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excitation at 340 nm, the CMP film emitted a deep-blue
luminescence (Scheme 1d) with two peaks at 374 and 399 nm,
respectively (Figure S6). The absolute fluorescence quantum
yield is 10%. In contrast, the spin-coated TPBCz film gave
a fluorescence spectrum similar to that of the CMP film, but
its fluorescence quantum yield is only 1%. The network
structure in the CMP film greatly enhances the light-emitting
activity.[3e] Since the CMP film allows an extended p conju-
gation, we further investigated the fluorescence depolariza-
tion profiles of the CMP films, which are considered to reflect
the occurrence of photochemical events in the microporous
network. The suppression of Brownian motion in a viscous
medium should result in fluorescence depolarization occur-
ring predominantly by exciton migration along the conjugated
chain. The TPBCz monomer showed a fluorescence depola-
rization value of 0.044 in poly(ethylene glycol) (Figure S7). In
contrast, the CMP film exhibited a significantly depolarized
fluorescence with an extremely low depolarization value of
0.002. This observation demonstrates that the CMP film
facilitates exciton migration over the network, which endows
the film with a collective response, a key factor to enhance the
sensitivity.
Figure 2. a) Normalized fluorescence intensity of the CMP films upon
exposure to vapors of benzonitrile (BN, black line), 1,2-dinitrobenzene
(DNB, red line), hexafluorobenzene (HFB, blue line), and 1,4-benzo-
quinone (BQ, green line) for different periods of time. Photos:
fluorescence quenching by BQ vapor. b) Enhancement of fluorescence
intensity of the CMP films upon exposure to vapors of toluene (black
line), benzene (blue line), and cholorobenzene (CB, red line) for
different periods of time. Photos: enhancement of fluorescence
intensity upon exposure to CB vapor.
Chemosensing experiments were conducted by exposing
CMP films to arene vapors for specific periods of time at 258C
followed by monitoring with fluorescence spectroscopy. The
air was not removed from the micropores of the CMP films
prior to their exposure to arene vapors. We first investigated
the effect of the thickness of CMP films on the chemosensing
properties. As shown in Figure S8, the CMP film with
a thickness of 10 nm exhibited the best performance. For
each chemosensing experiment, several individual CMP films
with a thickness of 10 nm were used in parallel experiments,
and the results showed excellent reproducibility.
p conjugation, exhibited a maximum quenching percentage of
only 43% after 120 s exposure under otherwise identical
conditions (Figure S10). These results indicate that the
function of the CMP films is multifold: the extended p-
conjugation network allows exciton migration, the porous
skeleton provides a broad interface for electron transfer, and
the micropores hold the arene molecules. These features
cooperate to facilitate the signaling process and improve the
response. The CMP films offer a practical platform for
fabricating chemosensors, which feature a precisely con-
trolled structure and a simple fabrication process together
with excellent reproducibility and high performance.
The CMP films are extremely sensitive to arenes, as shown
in Figures 2 and S9. For example, upon exposure to the vapor
of benzonitrile (BN) for only 20 s, the fluorescence of the
CMP films was significantly quenched (Figure 2a, black line),
and only 33% of the intensity of the pristine CMP film
remained. As the exposure time was prolonged, further
quenching was observed, and the fluorescence gradually
settled at 20% of its original intensity. Interestingly, the
fluorescence-off chemosensing was not specific to BN, but
was widely applicable to other electron-deficient arenes. The
CMP films exhibited an enhanced response to 1,2-dinitro-
benzene (DNB) with 75% of the fluorescence quenched upon
exposure for 20 s (Figure 2a, red line). Notably, 87% of the
fluorescence was quenched upon exposure to hexafluoroben-
zene (HFB) for 20 s (Figure 2a, blue line). The most explicit
quenching of fluorescence was observed with 1,4-benzoqui-
none (BQ). A 20 s exposure resulted in a 92% loss of
fluorescence (Figure 2a, green line and photos). After 120 s
exposure, the fluorescence of CMP films was completely
quenched. The degree of fluorescence quenching is in good
agreement with the trend in the lowest unoccupied molecular
orbital (LUMO) of arenes, as a result of an enhanced driving
force for photoinduced electron transfer from the CMP films
to arenes.[8] Therefore, a lower LUMO energy level gives
a higher detection sensitivity. In contrast, spin-coated TPBCz
films, which are nonporous and do not have an extended
The CMP films are also sensitive to electron-rich arenes.
In contrast to electron-deficient arenes that quench fluores-
cence, electron-rich arenes enhanced the fluorescence inten-
sity of the CMP films, thus allowing fluorescence-on sensing
(Figure S11). For example, upon exposure to toluene vapor
for 20 s, the fluorescence intensity of the CMP films increased
by 20% (Figure 2b, black line). As the exposure time was
prolonged, further enhancement was observed, whereas the
fluorescence intensity reached a 46% increment upon 120 s
exposure. Similarly, benzene vapor triggered a 59% enhance-
ment on 120 s exposure (Figure 2b, red line). Remarkably,
upon exposure to chlorobenzene (CB) vapor, the fluores-
cence intensity was increased by 81% in 20 s, and by 122% in
120 s (Figure 2b, blue line and inset). In contrast, spin-coated
TPBCz films exhibited a very limited change in fluorescence
intensity with only 19% enhancement for CB after 120 s
exposure under otherwise identical conditions (Figure S12).
The flow of electrons of arenes to the conduction band of
TPBCz-CMP enhances the fluorescence intensity, as
observed for bulk CMP solids.[3f]
Time-resolved fluorescence spectroscopy was utilized to
investigate the kinetics of electron transfer. The CMP film
exhibited a fluorescence lifetime (t0) of 3.25 ns, which was
decreased to 1.03 and 1.86 ns (tDA) upon exposure to BQ or
CB vapor for 20 s, respectively (Figure 3a, Table S1). The
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Angew. Chem. Int. Ed. 2014, 53, 4850 –4855