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DOI: 10.1039/C7CC05773C
COMMUNICATION
Journal Name
The absorption spectra of DFC and DTC in various solvents are
shown in Fig. S1 and S2 (ESI), and their absorption data are
summarized and listed in Table S1 and S2 (ESI), respectively,
showing that the absorption maxima of DFC-c were shorter
than that of DTC-c in the range of 56 nm to 66 nm varying from
the solvents. As shown in Fig. S1 and S2 (ESI), remarkable
solvent dependence was observed for the photochromic
reaction of DFC and DTC, respectively. It is found that
relatively high polar solvents (dichloromethane, acetonitrile,
and dimethyl formamide) are more beneficial to the
photoisomerization with the enhancement of absorption
coefficient of the corresponding closed-ring isomer. These
findings indicate that molecule DFC as well as DTC has
relatively large dipole moment and the molecule at the π−π*
excited state is more stable in polar solvents.10 Additionally,
the enhancement of absorption coefficient was observed for
the closed-ring form DFC-c with respect to DTC-c in the same
solvent. Under irradiation with 313 nm light, the
photocyclization conversion of DFC was determined to be as
high as 39.8% by the 1H NMR analysis (Fig. S3-S6, ESI),
compared with that of 27.5% for DTC in acetonitrile. Quantum
yields of cyclization (Φo→c) and cycloreversion (Φc→o) in
acetonitrile were also calculated to be the order of 22.3% and
15.1% for DFC, whereas DTC showed value on the order of
16.6% and 20.3%, respectively (the detailed calculation
method as shown in the ESI). It is found that DFC possesses
higher photocyclization conversion and quantum yield of
Scheme 1. Switching process of diheteroarylethene derivatives controlled by ultraviolet
and visible light.
As known that the synthetic difficulty of furan-based DAEs is
a big obstacle for their development, especially the metal-
mediated cross coupling in the synthesis of furan derivatives.
Therefore, we devised a new protocol to exploit the synthesis
of DFC, which was obtained in three steps starting from
commercially available 5-methylfurfural. As shown in Scheme
S2, bromination at the 4-position, subsequent Miyaura
boration, and coupling with 1,2-dibromocyclopentene
afforded the target compound DFC in the total yield of 33%.
This procedure has good functional group tolerance and
provides the mild reaction conditions like avoiding halogen-
lithium exchange with n-BuLi and protection-deprotection of
the aldehyde. Furthermore, inspired by synthetic protocol for
diarylethenes,5e,9 a conventional workup procedure of the
Suzuki coupling reaction turned to prepare DFC on a gram
scale. The chemical structures of DFC and other key
intermediate products were well confirmed by 1H NMR, 13C
NMR, and HRMS (see the ESI for details). The diverse
transformation of aldehyde groups of DFC provides various
pathways of modification of the switching moiety and allows
tuning of the photoswitching properties for different
application systems.
cyclization than that of DTC
. In comparison with the
representative 1,2-bis(furan-3-yl) hexafluorocyclopentene
The photochromic behaviors of DFC and its reference
compound DTC were evaluated in a series of solvents with
varying polarity index, including hexane, toluene,
dichloromethane, acetonitrile, and dimethyl formamide. As
expected, DFC exhibits a typical photochromic response of
diarylethene derivatives under alternative illumination with
ultraviolet and visible light in these trial solutions. Fig. 1A
shows the absorption spectral changes of DFC in acetonitrile.
Upon irradiation with 365 nm light, a new absorption band
centered at 522 nm appeared and gradually increased, which
is characteristic for the formation of the closed-ring isomer
DFC-c, accompanied by the colorless solution turned to pink
(Fig. 1A inset). Upon irradiation with visible light (≥ 520 nm),
the pink solution was bleached back to colorless solution and
the original absorption spectrum was recovered. DTC also
showed reversible photoisomerization along with the color
interchange between colorless and blue, as shown in Fig. 1B.
derivatives, we found that the absorption maximum of DFC is
close to that of
5 (525 nm) in hexane and 7 (533 nm) in
methanol. The Φo→c value of DFC in acetonitrile is lower than
that of the reported compounds
5,
6
and
7
; whereas, the Φc→o
value of DFC is higher than that of
5
and
7.
Addition to the primary color change, the fluorescent
modulation associated with isomerization of DAEs is regarded
as a promising way to achieve non-destructive readouts and
security recordings as well as nanoscopic visualization.11 It is
noteworthy that DFC without decorating
a fluorophore
showed a strong cyan fluorescence (Fig. 2 inset), whereas no
fluorescence was observed for DTC in trial solvents. Fig. 2 and
Fig. S7 (ESI) display the emission spectral changes of DFC upon
photo-irradiation with 365 nm light when excited at 326 nm.
The emission peak of DFC was observed at 465 nm, and the
intensity decreased by ca. 55% till the photostationary state
(PSS) was reached under irradiation with 365 nm light. The
Fig. 1 UV−vis absorption changes of (A) DFC (10 μM) and (B) DTC (10 μM) in acetonitrile
upon irradiation with 365 nm light at 298 K. Inset: the corresponding photographic
images upon irradiation with UV and visible light.
Fig. 2 Fluorescence changes of DFC (10 μM) in acetonitrile upon irradiation with 365
nm light at 298 K, λex
= 326 nm. Slits: 5 nm/ 5 nm. Inset: the corresponding
photographic images upon irradiation with UV and visible light.
2 | J. Name., 2012, 00, 1-3
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