One-pot synthesis of dual-state emission (DSE) luminogens containing the V-shape furo[2,3-b]furan scaffold

Article abstract of DOI:10.1016/j.cclet.2020.02.038

To discover novel fluorophores of solution and solid dual-state emission (DSE) materials, unique V-shape furo[2,3-b]furans have been designed and synthesized by a one-pot method for the first time and their photoluminescent properties have been explored in benzene, THF, DMF and DMSO, as well as in the solid state. As the best example, 2,5-bis(4-(9H-carbazol-9-yl)phenyl)-6a-amino-3a,6a-dihydrofuro[2,3-b]furan-3,3a,4-tricarbonitrile (3g) exhibited solution and solid DSE properties in THF, benzene, and in the solid state with quantum yields of 55%, 92%, and 45%, respectively.

Full text of DOI:10.1016/j.cclet.2020.02.038

Journal Pre-proof
One-pot synthesis of dual-state emission (DSE) luminogens containing
the V-shape furo[2,3-b]furan scaffold
Jie Zhou, Manna Huang, Xinhai Zhu, Yiqian Wan
PII:
S1001-8417(20)30098-X
https://doi.org/10.1016/j.cclet.2020.02.038
CCLET 5479
DOI:
Reference:
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Chinese Chemical Letters
Received Date:
Revised Date:
Accepted Date:
8 January 2020
11 February 2020
20 February 2020
Please cite this article as: Zhou J, Huang M, Zhu X, Wan Y, One-pot synthesis of dual-state
emission (DSE) luminogens containing the V-shape furo[2,3-b]furan scaffold, Chinese
Chemical Letters (2020), doi: https://doi.org/10.1016/j.cclet.2020.02.038
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Chinese Chemical Letters
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Communication
One-pot synthesis of dual-state emission (DSE) luminogens containing the V-shape
furo[2,3-b]furan scaffold
a,†
a,
b
a*

Jie Zhou , Manna Huang , Xinhai Zhu , Yiqian Wan
a School of Chemical Engineering and Technology, Guangdong Engineering Technology Research Center for Platform Chemicals from Marine Biomass and
Their Functionalization, Sun Yat-sen University, Zhuhai 519082, China
b Instrument Analysis & Research Center, Sun Yat-sen University Guangzhou 510275, China
 Corresponding authors.
E-mail addresses: huangmn25@mail.sysu.edu.cn (M. Huang), ceswyq@mail.sysu.edu.cn (Y. Wan)
† This author now is working in Hengyang Normal University.
Graphical Abstract
A novel one-pot method was established for the synthesis of unique V-shape furo[2,3-b]furans to explore their
photoluminescence both in several solutions and in the solid state. A best example, 3g exhibited solution and solid dual-state
emission (DSE) properties in THF, benzene, and in the solid state with quantum yields of 55%, 92%, and 45%, respectively.
ARTICLE INFO
ABSTRACT
Article history:
To discover novel fluorophores of solution and solid dual-state emission (DSE) materials,
Unique V-shape furo[2,3-b]furans have been designed and synthesized byaone-pot method for
the first time and their photoluminescent properties have been explored in benzene, THF, DMF
and DMSO, as well as in the solid state. As the best example, 2,5-bis(4-(9H-carbazol-9-
yl)phenyl)-6a-amino-3a,6a-dihydrofuro[2,3-b]furan-3,3a,4-tricarbonitrile (3g) exhibited solution
and solid DSE properties in THF, benzene, and in the solid state with quantum yields of 55%,
92%, and 45%, respectively.
Received 8 January 2020
Received in revised form 11 February 2020
Accepted 18 February 2020
Available online
Keywords:
One-pot synthesis
Furo[2,3-b]furan
Selenium dioxide
V-Shape
Dual-state emission
Conventional organic fluorophores generally exhibit highly
efficient luminescence in dilute solution owing to the presence of
planar polycyclic -conjugated frameworks and have gained
extensive applications in relatively dilute solution [1]. However,
their aggregation-caused quenching (ACQ) is often detrimental to
of organic light-emitting diodes (OLED) [2], optical devices [3],
and organic luminescent displays [3a, 4]. In contrast to this
effect, Tang and co-workers observed and conceptually coined
aggregation-induced emission (AIE) at the turn of the century [5].
Since then, numerous organic AIEgens have been developed
through restricting intramolecular motion, and they have been
p—ra—ctic—al applications in the solid state, such as in the fabrication

used in a wide range of applications including chemo/ biosensors
[6] and bioimaging [7], OLEDs [2b], solar cells [8], and optical
devices [9], among others [10].
It should be noted that there remains a significant gap between
ACQ
and
AIE
photoluminogens
[11].
Developing
photoluminogens that are highly efficient both in solution and in
the solid state (i.e., dual-state emission, DSE), is therefore
important in order to bridge the gap so that both meet the
fabrication requirements of various functional materials, as well
as to provide additional materials for deeper exploration of the
differences of photoluminescence in different types of solvents
[11,12]. As a result, several typical solution and solid DSE
luminogens have recently been developed; however, solution and
solid DSE luminogens that are active in all types of solvents (all-
powerful solution and solid DSE molecules) are rare [13]. In
contrast, solution and solid DSE molecules that are active only in
the solid state, or in particular single solvents such as THF [14],
dichloromethane [12, 15], chloroform [16] and other particular
types of solvents, have been developed [13a-c, 17].
The furo[2,3-b]furan structure, a fused cyclic acetal, exists in
several biologically active natural products and pharmaceuticals
[18]. However, the parent furo[2,3-b]furan system and
substituted derivatives are not widely known as luminogens. It
was easy to determine that the donor-acceptor-donor (D-A-D) V-
shape scaffold [19] in 4-tricyanofuro-[2,3-b]furans would
enhance the intramolecular charge transfer (ICT) between donor
and acceptor moieties. In addition, considering the other reported
types of V-shape photoluminescence potentially removes the
tendency of short-range π-π intermolecular interactions that lead
to quenching of the fluorescence [20], and we assumed that
compounds containing the unique V-shape furo[2,3-b]furan
scaffold would exhibit luminescence both in solution and in the
solid state.
Scheme 1. Plausible mechanism of the novel protocol.
Initially, the desired product 3a was obtained from 2-
chlorobenzoylacetonitrile (1a) (0.5 mmol) by reacting with
malononitrile (2) in isolated yield of 10% by means of oxidation
of 1.1 equiv. of SeO2 in CH3CN in the presence of 1.1 equiv. of
NH4H2PO4 at room temperature for 12 h (Table 1, entry 1).
Further optimization of the main reaction conditions, including
additives, solvents and ratio of starting materials (Table 1), gave
rise to a novel one-pot protocol for the synthesis of 6a-amino-
2,5-diaryl-furo[2,3-b]furan-3,3a,4(6aH)-tricarbonitriles: namely,
0.5 mmol of 1a was treated with 1.1 equiv. of 2 and 0.75
equivalent of SeO2 in CH3CN (2 mL) inthe presence of 0.5
equivalent of benzoic acid at room temperature for 12 h (Table 1,
entry16).
Table 1
Optimization of the model reaction.a
To develop alternative methods for synthesis of the furo[2,3-
b]furan core and to search for novel solution and solid DSE
luminophores, we report the design and synthesis of novel
solution and solid DSE luminogens based on the V-shape
furo[2,3-b]furan scaffold.
SeO2
(equiv.)
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
0.5
Yield
(%)b
10
18
20
n.d.
8
n.d.
n.d.
13
n.d.
n.d.
trace
23
15
13
40
42
10
36
28
Entry 2/1a
Additive (equiv.)
Solvent
1
2
3
4
5
6
7
8
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
2
NH4H2PO4 (1.1)
HOAc (1.1)
PhCOOH (1.1)
TsOH (1.1)
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
EtOH
In the only reported synthetic method [19] for preparation of
6a-amino-2,5-diaryl-furo[2,3-b]furan-3,3a,4(6aH)-tricarbonitrile,
2-bromomalononitrile
is
reacted
with
various
2-
KH2PO4 (1.1)
PhCOOH (1.1)
PhCOOH (1.1)
PhCOOH (1.1)
PhCOOH (1.1)
PhCOOH (1.1)
PhCOOH (1.1)
PhCOOH (0.5)
PhCOOH (2)
PhCOOH (3)
PhCOOH (0.5)
PhCOOH (0.5)
PhCOOH (0.5)
PhCOOH (0.5)
PhCOOH (0.5)
cyanoacetophenones to afford the target compounds in moderate
yields. Considering the cost and the commercial availability of 2-
bromomalononitriles, we tried more readily available
malononitriles instead of 2-bromomalononitriles to develop a
novel preparative method. As shown in Scheme 1, SeO2 was
assumed to oxidize malononitrile to 2-hydroxy-malononitrile,
which can then react with 3-oxo-3-arylpropane-nitriles to provide
the target compounds.
DMF
THF
9
Toluene
1,2-DCE
dioxane
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
10
11
12
13
14
15
16
17
18
0.75
3
0.75
0.75
19
a
0.5
Reaction conditions: 1a (0.5 mmol), 2, SeO2, additive, solvent (2
mL), r.t., 12 h.
b Isolated yield.
n.d.: not detected by TLC; trace: detected by TLC.
Based on the effective protocol, we designed two series of 6a-
amino-2,5-diaryl-furo[2,3-b]furan3,3a,4(6aH)tricarbonitriles
(with and without a phenyl group spacer). It should be noted that
the phenyl group spacer was envisioned to allow the possibility

of extending the conjugation and increasing intermolecular π-π
interaction, thus leading to restriction of intramolecular rotation,
which would result in effective photoluminescence. The target
compounds were obtained although the isolated yields were
moderate (Scheme 2) because of the expected side reaction of
trimerization of acetonitriles (compound 1) as reported
previously [21].
Scheme 2. Scope of the 3-oxo-3-arylpropanenitriles.
The photoluminescence properties of the compounds were
then explored, both in solution and in the solid state, to gain
further mechanistic insight into whether the V-shape scaffold
helps to avoid the short-range π-π intermolecular interactions that
lead to fluorescence quenching [20a]. As shown in Table S1
(Supporting information), type I compounds with phenyl spacer
(3k, 3l) exhibited better photoluminescence (PL) efficiency than
their counterparts without a phenyl spacer (type II compounds 3b
and 3d). We then focused on the type I compounds to investigate
the AIE/ACQ properties. The results (Fig. S6 in Supporting
information) of classic ACQ/AIE distinctive experiments (i.e.,
determination of PL spectra in H2O/THF mixture with different
water contents) [22] indicated that 3i, 3m, and 3n exhibited clear
ACQ phenomena; meanwhile, 3h, 3j, and 3k, exhibited AIE
phenomena. Interestingly, as shown in Table 2 and Fig. 1, 3g and
3l exhibited the desired solution and solid DSE properties in
THF, benzene, and in the solid state with PL efficiencies of 55%,
92%, and 45% and 17%, 14%, and 18%, respectively, although
they showed reduced solution and solid DSE PL efficiency in
DMF (0.1% and 4%, respectively) and DMSO (6% and 2%,
respectively). The relatively high fluorescence quantum yield of
carbazole is thought to result from the nonbonding orbital
overlap of the adjacent carbon atoms on the carbazole ring, while
the enhanced basicity of the molecule in the excited state
interacts with more acidic DMF, possible affording a great non-
radiative and a leading to diminished PL efficiency. The most
polar solvent, DMSO, reduced the energy level of the excited
states, reducing the difference between the ground and excited
states, which could be the main reason for the largest Stokes shift
values of 179 nm and 178 nm, respectively.
Table 2
Optical properties of the compounds.
λEm
(nm)
438
544
488
455
512
387
504
433
421
472
lifetime
(τ, ns)
2.6
3.6
4.2
2.7
6.2
2.2
2.4
Compd.
Solvents
λabs (nm) a
ϕF (%)b
DMF
DMSO
THF
Benzene
Solid
DMF
DMSO
THF
Benzene
Solid
342
365
371
386
397
294
326
332
338
400
0.1
6
55
92
42
4
3g
2
3l
0.69
0.69
2.8
17
14
18
a Longest wavelength absorption maximum.
b Absolute fluorescence quantum yield.

(b)
(a)
1.0
0.8
0.6
0.4
0.2
0.0
DMF
DMF
DMSO
THF
Benzene
Solid
1.0
0.8
0.6
0.4
0.2
0.0
DMSO
THF
Benzene
Solid
Acknowledgments
This work was supported by grants from the National Natural
Science Foundation of China (No. 21702239), Guangzhou
Science and Technology Plan Projects (No. 201707010271), the
Fundamental Research Funds for the Central Universities (No.
16lgpy16).
300
400
500
600
700
400
500
600
700
800
(nm)
 (nm)
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(Excited by the longest wavelength absorption maximum. The solid
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