Effect of the linkages on the self-assembly and photophysical properties of 4,7-diphenyl-2,1,3-benzothiadiazole-based luminescent polycatenars

Article abstract of DOI:10.1016/j.molliq.2019.04.121

Three series of 4,7-diphenyl-2,1,3-benzothiadiazole (DBTD)based polycatenars containing a central 4,7-diphenyl-2,1,3-benzothiadiazole moiety connected to 3,4,5-trialkoxyl benzene units at both ends through ether (-OCH₂-), ester (-OOC-)or amide (-HNCO-)linkages were synthesized via Suzuki coupling reaction as key step. The polarities of the linkages had great effect on their self-assembly and photophycial properties. Both ether and amide compounds were mesogens, while the ester compounds were non-mesogens. The ether compounds displayed Col_hex/p6mm phases, while the amide compound displayed two kinds of columnar phases i.e. columnar rectangular phase with p2mm and columnar hexagonal phase with p6mm lattices depending on temperature. The column phases could be aligned in electric field or under mechanical shearing. The ether and amide compounds showed the significant red-shifted maximum absorption and emission. In the solid and gel states, both ether and amide compounds were yellow luminescence, while ester compounds were green luminescence.

Full text of DOI:10.1016/j.molliq.2019.04.121

Accepted Manuscript
Effect of the linkages on the self-assembly and photophysical
properties
of
4,7-diphenyl-2,1,3-benzothiadiazole-based
luminescent polycatenars
Jinliang Hu, Yulong Xiao, Qing Chang, Hongfei Gao, Xiaohong
Cheng
PII:
S0167-7322(19)30078-9
DOI:
Reference:
https://doi.org/10.1016/j.molliq.2019.04.121
MOLLIQ 10844
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
5 January 2019
16 April 2019
23 April 2019
Please cite this article as: J. Hu, Y. Xiao, Q. Chang, et al., Effect of the linkages on
the self-assembly and photophysical properties of 4,7-diphenyl-2,1,3-benzothiadiazole-
based luminescent polycatenars, Journal of Molecular Liquids, https://doi.org/10.1016/
j.molliq.2019.04.121
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ACCEPTED MANUSCRIPT
Effect of the linkages on the self-assembly and photophysical
properties of 4,7-diphenyl-2,1,3-benzothiadiazole-based luminescent
polycatenars
Jinliang Hu,‡[a] Yulong Xiao,‡[a] Qing Chang,[a] Hongfei Gao,*[a] Xiaohong Cheng,*[a]
[a] Key Laboratory of Medicinal Chemistry for Natural Resources, Chemistry Department, Yunnan University
Kunming,
Yunnan 650091,
P. R. China
Fax: (+86) 871 65032905
E-mail: xhcheng@ynu.edu.cn
‡Both authors contributed equally to this work
Abstract: Three series of 4,7-diphenyl-2,1,3-benzothiadiazole (DBTD) based polycatenars
containing a central 4,7-diphenyl-2,1,3-benzothiadiazole moiety connected to 3,4,5-trialkoxyl
benzene units at both ends through ether (-OCH2-), ester (-OOC-) or amide (-HNCO-) linkages
were synthesized via Suzuki coupling reaction as key step. The polarities of the linkages had great
effect on their self-assembly and photophycial properties. Both ether and amide compounds were
mesogens, while the ester compounds were non-mesogens. The ether compounds displayed
Colhex/p6mm phases, while the amide compound displayed two kinds of columnar phases i.e.
columnar rectangular phase with p2mm and columnar hexagonal phase with p6mm lattices
depending on temperature. The column phases could be aligned in electric field or under
mechanical shearing. The ether and amide compounds showed the significant red-shifted
maximum absorption and emission compared to those of ester compounds. In the solid and gel
states, both ether and amide compounds were yellow luminescence, while ester compounds were
green luminescence.
Keywords: 2, 1, 3-Benzothiadiazole; Luminescent liquid crystals; Gel; Self-assembly; Linkages
1. Introduction
Liquid crystals (LCs) are amazing materials which combine ordered structure and mobility on the
molecular level. With the development of science and technology, design of novel LC advanced
functional materials with self-assembly and self-healing is in great demand [1-3]. Particularly, the
columnar LCs with the ability to form uniaxial orientation by the applied electric field or under
mechanical shearing have great potentials in ferroelectric materials [ 4 - 6 ] as well as
one-dimensional (1D) transportation of charge carriers [7-12]. The molecular shape, central core,
linking group and terminal units [13,14] are crucial for control the molecular self-organization and
corresponding functions.
Luminescent LCs combining fluorescence and mesomorphism [15-19] have arisen intensive
research interesting due to their polarized emission properties [20,21]. Such materials have wide
applications as light source for liquid crystal displays (LCDs), and have great potentials in

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three-dimensional (3D) imaging systems and medical field [22] etc.
One of the most suitable heterocycles to construct luminescent materials is
2,1,3-benzothiadiazole (BTD) [23-25]. The BTD derivatives has strong fluorescence properties in
both solution and solid states, large Stokes shift [26-28] and high photosatbility [29-31].
However to our surprise, till now there are only few reports about BTD based luminescent LCs,
most of them represented smectic and nematic phases [25,32-38]. Although few BTD polycatenars
were reported too, either nonspecific LC phases [39,40] or no LC properties are reported in those
cases [41-43]. Therefore in our previous report, we have successfully realized columnar phases
with BTD based polycatenars carrying a rather long rigid core [44]. The importance of
luminescent columnar phases promoted us to study further variation of the molecular structure in
detail.
There are a few reports about using 4,7-diphenyl-2,1,3-benzothiadiazole (DBTD) core [45] to
construct functional materials [46-55]. DBTD has been connected with N,N-diarylamino donor
terminus to construct donor–π-bridge–acceptor–π-bridge–donor (D–π–A–π–D) type DBTD
fluorescent dyes with enhanced two-photon absorption cross-sections [46,47], and DBTD has also
been connected with alkoxy, alkoxymethyl, carboalkoxy substituents at both ends for fluorescent
host–guest LCDs [48]. All these compounds have a linear rod-like conformation and their LC
properties have never been reported. Although ether and the reverse -COO- linkages have been
used to connect the terminal groups (compounds 12-14, Fig. S1) to the central DBTD unit, no
amide linkage has been used.
It is well known that the linking group between two aromatic units can generate great influence
on LC and photophysical properties of the molecules. There are many literatures reported the
effect of the linking groups for covalently formed LCs [56-62], however systematic studies on the
effect of the linking group on LC properties of DBTD based polycatenars are still missing.
Therefore this paper deals with the synthesis and properties of three series of DBTD based
polycatenars E/n, C/n and A/n (E = ether, C = carboxylate, A = amide, and n = the length of the
terminal alkyl chains) containing central DBTD moiety connected to 3,4,5-trialkoxylbenzene units
at both ends via ether, ester or amide linkages (Fig. 1). The influence of the polarities of the
linkages on their self-assembly and photophysical properties was analyzed in detail.
Fig. 1 The molecular structures of compounds E/n, C/n and A/n.
2．Results and discussion
2.1 Synthesis
The synthesis of the target molecules E/n, C/n and A/n is showed in Scheme 1.
3,4,5-Trihydroxy-benzoicacimethylester was firstly reacted with appropriate alkyl bromides
giving 1/n. 1/n was reduced with LiAlH4 and the obtained 3,4,5-trialkoxybenzyl alcohols 2/n were
then reacted with SOCl2 yielding benzyl chlorides 3/n. Hydrolysis of esters 1/n in the presence of

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KOH yielded 3,4,5-trialkoxybenzoic acids 4/n. The commercially available o-phenylenediamine
reacted with SOCl2 yielded 2,1,3-benzothiadiazole 6 [63]. Bromination of 6 with molecular
bromine produced 4,7-disubstituted regioisomer 7 [ 64 ]. 7 was coupled with 4-methoxy
benzeneboronic acid via Suzuki coupling reaction. Demethylation of 8 using HBr produced
compound 9 [65], which was etherified with 3,4,5-trialkoxybenzylchlorides 3/n giving the ether
compounds E/n. 9 was acylated with the appropriate 3,4,5-trialkoxybenzoic acids 4/n to give the
ester compounds C/n. The amine 10 was acylated with 3,4,5-trialkoxybenzoylchlorides 5/n,
leading to the amide compounds A/n. The final compounds were purified by column
chromatography, and the structures and purities of all target compounds were confirmed by
1H-NMR, 13C-NMR (Fig. S2-S19) and elemental analysis. For more details, see the Supporting
Information.
Scheme 1 Synthesis of compounds E/n, C/n and A/n; Reagents and conditions: i) CnH2n+1Br, DMF, K2CO3, 90 °C,
12 h; ii) LiAlH4, THF, RT, 2 h; iii) SOCl2, THF, RT, 5 h; iv) C2H5OH, KOH, 80 °C, 12 h; v) THF, SOCl2, 70 °C, 1
h; vi) SOCl2, Et3N, CH2Cl2, RT, 4 h; vii) Br2, HBr (40% in water), 100 °C, 6 h; viii) 4-methoxybenzene boronic
acid, Pd(PPh3)4, Cs2CO3, KF, THF, H2O, 70 °C, 12 h; ix) 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)aniline,
Pd(PPh3)4, K2CO3, THF, H2O, 70 °C, 12 h; x) tetrabutylammonium bromide, HBr (33% in HOAc), 100 °C, 12 h; xi)
3/n, DMF, K2CO3, 90 °C, 12 h; xii) 4/n, DCC, DMAP, CH2Cl2, 0-5°C, 12 h; xiii) 5/n, pyridine, 80 °C, 12 h.
2.2 Liquid crystalline properties
The LC behaviors of DBTD based polycatenars E/n, C/n, and A/n were investigated by polarizing
optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD).
The corresponding phase transition data were collected in Table 1.
For these three series of compounds, ether (E/n) and amide (A/n) polycatenars were mesogens
whereas ester polycatenars (C/n) were non-mesogens.
For ether polycatenars, lower homologues E/n (n = 10 - 14) were monotropic (metastable)
mesogens, further increasing the alkyl chain length to n = 16, compound E/16 was enantiotropic
(thermodynamically stable) mesogen. However the highest ether homologue E/18 was only crystal
with a high melting temperature at 81 °C, the high melting temperature suppressed the occurrence
of LC phase (Table 1). The textures of these columnar mesophases were characterized by typical
spherulitic domains with some homeotropic regions (Fig. 2a for compound E/12, for additional

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examples, see Fig. S20), suggesting columnar phases with a preferentially uniaxial character [66].
Table1 Phase types, phase transition temperatures with corresponding enthalpy values of compounds E/n, C/n and
A/n. a
Comp.
T/ºC [ΔH/kJ mol-1]
a, b/nm
(T/ºC)
μ
Heating
Cooling
Cr 32 [31.3] Iso
Iso 32 [1.5] Colhex/p6mm 0 [8.3] Cr
3.90 (25)
4.10 (40)
4.53 (40)
4.55 (45)
-
3
3
3
3
-
E/10
E/12
E/14
E/16
E/18
Cr 64 [68.6] Iso
Iso 51 [1.8] Colhex/p6mm 2 [9.6] Cr
Iso 46 [1.1] Colhex/p6mm 26 [62.3] Cr
Iso 62 [3.9] Colhex/p6mm 43 [91.1] Cr
Cr1 40 [58.0] Cr2 70 [70.7] Iso
Cr 51 [93.7] Colhex/p6mm 64 [3.9] Iso
Cr1 62 [11.7] Cr2 69 [0.4] Cr3 81 [2.9] Iso 56 [26.3] Cr
Iso
Cr 72 [24.0] Iso
Cr 73 [21.2] Iso
Iso 61 [28.9] Cr
Iso 64 [25.7] Cr
-
-
-
C/12
C/16
A/12
-
Cr 85 [3.9] Colrec/p2mm 144 [2.4] Iso 141 [3.0] Colrec/p2mm 76 [1.9] Cr
Colhex/p6mm 150 [1.7] Iso
5.86, 2.71
(130)
3
3.91 (145)
-
3
-
Cr1 78 [27.3] Cr2 88 [11.9] Cr3 143 Iso 114 [46.4] Cr3 81 [7.8] Cr2 72
A/16
[39.8] Iso
[11.7] Cr1
a Transition temperatures were determined by DSC (peak temperatures, second scan, 10 K min-1). Abbreviations of
the phases: Cr = crystalline solid; Iso = isotropic liquid; Colrec/p2mm = rectangular columnar phase with plane
group p2mm; Colhex/p6mm = hexagonal columnar phase with plane group p6mm; a, b = lattice parameter measured
by SAXS; μ = the number of molecules in each unit cell with h corresponding to the d-value of the wide angle
scattering. For Colrec/p2mm phase: μ = abh(NA/M) ρ; Colhex/p6mm phase: μ = (a2/2) h(N /M) ρ, N = Avogadro
3
A
A
constant, M = molecular mass, assuming a density of ρ = 1 g·cm-3.
SAXS were carried out for all the ether compounds E/n (n = 10-16) (see Fig. 2b, Fig. S22-S24
and Tables S1-S4) and E/12 as the representative compound was discussed here. There were four
small-angle reflections with 1/d values in a ratio of 1 : 31/2 : 2 : 71/2, which could be indexed to the
10, 11, 20, and 21 reflections of a hexagonal lattice (Fig. 2b) with ahex = 4.10 nm (T = 40 °C). The
lattice parameters of the hexagonal phase of compounds E/n (n = 10-16) increased from 3.90 nm
(n = 10) to 4.55 nm (n = 16) (see Tables S1-S4). The number of molecules μ organized in a
stratum of the columns with a height of h = 0.45 nm (a typical value for the maximum of the
diffuse wide angle scattering) was calculated to be about 3 for all compounds E/n (see Table 1).
To realize the maximum of the dipolar interactions, the central BTD dipole of three molecules at
the cross section should point to the center of the supramolecular disc [58,62]. Afterwards these
discs stacked into columns with about 60° alternation along the columnar axis from one disc to the
next. The alkyl chains filled the remaining space at the periphery of columns (the inserts of Fig.
2b). The model was supported by the reconstructed electron density map (Fig. 2c), where the high
electron density regions (purple areas), the medium electron density shells (blue and green areas)
and the lowest electron density regions (red areas) represent BTD cores, aromatic cores and fluid
alkyl chains, respectively. The model was also supported by molecular dynamics (MD) annealed
model (Fig. 2d) [67].

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(b)
(a)
(d)
(c)
Fig. 2 Characterization of compound E/12: (a) texture under POM at T = 40 °C on cooling from the isotropic state;
(b) SAXS diffractogram of the Colhex/p6mm phase at T = 40 °C on cooling from the isotropic state; the inserts
show the self-assembly model of Colhex/p6mm phase and the CPK molecular model of the molecules arrangement
in a circular disk; (c) reconstructed electron density map for the Colhex/p6mm phase from the SAXS diffractogram
of (b); (d) snapshot of the Colhex/p6mm phases after molecular dynamics (MD) annealing.
All the ester compounds C/n were crystals (Table 1). In contrary, the amide compound A/12
was enantiotropic mesogen, whereas the higher amide homologue A/16 was a crystal due to its
high melting temperature. Spherulite-like textures with some dark regions confirmed the columnar
phase nature of A/12 (Fig. 3a,b) [66]. By heating the sample, there was a sudden change of the
texture at 145 °C (Fig. 3b), suggesting the presence of two different columnar phases. However
cooling from isotropic state, the texture remained unchanged between 141 °C and 76 °C,
suggesting there was only one columnar phase during the cooling process. These observations
were corresponding to the DSC trace of amide compound A/12 (Fig. S21i), where there were three
phase transitions occurred during heating corresponding to Cr-Col1, Col1-Col2 and Col2-Iso phase
transitions, while only one LC transition could be observed during cooling process. The phase
structures were confirmed by XRD investigation. SAXS pattern for the columnar phase at lower
temperature showed one strong reflection and three weak reflections indicating a rectangular
columnar phase with p2mm lattice (arec = 5.86 nm, brec = 2.71 nm, T = 130 °C, Fig. 3c and Table
S5), while the SAXS pattern of higher temperature columnar phase showed one strong and two
weak reflections with the 1/d values in a ratio of 1 : 31/2 : 2, indicating a hexagonal columnar
phase with p6mm lattice (ahex = 3.91 nm, T = 145 °C, Fig. 3d and Table S6). Based on the lattice
parameters, it could be calculated that there were about 3 molecules in each stratum of the
columns with h = 0.52 nm (Fig. S25) of these two kinds of columnar phases (Table 1). At low
temperature, the mesogens self-assembled into p2mm rectangular columnar phase, at higher
temperature, the increasing flexibility of the alkyl chains led to the transition of the p2mm to

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higher symmetric lattice p6mm columnar phase. Due to the H-bonding interactions between the
amide groups of adjacent molecules, the three amide molecules would organized parallel to form
an oval or circular shaped disk surrounded by flexible alkyl chains [68]. Stacking of the disks led
to columns, which further organized into columnar phases with different lattices (the inserts of Fig.
3c,d). The models were supported the reconstructed electron density map (Fig. S26) and molecular
dynamics (MD) annealed models (Fig. 3e,f).
(a)
(b)
Colhex/p6mm
Colrec/p2mm
(c)
(d)
(f)
(e)
Fig. 3 Characterization of compound A/12: (a) texture as seen between crossed polarizers at T = 120 °C on heating;
(b) texture as seen between crossed polarizers at T = 145 °C on heating; (c) SAXS diffractogram of the
Colrec/p2mm phase at T = 130 °C on heating; the inserts show the model of Colrec/p2mm phase and the molecules
arrangement in an oval disk; (d) SAXS diffractogram of the Colhex/p6mm phase at T = 145 °C on heating; the
inserts show the model of Colhex/p6mm phase and the molecules arrangement in a circular disk; (e) snapshot of the
Colrec/p2mm phases after MD annealing; (f) snapshot of the Colhex/p6mm phases after MD annealing.
Under POM, the LC film of ether compounds between two patterned indium tin oxide (ITO)
electrodes with the thickness of 7 μm showed a dark view by applying a direct current electric
field (0.5 V μm-1) about 43 s (Fig. 4), indicating these columnar LCs had the ability to orient under
the electric fields. When the electric field was removed, the birefringent texture recovered in about
50 s. These observations might indicate that the polarization of the BTD units was along the

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columnar axis [69].
By applying the same strength of direct current electric field (0.5 V μm-1), the columnar phase
of amide samples could not orient, this demonstrated that the polarities of amide compounds were
much stronger than those of the ether compounds or the self-assembled models were different
from those of ether compounds.
(a)
(b)
Vertical Electric Field
Without Vertical
Electric Field
Fig. 4 Polarized optical microscopic image of E/12 in the columnar state at 45 ºC before apply the vertical electric
field (a) and after apply the vertical electric field 43 s (b).
The columnar LCs could form macroscopically homogeneous arrangement by mechanic
shearing [11]. The textures of Colhex/p6mm phase of E/12 before and after shearing were shown in
Fig. 5. The transition from polydomain to monodomain of the column could be realized by
shearing the self-assembled sample which was sandwiched between two glass plates. The POM
image revealed that the direction of the long axis of columns was parallel to the shearing direction
(Fig. 5b), which could be confirmed by the birefringence of E/12 changing periodically from light
to dark upon a 45° rotation under the crossed Nicols condition (Fig. S28) [11]. The
macroscopically uniform alignment of columns might lead to anisotropic charge carrier transport
along the molecular stacking [70,71].
(a)
(b)
Fig. 5 (a) The texture of Colhex/p6mm phase of E/12 between two glass plates at T = 40 °C without shearing; (b)
the texture of Colhex/p6mm phase of E/12 between two glass plates with the columns being parallel to the shear
direction. Abbreviations of directions: A: analyzer direction; P: polarizer direction; S: shearing direction.
2.3. Gel property
The polarities of linking groups should have large influence on the self-assembly of the gels
[58-60]. To get insight into this effect, the gelation behaviors of the representative compounds
E/12, C/12 and A/12 were investigated in various organic solvents (6.0 mg mL-1). The results
were collected in Table 2. All these polycatenars could dissolve in nonpolar solvents such as

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n-hexane, cyclohexane and toluene, but were insoluble in acetonitrile. Ether and ester compounds
E/12 and C/12 could form yellow and green fluorescence organogels under 365 nm UV light
respectively in ethyl acetate (see the inserts of Fig. 6a,b), while amide compound A/12 could form
yellow fluorescence organogels under 365 nm UV light in ethyl acetate and DMF (see the inserts
of Fig. 6c,d). To investigate the thermal stability of these gels, Tgel (the gel-to-sol phase transition
temperature) values were measured by the “test-tube-tilting” method [72]. Tgel values of
compounds E/12, C/12 and A/12 were 37 ºC, 45 ºC, 62 ºC and 65 ºC, respectively (Table S7).
Table 2 Gelation test results of compound E/12, C/12 and A/12a
Solvent
E/12
G
C/12
G
A/12
G
Ethyl acetate
Acetone
P
P
P
DMF
P
P
G
Toluene
S
S
S
Acetonitrile
Chloroform
n-Hexane
Cyclohexane
1,4-Dioxane
IS
S
IS
S
IS
S
S
S
S
S
S
S
PG
PG
PG
a G = gelation, S = soluble, IS = insoluble, P = precipitation, G = gelation, PG = partial gelation.
(a)
(b)
(c)
(d)
Fig. 6 Selected SEM images of the xerogel made from (a) E/12 in ethyl acetate, scale bar is 5 μm; (b) C/12 in
ethyl acetate, scale bar is 20 μm; (c) A/12 in ethyl acetate, scale bar is 1 μm; (d) A/12 in DMF, scale bar is 4 μm.
The inserts show the images of the gels under 365 nm UV light.
The SEM images of the xerogels of E/12, C/12 and A/12 formed in different solvents were
shown in Fig. 6. Compound E/12 with less polar ether linking group could form 3D fibrous
networks in ethyl acetate solvent (Fig. 6a). The diameter of the fibers was about 89-625 nm and

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the length was more than 10 μm. With increasing the polarity of the linking group, compound
C/12 with ester group (middle polarity) formed gel with belt morphologies (Fig. 6b). The
approximate width of the belts was 0.8-7.2 μm. The length was more than 4.4 μm. When the
linkage was replaced by the strongest polar amide group, compound A/12 could also form 3D
networks consisting of entangled helical fibers (Fig. 6c). The approximate diameter of the fibers
was 36-182 nm. The length was more than 8 μm. Therefore the polarities of linking groups had a
significant effect on the morphologies of gels. The dipolar-dipolar interaction between polar
solvents and BTD unit or linkages, as well as other non-covalent interactions such as π-π
interaction, hydrogen-bonding interaction between the amide groups etc. (Fig. S29) could all drive
the formation of the gels. Furthermore, ester and amide units in compounds C/12 and A/12 led to
stronger intermolecular dipolar-dipolar interaction and hydrogen-bonding interaction, therefore
the ester C/12 formed nanobelt morphologies while the amide A/12 formed helical entangled
fibers. Most interesting, sphere structures aggregates (the diameter of 5.5-10 μm) composed of
helical fibers with the diameter of 73-290 nm and the length of more than 1.6 μm were observed in
xerogel of amide compound A/12 from more polar DMF solvent. This might be due to the effect
of the solvent polarities on the noncovalent interactions, especially intermolecular hydrogen
bonding interaction, which promoted the self-assembly [73-76].
On the basis of these results, it is assumed that the polarities of linking groups and the solvent
have remarkable effects on the self-assembled morphologies of DBTD based polycatenar gels.
2.4. Absorption and emission properties
The UV-vis absorption and fluorescence spectroscopic data in CH2Cl2 (DCM) solution and in the
solid state of compounds E/12, C/12 and A/12 were shown in Fig. 7 and Fig. S30. All
polycatenars exhibited a strong absorbing band (ε = 1.9 - 20.8 × 104 Lmol-1cm-1) between 282-308
nm which might be caused by the π-π* transition and the other absorbing band (ε = 0.7 – 6.0 × 104
Lmol-1cm-1) between 382-426 nm owing to the charge transfer (CT) transition arising from the
donor-acceptor chromophore [41,55]. Additionally, the red shifts (about 1-16 nm, see Fig. 7) of
their absorption peaks in the films indicated that the π-stacked aggregates adopt a J-type parallel
stacking mode in the solid state [77].
The polarities of the linkages affected the photophysical properties significantly. The solution of
ether compound E/12 exhibited two absorption maxima at 282 nm and 410 nm (Fig. 7a). Ester
compound C/12 exhibited two absorption maxima at 283 nm and 383 nm (Fig. 7b), while the
amide compound A/12 exhibited two absorption maxima at 305 nm and 403 nm (Fig. 7c). The
first absorbing maxima wavelength was in the order: amide A/12 (305 nm) > ether E/12 (282 nm)
≈ ester C/12 (283 nm), while the second absorbing maxima wavelength was in the order: ether
E/12 (410 nm) > amide A/12 (403 nm) > ester C/12 (382 nm). The emission maxima wavelength
was in the order: amide A/12 (547 nm) > ether E/12 (539 nm) > ester C/12 (501 nm) (Fig. 7). The
same orders were observed in the solid films of these compounds. This should be ascribed to that
the electro donating abilities of both ether and amide units were stronger than that of ester group.
Therefore the ether and amide units had stronger effects on the electron mobility of the BTD unit.
As a result, the ether and amide compounds exhibited stronger electro resonance effect than the
ester compounds, which caused the significant red-shift of the absorption and emission spectrum
of ether and amide compounds as compared to ester compounds. Additionally, we calculated the
energy band gaps of E/12, C/12 and A/12 from the onsets of their films absorption [78], which

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were about 2.54 eV, 2.84 eV and 2.56 eV, respectively (Fig. S31). These values were in the order:
ether E/12 (2.54 eV) < amide A/12 (2.56 eV) < ester C/12 (2.84 eV), which agreed with the above
electro resonance effect. Both the solution and film of ether and amide compounds were yellow
emission, while the ester compounds were green emission. All these polycatenars displayed strong
fluorescence (ΦFL = 0.34-0.46, see Table 3) with large Stokes shifts (119-135 nm, see Table 3).
(a)
(b)
(c)
Fig. 7 Normalized absorption spectra (left) and photoluminescence spectra (right) of compounds (a) E/12, (b) C/12
and (c) A/12 recorded in DCM solution (c = 10-5 mol L-1) (green lines) and thin solid film (red lines) at room
temperature. The inserts are the images of compounds E/12, C/12 and A/12 respectively in DCM solution under
the irratadiation with UV 365 nm.
Table 3 UV-visible absorption and emission data of compounds E/12, C/12 and A/12 in CH2Cl2 solution.
c
Compound
Absorption
Emissionb
λmax (nm)
Stokes shift/nm
(cm-1)
ΦFL
λmax (nm) (ε) a
282 (7.0 × 104), 410 (2.6 × 104)
283 (6.3 × 104), 382 (1.5 × 104)
305 (3.0 × 104), 403 (0.9 × 104)
539
501
538
128 (5837)
119 (6218)
135 (6227)
0.44
0.46
0.34
E/12
C/12
A/12
a Units = Lmol-1cm-1, c = 1 × 10-5 mol/L; b Excited at absorption maxima band; cRelative to quinine sulphate in 1
M H2SO4 (ΦFL = 0.55) as the standard [79].
The absorption spectra of compounds E/12, C/12 and A/12 were nearly independent of solvent
polarity (Fig. S32a,c,e). However, the emission spectra of these polycatenars were solvatochromic
(Fig. S32b,d,f and Table 4), which indicated that these polycatenars possessed strong
intramolecular charge transfer. The solvatochromic effect (Δλem = λem,DMF - λem,n-Hexane) was in the
order: amide A/12 (Δλem = 44 nm) > ether E/12 (Δλem = 37 nm) > ester C/12 (Δλem = 35 nm),
which further confirmed that the electro donating abilities of both ether and amide units are
stronger than that of ester group.

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Table 4 Charge-transfer maximum emission wavelength (λem/nm) in different solvents.
n-Hexane
31.0
Toluene
33.9
524
THF
37.4
533
500
551
DMF
43.2
543
ET(30)a
E/12
506
480
496
515
C/12
531
532
575
A/12
a
ET(30) [kcal/mol] is the empirical parameter of solvent polarity [80]. The excitation wavelengths are 410 nm,
382 nm and 403 nm for compounds E/12, C/12 and A/12 respectively.
2.5. Photoinduced charge separation property
BTD-based fluorophores have attracted much attention because they have potential applications in
organic photovoltaic (OPV) cells [81]. The fluorescence of E/12 was significantly quenched with
increasing concentration of C70 (Fig. 8), indicating the presence of photoinduced charge separation
process between E/12 and C70 [82,83]. According to the Stern–Volmer equation [84]:
F0/F= 1 + Ksv [C]
here, F0 and F represent the fluorescence intensity in the absence and present of C70, respectively,
and [C] is the concentration of C70, the quenching constant (KSV) of C70 to E/12 is calculated to be
6.72 × 104 M-1. This indicated that electron transfer could exist between the DBTD fluorophore
and C70 [85].
(a)
(b)
without C70 with C70
Fig. 8 (a) Emission spectra of E/12 (1.0 × 10-6 M) in CHCl3 with increasing concentration of C70 (1.0 × 10-6 M):
0.0 (blank), 1.0 equiv. (1), 2.0 equiv. (2), 3.0 equiv. (3), 4.0 equiv. (4), 5.0 equiv. (5), 6.0 equiv. (6), 7.0 equiv. (7),
8.0 equiv. (8); The insets are images of E/12 without and with C70 in CHCl3 under the irradiation with UV 365 nm.
(b) Sterne-Volmer quenching plots for compound E/12.
3．Conclusion
In summary, the effect of different linkages on the self-assembly and photophysical properties of
DBTD-based polycatenars have been systematically studied. Very flexible ether linkage could
enhance the micro-segregation between the central rigid core and terminal flexible chains, while
the strong polar amide linkage could increase the core-core interaction due to its high polarity and
its formation intermolecular hydrogen-bonding ability. These effects led to the emergence of
mesogenic properties for both ether and amide compounds. While the middle polar ester linkage,
which could enhance neither the flexibility of the terminal chains nor the core-core interaction,

ACCEPTED MANUSCRIPT
inhibited the occurrence of LC properties. Different polarities of the linkages also led to different
packing models for the LC phases. For ether compounds the molecules would form triangular
discs and stack into polar p6mm columnar phases, whereas for the amide compounds, the
molecules would organize parallel to form an oval or circular shaped disks and finally
self-assembled into p2mm and p6mm columnar phases respectively. Additionally, ether and amide
DBTD polycatenars could form yellow emissive gels while ester ones could form green emissive
gels with different morphologies in organic solvents. The uniform alignment of the columns has
been achieved. Charge transfer between DBTD polycatenar and C70 has been demonstrated.
Overall, our research paved a new way for the proper design of DBTD based luminescent
columnar LCs, which had potentials in optoelectronic devices.
Acknowledgements
This work was supported by the National Natural Science Foundation of China [Nos. 21602195,
21664015 and 21865038], the Yunnan Natural Science Foundation [Nos. 2017FB011 and
2016FD008], the program for Innovative Research Team (in Science and Technology) in University
of Yunnan Province for financial supports (2018FY001(-012)), and Yunnan Province Excellent
Youth Training Project (2018YDJQ030). We thank beamline 1W2A at Beijing Synchrotron
Radiation Facility (BSRF) and beamline BL16B1 at Shanghai Synchrotron Radiation Facility
(SSRF), China.
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ACCEPTED MANUSCRIPT
Graphical abstract
Three novel series 4,7-diphenyl-2,1,3-benzothiadiazole based luminescent polycatenars with
different linkages have been synthesized. Depending on the polarity of the linkage, such
molecules can organize into columnar phases with different lattices in their bulk states and
colorful gels with different morphologies in organic solvents.
Highlights
Novel DBTD based polycatenars with different linkages have been synthesized.
The effects of the polarities of the linkages on their properties were investigated.
Such polycatenars could form columnar phases with different lattices.
Such polycatenars could form gels with different morphologies.
Such polycatenars exhibited strong fluorescence in both solution and bulk states.