Tetra-benzothiadiazole-based [12]Cycloparaphenylene with Bright Emission and Its Supramolecular Assembly

Article abstract of DOI:10.1002/anie.202008505

The radial conjugated π-system of cycloparaphenylenes (CPPs) makes them intriguing fluorophores and unique supramolecular hosts. However, the bright photoluminescence (PL) of CPPs was limited to the blue light and the supramolecular assembly behavior of l

Full text of DOI:10.1002/anie.202008505

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Accepted Article
Title: Tetra-benzothiadiazole-based [12]Cycloparaphenylene with
Bright Emission and its Supramolecular Assembly
Authors: Zhen-Lin Qiu, Chun Tang, Xin-Rong Wang, Yang-Yang Ju,
Ke-Shan Chu, Ze-Ying Deng, Hao Hou, Yu-Min Liu, and
Yuan-Zhi Tan
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10.1002/anie.202008505
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ICATION
enzothiadiazole-based [12]Cycloparaphenylene with
Emission and its Supramolecular Assembly
u,[a] Chun Tang,[a] Xin-Rong Wang,[a] Yang-Yang Ju,[a] Ke-Shan Chu,[a] Ze-Ying Deng,[a]
Yu-Min Liu, [a] Yuan-Zhi Tan*[a]
adial conjugated -system of cycloparaphenylenes
them as intriguing fluorophores and unique
host, however, the bright photoluminescence (PL) of
d to the blue light and the supramolecular assembly
CPPs was rarely investigated. Here we present the
ra-benzothiadiazole-based [12]cycloparaphenylene
ich exhibits a lime to orange PL with an excellent
p to 82%. The PL quantum yield of TB[12]CPP can
ved to 98% in polymer matrix. Benefiting from its
B[12]CPP can accommodate a fullerene derivative
ex complexes of fullerene and buckybowl through
 and C-H··· interactions. The latter one
e first case of ternary supramolecule of CPPs.
(PAHs) based on C-H··· interactions was achieved[12], as a
complement to the  complex. Among them, the ring size
plays an important role in the supramolecular assembly of CPPs.
For instance, the CPPs smaller than [10]CPP only show ability
to accommodate solvent molecules. On the contrary, the
enlarged inner space of large CPPs, such as [12]CPP, provides
the additional opportunities to accommodate larger and more
complex guests other than bare fullerenes.
Here we show the synthesis of tetra-benzothiadiazole-based
[12]cycloparaphenylene (TB[12]CPP) by a platinum-mediated
cyclization[8a, 13]. The structure of TB[12]CPP was unambiguously
identified by mass spectroscopy, NMR and single crystal X-ray
diffraction (SCXRD). Introducing benzothiadiazole units red-
shifts the UV-Vis absorption and PL of TB[12]CPP by 89 nm and
119 nm, respectively, compared with the pristine [12]CPP.
TB[12]CPP shows a high PLQY up to 82%. In polymer matrix, its
PLQY can be improved to nearly 100%. Taking advantage of the
enlarged size of TB[12]CPP, TB[12]CPP can assemble with a
Diels-Alder adduct of C60 and anthracene (anthracene-C60) by
both  and C-H··· interactions. More importantly, the ternary
complexes of CPPs are achieved for the first time by hosting the
concave-convex supramolecule of fullerene (C60 or C70) and
buckybowl (trithiasumanene) in the inner cavity of TB[12]CPP.
henylenes (CPPs), composed of para-linked
regarded as the shortest segment of carbon
) and thus also referred as carbon nanohoops[1].
of CNT, CPPs were used as the seed molecules
of well-defined single wall CNTs[2]. Different from
-phenylenes and cyclic-ortho-phenylenes[3], the
Ps was achieved until last decade[4], that is likely
larger ring strain of CPPs. The cyclic conjugated
PPs renders them unique electronic and optical
r instance, most of CPPs present highly emissive
high quantum yield and large Stokes-shift[6]. In
macrocyclic structure of CPPs hinders the
 stacking, consequentially makes CPPs more
rent solvents than their linear counterparts[7],
od solvent tolerance of their photoluminescence
the CPPs with high PL quantum yield (PLQY)
ght[5]. Although the red-shifted PL up to 500 nm
ed by decreasing the size of CPPs[8] or
donor-acceptor structure[9], these strategies to
CPPs resulted in a dramatic decrease of PLQY.
her hand, the shape-persistent macrocyclic
PPs provides inner cavity for supramolecular
hich has attracted increasing interests. The
-system of CPPs enables effective 
h spherical fullerenes[11]. The first reported CPP
is C60@[10]CPP, which is regarded as the
peapod[11a]. Moreover, the assembly of carbon
h planar or curved polyaromatic hydrocarbons
Figure 1. Synthesis of TB[12]CPP. (a) ssynthetic route of TB[12]CPP. (b) The
mass spectra of TB[12]CPP. The isotoopic distribution for the mass peak of
TB[12]CPP is shown as the insert figuree. (c) 1H NMR spectrum of TB[12]CPP
measured in CDCl3.
C. Tang, X. R. Wang, Y. Y. Ju, K. S. Chu, Z. Y. Deng, H.
.M. Liu, Prof. Dr. Y. Z. Tan
The bottom-up organic synthesis of CPPs facilitates the
incorporation of chromophores into the scaffold of CPPs.
Benzothiadiazole is the widely used building unit to red-shift the
Laboratory for Physical Chemistry of Solid Surfaces,
ve Innovation Center of Chemistry for Energy Materials,
tment of Chemistry, College of Chemistry and Chemical
g, Xiamen University, Xiamen 361005, China
anzhi_tan@xmu.edu.cn
optical absorption and PL of the conjugated polymers[14]
.
Thereby, the incorporation of benzothiadiazole units can impart
CPPs with enhanced emission performance, which was also
demonstrated in the Jasti’s recent work[15]. Accordingly, a
rational repeating unit 4,7-diphenyl-benzothiadiazole was
designed to construct TB[12]CPP, in which the platinum-
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10.1002/anie.202008505
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mediated assembly method was used for the cyclization[8a, 13]
.
Vis spectrum of TB[12]CPP measured in chloroform, shows two
major absorption bands at 320 and 428 nm, which is red-shifted
by 89 nm and 27 nm with respect to that of [12]CPP[18] and 4,7-
diphenyl-benzothiadiazole (Figure S6), respectively. The
extinction coefficient of TB[12]CPP was measured to be 8.3×104
M-1cm-1 at 318 nm and 6.4×104 M-1cm-1 at 427 nm, comparable
with that of [12]CPP (1.4×105 M-1cm-1),[18] but an order of
magnitude higher than that of 4,7-diphenyl-benzothiadiazole
(6.8×103 M-1cm-1 at 401 nm). According to the time-dependent
density functional theory (TD-DFT) calculations (Supporting
Information S3 and Figures S9-S10), the absorption band at 428
nm of TB[12]CPP was assigned to the transitions from S0 to S2
and S0 to S3. The transition of S0 to S1 is symmetrically forbidden,
akin to other symmetric CPPs.[19]
Frist, the para-borylated 4,7-diphenyl-benzothiadiazole was
synthesized by Miyaura borylation of 4,7-bis(4-bromophenyl)-
benzothiadiazole. Then, the para-borylated 4,7-diphenyl-
benzothiadiazole was reacted with Pt(COD)Cl2 in dry THF under
reflux for 24 h. Then the resultant mixture was subjected to
reductive elimination in toluene at 110 oC for 48 h in presence of
triphenylphosphine (Figure 1a). After reaction, the crude
products were extracted by dichloromethane and separated by
silica gel column chromatography to obtain TB[12]CPP (10%
over two steps) (Supporting Information S2 and Figures S1-S5).
The high-resolution MALDI-TOF mass spectrum of TB[12]CPP
(C72N8S4H40) showed an experimental molecular weight of
1144.224 Da (calculated 1144.225 Da) (Figure 1b). The 1H NMR
spectrum of TB[12]CPP shows two double and one singlet
signals (Figure 1c). Both the mass spectrometry and NMR
analysis (Figure 1 and Figures S3-S5) confirm the successful
synthesis of TB[12]CPP.
Figure 3. Optical properties of TB[12]CPPP. (a) absorption (solid lines) and PL
spectra (dashed lines) of TB[12]CPP in cchloroform solution (red), powder (blue)
and PMMA film (black). Photographs off the solution, powder and PMMA film
TB[12]CPP under a UV lamp are shown as the insert figure.
Figure 2. Crystal structure of TB[12]CPP. (a. b.) Top and side views. Thermal
ellipsoids were set at 50% probability level. The inner DMF molecules in the
side view was represented in spacefill model for clarity. The non-conventional
hydrogen bonds were shown as sky blue dashed lines. (c) The packing
structure of TB[12]CPP in solid state. The hydrogen atoms and DMF
molecules were omitted in packing structure.
The PL spectrum of TB[12]CPP in chloroform shows a
emission peak at 569 nm, which is attributed to the transition of
S1 to S0 by TD-DFT calculations (Figure S11). Owing to the
symmetry broken in the excited state, the forbidden transition of
S0 to S1 in the ground state becomes allowed in the excited state,
accounting for the large Stokes-shift (142 nm) of TB[12]CPP.
Compared with emission of [12]CPP at 450 nm and 4,7-
diphenyl-benzothiadiazole at 501 nm (Figure S6), the emission
of TB[12]CPP is red-shifted by 119 nm and 68 nm in chloroform.
The PLQY of TB[12]CPP in chloroform were measured to be 81%
in terms of the absolute method using integrating sphere, higher
than that of 4,7-diphenyl-benzothiadiazole (61%) and the
reported CPPs with emission in the similar wavelength range.[8-9]
The PL of TB[12]CPP in different solvents was investigated. As
shown Table S1, with increasing polarity of solvents, the PL
peaks shift from 555 nm to 586 nm, corresponding to a color
change of PL from lime to orange (Figure S7). The linear
relationship between the wavenumber of TB[12]CPP emission in
different solvent and the solvent parameter ET(30) (Figure S8) [20]
manifests a positive solvatofluorochromism of TB[12]CPP. The
PLQY measured in these solvent ranges from 82% to 59%
(Table S1), demonstrating a good solvent tolerance.
The structure of TB[12]CPP was further revealed by SCXRD
(Figure 2). The crystals of TB[12]CPP were grown by slow
evaporation of its N,N-dimethylformamide (DMF) solution. In the
crystalline state, TB[12]CPP adopts a conformation with two
adjacent benzothiadiazole units above and the other two below
the plane of the inner cycle (Figure 2b). The small variation
between the shortest and longest distances through the ring
centroid (16.2–16.8 Å, Figure 4g) indicates the high circularity of
TB[12]CPP. Interestingly, four ordered DMF molecules are
hosted inside the TB[12]CPP (Figures 2a and 2b), forming a
supramolecular tetramer by non-conventional hydrogen bonds[16]
(Figure 2a), which indicates the possibility of supramolecular
assembly inside CPP rings. Similarly with [12]CPP,[17]
TB[12]CPP packs into a tubular structure (Figure 2c). Between
the tubular supramolecular structures, TB[12]CPP aligns in a
herringbone manner (Figure 2c).
TB[12]CPP is well soluble in common organic solvents, such
as toluene, chloroform, THF and DMF. Different from the nearly
colorless solution of [12]CPP, the solution of TB[12]CPP is
yellow, indicating an obvious red-shift of its absorption. The UV-
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10.1002/anie.202008505
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ICATION
the UV-Vis absorption and PL of TB[12]CPP in
(Figures 4c and 4e), which manifests the formation of ternary
complex (trithiasumanene⊃C60/C70)@TB[12]CPP. Different from
the circular comformation in (DMF)4@TB[12]CPP and elliptical
e further investigated. The TB[12]CPP powder
oadened absorption bands at 317 and 440 nm
on onset shifted to 600 nm (Figure 3). Similarly,
2]CPP powder red-shifted to 610 nm. Such red-
mplies strong intermolecular interactions in the
quentially, it is not surprising that the PLQY of
wder decreased to 12%, caused by aggregation-
hing. In contrast, in polymethyl methacrylate
the profile of absorption and PL spectra of
ps nearly unchanged (Figure 3), indicating a well
TB[12]CPP in PMMA matrix. Interestingly, the
A film increases to 98%, owing to the reduced
on of TB[12]CPP in the solid matrix. The bright
12]CPP in solid matrix promises its applications
al devices.
comformation
in
anthracene-C60@TB[12]CPP
and
(trithiasumanene⊃C60)@TB[12]CPP, an oval shaped TB[12]CPP
was observed in (trithiasumanene⊃C70)@TB[12]CPP (Figures
4g-4j), propably due to the larger size of C70, which establishes
TB[12]CPP as a shape-adaptable host.
structure of CPPs is suitable for supramolecular
e
supramolecular complexes of CPPs and
most widely investigated, which could mimic the
a, 10b]. As revealed by SCXRD, the inner cavity of
an average diameter of 16.5 Å, much larger
ad, fullerene derivatives have larger molecular
ctional group can afford additional intermolecular
h CPPs. Accordingly, we chose anthracene-C60
molecule to assemble with TB[12]CPP. By
carbon disulfide solution of anthracene-C60 and
eir cocrystals can be obtained. As shown in
d 4b, anthracene-C60 assembles into the inner
2]CPP in a “slant standing” orientation. The
t (Ka) of anthracene-C60@TB[12]CPP in toluene
to be 1.87±0.05 × 104 M-1 by fluorescence
rting Information S5 and Figure S13). As a result
tion of elongated anthracene-C60, the hoop of
s deformed into an elliptical comformation with
axis of 17.8 and 14.7 Å, respectively (Figure 4h).
nthracene-C60 interacts with the -system of
 interactions (3.25-3.42 Å, pink dash lines in
lerene cage and C-H··· interactions[21] (2.7 Å) of
iety, which exemplifies the first case of CPP
ning with  and C-H··· interactions.
molecular structures of (DMF)4@TB[12]CPP
ssibility to host a supramolecular complex in the
]CPP. Then we screened a series of ternary
of TB[12]CPP, fullerene and small PAHs, and
nary cocrystals of TB[12]CPP, C60/C70 and
[22] were obtained by solvent evaporation. Shown
ructures (Figures 4c-4f), inside the ring of
60/C70 and trithiasumanene assemble in
a
x manner with the shortest intermolecular C···C
15 Å, implying their strong  interactions.
e⊃C60/C70 complex adopts a “slant standing”
ed to TB[12]CPP as well (Figures 4d and 4f).
umanene⊃C60/C70 and TB[12]CPP, the fullerene
complex interacts with TB[12]CPP by 
h the C···C distances range from 3.31 to 3.42 Å
4e), while hydrogens of trithiasumanene forms
tions with the phenylene unit of TB[12]CPP
Figure 4. Structures of the supramolecuular assembly of TB[12]CPP. (a. b.) top
and side views of anthracene-C60@TB[112]CPP. (c. d.) top and side views of
(trithiasumanene⊃C60)@TB[12]CPP. (ee. f.) top and side views of
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ICATION
C70)@TB[12]CPP. The and C-H··· interactions are
k and sky blue dash lines, respectively. The inner guests in
e represented in spacefill model for clarity. The structures of
MF)4@TB[12]CPP (g), anthracene-C60@TB[12]CPP (h),
[1]
[2]
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C60)@TB[12]CPP
(j)
and
C70)@TB[12]CPP (k). The centroids of hoop were
red dots. The shortest and longest distances through the
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constants
of
e⊃C60)@TB[12]CPP
and
e⊃C70)@TB[12]CPP in toluene were determined
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=
04 M-1) and smaller binding constant of C70 to
= 3.20±0.07 × 104 M-1) (Figures S12 and S13), a
nding effects of trithiasumanene⊃C60/C70 was
expected, DFT calculations of these TB[12]CPP
arly reveal the larger binding affinities for
e⊃C60/C70)@TB[12]CPP (-60.94 and -66.37 Kcal
with that of C60/C70@TB[12]CPP (-36.44 and -
(Figure S14).
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rent from blue emission of the reported bright
orange emission of TB[12]CPP with high PLQY
was achieved in different solvents. The PLQY of
polymer matrix can further increase to 98%.
d optical properties can promise its applications
ging and optical organic devices. Benefiting from
inner space, TB[12]CPP assemble with
or trithiasumanene⊃C60/C70 complex by both
 interactions. The latter one realizes the ternary
PP. These assemblies of TB[12]CPP establishes
ge CPPs to accommodate complex guests and
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financially supported by the Ministry of Science
ology
of
China
(2017YFA0204902,
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1155, 21721001). The authors thank Prof. Xu
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oparaphenylene, photo luminescence,
pramolecular assembly
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COMMUNICATION
Z. L. Qiu, C. Tang, X. R. Wang, Y. Y. Ju,
K. S. Chu, Z. Y. Deng, H. Hou, Dr. Y.M.
Liu, Prof. Dr. Y. Z. Tan
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Page No. – Page No.
Tetra-benzothiadiazole-based
[12]Cycloparaphenylene with Bright
Emission and its Supramolecular
Assembly
right host : A benzothiadiazole-based [12]cycloparaphenylene (TB[12]CPP) is
btained and characterized. TB[12]CPP exhibits a lime to orange emission with a
uantum yield up to 98%, ranking it as one of brightest CPPs. As a supramolecular
ost, TB[12]CPP is “bright” as well, showing adaptable ring structure. A ternary
ssembly between TB[12]CPP, fullerene and buckybowl is realized.
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