Br Br B B
Chapter 2
Table 1. Physical properties of the PFO-POSS copolymers.
Tda(oC) Mn Mw PDI Yield(%)
PFO 372 27,000 51,000 1.86 96
PFO-POSS-1% 382 21,000 42,000 1.96 78
PFO-POSS-3% 381 20,000 37,000 1.85 68
PFO-POSS-5% 397 16,000 31,000 1.93 79
PFO-POSS-10% 416 12,000 24,000 1.97 65
a Temperature at which 5% weight loss occurred, based on the initial weight.
Table 2. Optical properties of the PFO-POSS nanocomposites.
(UV, nm) a
λmax λmax (PL, nm) quantum yield
solutionb film solutionb film filmc
PFO 384 390 418 (441) 425 (448) 0.55
PFO-POSS-1% 374 383 417 (440) 423 (447) 0.57 PFO-POSS-3% 374 381 417 (437) 423 (447) 0.64 PFO-POSS-5% 372 381 417 (437) 423 (447) 0.67 PFO-POSS-10% 362 380 416 (436) 422 (446) 0.86
a The data in parentheses are the wavelengths of shoulders and subpeaks.
b The absorption and emission measured in THF.
c PL quantum yield estimated relative to a sample of poly-2,7-(9,9’-dioctylfluorene) (ΦFL=0.55).
Chapter 2
5 4 3 2 1
8 7 6
(c) D-POSS-diAF
(b) Cl-POSS
(a) 9,9’-Bis(4-aminophenyl)-2,7-dibromofluorene
ppm
Figure 1. 1H NMR spectra of (a) 3, (b) Cl-POSS, and (c) 4.
y x -NH- -CH2
--CH2
-*
*
*
Chapter 2
2500 2000 1500 1000 500
1023cm-1 1097cm-1
(e)
(d)
(c)
(b)
T% (a. u.)
Wavenumber (cm-1)
(a)
Figure 2. FTIR spectra of (a) PFO, (b) PFO-POSS-1%, (c) PFO-POSS-3%, (d) PFO-POSS-5%, and (e) PFO-POSS-10%
6 12 18 24 30
(f) (e)
(d) (c) (b) (a)
Intensity (a. u.)
2θ 10.5 Å
4.6 Å
8.0 Å 3.3 Å
Figure 3. X-Ray diffraction curves of PFO-POSS nanocomposite
Chapter 2
350 400 450 500 550 600 650
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Intensity (a. u.)
Wavelength (nm)
PFO
Fresh films 200oC for 1h 200oC for 2h
Figure 4 (a) PL spectra of PFO films before annealing (dotted line) and after annealing at 200 °C for 1 h (dashed line) and 2 h (solid line) under a nitrogen atmosphere.
1850 1800 1750 1700 1650 1600 (i) pure PFO
(ii) 5% POSS
(iii) 10% POSS
T% (a.u.)
Wavenumber (cm-1)
1713 cm-1 before baking 200oC for 6h
Figure 4 (b) FTIR spectra of (i) PFO, (ii) PFO-POSS-5%, and (iii) PFO-POSS-10%
before (solid line) and after (dashed line) baking at 200 °C for 6 h.
Chapter 2
Figure 5. UV–Vis absorption and PL spectra of (a) PFO-POSS-1% , (b) PFO-POSS-3%, (c) PFO-POSS-5%, and (d) PFO-POSS-10% films before (dotted line) and after (solid line) annealing at 200 °C for 2 h under a nitrogen atmosphere.
300 350 400 450 500 550 600 650
0.0
300 350 400 450 500 550 600 650
0.0
300 350 400 450 500 550 600 650
0.0
300 350 400 450 500 550 600 650
0.0
Chapter 2
POSS domain (a)
Figure 6. Transmission electron micrographs of (a) PFO-POSS-1%, (b) PFO-POSS-3%, (c) PFO-POSS-5%, and (d) PFO-POSS-10%.
20 nm
(b)
20 nm
(c)
100 nm
(d)
100 nm
Chapter 2
350 400 450 500 550 600 650 700 750 800
0.0
Figure 7. Electroluminescence spectra of the devices prepared from PFO-POSS and PFO in the configuration ITO/PEDOT/polymer/Ca/Al.
Figure 8. I–V curves of the devices prepared from PFO-POSS and PFO in the configuration ITO/PEDOT/polymer/Ca/Al.
Chapter 2
300 400 500 600
Optical density (a. u.) PL intensity (a. u.)
(e)
Figure 9. UV-vis absorption and Photoluminescence spectrum (excited at 380 nm) in THF of (a) PFO, (b) PFO-POSS-1%, (c) PFO-POSS-3%, (d) PFO-POSS-5%, (e) PFO-POSS-10%
200 400 600 800
Figure 10. TGA curves of polymer at a heating rate of 20 oC/min under nitrogen atmosphere. (a) DSC curves of PFO and PF-POSS-10% at a heating rate of 10 oC /min under nitrogen atmosphere.
Chapter 3
Chapter 3: Enhanced Luminance and Thermal Properties of Polyphenylenevinylene Copolymer Presenting
Side-Chain-Tethered Silsesquioxane Units
3-1 Introduction Materials
Emissive media based on electroluminescent (EL) polymers are currently under development for a number of display applications, [27, 57, 58] including large-area flat-panel displays that can be driven at low voltage. Polymer light-emitting diodes (PLEDs) are very promising candidates for the development of low-cost,
multicolored, large-area flat-panel displays because their molecular structures are readily modified and because they can be handled using a range of wet processing techniques. [59-60] A number of issues remain to be resolved, however, before commercialization of these devices can occur. The formation of excimers resulting from the aggregation of their molecular chains in the solid state, and rather short operating lifetimes, owing to their low thermal stabilities. Several attempts have been made to reduce the formation of aggregates of polymer chains in the solid state.
One such approach is the introduction of bulky organic units into the side chains of the polymer. This tactic has been used, for example, in the case of
poly(p-phenylenevinylene) (PPV)-based alternating copolymers containing
conjugated phenylenevinylene segments and nonconjugated spacers; [61-63] these bulky side groups disrupt the packing of the polymer chains, which results in the formation of amorphous PPVs displaying reduced aggregation. Another approach to
improving the efficiency of the devices is to blend hole-transporting and
electron-transporting materials to balance the injected charges. [64-66a] When such a device is operated for a long time, however, this method can cause some defect to occur in some cases. [66b-d] When such a device is operated for a long time,
Chapter 3
however, this method can cause some phase separation to occur, which is detrimental to the device’s performance. Other approaches include improving the antioxidative properties of the pendant groups or chain ends[67] and limiting chain mobility by blending[52] with a high-Tg polymer. One approach to not only preventing polymer chains from aggregating but also to improving the antioxidative properties of their pendent groups is to use inorganic pendent groups as the side chains of the conjugated polymers.
The chemistry of polyhedral oligomeric silsesquioxane (POSS) covalently
bonded to organic polymers has been developed recently. One set of members of the polyhedral oligomeric silsesquioxane family are octamers having the general formula (RSiO1.5)8; they consist of a rigid, cubic silica core having a nanopore diameter of ca.
0.3–0.4 nm. [23] The incorporation of (RSiO1.5)8 into some polymers leads to an enhancement of their thermal stability and mechanical properties. [68-69]
The first study in which POSS and conjugate polymers were combined involved tethering POSS to the chain ends of
poly(2-methoxy-5-[2-ethylhexyloxy]-1,4-phenylenevinylene) (MEHPPV) [70] and the luminescent polymer poly(9,9´-dioctylfluorene) (PFO). The enhanced
electroluminescence of these nanostructured polymers was attributed to POSS imparting a reduction in the degree of either aggregation or excimer formation. [67]
The approach of tethering POSS at the ends of a polymer’s chain, however, limits the number of POSS units that can be attached. In a previous study, we synthesized a series of side-chain-tethered POSS derivatives of polyimide as a method of lowering its dielectric constant. [71] More recently, side-chain-tethered PF-POSS copolymers have been synthesized; they display a stronger and purer blue electroluminanscence.
[71a] In this paper, we report a new series of asymmetric PPV derivatives presenting POSS units in their side chains. We synthesized these polymers using the Gilch
Chapter 3
polymerization method. We incorporated the POSS units into the PPV to improve its thermal stability and EL characteristics. The bulky silsequioxane group was introduced at the meta position of the phenyl substitutents to inhibits intermolecular interactions between the resulting polymer chains. Such meta substitution also helps to provide an amorphous state and better processibility. To the best of our
knowledge, the introduction of an inorganic side group, such as POSS, into PPV-based alternating copolymers has not yet been described. We believe that developing POSS/poly(p-phenylene vinylene) copolymers having well-defined architectures will allow its luminescence properties to be tailored more precisely through modifications of its molecular structure.
3-2 Experimental Section 3-2-1. Materials
Chlorobenzylcyclopentyl-POSS[70a] was synthesized according to literature procedures. THF was distilled under nitrogen from sodium benzophenone ketyl;
other solvents were dried using standard procedures. All other reagents were used as received from commercial sources, unless otherwise stated.
Chlorobenzylcyclopentyl-POSS. 1H NMR (300 MHz, CDCl3): 7.64 (d, J = 8.1 Hz, 2H), 7.37 (d, J = 8.1 Hz, 2H), 4.57 (s, 2H), 2.26–1.21 (m, 56H), 1.16–0.81 (m, 7H) ppm. 29Si NMR (600 MHz, THF): –67.8, –68.2, –79.6 ppm.
Synthesis of POSS-CH3 (1).
2,5-Dimethylphenol (238 mg, 1.95 mmol) was stirred with K2CO3 (4.58 g, 33.18 mmol) and KI (1.57 g, 9.48 mmol) in DMF (30 mL) and THF (15 mL) at room temperature for 1 h. A small amount of Cl-POSS (2.0 g, 1.95 mmol) was added and
Chapter 3
then the whole mixture was heated at 70 °C for 3 h. The reaction mixture was then slowly poured into water (300 mL) and extracted with chloroform (3 × 50 mL). The combined extracts were dried (MgSO4), the solvents were evaporated, and the residue was purified by column chromatography (hexane/ chloroform, 1:10) to afford 1 (1.86 g, 81%). 1H NMR (300 MHz, CDCl3): δ 7.70 (d, J = 8.1Hz, 2H), 7.51–7.31 (b, 3H), 7.03 (d, J = 6.9 Hz, 1H), 6.67 (s, 1H), 5.09 (s, 2H), 2.37 (s, 3H), 2.32 (s, 3H),
2.27–1.21 (m, 56H), 1.17–0.81 (m, 7H) ppm.
Synthesis of POSS-CH2Br(2).
A mixture of POSS-CH3 (1; 600 mg, 0.510 mmol), NBS (198.6 mg, 1.02 mmol), and AIBN (8.0 mg) was heated under reflux in carbon tetrachloride under nitrogen for 3 h.
The reaction mixture was filtered to remove succinimide, the solvent was evaporated, and the residue was purified by column chromatography (hexane/chloroform, 1:10).
1H NMR (300 MHz, CDCl3) δ: 7.73 (d, J = 8.1 Hz, 2H), 7.59 (d, J = 6.9 Hz, 1H), 7.38 (d, J = 8.1 Hz, 2H), 7.09 (d, J = 6.9 Hz, 1H), 7.01 (s, 1H), 5.18 (s, 2H), 4.73 (s, 2H), 4.57 (s, 2H), 2.26–1.21 (m, 56H), 1.16–0.81 (m, 7H) ppm. Anal. Calcd for C50H76Br2O13Si8 (%): C, 47.30; H, 6.03. Found: C, 47.18; H, 6.09.
General Procedure for the Synthesis of Copolymers POSS-PPV-co-MEHPPV.
A solution of potassium tert-butoxide (1 M in THF) was added to a solution of the monomer in dry THF, and then the mixture was stirred for 4 h. End-group capping was performed by heating the solution under reflux for 1 h in the presence of
tetrabutylbenzyl bromide. Addition of the THF solution to methanol precipitated the polymer, which was collected, washed with methanol, and stirred in a mixture of methanol and water (1:1) for 1 h. The polymer was collected, washed with methanol,
Chapter 3
filtered, and dried at 50 °C for 24 h. After cooling, the polymer was recovered by precipitating it into a mixture of methanol and acetone (4:1). The crude polymer was collected, purified twice by reprecipitation from THF into methanol, and subsequently dried under vacuum at 50 °C for 24 h. The 1H and 13C NMR spectra of MEHPPV and PPV-POSS appear to be identical because of the low content of POSS in the latter polymer.
3-2-2. Characterization.
1H, 13C, and 29Si nuclear magnetic resonance (NMR) spectra of the compounds were obtained using a Bruker DRX 300 MHz spectrometer. Mass spectra of the samples were obtained on a JEOL JMS-SX 102A spectrometer. Fourier transform infrared (FTIR) spectra of the synthesized materials were acquired using a Nicolet 360 FT-IR spectrometer. Gel permeation chromatographic analyses were performed on a Waters 410 Differential Refractometer and a Waters 600 controller (Waters Styragel Column). All GPC analyses of polymers in THF solutions were performed at a flow rate of 1 mL/min at 40 °C; the samples were calibrated using polystyrene standards. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements were performed under a nitrogen atmosphere at heating rates of 20 and 10 °C/min, respectively, using Du Pont TGA-2950 and TA-2000 instruments, respectively. UV–Vis absorption and photoluminescence (PL) spectra were recorded on a HP 8453 spectrophotometer and a Hitachi F-4500 luminescence spectrometer, respectively. Before investigating the thermal stability of the synthesized polymers, their polymer films were annealed in air at 200 °C for 2 h.
3-2-3. Device Fabrication and Testing.
The electroluminescent (EL) devices were fabricated on an ITO-coated glass
Chapter 3
substrate that was precleaned and then treated with oxygen plasma before use. A layer of poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS, Baytron P from Bayer Co.; ca. 40-nm thick) was formed by spin-coating it from an aqueous solution (1.3 wt%). The EL layer was spin-coated, at 1500 rpm from the
corresponding toluene solution (15 mg mL–1), on top of the vacuum-dried
PEDOT:PSS layer. The nominal thickness of the EL layer was 65 nm. Using a base pressure below 1 × 10–6 Torr, a layer of Ca (35 nm) was vacuum deposited as the cathode and a thick layer of Al was deposited subsequently as the protecting layer.
The current–voltage characteristics were measured using a Hewlett–Packard 4155B semiconductor parameter analyzer. The power of the EL emission was measured using a Newport 2835-C multi-function optical meter. The brightness was calculated using the forward output power and the EL spectra of the devices; a Lambertian distribution of the EL emission was assumed.
3-3 Results and Discussion
A. Polyphenylenevinylene Copolymer Presenting Side-Chain-Tethered Silsesquioxane Units Nanocomposites
Figure 1 displays the 1H NMR spectra of Cl-POSS, POSS-CH3 (1), and
POSS-CH2Br (2). The CH2 peak of Cl-POSS (4.47 ppm) shifted downfield to 5.14 ppm in POSS-CH3. The ratio of the peak areas of the benzylic CH2 and CH2Br protons is ca. 1:2. Taken together, these data suggest that Cl-POSS had reacted with 2,5-dimethylphenol to form POSS-CH3. Table 1 lists the thermal properties and molecular weight distributions of the POSS-PPV-co-MEHPPV copolymers. Both the thermal degradation and glass transition temperatures increased substantially as the amount of POSS in MEHPPV increased, particularly for the case where 10 mol%
POSS was tethered to MEHPPV: we observed an 83 °C increase in the value of Td
Chapter 3
and a disappearance of any glass transition.[72] This situation arose because the tethered bulky POSS enhanced the thermal stability and retarded the mobility of the polymer main chain. The molecular weights of the POSS-PPV-co-MEHPPV copolymers decreased upon increasing the POSS content; this phenomenon can be attributed to the steric hindrance caused by the POSS units during the polymerization process. Figure 2 displays FTIR spectra of MEHPPV copolymers containing different amounts of POSS. The FTIR spectrum of POSS displays two major
characteristic peaks: the Si–C band at 1038 cm–1 and the Si–O–Si band at 1123 cm–1.
Table 2 lists the wavelengths of the absorption, the location of the PL maxima, and the quantum yields of POSS-PPV-co-MEHPPV. The absorption and emission peak maxima of MEHPPV occurred at 499 and 553 nm, respectively; these values are close to those reported in the literature. [70] We observed no aggregation band in these spectra because THF is a good solvent for MEHPPV. The absortion and emission peaks for MEHPPV and POSS-PPV-co-MEHPPV are almost identical. For each polymer, the absorption peak maximum in solution (THF) is located between 499 and 494 nm, with a slight blue shift caused by the presence of POSS; the PL maxima occur at similar wavelengths for all of the polymers. Figure 3A presents the normalized absorption and PL emission spectra of the MEHPPV-POSS copolymer films. The quantum yields of the POSS-PPV-co-MEHPPV copolymers increased substantially as the amount of tethered POSS increased. [80] In particular, the quantum yield of MEHPPV containing 10% POSS was four times higher than that of pure MEHPPV (0.87 vs. 0.19). We attribute this finding to the steric hindrance caused by the POSS units in preventing aggregation of the PPV main chains, which, in turn, reduces the degree of dimer formation after excitation. This improved quantum yield, which has not been reported in any previous studies of POSS/PPV
Chapter 3
copolymers, is a direct result of employing this particular side-chain-tethered POSS architecture.
For fresh MEH-PPV film, the yellowish peak at ~590 nm originates from single chain exciton emissions, [76] whereas the reddish peak at 630 nm is related to
emissions from interchain species, such as aggregates or excimers. [76a] The
difference in the PL spectra of the fresh MEH-PPV and POSSPPV-co-MEHPPV film is small because both polymer chains have not reached equilibrium states by their preparation process (i.e. spin-coating). By annealing the polymer films at higher temperatures as in the work by Schwartz [77] and Yang Yang [78] et al., one could see some more profound changes in their PL spectra. For instance, Figure 3B shows that after annealing MEHPPV film at 150oC for 2 h under air, its PL spectrum
displays a red-shifted broad main peak at 630 nm, indicating formation of aggregates.
While the main emission peak for annealed POSS-PPV10-co-MEHPPV film remain near 590 nm, with a weak peak at 630 nm. Therefore, at the equilibrium states, there is a distinct difference in their PL spectra, due to the bulky and rigid POSS groups tethered to the side of MEHPPV chains. The same phenomena are also observed in EL spectra (Figure 5).
We have carried out by X-ray diffraction for confirming that interchain distance of PPV was increased by side-chain-tethered POSS. Figure 3C displays the X-ray diffraction curves of Cl-POSS, MEHPPV, and PPV-POSS. There are three distinct diffraction peaks at 2θ = 8.3, 19.1, and 26.1° for Cl-POSS (Fig. 3f), which correspond to d-spacings of 10.5, 4.6 and 3.3 Å, respectively. The d-spacing of 10.5 Å reflects the size of the Cl-POSS molecules; the other two spacings are owing to the
rhombohedral crystal structure of POSS molecules. [79] For pure MEHPPV and
Chapter 3
PPV-POSS copolymers, it is evident that they are amorphous and have no side chain alignment. The nearly amorphous structure of pure MEHPPV (Figure 3C-a) originates from the two highly asymmetric substituents, the methoxy and 2-methoxy 5-(2’-ethoxyhexyloxy) for MEH-PPV. [79] When POSS molecules were tethered to PPV, the average interchain distance increased appreciably from X-ray diffraction results. For instance, in the presence of 10% POSS (PPV-POSS-10%), the inter-chain distance increases to 4.6 Å (19.5°) from 4.0 Å (22.0°) for MEHPPV after
deconvolution of the X-ray diffraction curve.
Figure 4A presents a transmission electron microscopy (TEM) image of our POSS-PPV10-co-MEHPPV sample. [81] This image reveals that no large aggregates were formed, but small domains of POSS are present; these POSS domains are dispersed evenly in the polymer matrix—a situation that we confirmed by analyzing this sample’s energy dispersive spectrum (EDS; Figure 4A-(c)). The topology of POSS-PPV-co-MEHPPV copolymers films were studied with atomic force
microscopy (AFM). Figure 4B shows the height image and the phase image of MEH-PPV and POSS-PPV10-co-MEHPPV polymer films prepared with
chlorobenzene as the solvent. The surface roughness of PPV-POSS film is larger than that of pure MEHPPV (0.496 nm vs. 0.206 nm) due to the presence of POSS. The phase images also show that POSS groups are dispersed homogeneously in the whole system.
B. Electroluminescence (EL) Characteristics
Figure 5 displays the electroluminescence (EL) spectra of
POSS-PPV-co-MEHPPV devices. The EL device prepared from MEHPPV emits a strong peak at 590 nm and a vibronic signal in the range 610–620 nm, which is due presumably to the aggregation of MEHPPV and its excimer formation, as discussed
Chapter 3
earlier. The introduction of bulky siloxane units into the PPV side chains
presumably increases the interchain distance, thereby retarding interchain interactions and leading to a reduction in the degree of exciton migration to defect sites.[62]
Figure 6 displays the variations in the current density and brightness of the EL devices.
The turn-on voltage decreased to 2.5 V for PPV containing 10% POSS from 3.5 V for the pure-MEHPPV EL device. As indicated in Figure 6, a more than four-fold increase occurred in the maximum brightness of the
POSS-PPV10-co-MEHPPV-based device relative to that of the pure-MEHPPV EL device (2196 vs. 473 cd/m2) at a drive voltage of 9.5 V. The efficiency of POSS-PPV10-co-MEHPPV is 1.83 cd/A at a current density of 1221 A/m2. These improvements might be due to a decreased degree of aggregation upon the incorporation of the POSS units into the PPV chains.
3-4 Conclusions
We have synthesized a novel poly(p-phenylenevinylene) side-chain-tethered polyhedral silsesquioxane (POSS-PPV-co-MEHPPV) that possesses a well-defined architecture. This particular molecular architecture of PPV-POSS increases the quantum yield of MEHPPV significantly by reducing the degree of interchain aggregation; it also results in a much brighter red light from the EL device by decreasing the degree of aggregation between the polymer chains.
Chapter 3
Table 1. Physical Properties of the POSS-PPV-co-MEHPPV Copolymers.
Tg (°C) Tda(°C) Mn Mw PDI Yield (%)
MEHPPV 71 370 61,000 111,000 1.82 78
POSS-PPV1-co-MEHPPV 90 381 55,000 107,000 1.95 66
POSS-PPV3-co-MEHPPV 96 395 52,000 98,000 1.88 64
POSS-PPV5-co-MEHPPV * 417 48,000 91,000 1.90 69
POSS-PPV10-co-MEHPPV * 453 39,000 73,000 1.87 60
a Temperature at which 5% weight loss occurred, based on the initial weight.
* The glass transition disappeared because of the steric hindrance imposed on the main molecular chains by the POSS units.
Table 2. Optical Properties of the POSS-PPV-co-MEHPPV Nanocomposites.
λmax (UV, nm) λmax (PL, nm)a QY solutionb film solutionb film filmc
MEHPPV 499 517 553 (592) 591 (634) 0.19
POSS-PPV1-co-MEHPPV 499 512 552 (591) 588 (633) 0.43 POSS-PPV3-co-MEHPPV 498 512 552 (591) 586 (632) 0.62 POSS-PPV5-co-MEHPPV 497 511 552 (591) 585 (631) 0.84 POSS-PPV10-co-MEHPPV 494 505 551 (590) 584 (631) 0.87
a The data in parentheses are the wavelengths of the shoulders and subpeaks.
b The absorption and emission were measured in THF.
c PL quantum yield estimated relative to a sample of Rhodamine 6G (Φr = 0.95) [73-75].
Chapter 3
Scheme 1 a. Synthesis of POSS-PPV-co-MEHPPV copolymers.
a Reagents and conditions: i, trichloro[4-(chloromethyl)phenyl]silane, HNEt3Cl; ii, K2CO3, DMF/THF; iii, N-bromosuccinimide (NBS)/ AIBN/ CCl4; iv, tert-BuOK/
THF.
Chapter 3
Chapter 3
2000 1500 1000 500
T% (a.u.)
Wave number (cm
-1)
1123 1038
(a)
(b)
(c)
(d)
(e)
Figure 2 FTIR spectra of (a) MEHPPV, (b) POSS-PPV1-co-MEHPPV, (c) POSS-PPV3-co-MEHPPV, (d) POSS-PPV5-co-MEHPPV, and (e)
POSS-PPV10-co-MEHPPV.
Chapter 3
400 600 800
584 nm 505 nm
591 nm
PL intensity (a.u.)
MEHPPV
PPV-POSS-1
PPV-POSS-3
PPV-POSS-5
PPV-POSS-10
517 nm
O.D . (a.u.)
Wavelength (nm)
Figure 3A. UV–Vis absorption and PL spectra of (a) MEHPPV, (b) POSS-PPV1-co-MEHPPV, (c) POSS-PPV3-co-MEHPPV, (d) POSS-PPV5-co-MEHPPV, and (e) POSS-PPV10-co-MEHPPV recorded in the solid state.
550 600 650 700 750 800 (b)POSS10-PPV-co-MEHPPV
(a) MEHPPV
Intensity (a.u.)
Wavelength (nm)
RT
150oC for 2h
Figure 3B. Normalized (relative to their maximum wavelengths) PL spectra of (a) MEHPPV and (b) POSS-PPV10-co-MEHPPV annealed at room temperature and 150oC in the solid state.
Chapter 3
Figure 3D. Deconvoluted X-ray diffraction spectra of (a) MEHPPV and (b) POSS-PPV10-co-MEHPPV.
Figure 3C. X-ray diffraction spectra of (a) MEHPPV, (b) POSS-PPV1-co-MEHPPV, (c) POSS-PPV3-co-MEHPPV, (d) POSS-PPV5-co-MEHPPV, (e) POSS-PPV10-co-MEHPPV, and (f) Cl-POSS.
5 10 15 20 25 30
(f) (e) (d) (c) (b) (a)
11.2o 19.1o 26.1o
8.3o
Rhombohedral crystal structure of POSS molecules
Size of Cl-POSS molecules
Intensity (a.u.)
2θ
10 15 20 25 30
(b) POSS10-PPV-co-MEHPPV (a) MEHPPV
19.5o 22.0o
Intensity (a.u.)
2θ
Chapter 3
Figure 4A. (a) Transmission electron micrograph of POSS-PPV10-co-MEHPPV. (b) enlarged view. (c) EDS of POSS-PPV10-co-MEHPPV.
0 1 2 3 4 5 6 7 8 9 10
100 nm
(a)
POSS domain 100 nm
(b)
C
(c)
Cu
KeV
O Si Cu Cu
Chapter 3
roughness = 0.496 nm root-mean-square roughness = 0.206 nm root-mean-square (a)
(b)
Figure 4B. Surface roughness of thin films of (a) MEHPPV. (b) POSS-PPV10-co-MEHPPV.
Chapter 3
500 550 600 650 700 750
Intensity (a.u.)
Wavelength (nm)
PPV-POSS-5%
PPV-POSS-10%
MEHPPV
FWHM
Figure 5. Electroluminescence spectra of the devices prepared from
POSS-PPV-co-MEHPPV in the configuration ITO/PEDOT/polymer/Ca/Al.
Figure 6. I–L-V curves of the devices prepared from POSS-PPV-co-MEHPPV and
Figure 6. I–L-V curves of the devices prepared from POSS-PPV-co-MEHPPV and