synthesis and optical properties of organic-inorganic hybrid semi-interpenetrating polymer network...

Synthesis and Optical Properties of Organic–Inorganic Hybrid

Semi-Interpenetrating Polymer Network Gels Containing Polyfluorenes

Naofumi Naga,1 Tomoharu Miyanaga,1 Hidemitsu Furukawa2

1Department of Applied Chemistry, College of Engineering, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo

135-8548, Japan2Department of Mechanical Systems Engineering, Graduate School of Science and Engineering, Yamagata University, 4-3-16

Jonan, Yonezawa, Yamagata 992-8510, Japan

Correspondence to: N. Naga (E-mail: [email protected])

Received 17 September 2013; accepted 10 December 2013; published online 20 January 2014

DOI: 10.1002/pola.27077

ABSTRACT: Organic–inorganic hybrid semi-interpenetrating

polymer network (semi-IPN) gels containing polyfluorenes

(PFs) are synthesized by hydrosilylation reaction of joint

and rod molecules in toluene, where PFs are poly(9,9-dihexyl-

fluorene-2,7-diyl) (PF6) or, poly(9,9-dioctylfluorene-2,7-diyl) (PF8),

joint molecules are 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS),

or 1,3,5,7,9,11,13,15-octakis(dimethylsilyloxy)pentacyclo-[9,5,1,1,1,

1]octasilsesquioxane (POSS), and rod molecules are 1,5-hexa-

diene (HD) or 1,9-decadiene (DD). The semi-IPN gels containing

low molecular weight PF6 show higher photoluminescence effi-

ciency (/g) than the toluene solution of PF6L (/s). The semi-IPN

gels composed of long rod molecule of DD and cubic joint mole-

cule of POSS show the most effective increase in the emission

intensity. The emission intensity of PF6L increases as formation

of the network in the POSS-DD semi-IPN gel. The POSS-DD semi-

IPN gels containing high molecular weight PF6 and PF8 also

show the increase of emission intensity than those of the toluene

solutions. The semi-IPN synthesized in cyclohexane show synere-

sis and phase separation between network structure and PF

chains. The semi-IPN gels containing PF8 show emission peaks

at 450 and 470 nm derived from b-sheet structure of PF8. A

systematic study clears correlation between emission property

and network structure and/or composition of semi-IPN gels.

The semi-IPN gels provide emissive self-standing soft materials

with high efficiency and in a narrow wavelength range emission.

VC 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym.

Chem. 2014, 52, 973–984

KEYWORDS: fluorescence; gelation; gels; interpenetrating net-

works (IPN); luminescence; organic–inorganic hybrid gel; poly-

fluorene; semi-interpenetrating polymer network gel

INTRODUCTION Organogels are composed by polymer net-work in organic solvents. The organogels are used for variouspurposes, such as coagulant of oil, cosmetics, electrolytes, andso on. The networks in the organogels are divided into threeclasses. One is physical gel whose network is formed by non-chemical bond, such as hydrogen bond, ionic bond, coordinatebond, and hydrophobic bond. Another is chemical gel whosenetwork is formed by chemical bond.

The authors recently developed organo-chemical gels com-posed by organic–inorganic hybrid network in organic sol-vents. The organic–inorganic hybrid gels were synthesizedby a hydrosilylation reaction of multiple Si-H functionalcyclic siloxane, 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS)or cubic silsesquioxane 1,3,5,7,9,11,13,15-octakis(dimethylsi-lyloxy)pentacyclo-[9,5,1,1,1,1]octasilsesquioxane (POSS) witha,x-nonconjugated dienes, 1,5-hexadiene (HD), and 1,9-deca-diene (DD) in toluene.1,2 The gels are composed by geometri-cal multifunctional joint molecules and bifunctional rod

molecules. Characterization of the network structures of theobtained gels was quantitatively investigated by means of anoriginally developed analytical method of scanning micro-scopic light scattering (SMILS) system.3 The SMILS analysisof the gels cleared the extremely narrow distribution ofmesh size in the gels. Furthermore, the mesh size of the gelscould be controlled by the length of the a,x-nonconjugateddienes used, and the gels composed of long spacer monomerof DD or cubic crosslinking reagent of POSS containingformed large mesh size, about 1.5 nm, in the networkstructure.1,2

The mesh size of the organic–inorganic hybrid gels would besuitable to incorporate functional small molecules in themesh. The organic–inorganic hybrid gels were synthesized inthe presence of fluorescent molecules to add emission prop-erty to the gels.4 We found out that the gels containing pyreneshowed higher emission intensity than that of the toluenesolution of pyrene due to the effective isolated incorporation

Additional Supporting Information may be found in the online version of this article.

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of pyrene in the mesh of the gels, named “framed effect.” Thedeveloped emissive gels should be applicable to the emissionlayer of gel light-emitting device (GLED). The GLED is com-posed of organic solvent and conjugated polymer (physicalgel)5 or crosslinked polymer with fluorescent molecule (chem-ical gel)6,7 sandwiched between two electrodes. The GLED hasadvantage in processability of light-emitting device. We cameto an idea that the synthesis of the organic–inorganic hybridgel in the presence of linear conjugated polymers as fluores-cent molecule, termed semi-interpenetrating polymer network(semi-IPN) gel. This article reports synthesis of organic–inor-ganic hybrid semi-IPN gels from TMCTS or POSS, and HD orDD by means of a hydrosilylation reaction in the presence ofpolyfluorenes (PFs), poly(9,9-dihexylfluorene-2,7-diyl) (PF6),and poly(9,9-dioctylfluorene-2,7-diyl) (PF8) in toluene orcyclohexane as preliminary basic research for GLED, as shownin Scheme 1. Effect of network structure, network formationprocess, structure of PFs, and polarity of solvent on the emis-sion property of the semi-IPN gels was studied.

EXPERIMENTAL

MaterialsHD and DD (Tokyo Kasei Kogyo) were distilled over calciumhydride under nitrogen atmosphere. TMCTS (Chisso) andPOSS (Aldrich Chemical) were used without further purifica-tion. Platinum-divinyltetramethyldisiloxane complex Pt(DVS)(Chisso) was commercially obtained and used as received.

Low molecular weight PF6 (PF6L) was prepared by polymer-ization of 9,9-dihexyl-2,7-dibromofluorene in dimethylforma-mide using Ni(II)Cl2, 2,20-dipyridyl, triphenylphosphine, andZn at 100 �C for 6 h; Mn 5 2900, Mw/Mn5 2.9. High molecu-lar weight PF6 (PF6H) was prepared by Suzuki couplingreaction of 9,9-dihexyl-2,7-dibromofluorene and 9,9-dihexyl-fluorene-2,7-diboronic acid bis(1,3-propanediol) in tetrahy-drofura using tetrakis(triphenylphosphine)palladium(0) and

K2CO3 aq refluxing for 72 h, Mn5 14,000, Mw/Mn 5 4.9. PF8was commercially obtained from Aldrich Chemical and usedas received, Mn 5 29,000, Mw/Mn5 3.7. Toluene was driedover calcium hydride under refluxing for 6 h and distilledbefore use. The mole ratio of vinyl group in diene to Si-Hgroup in joint molecule was adjusted to 1.0. The molar ratioof HD or DD to the Pt(DVS) catalyst was 1:1025 in the reac-tion system. Samples were prepared by the following proce-dures with special care for getting rid of dust and measuredin as-prepared state at 25 �C.

Synthesis of Semi-IPN gelPOSS-DD semi-IPN gel containing PF6L (1.0 mM of fluoreneunit) (Run 9): 10.2 mg (0.01 mmol) of POSS, 5.5 mg (0.04mmol) of DD, 166 mL of toluene solution of PF6L (1.0 mM offluorene unit), and 38 mL of toluene solution of Pt(DVS) (4.03 1024 mmol) containing PF6L (1.0 mM of fluorene unit)were added to a sample tube of 4 mm diameter under thenitrogen atmosphere. After the sample tube was sealed byburning off, it was placed without stirring in the dark atroom temperature. The other semi-IPN gels were preparedwith the same procedures. The semi-IPN gels for the studiesof optical properties were prepared in an optical quartz cellof 0.7 mL volume equipped a seal cap according to the syn-thetic methods described above.

Analytical ProceduresQuantitative determination of minute mesh size of the gelswas performed with the SMILS system.5 The developed SMILSsystem enables us to scan and measure at many differentpositions in an inhomogeneous gel, in order to rigorouslydetermine a time- and space-averaged, that is, ensemble-averaged, (auto-)correlation function of fluctuating mesh sizein the gel. Analysis of the ensemble-averaged function makesit possible to quantitatively characterize the mesh-size distri-bution of network structure in inhomogeneous gels. Scanning

SCHEME 1 Synthesis of organic–inorganic hybrid semi-IPN gels containing polyfluorenes.

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measurement was performed at more than 25 points for eachsample to determine ensemble-averaged dynamic structurefactor. The determined correlation function was transformedto the distribution function of relaxation time by using numer-ical inversed Laplace transform calculation. For these gels, afew peaks of relaxation modes were observed in the distribu-tion function. Based on the observation of scattering-angle, q,dependence of the relaxation modes, all the observed modesusually have q2 dependence, which correspond to transla-tional diffusion. In the following, all the results were deter-mined at the scattering angle fixed at 90�. The observedmodes, as assigned to the cooperative diffusion of gel net-work, were used for the determination of radius of mesh(mesh size) (n; m) with Einstein–Stokes formula,

n516pn2sRKBsin 2 h

2

3gk2

where n, sR, KB, h, g, and k are refractive index of toluene orcyclohexane, Ensemble-averaged relaxation time (s), Boltz-mann constant (1.38 3 10223 JK21), scattering angle (90�),viscosity coefficient of toluene (5.22 3 1024 Nm2s21) orcyclohexane (8.21 3 1024 Nm2s21) at 298 K, wave length ofincident ray (4.42 3 1027 m), respectively.

Emission spectroscopy was investigated with a SHIMADZURF-5300PC equipped a 150 W xenon lamp. A slit of 5 nmwas applied, and the absorption was recorded by 1 nm at ascan rate of 600 nm min21. UV–vis absorption spectroscopywas conducted with a SHIMADZU UV-1600PC. A slit of 2 nmwas applied, and the absorption was recorded by 0.1 nm ata scan rate of 550 nm min21.

RESULTS AND DISCUSSION

Synthesis of Organic–Inorganic Hybrid Semi-IPN GelsContaining PF6L in TolueneThe hydrosilylation reaction of TMCTS or POSS and HD orDD was investigated in the presence of low molecular weightPF6L (1.0 mM of fluorene units) using Pt(DVS) catalyst intoluene at room temperature. Critical gel concentrations, thelowest monomer concentration which can yield gel, of thesemi-IPN gels of TMCTS-HD, TMCTS-DD, POSS-HD, or POSS-DD are 10.7, 10.6, 5.9, or 4.9 wt %, respectively. The criticalgel concentrations of the gels of TMCTS-HD, TMCTS-DD,POSS-HD, or POSS-DD without PF6L are 7.4, 5.7, 4.3, or 2.4wt %,1 respectively. The critical gel concentrations of thesemi-IPN gels are larger than that of the corresponding gelswithout PF6L. Reaction rates of the Si-H and diene ofTMCTS-HD, TMCTS-DD, POSS-HD, or POSS-DD in the solstate, less than critical gel concentration, determined by 1HNMR spectroscopy are 90, 72, 90, or 76%, respectively.These rates are almost same with those of the correspondinggels without PF6L.1,2 These results can be explained byinteraction between PF6L and network structure. The pres-ence of PF6L in the system would hinder not the hydrosilyla-tion reaction between molecular scale functional groups ofthe monomers but the steric macroscopic scale formation ofinfinite network structure.

Figure 1 shows the ensemble-averaged relaxation time distri-butions as a function of the relaxation time of some semi-IPN gels containing PF6L, and the network structure of thesemi-IPN gels is summarized in Table 1. The relaxation timeof the ensemble-averaged relaxation time distribution corre-sponds to the mesh size of the gel. The mesh size of the gelsis determined from relaxation time of the ensemble-averagedrelaxation time distribution using Einstein–Stokes formula.The standard deviation of the relaxation peak corresponds toa distribution of the mesh size. All the semi-IPN gels mainlyformed homogeneous network with mesh size (radius ofmesh) of 1.2–1.7 nm. Small relaxation peaks correspondingto hundreds nanometer size were detected in the semi-IPNgels with relatively low monomer concentration. These relax-ation peaks should be derived from the large defects in thenetwork structure, as previously reported.1 Figure 2 showsPL spectra of some semi-IPN gels containing PF6L (1.0-mMof fluorene units) excited by wavelength of 380 nm. All thesemi-IPN gels containing PF6L showed emission peaks ataround 423, 441, and 475 nm, assigned to the 0–0, 0–1, and0–2 intrachain singlet transition, respectively.8 The wave-lengths and the intensity ratio at around 423 and 441 nm(I0/I1) of emissions are independent of the combination andconcentration of the monomers. PL intensities of the semi-IPN gels were higher than that of the toluene solution ofPF6L. The PL intensity of the gels was estimated by the ratioof the PL quantum yield of PF6L in the gel (/g) and solution(/s), and summarized in Table 1. In the case of the semi-IPNgels of TMCTS-DD and POSS-DD, the /g//s increased withan increase in the monomer concentration. On the otherhand, the /g//s of TMCTS-HD and POSS-HD semi-IPN gelswas almost independent of the monomer concentration. The

FIGURE 1 Relaxation time distribution (with expanded chart)

as a function of relaxation time of TMCTS-HD, -DD, POSS-HD, -

DD semi-IPN gels containing PF6L in toluene, fluorene unit of

PF6L 5 1.0 mM.



gels with DD form larger mesh size than those with HD dueto the long molecular length of DD, as previously reported.Large mesh formed by DD would disperse PF6L chains moreeffectively than small mesh formed by HD. These structuraldifferences should cause the effective increase of the PLquantum yield in the POSS-DD semi-IPN gel. The semi-IPNgel of POSS-DD with 9.9 wt % monomer concentrationshowed the highest PL intensity and /g//s among the semi-IPN gels synthesized in this study. The POSS-DD semi-IPNgel will be used for further studies.

Network Formation Process of POSS-DD Semi-IPN GelContaining PF6L in TolueneNetwork structure and emission intensity of POSS-DD semi-IPN gel (monomer concentration: 9.9 wt %) containing PF6L

(1.0 mM of fluorene units) were traced during the gel forma-tion process. Time evolution of relaxation peak of SMILSanalysis and corresponding mesh size of the POSS-DD semi-IPN gel containing PF6L are shown in Figure 3. In the earlystage of the reaction (< 1 h), the relaxation peaks derivedfrom microgels were detected in the range from 1024 to1023 s. This relaxation peak disappeared after 5 h of thereaction due to the formation of infinite network by aggrega-tion and/or connection of the microgels. The relaxationpeaks detected at <1025 s, corresponding to about 2 nmsize, were derived from the mesh of POSS-DD network. Themesh size decreased as progressing of the reaction (5 min:2.3 nm, 9 h: 1.7 nm) due to the formation of dense and finemesh, as previously reported.1,2 Figure 4(a) shows the timeevolution of PL spectrum of the POSS-DD semi-IPN gel(monomer concentration: 9.9 wt %) containing PF6L (1.0mM of fluorene units), and the /g//s values are summarizedin Figure 4(b). The gel was generated in 20 min of the reac-tion. The emission intensity drastically increased during gelformation period, less than 30 min, and gradually increasedwith an increase in the reaction time after gel formation.These results indicate that formation of POSS-DD meshshould enhance the emission of PF6L.

We are now ready to consider the mechanism of emissionenhancement of PF6L in the POSS-DD semi-IPN gels in tolu-ene. Proposed network structures of the semi-IPN gels con-taining PF6L are shown in Scheme 2. It seems reasonable tosuppose that incorporation of PF6L in the mesh of POSS-DDwould prevent the polymer chains of PF6L from aggregatingand/or forming random coils and increase the fluorescentintensity. In the early stage of the formation POSS-DD semi-IPN gels, the relaxation peaks attributable to hundreds nano-meter size were detected in the SMILS analysis. The relaxa-tion peaks would be derived from microgels indicatingformation of imperfect network structure, as previously

TABLE 1 Network Structure and Emission Property of Semi-IPN Gel Containing PF6L in Toluene; Fluorene Unit: 1.0 mM

Run Monomer

Monomer

Concentration

(wt %)

Flu Unita

(mM) sR 3 1026 (s)

Mesh

Size (nm) rb

Emission

kmax (nm) I0/I1c /g//s

d

– 1.0 423, 441 1.06

1 TMCTS-HD 10.7 1.0 5.4, 511, 12,700 1.4, 136, 3,370 0.04, 0.17, 0.19 423, 441 1.12 1.13

2 TMCTS-HD 13.9 1.0 5.3, 598 1.4, 159 0.03, 0.15 423, 441 1.09 1.13

3 TMCTS-HD 17.1 1.0 5.7 1.5 0.04 422, 441 1.10 1.05

4 TMCTS-DD 8.3 1.0 6.3, 362, 6,970 1.7, 96.0, 1,850 0.03, 0.10, 0.21 422, 440 1.11 1.13

5 TMCTS-DD 13.5 1.0 6.5, 12,200 1.7, 3,250 0.03, 0.17 422, 441 1.11 1.32

6 POSS-HD 5.9 1.0 5.4, 168, 9,160 1.4, 44.5, 2,430 0.06, 0.16, 0.19 424, 442 1.06 1.47

7 POSS-HD 9.0 1.0 5.8, 16,600 1.6, 4,420 0.03, 0.15 424, 442 1.06 1.50

8 POSS-DD 4.9 1.0 6.1, 170, 5,060 1.6, 45.1, 1,340 0.03, 0.08, 0.13 423, 441 1.09 1.41

9 POSS-DD 9.9 1.0 4.6, 25,800 1.2, 6,860 0.04, 0.12 423, 441 1.08 1.98

a Concentration of PF6L, fluorene unit 5 1.0 mM.b Standard deviation of a peak of the ensemble-averaged relaxation

time distribution.

c Intensity ratio of the emission peaks derived from 0–0 and 0–1 singlet

transition of PF6L at around 420 and 440 nm.d Ratio of the PL quantum yield of PF6L in the gel (/g) to in toluene

solution (/s).

FIGURE 2 PL spectra of TMCTS-HD, -DD, POSS-HD, -DD semi-

IPN gels containing PF6L in toluene, fluorene unit of PF6L 5 1.0

mM, (i): PF6L solution (dot line), (ii) TMCTS-HD: 13.9 wt %, (iii)

POSS-HD: 9.0 wt %, (iv) TMCTS-DD: 13.5 wt %, (v) POSS-DD:

9.9 wt %, excitation wavelength 5 380 nm.


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reported in the POSS-DD gels without PF6L.2 In this case, apart of PF6L would be incorporated in the mesh of the gels,whereas other PF6L chains would be separated from themesh. The latter PF6L chains should aggregate and/or formrandom coils. As the reaction goes ahead, growth and/oraggregation of microgels formed infinite network structure,which would be enough to occupy the space in the semi-IPNgels with homogeneous mesh. In this case, the PF6L chainsshould be incorporated effectively in the mesh.

Effect of Concentration, Molecular Weight, and SideChain Length of PFs on the Emission Property of theSemi-IPN Gels in TolueneEffect of the concentration of PF6L in the POSS-DD semi-IPNgel on the PL quantum yield was investigated. Emission

spectra of PF6L in toluene solution were acquired beforethose studies, and summarized in Figure 5(a). Emissionintensity of PF6L/toluene decreased with an increase in thePF6L concentration from 0.1 to 2.0 mM. The emission peaksdropped in the semi-IPN gels containing more tha 1.0 mM offluorene unit. The I0/I1 value also decreased with anincrease in the concentration of PF6L, as summarized inTable 2. The decrease of the emission intensity and the I0/I1value with an increase in the PF6L concentration should bederived from self-quenching induced by aggregation and/orformation of random coils structure in the solution. Figure5(b) shows emission spectra of the POSS-DD semi-IPN gels(monomer concentration: 9.9 wt %) containing PF6L of 0.1–2.0 mM fluorene unit. Network structure and the emissionproperties of the semi-IPN gels are summarized in Table 2.

FIGURE 3 Time evolution of relaxation time distribution as a function of relaxation time (a) and mesh size (b) of POSS-DD (mono-

mer concentration: 9.9 wt %) semi-IPN gel containing PF6L in toluene, fluorene unit of PF6L 5 1.0 mM.

FIGURE 4 Time evolution of PL spectrum, before reaction (dot line), 5 min (gray line), and 6 h (black line) (a), excitation wave-

length 5 380 nm, and /g//s values (b) of POSS-DD semi-IPN gel containing PF6L (1.0 mM of fluorene units) in toluene, monomer

concentration 5 9.9 wt %.



The semi-IPN gels containing low concentration PF6L, 0.1mM of fluorene units, showed slightly lower emission inten-sity than the corresponding PF6L solution. The I0/I1 valuesin the semi-IPN gels were smaller than that in the toluenesolution, and decreased with an increase in the monomerconcentration. Whereas, the semi-IPN gel containing high-concentration PF6L, 2.0 mM of fluorene units, showed higheremission intensity than the corresponding PF6L solution, asobserved in the semi-IPN gel containing 1.0 mM of fluoreneunits. The emission wavelengths of PF6L in the semi-IPNgels were almost same with those in the toluene solution.Relationship between monomer concentration (wt % ofPOSS and DD) and /g//s of PF6L is summarized in Figure 6.

The /g//s values in the semi-IPN gel containing 0.1 mM ofPF6L were lower than that of the corresponding toluenesolution. Whereas, the semi-IPN gels containing high concen-tration of PF6L, 2.0 mM of fluorene units, showed slightlyhigher /g//s than that of the corresponding toluene solution,and increased with increasing of the monomer concentration.The same results were obtained in the semi-IPN gels con-taining PF6L with 1.0 mM of fluorene units, as mentionedabove.

One explanation of these phenomena is under mentioned. Inthe case of the low PF6L concentration, 0.1 mM fluoreneunits, the polymer concentration is low enough to prevent

SCHEME 2 Plausible network structure of POSS-DD semi-IPN gel containing PF6L in toluene (good solvent).

FIGURE 5 PL spectra of PFs in toluene solutions (a) and in POSS-DD semi-IPN gels (monomer concentration 9.9 wt %) (b); contain-

ing (i): 0.1 mM of PF6L (thin black line), (ii): 1.0 mM of PF6L (thick gray line), (iii): 2.0 mM of PF6L (thick black line), (iv): 1.0 mM of

PF6H (thin dot line), (v): PF8: 1.0 mM of PF8 (black dot line), concentration of PF 5 concentration of fluorene unit in PF, excitation

wavelength 5 380 nm.


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from aggregation of PF6L polymer chains in the toluenesolution. The formation of the network structure in POSS-DDsemi-IPN gel would cause the volume exclusion effect, and asmall amount of polymer chains may aggregate and/or formrandom coils to induce the self-quenching. PL spectra of thetoluene solution of PF6L [Fig. 5(a)] indicates that self-quenching of PF6L should occur in the toluene solution con-taining 1.0 and 2.0 mM fluorene units, as described above.In the case of POSS-DD semi-IPN gels, PF6L polymer chains

would be incorporated in the mesh of POSS-DD. The incorpo-ration of the polymer chains should prevent from self-quenching and induce the enhancement of fluorescent inten-sity. Although the volume exclusion effect also should becaused by the formation of POSS-DD mesh, incorporation ofPF6L into the mesh of POSS-DD would be effective toincrease the fluorescent intensity containing high concentra-tion of PF6L. Increase of the monomer concentration in thesemi-IPN gel should induce effective incorporation of PF6Lpolymer chains in the POSS-DD network.

The POSS-DD semi-IPN gels containing PF6H or PF8, 1.0 mMof fluorene units, were also synthesized to study the effect ofmolecular weight or side chain structure of the PF in thesemi-IPN gel on the emission property. The PL spectra ofPF6H or PF8 in toluene solution and POSS-DD semi-IPN gelsare shown in Figure 5(a,b), respectively. Both the semi-IPNgels showed higher PL quantum yield than the correspond-ing PFs solutions, /g//s 5 1.1–1.4. The /g//s values of PF6Hand PF8 were slightly lower than that of the semi-IPN gelcontaining PF6L. The results indicate that although a part ofPF6H or PF8 polymer chains should be incorporated into thePOSS-DD network, the high molecular weight of PF6H or thebulky side chain of PF8 should slightly decrease the incorpo-ration efficiency.

Synthesis of Organic–Inorganic Hybrid Semi-IPN GelsContaining PF6L in CyclohexaneThe semi-IPN gels containing PF6L (1.0 mM of fluoreneunits) were also synthesized in cyclohexane. Cyclohexane is

TABLE 2 Network Structure and Emission Property of POSS-DD Semi-IPN Gel Containing PF6L, PF6H, or PF8 in Toluene

Run

Monomer

Concentration

(wt %) PF

Flu Unit a

(mM) sR 3 1026 (s) Mesh Size (nm) rb

Emission


d

– PF6L 0.1 418, 440 1.54

10 4.9 PF6L 0.1 5.6, 308, 13,000 1.5, 81.6, 3,460 0.03, 0.17, 0.13 421, 442 1.26 0.91

11 9.9 PF6L 0.1 5.5 1.5 0.03 422, 442 1.21 0.89

– PF6L 1.0 423, 441 1.06

8 4.9 PF6L 1.0 6.1, 170, 5,060 1.6, 45.1, 1,340 0.03, 0.08, 0.13 423, 441 1.09 1.41

9 9.9 PF6L 1.0 4.6, 25,800 1.2, 6,860 0.04, 0.12 423, 441 1.10 1.98

– PF6L 2.0 425, 442 0.95

12 4.9 PF6L 2.0 5.0, 679 1.3, 180 0.03, 0.11 425, 441 0.95 1.14

13 9.9 PF6L 2.0 5.7, 17,900 1.5, 4,740 0.04, 0.23 425, 441 0.96 1.39

– PF6H 1.0 425, 442 0.96

14 4.9 PF6H 1.0 6.6, 178, 2,130 1.8, 47.2, 565 0.09, 0.22, 0.64 425, 442 0.98 1.12

15 9.9 PF6H 1.0 5.3, 19,200 1.4, 5,090 0.03, 0.1 424, 442 1.06 1.36

– PF8 1.0 425, 443 0.95

16 4.9 PF8 1.0 6.3, 191, 3,580 1.7, 50.7, 951 0.07, 0.28, 0.46 424, 442 1.03 1.39

17 9.9 PF8 1.0 5.4, 27,600 1.4, 7,340 0.04, 0.14 425, 441 1.05 1.40

a Concentration of PF, fluorene unit.b Standard deviation of a peak of the ensemble-averaged relaxation

time distribution.


transition of PF at around 420 and 440 nm.d Ratio of the PL quantum yield of PF6L in the gel (/g) to in toluene

solution (/s).

FIGURE 6 Relationship between monomer concentration and

/g//s of polyfluorene in POSS-DD semi-IPN gel (white circle):

0.1 mM of PF6L (gray circle): 1.0 mM of PF6L (black circle): 2.0

mM of PF6L (triangle): 1.0 mM of PF6H (square): 1.0 mM of

PF8, concentration of PF 5 concentration of fluorene unit in PF.



a poor solvent for PFs. Figure 7 shows the ensemble-averaged relaxation time distributions as a function of therelaxation time of the semi-IPN gels containing PF6L. Net-work structure of the semi-IPN gels is summarized in Table3. The semi-IPN gels of low monomer concentration formedthe network with various mesh sizes due to the inhomogene-ity of the network structure. Increase of the monomer con-centration should form infinite network structure, whichwould be enough to occupy the space in the semi-IPN gelswith homogeneous network structure, as observed in thesemi-IPN gels in toluene. Figure 8 shows PL spectra of some

semi-IPN gels containing PF6L (1.0 mM of fluorene units).All the semi-IPN gels containing PF6L showed emissionpeaks at around 422 and 438 nm. PL intensities of the semi-IPN gels were lower than that of the cyclohexane solution ofPF6L. The ratio of the PL quantum yield of PF6L in the gel(/g) to in cyclohexane solution (/s), /g//s, are summarizedin Table 3. Increase of the monomer concentration decreasedthe /g//s. The increase of the monomer concentrationshould enhance the excluded volume effect, which decreasesthe solubility of PF6L. The decrease of the solubility shoulddecrease the PL quantum yield of PF6L, especially in thesemi-IPN gels composed by long spacer monomer of DD. Themesh size around 1 nm decreased with an increase in themonomer concentration. All the resulting gels were slightlywhite muddy.9 These phenomena should be derived fromsyneresis of the semi-IPN gels in cyclohexane.

FIGURE 7 Relaxation time distribution (with expanded chart)

as a function of relaxation time of TMCTS-HD, -DD, POSS-HD, -

DD semi-IPN gels containing PF6L in cyclohexane, fluorene

unit of PF6L 5 1.0 mM.

TABLE 3 Network Structure and Emission Property of Semi-IPN Gel Containing PF6L in Cyclohexane; Fluorene Unit: 1.0 mM

Run Monomer

Monomer

Concentration

(wt %)

Flu Unita

(mM) sR 3 1026 (s)

Mesh Size

(nm) rb

Emission


d

– 1.0 422, 436 0.88

18 TMCTS-HD 13.9 1.0 5.1, 12,000 0.8, 1,980 0.06, 0.09 423, 438 0.83 0.95

19 TMCTS-HD 17.1 1.0 5.5, 19,500 0.9, 3,220 0.04, 0.09 421, 439 0.48 0.58

20 TMCTS-DD 8.3 1.0 9.8, 22,500 1.6, 3,720 0.03, 0.07 421, 439 0.63 0.47

21 TMCTS-DD 13.5 1.0 4.5, 56.6, 19,500 0.7, 9.3, 3,210 0.05, 0.08, 0.15 421, 439 0.43 0.22

22 POSS-HD 5.9 1.0 9.1, 14,800 1.5, 2,440 0.04, 0.06 422, 437 0.77 0.77

23 POSS-HD 9.0 1.0 7.5, 20,200 1.2, 3,340 0.03, 0.11 423, 438 0.93 0.58

24 POSS-DD 4.9 1.0 5.7, 447, 9,360 0.9, 73.9, 1,550 0.04, 0.22, 0.25 423, 438 0.74 0.66

25 POSS-DD 9.9 1.0 4.5, 13,500 0.7, 2,220 0.04, 0.07 421, 438 0.95 0.35

a Concentration of PF6L, fluorene unit 5 1.0 mM.b Standard deviation of a peak of the ensemble-averaged relaxation

time distribution.


transition of PF6L at around 420 and 440 nm.d Ratio of the PL quantum yield of PF6L in the gel (/g) to in toluene

solution (/s).

FIGURE 8 PL spectra of TMCTS-HD, -DD, POSS-HD, -DD semi-

IPN gels containing PF6L in cyclohexane, fluorene unit of

PF6L 5 1.0 mM, (i): PF6L solution (dot line), (ii) TMCTS-HD: 13.9

wt %, (iii) POSS-HD: 9.0 wt %, (iv) POSS-DD: 9.9 wt %, (v)

TMCTS-DD: 13.5 wt %, excitation wavelength 5 380 nm.


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Network Formation Process of POSS-DD Semi-IPN GelContaining PF6L in CyclohexaneNetwork structure and emission intensity were traced duringthe formation of POSS-DD semi-IPN gel (monomer concentra-tion: 9.9 wt %) containing PF6L (1.0 mM of fluorene units)in cyclohexane. Time evolution of relaxation peak of SMILSanalysis and corresponding mesh size of the POSS-DD semi-IPN gel containing PF6L are shown in Figure 9. In the earlystage of the reaction within 5 min, the relaxation peaksderived from aggregated PF6L chains were detected at round1022 s. This relaxation peak gradually disappeared as thereaction time due to the incorporation of the PF6L chainsinto the POSS-DD network. The mesh size increased withincreasing the reaction time until 5 h from 0.9 to 1.3 nm. The

mesh size dropped to 0.9 nm at 8 h of the reaction timeaccompanied by the syneresis. The semi-IPN gel turned whitemuddy after 14 h of the reaction, and a relaxation peak corre-sponding to thousands nanometer was appeared in the SMILSanalysis. Figure 10(a) shows the time evolution of PL spec-trum of POSS-DD semi-IPN gel containing PF6L. The PL inten-sity of kmax at around 422 cm21 and 438 nm21 decreasedwith the increasing of the reaction time. The time evolution ofthe /g//s is summarized in Figure 10(b). The /g//s valuerapidly decreased within 8 h of the reaction time.

The network structure and emission behavior of PF6L in thePOSS-DD semi-IPN gel in cyclohexane can be explained bythe following model, as shown in Scheme 3. In the early

FIGURE 9 Time evolution of relaxation time distribution as a function of relaxation time (a) and mesh size (b) of POSS-DD semi-

IPN gel containing PF6L in cyclohexane, fluorene unit of PF6L 5 1.0 mM.

FIGURE 10 Time evolution of PL spectra, 5 min, 1, 3, 5, 14, 24 h (a), excitation wavelength 5 380 nm, and /g//s of POSS-DD semi-

IPN gel (b) containing PF6L in cyclohexane, fluorene unit of PF6L 5 1.0 mM.



stage of the reaction, formation of network structure wouldenhance excluded volume effect, and decrease solubility ofPF6L chains in the reaction system. The decrease of the solu-bility of PF6L should decrease the emission intensity and PLquantum yield. Progressing of the network formation wouldinduce the aggregation of PF6L chains, which forms largesize cluster, and syneresis of the semi-IPN gel, as observed.

Synthesis of POSS-DD Semi-IPN Gels Containing PF6H,and PF8 in CyclohexaneThe POSS-DD semi-IPN gel containing PF6H of 1.0 mM fluo-rene units was synthesized in cyclohexane. The PL spectra ofPF6H in cyclohexane solution and POSS-DD semi-IPN gels

are shown in Figure 11. Network structure and emissionproperties of the semi-IPN gels are summarized in Table 4.The PL intensity of PF6H solution is lower than that of PF6L.The higher molecular weight of PF6H should cause the self-quenching of polymer chains by forming random coils and/or aggregation. The PL intensity of POSS-DD semi-IPN gelscontaining PF6H slightly decreased with increasing of themonomer concentration as observed in the semi-IPN gelscontaining PF6L. The formation POSS-DD network structurewould induce excluded volume effect and decreases the solu-bility of PF6H in the semi-IPN gels.

The POSS-DD semi-IPN gels containing PF8 were also syn-thesized in cyclohexane. The ensemble-averaged relaxationtime distributions as a function of the relaxation time andPL spectra of the POSS-DD semi-IPN gels containing PF8 (1.0or 2.0 mM of fluorene units) in cyclohexane are shown inFigures 12 and 13, respectively. Network structure and emis-sion properties of the semi-IPN gels are summarized in Table4. In the semi-IPN gels of 4.9 wt % monomer concentration,a relaxation peak derived from hundreds nm was detected at1024 to 1023 s, as shown in Figure 12. The relaxation peakwas almost disappeared in the semi-IPN gels of 9.9 wt %monomer concentration, and another relaxation peak wasnewly appeared at around 1022 s corresponding to the sizeof 20,000 nm, as shown in Figure 12. Increasing of themonomer concentration induced syneresis of the semi-IPNgels. In the PL spectra of the semi-IPN gels, emission peakswere observed at 422 and 442 nm with a shoulder ataround 470 nm. The semi-IPN gels showed slightly higherPL quantum yield than the corresponding PF8/cyclohexanesolutions. The peak intensity at 442 nm increased with

SCHEME 3 Plausible network structure of POSS-DD semi-IPN gel containing PF6L in cyclohexane (poor solvent).

FIGURE 11 PL spectra of PF6H in cycloehxane solution (i) (dot

line), and POSS-DD semi-IPN gel (bold line), monomer concen-

tration: (ii) 4.9 wt %, and (iii) 9.9 wt % in cyclohexane, fluorene

unit of PF6H 5 1.0 mM, excitation wavelength 5 380 nm.


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increasing of the monomer concentration. The semi-IPN gelcontaining PF8 of 2.0 mM of fluorene units showed remark-able increase of the peaks intensity at 440 and 470 nm. Theprofile of the PL spectrum should be derived from the for-mation of b-phase. UV–vis absorption spectroscopy of thesemi-IPN gel showed an absorbance at 438 nm, derivedfrom b-phase of PF8.10–13 Increasing of the monomer con-centration should increase the excluded volume effect, anddecrease the solubility of PF8 in the semi-IPN gel. Thedecrease of the solubility causes the aggregation of PF8 inthe semi-IPN gels, and progressing of the aggregation shouldinduce the formation of b-phase in PF8.

CONCLUSIONS

Organic–inorganic hybrid semi-IPN gels containing PFswere synthesized using a hydrosilylation reaction of TMCTSor POSS, with HD or DD in the presence of PF6L, PF6H,PF8 in toluene, good solvent, or cyclohexane, poor solvent.In the case of the semi-IPN gels prepared in toluene, thePL efficiencies of PFs in the semi-IPN are higher than thatin the toluene solutions. The gels composed of long rodmolecule of DD and cubic joint molecule of POSS showedhighest intensity of the emission. The emission intensity ofPF6L increased as formation of the POSS-DD network. The

TABLE 4 Network Structure and Emission Property of POSS-DD Semi-IPN Gel Containing PF6H, or PF8 in Cyclohexane

Run

Monomer

Concentration

(wt %) PF

Flu Unita

(mM) sR 3 1026 (s)

Mesh Size

(nm) rb

Emission


d

– PF6H 1.0 426, 440 0.89

26 4.9 PF6H 1.0 5.4, 20,700 0.9, 3,420 0.03, 0.09 424, 440 0.91 0.66

27 9.9 PF6H 1.0 5.3, 52,300 0.9, 8,630 0.03, 0.19 424, 441 0.87 0.63

– PF8 1.0 423, 440 0.92

28 4.9 PF8 1.0 6.5, 354 1.1, 58.4 0.05, 0.15 423, 439 0.98 1.39

29 9.9 PF8 1.0 4.6, 25,800 1.2, 6,860 0.04, 0.12 423, 441 0.83 1.22

– PF8 2.0 425, 441 0.81

30 4.9 PF8 2.0 6.3, 161, 1,080 1.0, 26.5, 179 0.10, 0.21, 0.68 425, 441 0.82 1.17

31 9.9 PF8 2.0 5.8, 1,060, 19,200 1.0, 175, 3,170 0.04, 0.13, 0.15 424, 443 0.60 1.21

a Concentration of PF, fluorene unit.b Standard deviation of a peak of the ensemble-averaged relaxation

time distribution.


transition of PF at around 420 and 440 nm.d Ratio of the PL quantum yield of PF6L in the gel (/g) to in toluene

solution (/s).

FIGURE 12 Relaxation time distribution as a function of relaxa-

tion time of POSS-DD semi-IPN gels containing PF8 in cyclo-

hexane, fluorene unit of PF8 5 2.0 mM.

FIGURE 13 PL spectra of PF8 in cyclohexane solution (dot line)

and POSS-DD semi-IPN gel (thin or bold line) in cyclohexane,

containing 1.0 mM of PF8 (i): solution (thin dot line), in gels

with monomer concentration of (ii): 4.9 wt % (thin gray line),

(iii): 9.9 wt % (thin black line), or 2.0 mM of PF8 (iv): solution

(bold dot line), in gels of monomer concentration of (v): 4.9 wt

% (bold bray line), (vi): 9.9 wt % (bold black line), concentration

of PF8 5 concentration of fluorene unit in PF8, excitation wave-

length 5 380 nm.



POSS-DD semi-IPN gels containing high molecular weightPF6H and long side chain PF8 also showed the increase of/g than that of the toluene solutions of these PFs. Thesemi-IPN gels were also synthesized in cyclohexane, poorsolvent for PFs. Syneresis and phase separation betweennetwork structure and PF chains were observed in thesemi-IPN gels. The /g values of PFs in most of the semi-IPN gels were lower than that in the cyclohexane solutions.The semi-IPN gels containing PF8 showed emission peaksderived from b-sheet structure of aggregated polymerchains of PF8.

As noted above, it is important that no excimer emissionwas confirmed in this work. This leads to pure blue emissionin OLED applications. Also, no excimer emission may give aclue in understanding aggregation stereochemistry, that is,aggregation dose not occur in a face-to-face fashion. Thestudied semi-IPN gels in good solvent would be applicablefor an emission layer of GLED. Furthermore, the compositionof organic–inorganic hybrid network structure and PFs insome organic solvents should be also useful to control orstudy the formation or mobility of PFs. Further studies, espe-cially application for GLED, are now proceeding, and theresults will be reported elsewhere.

REFERENCES AND NOTES

1 N. Naga, E. Oda, A. Toyota, K. Horie, H. Furukawa, Macro-

mol. Chem. Phys. 2006, 207, 627–635.

2 N. Naga, Y. Kihara, T. Miyanaga, H. Furukawa, Macromole-

cules 2009, 42, 3454–3462.

3 Precise information of SMILS is available in Supporting

Information.

4 N. Naga, T. Miyanaga, H. Furukawa, Polymer 2010, 51, 5095–

5099.

5 S. C. Chang, Y. Yang, Appl. Phys. Lett. 1999, 75, 2713–2715.

6 Y. Hamada (SANYO Electric Co., Ltd.). JP 2003–77302A, 2003.

7 M. Yukawa (Semiconductor Energy Laboratory Co., Ltd.). JP

2006–11403A, 2006.

8 D. Neher, Macromol. Rapid Commun. 2001, 22, 1365–1385.

9 Photographs of the TMCTS-HD semi-IPN gels containing

PF6L in cyclohexane are available in Supporting Information.

10 UV–vis spectrum of a POSS-DD semi-IPN gel containing PF8

in cyclohexane is available in Supporting Information.

11 M. Grell, D. D. C. Bradley, M. Inbasekaran, G. Ungar, K. S.

Whitehead, E. P. Woo, Synth. Met. 2000, 111, 579–581.

12 C. Y. Chen, C. S. Chang, S. W. Huang, J. H. Chen, H. L. Chen,

C. I. Su, S. A. Chen, Macromolecules 2010, 43, 4346–4354.

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info:x-wiley/patent/200377302A



synthesis and optical properties of organic-inorganic hybrid semi-interpenetrating polymer network...

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