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λex =400 nm.;Fluorescence spectra i(7), k(9) and the dependence of
intensity on water spectra, j(7), l(9)in partly aggregated state .
when the water fraction was increased to 60%, the solution
showed a distinct color change from yellow to light green. The
fluorescence spectra also showed a moderate red-shift (about 6
nm) (Figure 2c
When the dye
was non-luminescent (Figure 3c
)
9
was dissolved in the pure MeCN solution, it
which could be attributed to
),
that the free rotation of methoxy group effectively consumed
the energy of the excitations via nonradiative relaxation
channels. As for the fluorescence spectra of dye
water fraction was increased to 10%, a modest fluorescence
enhancement behavior was observed as shown in Figure 2e
9, when the
.
However, with more water was induced to the solution, the
fluorescence spectra showed sharp decreasement and the
solution still seemed non-luminescent. While the water fraction
was increased to 80%, a light-yellow fluorescence was observed
(
Figure 3c), which might result from aggregation-induced
emission(AIE) effect. Meanwhile, as to the fluorescence spectra
of dye , a dramatic fluorescence enhancement was observed,
9
which could be attributed to AIEE effect, namely that the
enhancement of the fluorescence was related to the formation of
the aggregates of dye
9, which prevented the intramolecular
rotation and boosted the fluorescence. More importantly, it was
similar to the previous reports of AIE/AIEE-based
luminophores, and was in contrast to the aggregation–caused
quenching (ACQ) of classical luminophores, which were non-
luminescent or weakly luminescent in dilute solutions and
became modestly or highly emissive in the aggregate state75.
More interestingly, the fluorescence spectra exhibited a distinct
bathochromic shift (more than 53 nm). According to the
reported literature76, 77, dyes with twisted intramolecular charge
transfer (TICT) effect usually exhibited red-shift properties,
especially dyes with donor-acceptor or donor-acceptor-donor
Figure 3. Photographic images of the dyes (1×10-4 mol/L) in MeCN/water
solution (water fraction from 0% to 90%) at the wavelength of 365 nm: a (7),
b (8), c (9), d (10)
To explore the different photo-physical properties of dye 7-
10, especially bearing tetraphenylethene, we utilized the general
method to investigate the fluorescence spectra of the complexes
in MeCN/water solution with different water fractions. The
photographs and fluorescence spectra were shown in Figure 2
and Figure 3. When the dyes in the mixture formed some
aggregates, the dyes were gradually dissolved in the solution by
shaking the mixture for about 10min and letting the mixture
stand for 1 day.
structures. As for dye
9,
the methoxy-substituted
tetraphenylethene acted as donor, while the difluoroboron
complex acted as acceptor, which also led to its bathochromism.
More interestingly, the fluorescence spectra of dye
9 in the
solution (Figure 2e) or in the aggregated state (Figure 2k) did
not show much difference.
Similar to dye 7, the pure MeCN solution of 10 emitted red
When
7
was dissolved in MeCN (1×10-4 mol/L), the pure
light. With the increasement of water fraction to 60%, the
fluorescence spectra of 10 showed a decrease and the color of
the solution became faint. And the color of the solution became
yellow with the water fraction up to 70%, and the fluorescence
spectra showed a dramatical enhancement. The fluorescence
spectra showed distinct decreasement when the water fraction
was increased to 90%, and the color of the solution also became
faint. And the fluorescence spectra also exhibited a blue-shift
(more than 50 nm). The reason why dye 10 did not show the
MeCN solution emitted red light (Figure 3a.). With an
increasing content of water from 0 to 10%, the fluorescence
spectra showed obvious fluorescence decreasement. While the
water fraction was increased to 60%, the intensity of
fluorescence decreased but the rate of decreasement was not
like before. With the water fraction was increased to 90%, the
fluorescence increased modestly. Meanwhile, the color of the
solution changed from red to light-yellow, which could be
attributed to aggregation-caused quenching effect (ACQ effect).
More interestingly, the florescence spectra showed obvious blue
shift (about 85 nm) (Figure 2a), which might be attributed to
intramolecular charge transfer (ICT) from tetraphenylethene to
boron complex. In comparison to the fluorescence spectra of the
AIE or AIEE effect, in comparison to dye
diethylamino group might consume the excited-stated energy by
rotation and hinder the planarity of dye 10
Based on the absorption and fluorescence spectra studies
of dyes 7-10 and 10 were chosen for further study. The
photo-physical properties of and 10 in various organic
9 was that the
.
,
8
dye
7 dissolved in the solution, the fluorescence spectra i
8
exhibited more distinct blue-shift (about 100 nm), which might
be attributed to the aggregated state that released energy of
transition state.
solvents were investigated (as shown in Figure 2.), and detailed
data were summarized in Table S1 (in supporting information)
As for dye 8, it emitted strong yellow light when dissolved
in pure MeCN solution (Figure 3b). With an increasing water
fraction, the fluorescence intensity decreased gradually. And