Click assembly of dye-functionalized octasilsesquioxanes for highly efficient and photostable photonic systems

Article abstract of DOI:10.1002/chem.201100512

New hybrid organic-inorganic dyes based on an azide-functionalized cubic octasilsesquioxane (POSS) as the inorganic part and a 4,4-difluoro-4-bora-3a,4a- diaza-s-indacene (BDP) chromophore as the organic component have been synthesized by copper(I)-cataly

Full text of DOI:10.1002/chem.201100512

DOI: 10.1002/chem.201100512
Click Assembly of Dye-Functionalized Octasilsesquioxanes for Highly
Efficient and Photostable Photonic Systems
M. Eugenia Pꢀrez-Ojeda,[a] Beatriz Trastoy,[b] ꢁÇigo Lꢂpez-Arbeloa,*[c] Jorge BaÇuelos,[c]
ꢃngel Costela,[a] Inmaculada Garcꢄa-Moreno,*[a] and Jose Luis Chiara*[b]
Dedicated to the memory of Professor Roberto Sastre
Abstract: New hybrid organic–inorgan-
ic dyes based on an azide-functional-
ized cubic octasilsesquioxane (POSS)
as the inorganic part and a 4,4-di-
fluoro-4-bora-3a,4a-diaza-s-indacene
(BDP) chromophore as the organic
component have been synthesized by
copper(I)-catalyzed 1,3-dipolar cyclo-
addition of azides to alkynes. We have
studied the effects of the linkage group
of BDP to the POSS unit and the
degree of functionalization of this inor-
ganic core on the ensuing optical prop-
erties by comparison with model dyes.
The high fluorescence of the BDP dye
is preserved in spite of the linked chain
at its meso position, even after attach-
ing one BDP moiety to the POSS core.
The laser action of the new dyes has
been analyzed under transversal pump-
ing at 532 nm in both the liquid phase
and when incorporated into solid poly-
meric matrices. The monosubstituted
new hybrid dye exhibits high lasing ef-
ficiency of up to 56% with high photo-
stability, with its laser output remaining
at the initial value after 4ꢀ105 pump
pulses in the same position of the
sample at a repetition rate of 30 Hz.
However, functionalization of the
POSS core with eight fluorophores
leads to dye aggregation, as quantum
mechanical simulation has revealed,
worsening the optical properties and
extinguishing the laser action. The new
hybrid systems based on dye-linked
POSS nanoparticles open up the possi-
bility of using these new photonic ma-
terials as alternative sources for optoe-
lectronic devices, competing with
dendronized or grafted polymers.
Keywords: azides · click chemistry ·
dyes/pigments
quioxanes
· hybrids · silses-
Introduction
or alkoxide group).[1] Thanks to their rigid inorganic cores,
POSS are endowed with considerable chemical and thermal
stability, which can be channeled to their pendant organic
groups.
Fully condensed polyhedral oligosilsesquioxanes (POSS) are
unique nanometer-sized hybrid inorganic–organic materials
of chemical composition (RSiO1.5)n, which can be readily
synthesized by hydrolytic condensation of trifunctional orga-
nosilicon monomers RSiX3 (R=organic group; X=halogen
POSS nanoparticles have found novel applications in pho-
tonics and electronic devices,[2] significantly enhancing the
thermal, mechanical, and physical properties of the final ma-
terials and opening the challenge to synthesize new lumines-
cent hybrid matrices with optoelectronic properties compa-
rable to those of dendronized or grafted conjugated poly-
mers.[3] POSS nanoparticles can be dispersed at a molecular
level (0.5–5 nm)[4] and, because of their synthetically well-
controlled functionalization, can be incorporated into poly-
mers by different polymerization techniques with minimal
processing disruption.[5] This excellent dispersion at the mo-
lecular scale and the copolymerization with organic mono-
mers prevents phase separation, thereby ensuring macro-
scopic homogeneity of the resultant materials.[6] In this way,
new optical hybrid materials based on POSS nanoparticles
as the inorganic part overcome some of the most important
limitations intrinsic to sol–gel hybrid composites while main-
taining the combined physical, chemical, and mechanical ad-
vantages of organic–inorganic systems.[7]
[a] M. E. Pꢁrez-Ojeda, Prof. Dr. ꢂ. Costela, Prof. Dr. I. Garcꢃa-Moreno
Instituto Quꢃmica-Fꢃsica “Rocasolano”, C.S.I.C.
Serrano 119, 28006 Madrid (Spain)
Fax : (+34)915642431
E-mail: i.garcia-moreno@iqfr.csic.es
[b] B. Trastoy, Dr. J. L. Chiara
Instituto de Quꢃmica Orgꢄnica General, C.S.I.C.
Juan de la Cierva 3, 28006 Madrid (Spain)
Fax : (+34)915644853
E-mail: jl.chiara@iqog.csic.es
[c] Prof. Dr. ꢅ. Lꢆpez-Arbeloa, Dr. J. BaÇuelos
Departamento de Quꢃmica Fꢃsica
Universidad del Paꢃs Vasco-EHU
Facultad de Ciencias y Tecnologꢃa
Apartado 644, 48080 Bilbao (Spain)
Fax : (+34)946013500
We demonstrated, for the first time, the behavior of
POSS-doped systems as disordered nanomaterials, which
was to the best of our knowledge a possibility never consid-
E-mail: inigo.lopezarbeloa@ehu.es
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201100512.
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Chem. Eur. J. 2011, 17, 13258 – 13268

FULL PAPER
ered before.[8] The dispersion of POSS nanoparticles at a
molecular level defines highly homogeneous materials that,
when doped with lasing dyes, allow coherent laser emission
but, in addition and in spite of their nanometer size, the
POSS particles sustain a weak optical scattering that helps
lasing by elongating the light path inside the gain media,
thus providing an extra feedback, a phenomenon central to
the process called “incoherent random lasing” or “lasing
with intensity feedback”.[9] In this way, the laser action in
systems based on dye-doped POSS materials is significantly
enhanced, in both the liquid and solid phases.[7]
The unique chemical and optical properties exhibited by
POSS nanoparticles have led us to design new hybrid pho-
tonic systems based on POSS labeled with fluorescent dyes
as pendant groups on their rigid inorganic cores. Herein, we
report the synthesis and characterization of new hybrid or-
ganic–inorganic dyes based on azide-functionalized POSS as
the inorganic part, and a 4,4-difluoro-4-bora-3a,4a-diaza-s-
indacene (BDP) chromophore as the organic component,
which was selected for its interesting photophysical and pho-
tochemical properties both in the liquid phase and in doped
solid matrices.[10] It was anticipated that the new hybrid sys-
tems would exhibit highly efficient, stable, and tunable laser
emission with improved thermal properties owing to the
chemical attachment of the fluorophore to the rigid inorgan-
ic framework, strengthening their biomedical and photonic
applications. To study the effects of both the linkage group
through which BDP is attached to the POSS unit and the
degree of functionalization of the inorganic core on the opti-
cal properties, we proceeded to synthesize model dyes as
well as mono- and octa-substituted BDP–POSS hybrid de-
rivatives.
Results and Discussion
Synthesis and characterization
We recently described the synthesis of octakis(3-azido-
ACHTUNGTRENNUNGpropyl)ACHTUNGTRENNUNGoctasilsesquioxane (2), a highly symmetrical and
topologically ideal cube-octameric POSS monomer contain-
ing eight azide groups (Scheme 1).[11] Compound 2 could be
readily obtained in one-step from commercially available
octakis(3-aminopropyl)octasilsesquioxane (1) using a highly
efficient diazo-transfer reaction promoted by nonaflyl
azide,[12] a shelf-stable diazo-transfer reagent. The very mild
conditions of this reaction prevented nucleophile-induced
cage rearrangements,[13] which are common in alternative
routes to 2 involving nucleophilic substitution reactions with
azide ion.[14] Compound 2 is an excellent nano building
block for the synthesis of new functional nanocages with
perfect 3D cubic symmetry through copper(I)-catalyzed 1,3-
dipolar azide–alkyne cycloaddition (CuAAC)[15] with a vari-
ety of terminal alkynes.[11,14a,c,d] The versatility of this ap-
proach has been demonstrated by the preparation of the
dye–POSS cluster 4 using the alkyne-substituted BDP fluo-
rescent dye 3 (Scheme 1).[11]
Scheme 1. a) CF
3CATHUGNNERT(UNNG CF2)3SO2N3, NaHCO3, cat. CuSO4, Et2O/H2O/MeOH,
RT, 16 h; b) cat. CuSO4·H2O, sodium ascorbate, CH2Cl2/H2O, RT, 4.5 h
(2/3 molar ratio=1:10); c) cat. [Cu
(MW), 6 h (2/3 molar ratio=10:1).
ACHTUNGTRNE(NUNG C186tren)]Br, iPr2NEt, toluene, 808C
We have now studied the monofunctionalization of octa-
azide 2 with BDP dye 3. This reaction affords a POSS deriv-
ative 5 labeled with a single fluorescent probe and contain-
ing seven additional reactive azide groups suitably predis-
posed for further functionalization with any molecule of in-
terest having a terminal alkynyl group (Scheme 1). Besides,
compound 5 would be an interesting hybrid dye for the
preparation of solid-state laser materials with improved
thermal and chemical stability. Full details of our study of
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J. L. Chiara, ꢅ. Lꢆpez-Arbeloa, I. Garcꢃa-Moreno et al.
the CuAAC monofunctionalization reaction of octa-azide 2
under different reaction conditions will be published else-
where. The optimized conditions involved the use of a ten-
fold molar excess of 2 over alkyne 3, to guarantee a high
statistical selectivity for the monofunctionalized product 5,
and the recently described[16] [Cu
ACHTNUTRGNE(UNG C186tren)]Br (C186tren=
tris(2-dioctadecylaminoethyl)amine) catalyst with added
Hꢈnigꢉs base in toluene as solvent under microwave heating.
These optimized conditions afforded a high yield of 5
(82%), close to the expected statistical value (95.6%). The
rest of the alkyne 3 was transformed into a complex mixture
1
Scheme 2. Synthesis of model BDP dye 6.
of polytriazolyl POSS products, as shown by H NMR analy-
sis of the remaining mixed fractions from column chroma-
tography. The structure of 5 was unambiguously confirmed
by its high-resolution mass spectrometry and multinuclear
(1H, 13C, 29Si) NMR spectroscopy data (see the Supporting
Information).
the new BDP dyes on different experimental parameters,
such as the linkage group through which the chromophore is
attached to the POSS core, the degree of functionalization
of the core, the nature of the solvent, and the composition
of the host matrix.
We have studied the thermal stabilities of POSS deriva-
tives 4 and 5 by thermogravimetric analysis (TGA) (see the
Supporting Information). TGA of compound 4 under nitro-
gen atmosphere showed an initial 7.4% mass loss at about
1008C attributable to the loss of water from the hygroscopic
compound, followed by a 48% mass loss at about 3648C
due to degradation of the POSS itself. In air, the thermo-
gram again showed an initial 5.8% mass loss of water at
about 1008C, followed by a two-stage decomposition process
characterized by 26.7% and 48.4% mass losses starting at
around 3648C and 4458C, respectively, with a final char
yield of 14.6% at 8008C, which is slightly higher than ex-
pected for just SiO2 formation (calculated 11.1%). For com-
parison, the model BDP dye PM567 (Figure 2) showed an
onset decomposition temperature of around 2048C in its
thermogram in air (see the Supporting Information), which
is about 1608C lower than that of hybrid BDP–POSS cluster
4, confirming our expectations concerning the thermal stabi-
lizing effect of the covalently bonded POSS core. TGA of
compound 5 under nitrogen showed a two-stage decomposi-
tion process with an onset temperature of about 1478C and
a mass loss of 13.7%, attributed to the loss of seven N2 mol-
ecules from decomposition of the seven azide groups, fol-
lowed by a second mass loss of 24.7% starting at about
3808C. In air, an initial 14.0% mass loss was observed start-
ing at about 1388C, corresponding again to loss of N2 from
the seven azide groups, followed by a 45.7% mass loss start-
ing at about 3148C, with a final char yield of 34.7% at
8008C, which is also in this case somewhat higher than ex-
pected for SiO2 formation (calculated 32.2%).
Influence of substitution at C-8 of PM567 (compounds 3
and 6): Before attaching the BDP derivatives to a POSS
core, it is essential to characterize the influence of the link-
ing unit on the photophysics of the BDP chromophore.
Hence, appropriate model dyes were firstly analyzed.
Photophysical characterization: The absorption spectra and
fluorescence decay curves of model dyes 3 and 6 measured
in the same solvent are depicted in Figure 1. In general, the
Figure 1. Absorption and fluorescence spectra of compounds 3 (a) and 6
(b) in cyclohexane.
To study the photophysical properties of the BDP–POSS
constructs 4 and 5, we also prepared the new BDP dye 6 as
a model system in which a methyl group is attached in place
of the POSS core. Compound 6 was readily obtained by the
CuAAC reaction of 3 with 1-azidobutane (Scheme 2).
shape and position of the spectral bands of both model dyes
bearing para-phenyl substituents are similar to those of the
parent PM567 dye (Scheme 3)[17] and other 8-phenyl ana-
logues.[18] The steric hindrance introduced by the methyl
groups flanking the meso position of the chromophore ham-
pers the resonant interaction between the electronic clouds
of the phenyl group and the BDP core. In fact, such a con-
strained structure results in an almost perpendicular disposi-
tion of the phenyl group with respect to the chromophoric
plane, reducing its influence on the BDP core.[19]
Photophysical and lasing characterization
Studies were carried out to analyze the dependences of both
the photophysical properties and the laser performances of
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Hybrid Organic–Inorganic Dyes Assembled by Click Chemistry
FULL PAPER
Laser properties: The lasing behavior of model dyes 3 and 6
was analyzed according to the following protocol. First, we
carried out a systematic analysis of the laser action of the
new dyes in the liquid phase to guide the selection of the
best dye/host matrix combination among the quasi-unlimited
compositions and structures of solid materials with a view to
optimizing both the lasing efficiency and the photostability.
The dependence of the laser action on the concentration
of the new BDP dyes was analyzed in ethyl acetate by vary-
ing the dye concentration while keeping the other experi-
mental parameters constant. Under these experimental con-
ditions, broad-line-width laser emission peaked at around
558 nm, with a pump threshold energy of about 0.8 mJ, a
beam divergence of about 5 mrad, and a pulse duration of
around 8 ns FWHM (full-width at half-maximum), was ob-
tained from the new dyes when placed in a simple plane-
plane non-tunable resonator.
Scheme 3.
Table 1 lists the photophysical properties of dyes 3–6 in a
common solvent. For comparison purposes, the correspond-
ing data of the parent BDP dye (PM567), recorded under
Concentrations of 5ꢀ10À4 m and 6ꢀ10À4 m resulted in the
highest lasing efficiencies (defined as the ratio between the
energy of the dye laser output and the energy of the pump
laser incident on the sample surface) for compounds 3
(61%) and 6 (60%), respectively. The actual effect of the
solvent on the dye laser action was analyzed in solutions
with concentrations set at the values that optimize the lasing
action, using the same solvents that were selected to analyze
the photophysical properties of the new dyes. In all of the
selected solvents, the model dyes lased with high efficiency
(Table 2), their performances exceeding those of the parent
dye PM567 (35%) and other 8-substituted BDP dyes when
pumped under identical experimental conditions.[21]
Table 1. Photophysical properties of compounds 3, 4, 5, 6, and PM567
(reference dye)[17] in cyclohexane.[a]
Compounds labs
emax lfl
f
t
kfl
knr
3
527.5
8.5 542.0 0.54 2.96
523.0 38.0 545.0 0.25 3.66 (59%)
2.15 (24%)
1.82 1.55
–
4[b]
–
0.35 (17%)
5
6
526.0
526.0
522.5
5.8 540.0 0.60 3.86
8.1 540.0 0.67 3.74
9.3 537.0 0.70 5.60
1.55 1.03
1.79 0.88
1.25 0.53
PM567
[a] Absorption (labs, Æ0.5 nm) and fluorescence (lflu, Æ0.5 nm) wave-
length, molar absorption (emax, 104 mÀ1 cmÀ1), fluorescence quantum yield
(f, Æ0.05) and lifetime (t, Æ0.05 ns), radiative (kfl, 108 sÀ1), and nonra-
diative (knr, 108 sÀ1) deactivation rate constants. [b] Compound 4 was
found to be insoluble in cyclohexane, hence the data shown were ob-
tained in acetone. The full data in different solvents are listed in Ta-
bles S1 and S2 in the Supporting Information.
Table 2. Laser properties[a] of the new 8-functionalized BDP dyes in the
liquid phase.
Compound 3
Compound 5
Compound 6
Solvent
CF3CH2OH 57
Eff [%] lla [nm] Eff [%] lla [nm] Eff [%] lla [nm]
558
563
562
558
559
562
47
52
51
61
50
25
558
560
562
560
561
561
58
50
56
60
52
21
558
558
560
558
557
555
MeOH
EtOH
EtOAc
acetone
50
52
61
50
identical experimental conditions, are also included in
Table 1 (see also Table S1 in the Supporting Information for
photophysical data in different solvents). With respect to
the PM567 dye, the presence of a p-phenyl group linked to
the meso position of the BDP core induced a slight batho-
chromic shift of the absorption and fluorescence bands, an
increase in the nonradiative deactivation constant, and, con-
sequently, a slight decrease in the fluorescence quantum
yield and lifetime. It has previously been reported that the
free rotation of such bulky groups enhances the internal
conversion processes, and hence drastically reduces the fluo-
rescence of the dye.[20] However, in these model dyes, the
steric interaction with the flanking methyl groups seems to
hinder, at least to some extent, the rotation of the phenyl
ring.[19] In spite of this geometrical restriction, it seems that
the phenyl group might have some rotational freedom, in-
creasing the vibrational coupling with the BDP core, which
could explain the slight decrease in the fluorescence of the
model dyes.[18]
cyclohexane 35
[a] Eff: energy conversion efficiency, lla: peak wavelength of the laser
emission.
The new dyes proved to be highly photostable since, after
100000 pump pulses at 10 Hz, compounds 3 and 6 retained
90 and 80% of their initial laser outputs, respectively, which
represents a significant improvement in useful lifetime com-
pared with commercial PM567 as well as other 8-substituted
BDP dyes when pumped under otherwise identical experi-
mental conditions (Table 2 and Figure 2).[21] This enhance-
ment may be related to a higher photochemical stabilization
of the chromophores rather than to a decline in the nonra-
diative deactivation processes, since the new dyes have simi-
lar values of knr as the parent PM567. In addition, the lasing
behavior of the new dyes showed good correlation with
their photophysical properties in dilute solutions. Thus, the
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J. L. Chiara, ꢅ. Lꢆpez-Arbeloa, I. Garcꢃa-Moreno et al.
tained similar values to those measured in the liquid phase.
In this regard, it has to be taken into account that the sur-
face finishes of the solid samples relevant to the laser opera-
tion were not laser-grade, which is more detrimental to laser
efficiency than to laser photostability. To put the present re-
sults into perspective, the lasing parameters of PM567 in
PMMA were also measured under the same conditions. The
results obtained (a laser efficiency of 28%, with the emis-
sion dropping to zero after 100000 pump pulses)[22] were
clearly inferior to those obtained for the new 8-functional-
ized BDP dyes.
The photophysical and lasing properties of the new model
BDP dyes in solution indicated that a very polar protic sol-
vent such as 2,2,2-trifluoroethanol would also be a good
liquid medium for laser operation. To mimic this solvent, we
selected the monomer 2,2,2-trifluoroethyl methacrylate
(TFMA) for the preparation of linear copolymers with dif-
ferent proportions of MMA. The incorporation of the new
dyes 3 and 6 into this fluorinated organic matrix did not im-
prove their laser performances as compared with those ob-
tained in pure PMMA homopolymer (Table 3). In fact, the
presence of the fluorinated monomer in the matrix slightly
decreased both the lasing efficiency and the photostability
of the dyes. Although photobleaching of dyes can occur
through several different mechanisms and, from a general
point of view, can be considered to be quite complex, at low
irradiances and under ambient atmosphere the primary pho-
todegradation event of chromophores is believed to be
photo-oxidation. As a result, factors that accelerate oxygen
diffusion, such as the higher oxygen permeability of fluori-
nated materials, would be expected to reduce the photosta-
bility of the new model BDP dyes.
In summary, the two new analogues of dye PM567, com-
pounds 3 and 6, have demonstrated similar photophysical
properties and higher lasing efficiencies and photostabilities
than the parent dye PM567, both in the liquid phase and
when incorporated into solid matrices. Therefore, the
chosen models are suitable candidates to be linked to the
POSS unit, since the unique photophysical properties of a
BDP chromophore such as PM567 are preserved after the
introduction of the alkynyl or 1,2,3-triazolyl substituents at
the para-position of the phenyl ring. Furthermore, the at-
tachment of the BDP unit to the POSS core is known to be
an efficient means of photostabilizing BDP laser dyes.
Figure 2. Normalized laser-induced fluorescence emission as a function of
the number of pump pulses for PM567 (a), 6 (b), 3 (c), and 5 (d) dye sol-
utions in ethyl acetate. The residual laser-induced fluorescence emissions
after 100000 pulses for (a) to (d) were 71.4, 78.8, 89.5, and 97.3%, re-
spectively. Pump energy and repetition rate: 5.5 mJpulseÀ1 and 10 Hz, re-
spectively.
similarity between the photophysical properties was also
manifested in similar laser behavior for both dyes. Looking
at the dependence of the laser action of each new dye on
the nature of the solvent, it can be appreciated that the
higher the fluorescence quantum yield, the higher the lasing
efficiency.
The laser action of the new BDP dyes 3 and 6 in the solid
state was analyzed in samples synthesized with the dye con-
centration that induced the highest lasing efficiency in liquid
solution (5ꢀ10À4 to 6ꢀ10À4 m, depending on the dye).
Methyl methacrylate (MMA) was chosen as the main mono-
meric component of the formulations because this ester
mimics ethyl acetate, a solvent in which both model dyes
display high lasing efficiencies.
First, compounds 3 and 6 were incorporated as true solu-
tions into the solid homopolymer poly(methyl methacrylate)
(PMMA), to delineate the effect of the 8-substituent on
their lasing action when pumped under the experimental
conditions described above. The results obtained are sum-
marized in Table 3. No significant differences were observed
in the wavelength of the maximum laser emission of each
dye between their liquid and solid solutions. Lasing efficien-
cies of 40 and 38%, respectively, were measured, which are
lower than those obtained from the corresponding solutions
in ethyl acetate, whereas the lasing photostability main-
Influence of the BDP–POSS click assembly—monosubstitu-
tion (compound 5):
Photophysical characterization: The linkage of the BDP
moiety to the POSS core (compound 5) had only a minor
effect on the spectral band positions and on the fluorescence
lifetime, which remained close to those of the model BDP
bearing the linking unit (compound 6, Table 1). However,
the absorption transition probability was more affected by
the presence of POSS (the molar absorption decreased by
around 25%) than the fluorescence transition, since the
fluorescence quantum yield decreased by only around 10%
Table 3. Laser properties of the new photosensitized materials.
Compound 3
Material[a] Eff
lla
[nm] [%] [%]
Compound 5
Eff lla
[nm] [%] [%]
Compound 6
Eff lla
[nm] [%]
I
I
I
[%]
A
B
C
40
36
560
560
97
82
52
560
100 38
31
100
559
558
77
72
56
558
[a] A: PMMA; B: Co(MMA/TFMA, 70:30); C: Co(MMA/8MAPOSS,
87:13).
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Hybrid Organic–Inorganic Dyes Assembled by Click Chemistry
FULL PAPER
(Table 1). This behavior may be attributed to a reduction/
enhancement of the radiative/nonradiative deactivation pro-
cesses, respectively, explaining the maintenance of the fluo-
rescence lifetime (Table 1). The reduction of the kfl values is
correlated with the decrease in the absorption probability,
while the enhancement of the knr values should be related to
the large pendant POSS framework. A molecular structure
with high conformational freedom increases the flexibility of
the dye, thereby favoring internal conversion processes.[20] In
any case, the resulting hybrid dye retained a high fluores-
cence capacity (up to 0.65, with lifetimes of around 4–6 ns;
see Table S1 in the Supporting Information).
same position of the sample at a repetition rate of 30 Hz
(Figure 3). The new hybrid dye dissolved in pure PMMA ex-
hibited high photostability, without any sign of degradation
Laser properties: The laser action of the new hybrid dye 5
was evaluated following the protocol described above.
Under the selected experimental conditions, a concentration
of the new hybrid BDP dye of 7.5ꢀ10À4 m assured an optical
density at the pumping wavelength (532 nm) similar to that
selected for the characterization of the 8-functionalized
BDP dyes 3 and 6. The hybrid dye 5 lased at around 560 nm
with an efficiency ranging from 60% (ethyl acetate) to 25%
(cyclohexane), and showed high photostability with no sign
of degradation in its laser output after 100000 pump pulses
at a repetition rate of 10 Hz (Table 2 and Figure 2). It
should be noted that although the lasing performances of
dyes 5 and 3 were similar, the absorption and fluorescence
probabilities were lower for the hybrid dye. This fact can be
related to our initial hypothesis: the POSS particles, with
sizes below 5 nm, act as weak scattering centers in the Ray-
leigh limit (particle size much smaller than the emission
wavelength), increasing the effective optical path inside the
gain medium in a process known as non-resonant feedback
(NRF) lasing, incoherently supplementing the conventional
laser action in such a way as to increase the efficiency of the
laser system.[8,23] Under laser irradiation, the opening up of
this new non-resonant feedback pathway explains the high
laser performance of the new BDP–POSS cluster, as well as
the lack of correlation with its photophysical properties,
which were recorded under much lower excitation intensi-
ties.
Incorporation of the new BDP–POSS dye into PMMA re-
markably improved the laser action as compared to that re-
corded with dye 3 in the same matrix (material A, Table 3).
Thus, for the hybrid dye, a laser efficiency as high as 52%
was recorded, without any sign of degradation after 100000
pump laser pulses in the same position of the sample at a
repetition rate of 10 Hz. The incorporation of methacryl-
POSS nanoparticles (8MAPOSS cage mixture, Scheme 3)
into this medium resulted in a further enhancement of the
lasing performance. In this way, a new solid material based
on a copolymer of MMA with a 13% weight ratio of
8MAPOSS doped with hybrid dye 5 reached a lasing effi-
ciency of up to 56%, while maintaining a high photostability
(material C, Table 3).
Figure 3. Normalized laser output as a function of the number of pump
pulses in the same position of the sample for the new hybrid dye 5 incor-
porated into PMMA. Pump energy and repetition rate: 5.5 mJpulseÀ1
and 30 Hz, respectively.
of its laser output after 400000 pump pulses. Thus, regarding
laser efficiency and photostability, the new hybrid BDP–
POSS cluster improved our previous results based on hybrid
matrices doped with the parent PM567 dye, even when
these matrices were based on copolymers of MMA with dif-
ferent weight ratios of 8MAPOSS.[22,24]
Influence of the BDP–POSS click assembly—octa-substitu-
tion (compound 4):
Photophysical characterization: This multichromophoric
hybrid dye was found to be insoluble in apolar solvents,
such that not even dilute (10À6 m) solutions could be ob-
tained, but dissolved well in polar media such as acetone,
ethyl acetate, and 2,2,2-trifluoroethanol. Figure 4 shows the
corresponding absorption and fluorescence spectra, together
with the fluorescence decay curves. The presence of eight
BDP units in the same molecule led to a large increase in
the absorption transition probability, with emax being as high
as 38ꢀ104 mÀ1 cmÀ1 in acetone (Table 1), probably the largest
reported for a BDP-based system. The fluorescence proper-
ties of compound 4 depended on the nature of the solvent.
Indeed, whereas in ethyl acetate the fluorescence quantum
yield was high (0.62) and the decay curve could be interpret-
ed as monoexponential with a lifetime of 5.4 ns, an increase
in solvent polarity led to a loss of the fluorescence ability,
most notably in trifluoroethanol (see Table S2 in the Sup-
porting Information). In acetone, the decay curve became
multiexponential, consisting of two components with life-
times of 2.1 and 3.6 ns (Table 1), which could be assigned to
different microenvironments of the BDP units in compound
To better assess the laser photostability of the new hybrid
BDP–POSS dye 5, we proceeded to carry out a longer run
of pumping under more drastic conditions by irradiating the
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13263

J. L. Chiara, ꢅ. Lꢆpez-Arbeloa, I. Garcꢃa-Moreno et al.
conformations. In all cases, the final optimized geometry
(Figure 5) revealed that the phenyl rings and their attached
indacene subunits were not coplanar, as expected. Besides,
Figure 4. A) Absorption and fluorescence spectra of compound 4 scaled
by its molar absorption and fluorescence quantum yields, respectively, in
ethyl acetate (a), acetone (b), and trifluoroethanol (c). The normalized
absorption spectra of PM567 (dashed) and compound 4 (solid) are also
included. B) Fluorescence decay curves.
Figure 5. Optimized geometry (at AM1 semiempirical level) of a simpli-
fied model of compound 4 lacking four of the eight phenyl-BDP substitu-
ents: (a) front view; (b) side view.
4 (for instance, a chromophore surrounded by other BDP
moieties or by solvent), and a third fast component (0.3 ns)
due to a quenching process responsible for the decrease in
the fluorescence quantum yield. In the most polar medium,
the fluorescence emission was almost negligible and the
decay curve was multiexponential and characterized by very
short lifetimes.
the BDP chromophores did not occupy the available free
volume, but rather tended to be in close contact, allowing
through-space interactions between them. In fact, it was ob-
served that the BDP units tended to be paired, with a cofa-
cial arrangement (Figure 5), allowing a p–p interaction and,
consequently, the formation of H-type or “sandwich” aggre-
gates, in which the transition moments of the chromophores
are in a parallel arrangement.[25]
The self-association of the BDP chromophores was corro-
borated by other experimental findings. Comparison of the
normalized absorption spectra of the octasubstituted POSS
4 and the parent PM567 dye indicated that the spectrum of
the hybrid material was wider, with increased absorbance in
the hypsochromic shoulder region, which is characteristic of
H-type aggregates (Figure 4). Besides, the absorption proba-
bility of compound 4 does not correspond to the sum of
eight BDP units (the emax of model dye 6 was measured as
8.1ꢀ104 mÀ1 cmÀ1; Table 1). We have pointed out previously
that the linkage of the BDP unit to the POSS core (com-
pound 5) led to a slight reduction in the absorption transi-
tion probability.
To gain a deeper insight, we tried to simulate theoretically
the most stable ground-state conformation of compound 4
by means of the AM1 semiempirical method. Taking into
account the large number of possible conformations of this
molecule, we followed two different approaches for the ge-
ometry optimization. On the one hand, a full optimization
of the octasubstituted POSS was performed starting from a
geometry with the BDP chromophores located as far as pos-
sible from each other and with the phenyl substituents ori-
ented coplanar to the BDP system. On the other hand, we
carried out a sequence of stepwise building of the molecule
followed by full geometry optimization at each step starting
from the bare octapropyl-POSS core, then adding the eight
triazolyl rings and finally four of the eight phenyl-BDP sub-
stituents on one of the faces of the POSS cube, to ultimately
obtain a simplified model of 4 in an energy-minimized con-
formation. One should keep in mind the difficulty in han-
dling such large and flexible structures, with many allowed
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Hybrid Organic–Inorganic Dyes Assembled by Click Chemistry
FULL PAPER
Although BDP dyes usually have a low tendency to self-
associate,[20c] some authors have claimed the presence of ag-
gregates in confined environments or in multichromophoric
dyes, in which the BDP cores are closely disposed through
molecular bridges.[26] Owing to the hydrophobicity of the
BDP dye, an increase in the polarity in the surrounding en-
vironment forces the chromophores into closer association,
favoring dye aggregation. Indeed, the hypsochromic absorp-
tion shoulder was clearer and the calculated molar fraction
of the aggregate was higher in polar solvents (trifluoroetha-
nol). Quantum mechanical calculations suggest that in such
an H-type dimer, the BDP monomeric units are mutually
disposed with a dihedral angle of 88 between them and sepa-
rated by 5 ꢊ. However, due to the flexibility of the linking
chains, the chromophores are not held tightly in a cofacial
manner, which leads to a low exciton coupling and a low
splitting of the absorption bands of the aggregate,[27] thus ac-
counting for the only slight changes observed in the absorp-
tion spectrum of the octasubstituted POSS compared to that
of the free BDP dye (Figure 4). Indeed, a rough estimate of
the degree of aggregation[28] predicts a molar fraction of
around 0.8 for the monomer and 0.10 for the dimer (0.20
for the monomeric units of the aggregate).
Aggregation is the main factor responsible for the de-
crease in the fluorescence ability and the short lifetime in
polar media. Apart from the static fluorescence quenching
induced by the H-type aggregates due to their inactive ab-
sorption in fluorescence, the multi-exponential decay in
polar media was indicative of complex excited-state dynam-
ics. Typically, non-fluorescent H-aggregates undergo deacti-
vation of the monomer excited states by energy-transfer
processes.[28] The formation of a fluorescent excimer is ruled
out since the recorded fluorescence band resembled that of
the model BDP dye, no new fluorescence bands were de-
tected, and the deconvolution of the decay curves was the
same regardless of the emission wavelength. Besides, the
spatial proximity between the BDP units, as revealed in the
optimized geometry of the octasubstituted POSS (Figure 5),
could lead to extra quenching processes (i.e., interconver-
sion between aggregates and monomers) producing an over-
all loss of fluorescence capacity due to the flexibility of the
spacer connecting the BDP units to the POSS core, which
could allow a range of different relative arrangements of the
BDP units contributing to the loss of fluorescence.[21c] In this
sense, the full optimization of compound 4 predicted a slight
loss of planarity in the BDP chromophores, showing a but-
terfly-like distortion along the transversal axis, while in the
monosubstituted POSS (compound 5) the indacene core re-
mained fully planar. This lack of planarity, probably due to
the high steric hindrance of such a constrained structure in
the octasubstituted POSS, should lead to an increase in the
internal conversion probability.[29] In view of these results,
the octasubstituted POSS 4 is deemed to be unsuitable for
use as a dye laser.
nonradiative pathways, mainly due to the presence of aggre-
gates, greatly enhanced the losses in the resonator cavity,
preventing the detection of the laser signal.
Conclusion
Octakis(3-azidopropyl)octasilsesquioxane (2) is a topologi-
cally ideal nano building block for the efficient synthesis of
mono- and octa-functionalized fluorescent nanocages
through CuAAC reaction with alkyne-substituted BDP dyes.
The controlled monofunctionalization of octa-azide 2 with
BDP dye 3 resulted in a fluorescently labeled POSS deriva-
tive 5 containing seven additional reactive azide groups suit-
ably predisposed for further functionalization through
CuAAC with any molecule of interest having a terminal al-
kynyl group. Full dye-substitution of POSS afforded a
hybrid system characterized by low fluorescence ability,
mainly in polar media. Quantum mechanical simulation has
provided a molecular basis that allows insight into the com-
position–structure–properties relationship of these hybrid
systems. The optimized molecular geometry suggests that
the BDP chromophores tend to be paired, leading to aggre-
gation, which effectively quenches both fluorescence and
laser emissions. However, the linkage of one BDP unit to
the POSS core had only a minor effect on the photophysics
of the dye, while significantly improving the laser properties
of the final system with respect to those exhibited by the
model dyes. In fact, the new hybrid dye exhibited lasing effi-
ciencies of up to 60% (in the liquid phase) and 56% (in
solid matrices), with high photostability, since the laser
output remained at its initial value under very demanding
pumping conditions (4ꢀ105 pump pulses in the same posi-
tion of the sample at 30 Hz repetition rate). The new BDP–
POSS cluster gives rise to a non-resonant feedback mecha-
nism, which enhances its coherent laser performance. The
versatility in the synthesis of the hybrid systems based on
dye-linked POSS nanoparticles, together with their im-
proved optical properties and their nanofabrication capabili-
ty, opens up the possibility of using these new photonic ma-
terials as alternative sources for optoelectronic devices, com-
peting with dendronized or grafted polymers.
Experimental Section
General methods for synthesis and chemical characterization: All melting
points were measured with a Reicher Jung Thermovar micro-melting ap-
paratus. Proton and carbon-13 nuclear magnetic resonance (1H NMR and
13C NMR) spectra were recorded on
a Bruker AMX-300 (300 and
75 MHz, respectively), a Varian INOVA 300 (300 and 75 MHz, respec-
tively), or a Varian INOVA 400 (400 and 100 MHz, respectively) spec-
trometer. Silicon-29 nuclear magnetic resonance spectra were measured
on a Varian INOVA 400 spectrometer (79.5 MHz). Chemical shifts are
expressed in parts per million (d scale) downfield from tetramethylsilane
and are referenced to residual peaks of the deuterated NMR solvent
used or to internal tetramethylsilane. Data are presented as follows:
Laser properties: Hybrid dye 4 did not lase even under dras-
chemical shift, multiplicity (s=singlet, d=doublet, t=triplet, m=mul
ACHTUNGTRENNUNGti-
tic pumping conditions. Indeed, all of the abovementioned
ACHTUNGERTNpNUNG let and/or multiple resonances, br=broad), integration, coupling con-
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13265

J. L. Chiara, ꢅ. Lꢆpez-Arbeloa, I. Garcꢃa-Moreno et al.
stants in hertz (Hz), and assignment. Proton and carbon-13 assignments
are based on DQ-COSY, HSQC, and HMBC correlation experiments.
Thin-layer chromatography (TLC) was performed with Merck silica gel
60 F254 plates and Merck aluminum oxide neutral 60 F254 plates. Chroma-
tograms were visualized using UV light of wavelengths 254/365 nm. For
the detection of azides, the chromatograms were first dipped in a 1% (w/
v) solution of Ph3P in EtOAc, dried at RT, then dipped in a 1% or 5%
(w/v) solution of ninhydrin in 95% aqueous EtOH, and finally charred
on a hot plate.[30] Column chromatography was performed with Merck
neutral aluminum oxide or Merck silica gel, grade 60, 230–400 mesh.
Mass spectra were recorded on a MALDI Voyager-DE PRO time-of-
flight (TOF) spectrometer (Applied Biosystems), using a 2,5-dihydroxy-
benzoic acid matrix, or on an Agilent/HP 1100 LC/MSD spectrometer
using ESI or APCI sources. Anhydrous solvents were prepared according
to standard methods by distillation over drying agents or by elution
through a Pure Solv column-drying system[31] from Innovative Technolo-
gy. All other solvents were of HPLC grade and were used as received.
All reactions were carried out under magnetic stirring and, if air- or
moisture-sensitive, in oven-dried glassware under argon. Microwave irra-
diation experiments were performed with a single-mode Discover System
from CEM Corporation, using standard Pyrex tubes (10 or 35 mL capaci-
ty) sealed with a rubber cap.
raphy (SiO2; hexane/EtOAc, 12:1 to 5:3) to recover excess starting mate-
rial 2 (113 mg, 94% recovery of excess 2 employed) and 5 as a red vis-
cous oil (15.1 mg, 82%). Rf =0.61 (hexane/EtOAc, 5:3); 1H NMR
(400 MHz, CDCl3): d=0.71–0.76 (m, 14H; Si-CH2CH2CH2), 0.83–0.98
(m, 2H; Si*CH2CH2CH2), 0.97 (t, 6H, J=7.55 Hz; CH3CH2), 1.34 (s, 6H;
CH3-C1, CH3-C7), 1.66–1.74 (m, 14H; SiCH2CH2CH2), 2.06–2.13 (m, 2H;
Si*CH2CH2CH2), 2.30 (q, 4H, J=7.51 Hz; CH2CH3), 2.54 (s, 6H; CH3-
C3, CH3-C5), 3.26 (td, 14H, J=6.83, 1.42 Hz; CH2N3), 4.43 (t, 2H, J=
7.11 Hz; CH2-N=N), 7.36 (d, 2H, JAB =8.43 Hz; 2ꢀCH phenyl), 7.97 (d,
2H,
JAB =8.43 Hz; 2ꢀCH phenyl), 7.86 ppm (s, 1H; 1,2,3-triazole);
13C NMR (100 MHz, CDCl3): d=9.3 (SiCH2CH2CH2), 12.6 (CH3), 12.7
(CH3), 14.9 (CH3CH2), 17.3 (CH3CH2), 22.7 (SiCH2CH2CH2), 24.4
(Si*CH2CH2CH2), 52.8 (CH2-N=N), 53.5 (CH2N3), 120.1 (CH, 1,2,3-tria-
zole), 126.4 (CH, phenyl), 129.2 (CH, phenyl), 130.9, 131.3, 133.0, 135.9,
138.5, 139.8 (C in 1,2,3-triazole), 147.4, 154.1 ppm [Si*=silicon atom with
the (1,2,3-triazol-1-yl)propyl substituent]; 29Si NMR: d=À66.92, À66.97,
À67.53 ppm (3:4:1 relative intensities); UV/Vis (EtOAc): lmax =523 nm
(e=47427 molÀ1 m3 cmÀ1); MS (API-ESI): m/z: 1493.3 [M+H]+, 1475.4
[MÀNH4+].
BDP dye 6: a) Synthesis of 1-butylazide: A solution of 1-bromobutane
(1.0 g, 7.5 mmol) and NaN3 (950 mg, 14.6 mmol) in DMF (15 mL) was
stirred for 15 h at 1208C. The mixture was then poured into water and
extracted three times with toluene (final concentration 0.04m assuming
the reaction to be quantitative), and the combined extracts were dried
(Na2SO4) and used without further purification. b) CuAAC reaction:
Materials: Pyrromethene 567 (laser grade, Exciton) with a purity >99%
(checked by spectroscopic and chromatographic methods) was used as re-
ceived. Solvents for laser studies were of spectroscopic grade (Merck, Al-
drich, or Sigma) and were used without purification. Linear and cross-
linked copolymers were obtained by copolymerization of methyl metha-
crylate (MMA) with different volumetric proportions of the monofunc-
tional fluorinated monomer 2,2,2-trifluoroethyl methacrylate (TFMA)
and of methacryl-POSS (8MAPOSS cage mixture, from Hybrid Plastics).
All monomers were purchased from Aldrich. MMA was purified before
use, while TFMA and 8MAPOSS were used as received. 2,2’-Azobis(iso-
butyronitrile) (AIBN) (Acros) was used as a thermal initiator of poly-
merization. Azido-POSS 2 was prepared as described previously.[11] Cop-
[CuACHTUNGRTNEUNG(C186tren)]Br (11 mg, 0.006 mmol) and iPr2NEt (32 mL, 0.185 mmol)
were added to a solution of 1-butylazide in toluene (2.23 mL, 0.04m,
0.080 mmol) containing 4,4-difluoro-8-(4’-ethynylphenyl)-1,3,5,7-tetra-
methyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (3) (25 mg, 0.062 mmol)
under argon. After stirring for 3 h at 808C under microwave irradiation,
the solvent was removed under reduced pressure and the residue was pu-
rified by flash column chromatography (hexane/EtOAc, 1:5) to afford 6
as a red crystalline powder (28 mg, 90%). Rf =0.44 (hexane/EtOAc, 5:3);
1
m.p. (from EtOAc): 232–2358C; H NMR (400 MHz, CDCl3): d=0.98 (t,
per(I) catalyst [Cu
(C186tren)]Br (C186tren=tris(2-dioctadecylaminoe-
6H, J=7.5 Hz; CH3CH2), 1.00 (t, 3H, J=7.3 Hz; CH
3ACHTUNGTREN(UNNG CH2)3N), 1.34 (s,
thyl)amine) was prepared according to described procedures.[16a]
6H; CH3-C1, CH3-C7), 1.37–1.49 (m, 2H; CH2A(CH2)2N), 1.88–2.04 (m,
CHTUNGTRENNUNG
2H; CH2CH2N), 2.31 (q, 4H, J=7.5 Hz; CH2CH3), 2.54 (s, 6H; CH3-C3,
CH3-C5), 4.44 (t, 2H, J=7.2 Hz; CH2N), 7.35 (d, 2H, JAB =8.3 Hz; CH
phenyl), 7.84 (s, 1H; 1,2,3-triazole), 7.97 ppm (d, 2H, JAB =8.3 Hz; CH
phenyl); 13C NMR (100 MHz, CDCl3): d=12.1 (CH2CH3), 12.7 (CH3-C1,
Compound 4: A solution of CuSO4·5H2O (2.5 mg, 0.010 mmol) and
sodium ascorbate (9 mg, 0.045 mmol) in water (0.6 mL) was added to a
solution of azido-POSS 2 (20 mg, 0.018 mmol) and 4,4-difluoro-8-(4’-ethy-
nylphenyl)-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene
(3)[32] (72 mg, 0.178 mmol) in CH2Cl2 (0.9 mL). After stirring for 4.5 h at
RT, a saturated aqueous solution of EDTA (1 mL) was added, the mix-
ture was vigorously stirred for 30 min, the phases were separated, and
the aqueous layer was extracted with CH2Cl2 (3ꢀ3 mL). The organic
layers were combined, dried over Na2SO4, and the solvent was removed
under reduced pressure. The crude residue was purified by flash column
chromatography (hexane/EtOAc, 1:5) to afford 4 (54 mg, 70%) as a red
powder. M.p. (from CH2Cl2): 2908C (decomposition). Rf =0.75 (hexane/
EtOAc, 1:5); 1H NMR (400 MHz, CDCl3): d=0.68–0.75 (m, 16H; Si-
CH2CH2CH2), 0.93 (t, 48H, J=7.4 Hz; 16ꢀCH3CH2), 1.30 (s, 48H; 16ꢀ
CH3-C), 2.13–2.18 (m, 16H; SiCH2CH2CH2), 2.25 (q, 32H, J=7.4 Hz;
16ꢀCH2CH3), 2.51 (s, 48H; 16ꢀCH3-C), 4.46 (t, 16H, J=6.9 Hz;
SiCH2CH2CH2), 7.32 (d, 16H, JAB =8.2 Hz; 2ꢀCH Ar), 8.01 (d, 16H,
CH3-C7), 13.7 (CH3-C3, CH3-C5), 14.8 (CH
3ACHTUNGTRNEN(NUG CH2)3N), 17.2 (CH2CH3),
19.9 (CH2A(CH2)2N), 32.5 (CH2CH2N), 50.4 (CH2N), 119.9 (CH in 1,2,3-
CTHUNGTRENNUNG
triazole), 126.4 (CH phenyl), 129.0 (CH phenyl), 130.9, 131.4, 133.0,
135.7, 138.5, 139.9, 147.2, 153.9 ppm; UV/Vis (EtOAc): lmax (e)=522 nm
(108900 molÀ1 m3 cmÀ1); MS (API-ESI): m/z: 504.3 [M]+.
Preparation of solid polymeric samples: The new BDP derivatives were
incorporated into different solid matrices according to a previously de-
scribed procedure.[33] Solid monolith laser samples were cast in cylindrical
shape so as to form rods of 10 mm in diameter and 10 mm in length. A
cut was made parallel to the axis of the cylinder to obtain a lateral flat
surface of ꢀ6ꢀ10 mm. This surface, as well as the ends of the laser rods,
was prepared for lasing experiments by using a grinding and polishing
machine (Phoenix Beta 4000, Buehler) until an optical-grade finish was
obtained. The planar grinding stage was carried out with Texmet 1000
sandpaper (Buehler) using a diamond polishing compound of 6 mm as an
abrasive in mineral oil as a lubricant. The final polishing stage was realiz-
ed with a G-Tuch Microcloth (Buehler), using a Mastertex cloth disk
(Buehler) with diamond of 1 mm in mineral oil as an abrasive.
J
AB =8.2 Hz; 2ꢀCH Ar), 8.15 ppm (s, 8H; 1,2,3-triazole); 13C NMR
(100 MHz, CDCl3): d=8.7 (SiCH2CH2CH2), 11.9 (CH3), 12.5 (CH3), 14.6
(CH3-CH2), 17.0 (CH3-CH2), 24.1 (SiCH2CH2CH2), 52.4 (SiCH2CH2CH2),
120.7 (CH in 1,2,3-triazole), 126.1 (CH phenyl), 129.0 (CH phenyl),
130.1, 131.2, 133.1, 135.8, 137.9, 139.2 (C in 1,2,3-triazole), 147.1,
154.0 ppm; 29Si NMR (79.5 MHz, CDCl3): d=À67.1 ppm; UV/Vis
(EtOAc): lmax =523 nm, e=432362 molÀ1 m3 cmÀ1; MALDI-TOF (2,5-di-
hydroxybenzoic acid matrix): m/z: 4304 [MÀF]+.
Photophysical properties: Photophysical properties were measured from
dilute solutions of the dyes (around 2ꢀ10À6 m), prepared by adding the
corresponding solvent to the residue from an appropriate amount of a
concentrated stock solution in acetone, after vacuum evaporation of this
solvent. UV/Vis absorption and fluorescence spectra were recorded on a
Cary 4E spectrophotometer and on a SPEX Fluorolog 3–22 spectro-
fluorimeter, respectively. Fluorescence quantum yields (f) were evaluat-
ed from corrected spectra, using a diluted solution of PM567 dye (Exci-
ton, laser grade) (f=0.91 in methanol) as a reference.[17] Radiative decay
curves were recorded by the time-correlated single-photon counting tech-
Mono-BDP–POSS 5: [CuACTHNUTRGNEUNG(C186tren)]Br (2.2 mg, 0.001 mmol) and
iPr2NEt (6.5 mL, 0.037 mmol) were added to a solution of azido-POSS 2
(134 mg, 0.123 mmol) and 4,4-difluoro-8-(4’-ethynylphenyl)-1,3,5,7-tetra-
methyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (3) (5 mg, 0.012 mmol)
in toluene (1 mL) under argon. The mixture was stirred for 6 h at 808C
under microwave irradiation. The solvent was then removed under re-
duced pressure and the residue was purified by flash column chromatog-
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Chem. Eur. J. 2011, 17, 13258 – 13268

Hybrid Organic–Inorganic Dyes Assembled by Click Chemistry
FULL PAPER
nique (Edinburgh Instruments, model FL920). Fluorescence emission was
monitored at the maximum emission wavelength after excitation at
470 nm by means of a diode laser (PicoQuant, model LDH470) with
150 ps FWHM pulses. The fluorescence lifetime (t) was obtained after
deconvolution of the instrumental response signal from the recorded
decay curves by means of an iterative method. The goodness of the expo-
nential fit was assessed by statistical parameters (chi-squared, Durbin–
Watson, and analysis of the residuals). The rate constants of radiative
(kfl) and nonradiative (knr) deactivation were calculated according to kfl =
f/t and knr =(1Àf)/t, respectively.
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The ground-state geometries of the BDP–POSS hybrid dyes in the gas
phase were fully optimized by the semiempirical AM1 method imple-
mented in the Gaussian 09 software, compiled in an informatic cluster.
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Lasing properties: Liquid solutions of dyes were contained in 1 cm opti-
cal-path quartz cells that were carefully sealed to avoid solvent evapora-
tion during experiments. Both the liquid cells and the solid samples were
transversely pumped at 532 nm with 5.5 mJ, 6 ns FWHM pulses from a
frequency-doubled, Q-switched Nd:YAG laser (Monocrom OPL-10) at a
repetition rate of up to 10 Hz. Most representative samples were also
pumped at 30 Hz with 3.5 mJ, 10 ns FWHM pulses from a diode-pumped,
frequency-doubled, Q-switched Nd:YAG laser (Monocrom HALAZEN
532–12). Details of the experimental system can be found elsewhere.[24]
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Acknowledgements
We thank the Spanish Ministerio de Ciencia e Innovaciꢆn (projects
MAT2007-65778-C02-01, MAT2007-65778-C02–02, TRACE2009-0144,
CTQ-2006-15515-C02, CTQ2009-14551-C02-02, MAT2010-20646-C04-01,
MAT2010-20646-C04-03, and MAT2010-20646-C04-04), the Comunidad
de Madrid (project S2009/PPQ-1634 “AVANCAT”), and Gobierno Vasco
(IT339-10) for financial support. We also thank the Ministerio de Ciencia
e Innovaciꢆn for an FPU predoctoral fellowship to B.T. and the C.S.I.C.
for a JAE-PREDOC fellowship to M.E.P.-O. The SGI/IZO-SGIker UPV/
EHU is gratefully thanked for allocation of computational resources.
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Received: February 15, 2011
Revised: July 21, 2011
Published online: October 20, 2011
13268
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