Tetraphenylpyrene-bridged periodic mesostructured organosilica films with efficient visible-light emission

Article abstract of DOI:10.1021/cm9034787

Mesostructured organosilica films with strong blue fluorescence emission were synthesized by surfactant-templated sol-gel polycondensation using a 1,3,6,8-tetraphenylpyrene (TPPy)-containing organosilane precursor. The TPPy precursor, which contained four polymerizable silyl groups, was suitable for the preparation of mesostructured films with high TPPy content in the framework. The fluorescence quantum yields of the TPPy-bridged mesostructured organosilica films reached more than 0.7, despite the dense accumulation of TPPy units within the framework. Doping of the mesostructured films with fluorescence dyes enabled fine-tuning of the emission colors over a wide range of the visible spectrum. Such mesostructured organosilica films, in which different chromophores can be distributed into the framework and mesopores, have significant potential for luminescence applications.

Full text of DOI:10.1021/cm9034787

2548 Chem. Mater. 2010, 22, 2548–2554
DOI:10.1021/cm9034787
Tetraphenylpyrene-Bridged Periodic Mesostructured Organosilica Films
with Efficient Visible-Light Emission
Norihiro Mizoshita,†,‡ Yasutomo Goto,†,‡ Yoshifumi Maegawa,†,‡ Takao Tani,†,‡ and
Shinji Inagaki*,†,‡
†Toyota Central R&D Laboratories, Inc., Nagakute, Aichi 480-1192, Japan, and ‡Core Research for
Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Kawaguchi,
Saitama 332-0012, Japan
Received November 15, 2009
Mesostructured organosilica films with strong blue fluorescence emission were synthesized by
surfactant-templated sol-gel polycondensation using a 1,3,6,8-tetraphenylpyrene (TPPy)-containing
organosilane precursor. The TPPy precursor, which contained four polymerizable silyl groups, was
suitable for the preparation of mesostructured films with high TPPy content in the framework. The
fluorescence quantum yields of the TPPy-bridged mesostructured organosilica films reached more than
0.7, despite the dense accumulation of TPPy units within the framework. Doping of the mesostructured
films with fluorescence dyes enabled fine-tuning of the emission colors over a wide range of the visible
spectrum. Such mesostructured organosilica films, in which different chromophores can be distributed
into the framework and mesopores, have significant potential for luminescence applications.
Introduction
into the pore walls of PMOs as the R bridging group.5-18
The density, distribution, and molecular-scale ordering of
the bridging groups within pore walls can be controlled by
the molecular design of the precursors, optimization of
the synthesis conditions, and appropriate selection of the
co-condensation technique.19-30 Expansion of the varia-
tion of organic bridges has broadened the potential
applications of PMOs to optical materials, solid catalysts,
sensing systems, and electronic devices.31-35
Periodic mesoporous organosilica (PMO) is a versatile
inorganic/organic hybrid with mesoscale porous struc-
tures and molecular-scale functionalities.1-4 PMOs are
synthesized by surfactant-templated sol-gel polyconden-
sation of organic-bridged alkoxysilane precursor com-
pounds, generally represented as R[Si(OR’)3]n (n g 2).
Various organic species ranging from hydrocarbons and
heteroaromatics to metal complexes have been introduced
*Corresponding author. E-mail: inagaki@mosk.tytlabs.co.jp.
€
(1) Hoffmann, F.; Cornelius, M.; Morell, J.; Froba, M. Angew. Chem.,
(18) Wahab, M. A.; Hussian, H.; He, C. Langmuir 2009, 25, 4743–4750.
ꢀ
(19) Alvaro, M.; Benı
´
tez, M.; Cabeza, J. F.; Garcı
´
a, H.; Leyva, L.
Int. Ed. 2006, 45, 3216–3251.
J. Phys. Chem. C 2007, 111, 7532–7538.
(20) Wahab, M. A.; Sudhakar, S.; Yeo, E.; Sellinger, A. Chem. Mater.
2008, 20, 1855–1861.
(21) Yang, Y.; Sayari, A. Chem. Mater. 2008, 20, 2980–2984.
(22) Goto, Y.; Nakajima, K.; Mizoshita, N.; Suda, M.; Tanaka, N.;
Hasegawa, T.; Shimada, T.; Tani, T.; Inagaki, S. Microporous
Mesoporous Mater. 2009, 117, 535–540.
(23) Mizoshita, N.; Goto, Y.; Tani, T.; Inagaki, S. Adv. Funct. Mater.
2008, 18, 3699–3705.
(24) Inagaki, S.; Guan, S.; Ohsuna, T.; Terasaki, O. Nature 2002, 416,
304–307.
(25) Kapoor, M. P.; Yang, Q.; Inagaki, S. J. Am. Chem. Soc. 2002, 124,
15176–15177.
ꢀ~
ꢀ
(2) Descalzo, A. B.; Martı
´
nez-Manez, R.; Sancenon, F.; Hoffmann,
K.; Rurack, K. Angew. Chem., Int. Ed. 2006, 45, 5924–5948.
(3) Fujita, S.; Inagaki, S. Chem. Mater. 2008, 20, 891–908.
(4) Sayari, A.; Hamoudi, S. Chem. Mater. 2001, 13, 3151–3168.
(5) Inagaki, S.; Guan, S.; Fukushima, Y.; Ohsuna, T.; Terasaki, O.
J. Am. Chem. Soc. 1999, 121, 9611–9614.
(6) Melde, B. J.; Holland, B. T.; Blanford, C. F.; Stein, A. Chem.
Mater. 1999, 11, 3302–3308.
(7) Asefa, T.; MacLachlan, M. J.; Coombs, N.; Ozin, G. A. Nature
1999, 402, 867–871.
(8) Yoshina-Ishii, C.; Asefa, T.; Coombs, N.; MacLachlan, M. J.;
Ozin, G. A. Chem. Commun. 1999, 2539–2540.
(9) Kuroki, M.; Asefa, T.; Whitnal, W.; Kruk, M.; Yoshina-Ishii, C.;
Jaroniec, M.; Ozin, G. A. J. Am. Chem. Soc. 2002, 124, 13886–13895.
(10) Olkhovyk, O.; Jaroniec, M. J. Am. Chem. Soc. 2005, 127, 60–61.
(11) Peng, H.; Tang, J.; Yang, L.; Pang, J.; Ashbaugh, H. S.; Brinker,
C. J.; Yang, Z.; Lu, Y. J. Am. Chem. Soc. 2006, 128, 5304–5305.
(12) Maegawa, Y.; Goto, Y.; Inagaki, S.; Shimada, T. Tetrahedron Lett.
2006, 47, 6957–6960.
(13) Minoofar, P. N.; Dunn, B. S.; Zink, J. I. J. Am. Chem. Soc. 2005,
127, 2656–2665.
(14) Johansson, E.; Zink, J. I. J. Am. Chem. Soc. 2007, 129, 14437–
14443.
€
(15) Cornelius, M.; Hoffmann, F.; Ufer, B.; Behrens, P.; Froba, M.
J. Mater. Chem. 2008, 18, 2587–2592.
(16) Nguyen, T. P.; Hesemann, P.; Gaveau, P.; Moreau, J. J. E.
J. Mater. Chem. 2009, 19, 4164–4171.
(17) Takeda, H.; Goto, Y.; Maegawa, Y.; Ohsuna, T.; Tani, T.;
Matsumoto, K.; Shimada, T.; Inagaki, S. Chem. Commun. 2009,
6032–6034.
(26) Kapoor, M. P.; Yang, Q.; Inagaki, S. Chem. Mater. 2004, 16, 1209–
1213.
(27) Sayari, A.; Wang, W. J. Am. Chem. Soc. 2005, 127, 12194–12195.
€
(28) Cornelius, M.; Hoffmann, F.; Froba, M. Chem. Mater. 2005, 17,
6674–6678.
(29) Xia, Y.; Wang, W.; Mokaya, R. J. Am. Chem. Soc. 2005, 127, 790–
798.
(30) Mizoshita, N.; Goto, Y.; Kapoor, M. P.; Shimada, T.; Tani, T.;
Inagaki, S. Chem.-Eur. J. 2009, 15, 219–226.
(31) Hunks, W. J.; Ozin, G. A. J. Mater. Chem. 2005, 15, 3716–3724.
(32) Yang, Q.; Liu, J.; Zhang, L.; Li, C. J. Mater. Chem. 2009, 19, 1945–
1955.
(33) Angelos, S.; Johansson, E.; Stoddart, J. F.; Zink, J. I. Adv. Funct.
Mater. 2007, 17, 2261–2271.
(34) Liong, M.; Angelos, S.; Choi, E.; Patel, K.; Stoddart, J. F.; Zink,
J. I. J. Mater. Chem. 2009, 19, 6251–6257.
(35) Mizoshita, N.; Ikai, M.; Tani, T.; Inagaki, S. J. Am. Chem. Soc.
2009, 131, 14225–14227.
r
2010 American Chemical Society
pubs.acs.org/cm
Published on Web 03/23/2010

Article
Among these applications, organosilica hybrids with
Chem. Mater., Vol. 22, No. 8, 2010 2549
periodic mesostructures have significant potential for
luminescence applications.36,37 Acidic sol-gel polycon-
densation of organosilane precursors in the presence of
organic solvents yields highly transparent films favorable
for optical materials.36-38 Different fluorescent chromo-
phores can then be distributed into both the framework
(as a bridging group) and mesopores (as a dye dopant) of
PMO.13,14,39 In addition, PMOs have been found to
exhibit light-harvesting antenna properties, i.e., the
funneling of light energy absorbed by the framework
organics into dyes placed in the mesochannels through
efficient nonradiative energy transfer; therefore, flexible
tuning of the fluorescence emission intensities of the
framework and the dyes can be realized with almost no
energy transfer loss.39 These advantages of mesostruc-
tured organosilicas can lead the way to high-performance
luminescence applications.
Recently, we reported the construction of highly fluore-
scent periodic mesostructured organosilica films.23,40 We
focused on alkoxy-substituted oligo(phenylenevinyl-
ene) (OPV) precursors23 as visible-light-absorptive chromo-
phores and achieved efficient visible light emission in
dye-doped mesostructured OPV-silica hybrid films.40
The emission colors were successfully tuned from blue
to white and yellow by combining the blue emission of
the organosilica framework and the yellow emission
of a doped dye, which was excited by fluorescence reso-
nance energy transfer from the organosilica framework
(Figure 1). However, the preparation of mesostructured
films from 100% OPV precursors could not be achieved,
probably because of weak interactions between the tem-
plate surfactant micelles and the hydrolyzed precursors
with only two silyl groups on both ends of the large OPV
precursors. In addition, organosilica films with high OPV
contents exhibited relatively low fluorescence quantum
yields, because the hydrophobic OPV moieties tended to
form nonemissive side-by-side aggregates in the pore
walls.23 Therefore, the addition of a large amount of pure
silica precursors (67-80 wt % of tetraethyl orthosilicate
(TEOS)) was required to form periodic mesostructures
and achieve high fluorescence quantum yields, even
though the strong absorption of excitation light with a
high chromophore content is desirable for photolumines-
cent materials.36,37 Furthermore, vinylenes and acenes
used as highly fluorescent components in our previous
works22,23,40 are known to be photochemically reactive
Figure 1. Schematic illustration of color-tunable fluorescence emission
from dye-doped mesostructured organosilica film and photograph of a
transparent organosilica film spin-coated on a glass substrate.
and unstable,41-45 which is problematic in practical
applications. For the preparation of luminescent PMOs,
it is desirable to introduce a high density of visible-light-
absorptive, highly fluorescent, and photochemically
stable chromophores into the mesostructured framework
without strong quenching of fluorescence.
The aim of the present study was to introduce 1,3,6,8-
tetraphenylpyrene (TPPy) as a fluorescent bridging group
in a mesostructured organosilica framework. The use of
TPPy is suitable for the preparation of mesostructured
and highly fluorescent organosilica films for the following
reasons: (i) TPPy has an absorption in the near-UV to
visible-light wavelength region and exhibits strong blue
fluorescence;46 (ii) a vacuum-deposited solid film consist-
ing of 100% TPPy is reported to show a high fluorescence
quantum yield (ca. 0.68),47 which suggests that dense
accumulation of TPPy units into pore walls is possible
without strong fluorescence quenching; (iii) a four-armed
organosilane precursor can be designed by the introduc-
tion of polymerizable silyl groups onto the phenyl sub-
stituents, which facilitates periodic mesostructure forma-
tion from a precursor having a large TPPy chromophore
through interactions between the template surfactant
micelles and the four hydrophilic silyl groups; and
(iv) high photochemical stability can be expected for
TPPy chromophores that contain neither vinylenes nor
acenes.
(36) Tani, T.; Mizoshita, N.; Inagaki, S. J. Mater. Chem. 2009, 19, 4451–
4456.
(37) Goto, Y.; Mizoshita, N.; Ohtani, O.; Okada, T.; Shimada, T.; Tani,
T.; Inagaki, S. Chem. Mater. 2008, 20, 4495–4498.
(38) Sanchez, C.; Lebeau, B.; Chaput, F.; Boilot, J.-P. Adv. Mater. 2003,
15, 1969–1994.
(39) Inagaki, S.; Ohtani, O.; Goto, Y.; Okamoto, K.; Ikai, M.;
Yamanaka, K.; Tani, T.; Okada, T. Angew. Chem., Int. Ed. 2009,
48, 4042–4046.
In this article, we report the preparation of highly
fluorescent mesostructured organosilica films from
(43) Fox, M. A.; Li, W.; Wooten, M.; McKerrow, A.; Whitesell, J. K.
Thin Solid Films 1998, 327-329, 477–480.
(44) Anthony, J. E. Angew. Chem., Int. Ed. 2008, 47, 452–483.
ꢀꢁ
(45) Kytka, M.; Gerlach, A.; Schreiber, F.; Kovac, J. Appl. Phys. Lett.
(40) Mizoshita, N.; Goto, Y.; Tani, T.; Inagaki, S. Adv. Mater. 2009,
21, 4798–4801.
(41) Uda, M.; Momotake, A.; Arai, T. Tetrahedron Lett. 2005, 46,
3021–3024.
2007, 90, 131991.
(46) de Halleux, V.; Calbert, J.-P.; Brocorens, P.; Cornil, J.; Declercq,
ꢀ
J.-P.; Bredas, J.-L.; Geerts, Y. Adv. Funct. Mater. 2004, 14, 649–
659.
(42) Tian, L.; He, F.; Zhang, H.; Xu, H.; Yang, B.; Wang, C.; Lu, P.;
Hanif, M.; Li, F.; Ma, Y.; Shen, J. Angew. Chem., Int. Ed. 2007, 46,
3245–3248.
(47) Oyamada, T.; Uchiuzou, H.; Akiyama, S.; Oku, Y.; Shimoji, N.;
Matsushige, K.; Sasabe, H.; Adachi, C. J. Appl. Phys. 2005, 98,
074506.

2550 Chem. Mater., Vol. 22, No. 8, 2010
Mizoshita et al.
Table 1. Composition and Structural Properties of Organosilica Films
P123/TPPy-Si/
TEOSa (mg)
mesoscale
periodicityb (nm)
sample
F-0a
F-0b
F-0c
F-1a
F-1b
F-1c
F-2a
F-4a
40/60/0
60/60/0
80/60/0
40/30/30
60/30/30
80/30/30
40/20/40
40/12/48
8.8 (broad)
9.1 (broad)
9.7 (broad)
8.7
10.0
10.5
9.0
10.0
a Weights of the components dissolved in 2.0 mL of solvent. b The
largest d-spacing value obtained from XRD measurements.
and dried under reduced pressure to afford a light yellow solid
(1.62 g, 74%). 1H NMR (CDCl3) δ 8.16 (s, 4H), 7.97 (s, 2H), 7.63
(d, J=8.3 Hz, 8H), 7.31 (d, J=8.3 Hz, 8H), 5.59 (t, J=5.9 Hz,
4H), 3.87 (q, J=7.0 Hz, 24H), 3.33 (m, 8H), 1.76 (m, 8H), 1.27 (t,
J=7.0 Hz, 36H), and 0.73 (t, J=8.0 Hz, 8H) ppm; 13C NMR
(CDCl3) δ 154.5, 150.5, 137.7, 136.4, 131.3, 129.6, 128.0, 125.8,
Figure 2. Chemical structure of the TPPy-Si organosilane precursor.
TPPy-Si containing TPPy as a bridging unit (Figure 2).
The organosilica films exhibit efficient blue light emission
with quantum yields of over 0.7. The emission colors can
also be finely tuned over a wide range of the visible spect-
rum by the doping of fluorescent dyes into the meso-
structured films.
125.2, 121.4, 58.4, 43.5, 23.0, 18.2, and 7.6 ppm; IR (ATR, cm-1
)
3329 (NH st), 3039, 2974, 2928, 2885, 1716 (CdO st), 1533, 1489,
1203, 1165, 1070; MS (MALDI, m/z) calcd for 1558.6790 [M]þ,
found 1558.6809.
Experimental Section
Preparation of Organosilica Films. The TPPy-based precursor
TPPy-Si, TEOS, and P123 with the compositions given in
Table 1 were dissolved in 2.0 mL of a 1:1 (w/w) mixture of
tetrahydrofuran (THF) and ethanol, followed by the addition of
2 M hydrochloric acid (8 μL) and deionized water (40 μL). The
sol mixtures were stirred at room temperature for 24 h. Organo-
silica thin films were prepared by spin-coating of the solutions
onto quartz substrates (4,000 rpm, 30 s) and drying under
reduced pressure at room temperature for 24 h. The organosilica
films were stored in a dark place prior to optical measurements.
For the preparation of dye-doped mesostructured films, a 5-fold
scale sol mixture was prepared and the total amount of the
solution was adjusted to 10.0 mL using a volumetric flask
([TPPy-Si]=9.6 mM) in order to accurately weigh the amounts
of chromophores. Appropriate amounts of dyes (0-5.0 mol %
ratios to the amount of TPPy units) were added to the sol
solution using a 9.6 mM solution of dyes (solvent: THF for
Bodipy, ethanol for Rhd6G). The dye-doped organosilica films
were prepared in the same manner as the nondoped films.
Materials and Methods. All reagents and solvents were pur-
chased from Aldrich and Tokyo Chemical Industry and used
without further purification. A poly(ethylene oxide)-block-poly-
(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO)
triblock copolymer (EO20-PO70-EO20, P123, Aldrich) was used
1
as a nonionic template surfactant. H and 13C NMR spectra
were measured using a Jeol JNM-ECX400P spectrometer. Mass
spectra were recorded on a Bruker Daltonics Autoflex mass
spectrometer with matrix-assisted laser desorption/ionization
(MALDI). Infrared (IR) absorption spectroscopy (Thermo
Nicolet Avatar 360 FT-IR) was conducted using an attenuated
total reflection (ATR) attachment. X-ray diffraction (XRD)
measurements were performed using Cu-KR radiation (Rigaku
RINT-TTR, 50 kV, 300 mA). Transmission electron micro-
scopy (TEM) of the organosilica hybrid films was performed
using a Jeol JEM 2100F with an accelerating voltage of 200 kV.
In order to obtain high-contrast images, the organosilica
samples were annealed at 200 °C for 6 h and then immersed in
ethanol for 6 h to extract P123. UV-vis absorption spectra were
measured using a Jasco V-670 spectrometer. Fluorescence
spectra were obtained with a Jasco FP-6500 spectrometer.
Fluorescence quantum yields (within an error margin of (
3%) were determined using a photoluminescence quantum yield
measurement system equipped with a calibrated integrating
sphere (Hamamatsu Photonics, C9920-02). The Commission
Internationale de l’Eclairage (CIE) 1931 chromaticity coordi-
nates were calculated using a U6039 software (Hamamatsu
Photonics).
Results and Discussion
Preparation of TPPy-Bridged Mesostructured Films.
The precursor compound, TPPy-Si, was easily synthe-
sized by the reaction of 1,3,6,8-tetrakis(4-hydroxyphe-
nyl)pyrene46 with 3-triethoxysilylpropyl isocyanate and
purified by repetitive reprecipitation in toluene/hexane.
Figure 3 shows UV-vis absorption and fluorescence
emission spectra of TPPy-Si in a 2-propanol solution
(1.0 ꢀ 10-5 M). The absorption maximum (λmax) was 384
nm and the absorption edge reached into the visible light
region (ca. 420 nm). The emission wavelength (λem) and
fluorescence quantum yield (ΦF) excited at λ=400 nm
were 423 nm and 0.92, respectively; the TPPy-bridged
precursor is favorable as a blue-light-emitting component
of mesostructured organosilica films.
Synthesis of TPPy-Bridged Precursor, 1,3,6,8-Tetrakis[4-
(3-triethoxysilylpropylaminocarbonyloxy)phenyl]pyrene (TPPy-
Si). 3-Triethoxysilylpropyl isocyanate (1.98 g, 8.00 mmol)
was added to a mixture of 1,3,6,8-tetrakis(4-hydroxyphenyl)-
pyrene46 (0.80 g, 1.40 mmol), dry dichloromethane (80 mL), and
distilled triethylamine (10 mL). The reaction mixture was stirred
at room temperature for 24 h and then refluxed for 2 h. After
removal of the solvents using a rotary evaporator, the residue
was dissolved in toluene and filtered to remove insoluble
materials. Reprecipitation in toluene/hexane was repeated
twice, and the precipitate was collected by suction filtration
Mesostructured organosilica films with a TPPy
bridging group were obtained by acidic sol-gel polycon-
densation of TPPy-Si via an evaporation-induced

Article
Chem. Mater., Vol. 22, No. 8, 2010 2551
Table 2. Optical Properties of TPPy-Si and TPPy-Silica Hybrid Films
light transmittanceb
at 500 nm (%)
sample
λmax (nm)
λem (nm)
ΦF
TPPy-Sia
F-0a
F-0b
F-0c
F-1a
F-1b
F-1c
F-2a
F-4a
384
387
387
387
386
387
387
387
386
423
458
458
458
457
457
457
445
443
0.92
0.70
0.71
0.71
0.75
0.74
0.74
0.76
0.79
96
97
97
>99
>99
>99
>99
>99
a Measured in 2-propanol solution (1.0 ꢀ 10-5 M). b A quartz sub-
strate was measured as the background.
Figure 3. UV-vis absorption (gray) and fluorescence emission (black,
excited at λ = 400 nm) spectra of TPPy-Si in 2-propanol solution.
increase in the d-spacing values (Table 1, Figure 4b).
The formation of mesoscale porous structures was further
confirmed by TEM observation of the thermally annealed
and ethanol-washed samples (Figure 4c). For organosili-
ca film F-1a, wormholelike disordered mesopores are
observed. For F-4a prepared by addition of a large
amount of TEOS, a mesochannel array with a periodicity
of ca. 7 nm is formed in the film. The mesoscale periodi-
city of F-4a observed by TEM is smaller than that given in
Table 1 because of contraction of the mesostructures by
thermal annealing and template extraction (see the Sup-
porting Information). Here, it should be noted that large
amounts of the hydrophobic and bulky TPPy units were
successfully embedded within the framework with the aid
of enhanced interaction between the hydrophilic surface
of the micelles and the TPPy precursor with the adopted
silyl-terminated, four-armed molecular design.
Optical Properties of TPPy-Silica Mesostructured
Films. The TPPy-bridged mesostructured films exhibited
efficient blue light emission upon excitation by near-UV
to visible light (Table 2). Figure 5 shows UV-vis absorp-
tion and fluorescence emission spectra of the F-na mesos-
tructured organosilica films. The organosilica films
exhibited λmax of ca. 387 nm with strong absorption of
visible light around λ=400 nm (Figure 5a). Although the
absorption intensities decreased with the decrease in the
TPPy content, the spectral shape was unchanged and
similar to that of the precursor solution (Figure 3), which
indicated that the weak interaction between TPPy units
was preserved even at high TPPy concentration. With
respect to the emission spectra, all of the TPPy-containing
mesostructured films exhibited strong blue emission
around λ = 460 nm (Figure 5b). The ΦF of F-0a upon
excitation at λ=400 nm was 0.70 (Table 2). It is remark-
able that such a high fluorescence quantum yield is
achieved for a mesostructured organosilica prepared
from 100% organosilane precursor TPPy-Si. The TPPy
unit in the framework is not likely to form strong quench-
ing sites, even in the densely accumulated state.46 The ΦF
values of the organosilica films were increased up to 0.79
by the addition of TEOS (Table 2). The emission spectra
of F-na gradually shifted to the shorter wavelength region
with an increase in the amount of added TEOS, as shown
in Figure 5b, which indicates that highly fluorescent
monomer-like TPPy species increased in the organosilica
Figure 4. XRD patterns of (a) F-na and (b) F-1a-c. (c) TEM images of
the mesostructured films F-1a and F-4a.
self-assembly process. Table 1 gives the composition of
template surfactant P123, TPPy-Si, and TEOS in the sol
mixtures and the main d-spacing values (mesoscale peri-
odicity) obtained from XRD measurements. The XRD
patterns of all the films prepared in this study (denoted as
F-na, F-nb, and F-nc; n=weight ratio of TEOS to TPPy-Si
in the sol mixtures; a, b, and c indicate amounts of P123
(a, 40 mg, b, 60 mg, c, 80 mg)) indicated mesoscale perio-
dicity of 8.7-10.5 nm. Figure 4a shows XRD patterns of
the organosilica films prepared using the same amount of
P123 (F-na). A fairly broad diffraction pattern is observed
for F-0a, which indicates the formation of a less-ordered
mesostructure. With an increase in the amount of TEOS,
the diffraction peaks become conspicuous and the d-
spacing of the periodic mesostructure increases. Addition
of TEOS is effective for the enhancement of mesoscale
ordering, as reported for organosilica films containing
large hydrophobic bridging units.19-23 Increasing the
amount of P123 in F-1 films (F-1a-c) also improves the
ordering of the mesostructures, accompanied with an

2552 Chem. Mater., Vol. 22, No. 8, 2010
Mizoshita et al.
Figure 6. IR absorption bands of mesostructured films F-na correspond-
ing to the CdO stretching mode of the urethane bond.
mesostructured films were measured. Figure 6 shows
infrared absorption bands of the films in the range of
1680-1780 cm-1, which corresponds to the CdO stretch-
ing mode of the urethane moieties of the organic bridge.
The TPPy-silicahybrid films hadtwo absorption bands at
1716 and 1742 cm-1. The absorption band at 1742 cm-1 is
attributed to non-hydrogen-bonded CdO (see the Sup-
porting Information). The main absorption band observed
at 1716 cm-1 indicates that most of the urethane bonds are
in the weakly hydrogen-bonded state, because the strongly
hydrogen-bonded CdO of urethane linkage is reported to
Figure 5. (a) UV-vis absorption and (b) fluorescence emission spectra
(normalized at 455 nm) for F-na. The excitation wavelength is 400 nm.
exhibit an infrared absorption band at 1690-1700 cm-1 49
.
framework by further isolation of TPPy within the pure
silica framework. Therefore, the dilution of TPPy units in
the organosilica framework is effective for enhancing ΦF,
although the absorption intensity of the excitation light
decreases.
Comparing the infrared spectra of the F-na films, the
relative absorption intensity of the hydrogen-bond-free
CdO at 1742 cm-1 increased with increasing amount of
TEOS. These results suggest that the co-condensation of
TPPy-Si with TEOS partially suppresses the hydrogen-
bonded aggregation of TPPy units in the organosilica
framework, which may result in blue shifts of the fluores-
cence wavelengths, enhancement of the fluorescence quan-
tum yields, and high transparency of the films by hindering
the wrinkle formation during solvent evaporation.
Tuning of Emission Colors by Dye Doping. Doping of
fluorescent dyes into the TPPy-bridged mesostructured
films enabled flexible tuning of the fluorescence emission
colors of the films within a wide range of the visible
spectrum. As a host mesostructured film, F-1a was se-
lected due to the high content of TPPy units in the film,
good transparency, and a sufficiently high fluorescence
quantum yield. Two dyes, green-light-emitting Bodipy50
(ΦF=0.89 in 2-propanol) and yellow-light-emitting rhod-
amine 6G51 (Rhd6G, ΦF = 0.95 in 2-propanol), were
doped in the mesostructured film at concentrations of
0-5.0 mol % to the TPPy units (Figure 7). The broad
fluorescence spectrum of F-1a ranges from λ = 420 to
550 nm and sufficiently overlaps with the absorption
spectra of the fluorescent dyes; therefore, efficient excita-
tion energy transfer from the TPPy-silica framework to
the guest dyes can be expected. Figure 8 shows the
emission spectra of the dye-doped F-1a films upon excita-
tion at λ = 400 nm. The blue light emission of F-1a at
On the other hand, the spin-coated films of F-0a-c
prepared without TEOS showed a slight haze and 3-4%
decrease in light transmittance at λ=500 nm, whereas the
films prepared with TEOS exhibited high transparency
(Table 2). The baseline of the UV-vis spectrum of F-0a is
shifted upward, due to partial scattering of the incident
light, as shown in Figure 5a. Microscopic observation of
the organosilica films revealed that the partial light
scattering results from micrometer-scale wrinkles formed
on the surface of the F-0 films (see the Supporting Infor-
mation). The wrinkle formation is thought to be brought
about by heterogeneous shrinkage during solvent eva-
poration, especially for the F-0 films made from 100%
TPPy-Si. The TPPy-Si precursor is able to form hydro-
gen bonds through urethane moieties; therefore, the
concentrated precursors can form a dense hydrogen-
bonded network that affects the reactivity of the silyl
groups and the rate of evaporation of the solvents. The
addition of TEOS possibly weakens the hydrogen-
bonded aggregation of the organic moieties during the
evaporation-induced self-assembly process.48
To examine the hydrogen-bonded states and distri-
bution of the TPPy component in the framework,
infrared absorption spectra of the F-na organosilica
(48) In the sol mixtures of F-0a-c containing 100% TPPy-Si as a silica
source, precipitation of the TPPy derivatives and macroscopic
gelation of the mixtures occur in a few days after the preparation
of the sol mixtures. On the other hand, sol mixtures containing
TEOS remain as homogeneous solutions for at least one month.
These results indicate that the aggregation of TPPy-Si is sup-
pressed by the presence of TEOS even in the solution states.
(49) Hanabusa, K.; Tanaka, R.; Suzuki, M.; Kimura, M.; Shirai, H.
Adv. Mater. 1997, 9, 1095–1097.
(50) Ulrich, G.; Ziessel, R.; Harriman, A. Angew. Chem., Int. Ed. 2008,
47, 1184–1201.
(51) Kubin, R. F.; Fletcher, A. N. J. Lumin. 1983, 27, 455–462.

Article
Chem. Mater., Vol. 22, No. 8, 2010 2553
Figure 7. Chemical structures of fluorescent dye dopants and UV-vis
absorption and fluorescence emission spectra of the dyes in 2-propanol
solutions.
Figure 9. (a) Emission colors in the CIE 1931 chromaticity diagram
calculated from the fluorescence emission spectra of the dye-doped F-1a
films. (b) Photographs of the LED lamp (emission wavelength: 390 nm)
coated with a F-1a/Rhd6G(1.0 mol %) film.
exhibited fluorescence emissions between (0.15, 0.13) and
(0.41, 0.38). In particular, the F-1a/Rhd6G film containing
1.0 mol % Rhd6G exhibited a white light emission with
CIE coordinates of (0.32, 0.34). The dye-doped F-1a
fluorescent films were applied to the development of a
white light-emitting diode (LED). Light scattering loss is
generally inevitable in conventional white LED lamps
consisting of near-UV (e.g., λ=400 nm) LED chips and
micrometer-sized phosphor powders; however, the orga-
nosilica films, which are transparent and flexible in shape,
can suppress light scattering loss, leading to an improve-
ment in the external quantum efficiency of the light-emit-
ting system. Moreover, efficient light absorption and
strong visible-light emission can be achieved because of
the high content of fluorescent organic chromophores in
the transparent films. The dye-doped TPPy-silica films
were used as phosphors and LEDs as an excitation light
source. Figure 9b shows that the near-UV emission of a
commercial LED at λ=390 nm was successfully converted
to a white light emission by simply coating the transparent
F-1a/Rhd6G(1.0 mol %) film (ca. 10 μm thickness) at the
curved surface of the LED.
Figure 8. Fluorescence emission spectra of the (a) F-1a/Bodipy(0-5.0
mol %) and (b) F-1a/Rhd6G(0-5.0 mol %) films. The excitation wave-
length is 400 nm.
around λ=460 nm was quenched with an increase in the
dye concentration, with the subsequent appearance of
emission bands attributed to the fluorescence of the
doped dyes in the longer wavelength region. The two
dyes do not exhibit absorption bands at λ = 400 nm
(Figure 7); therefore, the fluorescence emission from the
dyes is caused by excitation energy transfer from TPPy
within the pore walls. The colors of the emissions from
dye-doped F-1a were plotted in the CIE 1931 chromati-
city diagram (Figure 9a). The emission colors of the F-1a/
Bodipy films changed from blue with CIE coordinates of
(0.15, 0.13) to green (0.22, 0.59). The F-1a/Rhd6G films
The fluorescence quantum yields of the dye-doped
films were significantly dependent on the guest dyes used.
The ΦF of the F-1a/Bodipy(1.0 mol %) film upon excita-
tion at λ=400 nm was 0.74, which is comparable to that
for the highly fluorescent nondoped F-1a. On the other
hand, the ΦF of the F-1a/Rhd6G(1.0 mol %) film
decreased to 0.43. The ΦF of the dyes doped in the

2554 Chem. Mater., Vol. 22, No. 8, 2010
Mizoshita et al.
mesostructured films were also measured by direct exci-
tation of the dyes. Although the ΦF value of Bodipy in the
1.0 mol % doped film was ca. 0.7-0.8 upon direct
excitation at λ =485 nm, that of Rhd6G excited at λ =
530 nm was ca. 0.2-0.3, which is much lower than the ΦF
in dilute 2-propanol solution. Decreased intensity and
slight red shift of the fluorescence emission from Rhd6G
at 2.0-5.0 mol % doping are also observed in Figure 8b,
which indicates that the fluorescence emission of Rhd6G
is partially quenched by dye aggregation in the meso-
structured film. Hydrophobic dyes such as Bodipy can
be well-dispersed in the hydrophobic cores of micellar
aggregates of the template surfactants.40 In contrast,
hydrophilic dyes such as Rhd6G are located and concen-
trated in the proximity of hydrophilic pore walls, which
might promote partial aggregation of the dye molecules.
periodic mesostructured organosilicas. The TPPy unit
was densely embedded within the framework of the
mesostructured films without strong fluorescence quen-
ching and the films exhibited efficient blue light emission
with quantum yields of over 0.7. Fluorescent dye doping
of the mesostructured films enabled color-tunable photo-
luminescence over a wide range of the visible spectrum,
including a white light emission with CIE coordinates of
(0.32, 0.34). The transparent and highly fluorescent orga-
nosilica hybrids with mesostructures have significant
potential for various luminescence applications including
LEDs and fluorescence sensing.
Acknowledgment. The authors are grateful to Dr. Tetsu
Ohsuna for performing the TEM observation.
Supporting Information Available: Optical photomicrographs
of F-0a and F-1a, additional infrared absorption spectra, and
XRD patterns of the films after extraction of the template
surfactant (PDF). This material is available free of charge via
the Internet at http://pubs.acs.org.
Conclusions
The four-armed TPPy unit was shown to be suitable as
a highly fluorescent bridging group for the formation of