of reflcns measd 21554 24282 0.0480 0.0 534 0.11 03 0. 132 2 0 .39 5, -0. 234 0.562, -0.201 cell dimens γ, deg vol, Å 3 Z Dc (g cm -3) -1 final R indices [ I>2σ(I)] R1a a wR2 - largest difference peak, hole (e Å 3 a ) R1 = Σ||F0| - |Fc||/Σ|F0|; wR2 = √{Σ[w(F02 – Fc2)2]/Σ[w(F02)2]} Structure of. .. ring and the azulene ring In Monoa, the angle between thiophene and the five-membered ring of azulene was found to be 43. 20 and 34 .40 In Monob, the torsion angle between thiophene and the five-membered ring of azulene ring was found to be 44.70 and 45.00 The large torsion angles arise from steric hindrance between the seven-membered ring of azulene and the thiophene ring The crystal structure of Oligoa... Monoa, Monob, 1 .3 83 S 1.69 1 1 .38 1 1 .34 4 1.410 1 1 .38 0 37 9 O 1.500 1.414 84 1 .3 1.414 1 72 3 1.461 1 40 1 1.40 7 1 3 68 6 39 1.468 1 0 1 .37 1 72 7 S 1 .34 5 1 71 0 Oligoa, and Oligob are found to be 0.015, 0.008, 0.011, 0.007 Å respectively O 81 1 3 (a) (b) Figure 4-12 (a), ORTEP drawing of MonoO6 and (b), bond distance in MonoO6 The packing arrangement of MonoO6 is of the “herringbone” type: the molecular... molecular structure and atomic numbering of MonoO6 138 As expected, a larger twist between the thiophene ring and the azulene ring was found The torsion angle between the thiophene and the five-membered ring of azulene is 400 (C2-C3-C15-S2) and 440 (C2-C1-C11-S1) Furthermore, because of the large steric effect of the long side group, a diminution of the angle between thiophene and azulene was found The... (b) Figure 4-18 Cyclic voltammogram of (a) Oligoa (1×10-3M) and (b) Oligob (1×10-3M) in CH2Cl2 solution containing n-Bu4NPF6 (0.1M) Scan rate 80 mV/s Conclusions In order to better understand the physical properties of the copolymers we obtained in Chapter 3, we designed and synthesized a series of monomers and oligomers as model compounds for the corresponding copolymers 149 In this chapter, models... axis; (b), b axis, and Monob viewed from (c), a axis; (d), c axis 130 Table 4-1 Crystal data and experimental details data Monoa Monob empirical formula C18H12S2 C20H16S2 fw 292.40 32 0.45 T (K) 2 23( 2) 2 23( 2) radiation wavelength, Å 0.710 73 0.710 73 crystal system Orthorhombic Orthorhombic space group Pbca Pbca a, Å 17 .32 67( 13) 7.5257 (3) b, Å 7.2617(5) 10.96 53( 5) c, Å 21.9512(16) 38 .4072(17) α, deg... 1998, 4 23 1 53 Chapter 5 Reason for the high conductivity of the azulene containing copolymers by studying their monomerTCNQ charge-transfer crystal structures and corresponding polymer-TCNQ charge-transfer complex Introduction In Chapter 3, we showed the high conductivities of a series copolymers containing azulene moiety in the main chain Upon doping with iodine or protonation with TFA, these copolymers. .. the thiophene and the five-membered ring of azulene was found to be 48.10 (C4-C5-C7S1), and the torsion angle between the thiophene and the benzene ring was found to be 9.10 (S1-C10-C12-C17) The torsion angle between thiophene and azulene is bigger than that of in the Monob However, because of the small torsion angle between the thiophene 132 ring and benzene ring, effective conjugation of Oligoa is . S S 1 . 3 8 9 1 . 4 0 2 1.456 1.459 1 . 4 1 2 1 . 4 0 9 1 . 7 2 6 1 .7 2 7 1 . 7 1 0 1 . 3 4 2 1 . 3 4 2 1.415 1.416 1 . 3 7 3 1 . 3 7 7 1.489 1 . 3 8 4 1 . 3 8 2 1 . 3 9 3 1 . 3 8 7 1 . 7 0 4 1 . 3 7 8 1 . 3 8 0 Monoa S S 1 . 4 0 3 1 . 4 0 4 1.461 1.465 1 . 4 1 5 1 . 4 1 5 1 . 7 3 3 1 . 7 3 5 1 . 7 0 9 1 . 3 5 3 1 . 3 4 7 1.4 23 1.428 1. 3 7 5 1 . 3 7 2 1.484 1 . 3 8 5 1 . 3 8 3 1 .39 1 1 . 3 90 1 . 7 0 8 1 . 3 8 8 1 . 3 8 5 Monob. 77.887(2) 90 vol, Å 3 236 2.5 (3) 1650.2(2) 5626.4( 13) 137 Z 4 2 8 D c (g cm -3 ) 1 .32 9 1 .33 8 1.1 63 abs coeff, mm -1 0.245 0 .31 9 0.2 13 F(000) 992 696 2112 θ range (deg) 1.98 -30 .04 1.96-25.00. S S 1 . 3 8 9 1 . 4 0 2 1.456 1.459 1 . 4 1 2 1 . 4 0 9 1 . 7 2 6 1 .7 2 7 1 . 7 1 0 1 . 3 4 2 1 . 3 4 2 1.415 1.416 1 . 3 7 3 1 . 3 7 7 1.489 1 . 3 8 4 1 . 3 8 2 1 . 3 9 3 1 . 3 8 7 1 . 7 0 4 1 . 3 7 8 1 . 3 8 0 Monoa