Bisthiophene/triazole based 4,6-diamino-1,3,5-triazine triblock polyphiles: Synthesis, self-assembly and metal binding properties

Article abstract of DOI:10.1016/j.molstruc.2019.05.038

Two series of 4,6-diamino-1,3,5-triazine triblock polyphiles consisting of an extremely long bisthiophene/triazole based rigid cores, with flexible alkyl chains at one end and a polar 4,6-diamino-1,3,5-triazine at the other end were synthesized. Col_h

Full text of DOI:10.1016/j.molstruc.2019.05.038

Accepted Manuscript
Bisthiophene/triazole based 4,6-diamino-1,3,5-triazine triblock polyphiles: Synthesis,
self-assembly and metal binding properties
Chao Liu, Hongfei Gao, Taihao Li, Yulong Xiao, Xiaohong Cheng
PII:
S0022-2860(19)30602-7
DOI:
https://doi.org/10.1016/j.molstruc.2019.05.038
MOLSTR 26545
Reference:
To appear in: Journal of Molecular Structure
Received Date: 19 December 2018
Revised Date: 21 March 2019
Accepted Date: 13 May 2019
Please cite this article as: C. Liu, H. Gao, T. Li, Y. Xiao, X. Cheng, Bisthiophene/triazole based 4,6-
diamino-1,3,5-triazine triblock polyphiles: Synthesis, self-assembly and metal binding properties, Journal
of Molecular Structure (2019), doi: https://doi.org/10.1016/j.molstruc.2019.05.038.
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ACCEPTED MANUSCRIPT
Bisthiophene/triazole based 4,6-diamino-1,3,5-triazine triblock
polyphiles: synthesis, self-assembly and metal binding properties
Chao Liu,‡[a] Hongfei Gao,‡[a] Taihao Li,[a] Yulong Xiao,[a] Xiaohong Cheng*[a,b]
[a] Key Laboratory of Medicinal Chemistry for Natural Resources, Chemistry School of Chemical
Science and Technology, Yunnan University, Kunming, 650091, PR China.
[b] School of Chemistry and Chemical Engineering, Yangtze Normal University, Fuling, 408100,
PR China.
Fax: (+86) 871 65032905
E-mail: xhcheng@ynu.edu.cn
‡Both authors contributed equally to this work

ACCEPTED MANUSCRIPT
Bisthiophene/triazole based 4,6-diamino-1,3,5-triazine triblock
polyphiles: synthesis, self-assembly and metal binding properties
Chao Liu,‡[a] Hongfei Gao,‡[a] Taihao Li,[a] Yulong Xiao,[a] Xiaohong Cheng*[a,b]
[a] Key Laboratory of Medicinal Chemistry for Natural Resources, Chemistry School of Chemical
Science and Technology, Yunnan University, Kunming, 650091, PR China.
[b] School of Chemistry and Chemical Engineering, Yangtze Normal University, Fuling, 408100,
PR China.
Fax: (+86) 871 65032905
E-mail: xhcheng@ynu.edu.cn
‡Both authors contributed equally to this work
Abstract: Two series of 4,6-diamino-1,3,5-triazine triblock polyphiles consisting of an extremely
long bisthiophene/triazole based rigid cores, with flexible alkyl chains at one end and a polar
4,6-diamino-1,3,5-triazine at the other end were synthesized. Colhex/p6mm mesophases were
displayed by all bisthiophene based 4,6-diamino-1,3,5-triazine derivatives, whereas both
Col /p6mm and Cub /
mesophases could be formed by corresponding triazole based
Pm3n
hex
I
4,6-diamino-1,3,5-triazine derivatives. Evidence for the formation of the extra H-bonding between
central triazole units and terminal 4,6-diaminotriazine groups which was responsible for the
formation of cubic phases in triazole based compounds was obtained based on FT-IR
measurements. Additionally, these triblock polyphiles can form organogels with interesting
morphologies in different solvents. The influence of the alkyl chain length and the polarities of the
heterocycles (bisthiophene/triazole) on the self-assembly of these compounds was systematically
studied. Finally, these triblock polyphiles showed dual selectivities towards Pb2+ and Fe3+ ions.
Key words: Diamino-1,3,5-triazine, Heterocycle, Self-assembly, Liquid crystal, Organogel,
Chemosensor
1.Introduction
Research on molecular self-assembly and self-assembled morphologies is of currently scientific
interest because of their widely applications in nanotechnologies [1]. Liquid crystals (LCs) [2,3]
combining order and mobility on the molecular level, supply perfect models to study the driving
forces of self-assembly [4]. The molecular shape, space filling and the microsegregation of
incompatible molecular parts decide the molecular self-assembled process and the self-assembled
morphologies [5]. The interface curvature among the regions formed by the microsegregation of
incompatible molecular parts into different domains, decide the self-assembled morphologies.
Increasing the intramolecular contrast could effectively reinforce the microsegregation and the
molecular self-assembly [6]. While the intramolecular contrast can be reinforced by forming
highly polar hydrogen bonds or elongation of the rigid core of the rod-like molecules [7]. On one

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hand, the formation of hydrogen bonding between polar groups such as hydroxyl, amino etc, gives
rise to strong cohesive forces in polar region. These forces produce temporary crosslinks among
the amphiphiles and enforce the micro-segregation which increases mesophase stability [5a]. On
the other hand, the extended rigid core allows efficient microsegregation between the rigid parts
and the aliphilic chains and supplies strongly attractive interactions, favouring a parallel
arrangement [8]. The length of the rigid part could be shortened if extra attractive forces such as
polar heterocycles are inserted [9,10]. According to the above mentioned LC designing principles,
we have recently designed series of triblock polyphilic mesogens composed of a long rigid
rod-like core with flexible alkyl chains at one end and a polar group such as glycerol [11],
4,6-diaminotriazine (1T/n) (Scheme1) [12] or imidazolium salt [13] at the other end. These
triblock polyphilic mesogens represented rich mesophases ranging from nematic, smectic and
especially columnar as well as cubic mesophases.
However the research on the self-assembly of these triblock polyphilic mesogens was only in
initial stage and the relationship between molecular structure and the occurrence of columnar or
cubic phases is worth further studying. Therefore herein we reported novel series of
4,6-diamino-1,3,5-triazine triblock polyphiles consisting of an extremely long
bisthiophene/triazole based rigid core, with flexible alkyl chains at one end and a polar
4,6-diamino-1,3,5-triazine at the other end (Scheme 1). To our surprise, although such two series
differed only in the type of heterocycle units contained in the rigid core, their mesophase behavior
was different. All bisthiophene based compounds displayed only columnar phases, while triazole
based compounds displayed both columnar and cubic phases. The influence of the alkyl chain
length and polarity of the heterocycle units on the self-assembly of these compounds are
investigated. Furthermore, evidence for the formation of the extra H-bonding between the central
triazole units and terminal 4,6-diaminotriazine groups which enhanced the core-interdigitated
aggregates leading to the formation of cubic phase in triazole based compounds, was obtained
based on IR measurements.
Scheme 1. Structures of the reported thiophene based triazine derivatives 1T/n, as well as bisthiophene based
triazine derivatives 2T/n and triazole based triazine derivatives Tr/n under investigation.
2.1. Materials and methods
Reactions requiring an inert gas atmosphere were conducted under argon and the glassware was
oven-dried (140 °C). Tetrahydrofuran (THF) was distilled from sodium prior to use. Commercially

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available chemicals were used as received [14].1H-NMR and 13C-NMR spectra were recorded on a
o
Bruker-DRX-500 spectrometer at 25 C using TMS as internal standard. Elemental analysis was
performed using an Elementar VARIO EL elemental analyzer. Thin-layer chromatography (TLC)
was performed on aluminum plates precoated with 5735 silica gel 60 PF254 (Merck). Column
chromatography was performed on Merck silica gel 60 (230-400 mesh). Fourier transform
infrared (FTIR) study was performed over the wavenumber, range of 4000-400 cm-1 by a Thermo
Fisher SCIENTIFIC Nicolet IS10 (Massachusetts, USA) FTIR impact 410 spectrophotometer
using KBr pellets. Temperature dependent FT-IR measurements were performed on solids in
anhydrous KBr pellets with a home-made heating stage (room temperature up to LCs stage) [15].
Column chromatography was performed with Merck silica gel 60 (230 - 400 mesh). The
intermediates and the final products were purified by column chromatography, their structures
1
were confirmed by H-NMR and the purity was checked by TLC, the structures of the final
products were additionally confirmed by 13C-NMR and elemental analysis. A Mettler heating
stage (FP 82 HT) was used for polarizing optical microscopy (POM, Optiphot 2, Nikon) and DSC
were recorded with a DSC 200 F3 Maia calorimeter (NETZSCH) at 5 K min-1 and 2 K min-1 [16].
(DSC 200 F3 Maia calorimeter was calibrate by using standard sample: C10H16, In, Sn, Bi, Zn,
CsCl).. Their optical properties (UV-vis and fluorescent emission) were done on a UNIC
UV2600A and HITACHI F-7000 spectrophotometers (conventional quartz cell 10 × 10 × 45 mm)
o
at 25 C, excitation and emission slits 5 nm wide) (Hitachi F-7000 spectrometer was calibrate by
using mercury lamp and quinine sulphate).
SEM experiments were carried out on a ZEISS SIGMA 300 scanning electron microscopy
(SEM, GER). All pictures were taken digitally. For the sample preparation, the gel was placed on
an aluminium foil for some time until the gel became dry gel, then the sample was gold plated,
finally the sample was put into the scanning electron microscopy for observation17. XRD
measurement of xerogels was used the X-ray powder diffraction (XRD, Rigaku Co., Tokyo,
Japan), analysis was conducted on a D/max-3B spectrometer with Cu Kα radiation.
Small-angle powder diffraction (SAXS) experiments were performed in transmission mode
with synchrotron radiation at the 1W2A SAXS beamline at Beijing Accelerator Laboratory and at
the beamline BL16B1 at Shanghai Synchrotron Radiation Facility (SSRF) [18]. A modified
Linkam hot stage with a thermal stability within 0.2 °C was used, with a hole for the capillary
drilled through the silver heating block and mica windows attached to it on each side. Samples
were held in the poly(imide) (Kapton) film. A MarCCD 165 detector was used. q calibration and
linearization were verified using several orders of layer reflections from silver behemate. Positions
and intensities of the diffraction peaks were measured using PeakSolveTM (Galactic).
For electron density reconstruction. Fourier reconstruction of the electron density was carried out
using the general formula for 2D periodic systems:
E(xy) = Σhk sqrt[I(hk)] exp[i2π(hx+ky) +ϕhk]
For the centro-symmetric structures considered in this work the phase angle ϕ can take up the
values of 0 or π. The choice of a phase combination was initially made on the merit of each
reconstructed electron density map obtained using the most intense reflections, combined with the
additional knowledge of the molecules (molecular shape, length, volume of each part and the

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distribution of electron density among the different moieties).
2.2. Synthesis
All the target compounds were synthesized via CuAAC click reactions or Pb(0) catalyzed
coupling reactions as key steps (Scheme 2). 4-Aminophenol was treated with sodium nitrite to
form corresponding diazonium salt and subsequent substituted with sodium azide to give
4-azidophenol 3. 3 was etherified with associated 3,4,5-trialkoxybenzyl chlorides 4/n to give the
3,4,5-trialkoxybenzyl 4-azidophenyl ethers 5/n. 4-Bromobenzonitrile was coupled with
trimethylsilyl acetylene in a Sonogashira coupling reaction to give compound 1 [19], which was
deprotected with K2CO3 to produce 4-ethynylbenzonitrile 2. CuAAC click reaction [20] between
aromatic azides 5/n and the 4-ethynylbenzonitrile 2 yielded benzyl 4-phenyl-1,2,3-triazole
aromatic nitriles 6/n. 2,5-Dibromothiophene was coupled with 4-methoxyphenylboronic acid in a
Suzuki coupling reaction to yield 2-(4-methoxyphenyl)thiophene 7, which was then coupled with
the 2-thiophenyl boric acid in
a
Suzuki coupling reaction, leading to the
5-(4-methoxyphenyl)-2,2'-bithiophene 8. 5-(4-Methoxyphenyl)-2,2'-bisthiophene 8 was then
brominated with N-bromosuccinimide (NBS) to yield 9 which was substituted by CuCN to
produce nitrile 10. 10 was demethylated to produce phenol 11 [21], then 11was etherified with 4/n
to give 12/n. Finally the nitrile groups of 6/n and 12/n were reacted with dicyandiamide
respectively, giving the target bisthiophene based compounds 2T/n and triazole based compounds
Tr/n. Detailed synthesis process and data are shown in the Supporting Information.
Scheme 2. Synthesis of the 4,6-diamino-1,3,5-triazine triblock polyphiles; Reagents and conditions: i) Pd(PPh3)4,
CuI, (i-Pr)2NH, toluene, RT, 12 h; ii) K2CO3, CH3OH, THF, RT, 2 h; iii) NaNO2, HCl, NaN3, 0-5 °C, 24 h; iv)
NaH, THF, 78 °C, reflux, 12 h; v) Sodium ascorbate, CuSO4·5H2O, THF, tert-butyl alcohol, H2O, RT, 20 h; vi)

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Dicyandiamide, KOH, 2-methoxyethanol, reflux 16 h; vii) Pd(PPh3)4, THF, H2O, K2CO3, 78 °C, reflux, 12 h; viii)
2-Thiophenylboric acid, Pd(PPh3)4, THF, H2O, K2CO3, 78 °C, reflux, 12 h; ix) NBS, THF, 0 °C-RT, 2 h; x) CuCN,
DMF, reflux, 16 h; xi) BBr3, CH2Cl2, 0 °C-RT, 16 h; xii) K2CO3, DMF, 90 ºC, 12 h; vi) Dicyandiamide, KOH,
2-methoxyethanol, reflux, 16 h.
2.3. Mesomorphic properties
The mesomorphism of the synthesized compounds was studied by polarizing optical microscopy
(POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The phase
transitions and corresponding enthalpy changes are shown in Table 1. All the
4,6-diamino-1,3,5-triazine triblock polyphiles are enantiotropic LCs.
Table 1 Thermal properties, XRD data and other data of compounds 2T/n and Tr/n.[a]
Comp.
2T/10
2T/12
2T/14
T/°C [∆H/kJ mol-1]
a/nm (T/°C)
6.20 (110)
6.19 (110)
6.51 (180)
ꢀ
θ (o)
37.1
40.4
39.6
Cr 95[b] Colhex/p6mm 192 [6.6] Iso
Cr 85[b] Colhex/p6mm 177 [0.4] Iso
Cr 77 [14.1] Colhex/p6mm 181 [2.7] Iso
9.7
8.9
9.1
2T/16
2T/18
Tr/12
Tr/14
Tr/16
Cr 110 [4.1] Colhex/p6mm 176 [0.3] Iso
Cr 85 [89.1] Colhex/p6mm 169 [2.5] Iso
Cr 183 [35.1] Colhex/p6mm 190[b]Iso
6.25 (120)
7.19 (150)
6.12 (110)
7.8
9.6
8.9
46.2
37.5
40.4
3.1
197[b]Iso
11.86 (185) 114.3
Cr 170 [11.4] Cub /
Pm3n
I
11.48 (180) 94.9
3.8
Cr 166 [17.3] Cub /
214 [0.3] Iso
Pm3n
I
[a]
Transition temperatures and transition enthalpies were determined by DSC (5 K min-1 and 2 K min-1) and
confirmed by POM, peak temperatures of the 1st heating scan are given; abbreviations: Cr = crystal, Colhex/p6mm
= hexagonal columnar phase with p6mm symmetry, Cub / = cubic phase with space group , Iso =
Pm3n
Pm3n
I
isotropic liquid, a = lattice parameter; ꢀ = number of molecules in the columnar slice for Colhex/p6mm phase (ꢀ =
(a2/2) h(NA/M)ρ, assuming density of ρ = 1 g/cm3 and height of columnar slice of h = 0.45 nm) or number of
3
molecules in each spheroidic aggregates on average for Cub /
phase (ꢀ = ncell/8; θ = projection of the cone
Pm3n
I
angle, calculated according to θ = 360/ꢀ [22]). [b] Transition temperatures were determined by POM.
2.3.1 Series 2T/n: hexagonal columnar phases
Typical fan shaped textures for bisthiophene compounds 2T/n were observed under POM,
indicating that all 2T/n could form columnar mesophases and the dark regions under POM
revealed that these columnar mesophases were optically uniaxial (Fig. 1a and Fig. S1). The
textures with a λ-retarder plate indicated that these columnar mesophases were optically negative,
indicating the orientation of the intramolecular π-conjugation route (i.e. the long axis of the
aromatic cores) was vertical to the column long axis (insert of Fig. 1a and Fig. S1b,d,f,h,j). These
columnar mesophases were further investigated by SAXS (Fig. 1b and Fig. S4-7). The XRD
pattern of the representative compound 2T/10 showed three reflection peaks at 5.35 (10), 2.69 (20)
and 2.03 (21) nm with the d-spacing ratios of 1 : 1/2 : 1/51/2 at the small angle region, revealing
hexagonal columnar phase with lattice parameter a = 6.34 nm (Fig. 1b and the other examples
were shown in Fig. S4-7). The number of molecules in the columnar slice was about 10, indicating

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4,6-diaminotriazine groups of these molecules formed the center of the disk by H-bonding
interactions, which were surrounded by the rigid cores. These disks stacked into cylinders by π-π
stacking, which finally self-assembled into hexagonal columnar phase and the space of adjacent
columns was filled with the flexible alkyl chains (Fig. 1d). The proposed core-shell model [23,24]
was in accordance with the electron density map (Fig. 1c).
(a)
(b)
(c)
(d)
High
Low
Fig. 1. (a) Textures under POM cooling at T = 180 °C; (b) XRD patterns at T = 110 °C; (c) Reconstructed electron
density map and (d) model for Colhex/p6mm phase of 2T/10.
2.3.2 Series Tr/n: transition from Col /p6mm and Cub /
Pm3n
hex
I
The lowest homologue Tr/12 could self-assemble into Colhex/p6mm phase structure which was
confirmed by POM, DSC and XRD investigations (Table 1, Fig. S2, S3 and S8). For the higher
homologues Tr/14 and Tr/16, optically isotropic phase (nonbirefringent) with high viscous was
observed under POM, indicating cubic mesophases (Fig. S2c-2d) [25]. The XRD pattern of the
representative compound Tr/14 showed three characteristic diffraction peaks at 5.93 (200), 5.28
(210) and 4.80 (211) in the small angle region, revealing cubic phase with space group of
Pm3n
[12,13,26,27] (Fig. 2a and another example was shown in Fig. S9). The lattice parameters are
11.86 and 11.48 nm calculated by XRD for Tr/14 and Tr/16 respectively. In such Cub /
Pm3n
I
phase, there are 8 spheroidic aggregates in each unit cell (Fig. 2b). Based on the size of the unit
cell and the molecular volume (determined by using crystal-volume increments) [28], there are
about 114.3 and 94.9 molecules in each aggregate for Tr/14 and Tr/16, respectively (Table1 and
Table S9). The molecular length of compound Tr/n is very long (about 4.6 nm), this should result

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in the formation of a larger size micelle (Fig. 2b).
(a)
(b)
Fig. 2. (a) XRD patterns of Cub /
of compound Tr/14 at T = 185 ºC; (b) model of the cubic phase of Tr/14.
Pm3n
I
2.3.3 Comparison of the mesophase behavior of compounds 2T/n and Tr/n with 1T/n
A comparison of LC behavior among 2T/n (L = 1.75 nm), Tr/n (L = 1.74 nm) and the previously
reported 1T/n (L = 1.35 nm) was conducted (Fig. 3a). These three series differed in the rigid core
length and the heterocycle units containing in the rigid cores. Both the melting and isotropic
temperatures of long core compounds 2T/n and Tr/n were higher than those of the previously
reported short core monothiophene compounds 1T/n [12], this should be ascribed to the
elongation of the rigid cores enhancing the intramolecular contrast and microsegregation of
incompatible molecular parts, and therefore being beneficial for the mesophase stability. The
dipole moment was in the order triazole-phenyl > thiophene > bisthiophene, thus the mesophases
of triazole derivatives Tr/n showed the highest melting and isotropic temperatures. This might be
due to the strong dipole-dipole interactions reinforcing the core-core interactions, and thus
increasing the mesophase stability. 1T/12 with shorter rigid core could self-assemble into
Cub /
phase with strong interfacial curvature [5, 12], whereas 2T/12 and Tr/12 could only
Im3m
I
form Colhex/p6mm phases with reduced interfacial curvature. It indicated that the long rigid cores
of 2T/12 and Tr/12 minimized the interface curvature leading to the formation of columnar
mesophase instead of cubic phase [29,30,31]. Most interestingly, although compounds 2T/n and
Tr/n had the same core lengths, 2T/n formed Colhex/p6mm phases absolutely, whereas the higher
triazole homologues Tr/14 and Tr/16 could self-assemble into Cub /
phases. This meant
Pm3n
I
that for the higher triazole homologues, in order to satisfy the maximum space filling, the
interdigitation of the aromatic cores in the centers of the micelles were required. This could be
realized by the formation of the extra H-bonding between triazole units and terminal
4,6-diaminotriazine groups for the triazole compounds, leading to the formation of the spherical
molecular aggregates. In order to demonstrate whether H-bonding between N atoms of triazole
units and terminal diamino groups existed in LC state, the FT-IR spectra were employed (Fig. 4).
In solid state, the FT-IR spectrum of representative compound Tr/14 showed two characteristic
peaks at 1236.6 cm-1 and 3420.3 cm-1, which can be assigned to N=N stretching vibration of
triazole unit [32] and N-H stretching vibration of amino [33], respectively. Whereas in LC state,
the peak at 1236.6 cm-1 showed obvious blue-shift (from 1236.6 to 1170.2 cm-1) and the peak at

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3420.3 cm-1 became much weaker, indicating that H-bonds existed between N atoms of triazole
units and terminal aminos in LC state of Tr/14. Additionally, the FT-IR spectrum of representative
compound 2T/18 in solid state showed one characteristic peak at 3467.2 cm-1, which can be
assigned to N-H stretching vibration of amino, whereas the peak showed blue shift from 3467.2
cm-1 to 3171.8 cm-1, revealing that only H-bonds between 4,6-diamino-1,3,5-triazine could be
formed in LC state of 2T/18. Therefore for triazole derivatives, polar heterocycle (triazole) could
momentarily joined the H-bonding networks of the 4,6-diamino-1,3,5-triazine, leading to the
larger molecular fluctuations, consequently might lead to the softness of the spherical molecular
aggregates, and this preferred aggregating into a Cub /
phase [34]. The possibility of
Pm3n
I
H-bonding with the polar heterocycle unit might reduce the incompatibility between aromatic core
and 4,6-diamino-1,3,5-triazine to some extent.These effects resulted in a strong interface curvature
and the formation of micellar cubic phases.
(a)
(b)
Fig. 3. (a) Dipole moments and core length of the different heterocycles; (b) bar graph summarizing phase
transitions of the 2T/n and Tr/n under investigation as well as the previously reported 1T/n [12].
(a)
(b)
Fig. 4. FT-IR spectra of (a) 2T/18 and (b) Tr/14 in solid state and LC state.
2.3. Gel properties
Gelation tests of the representative compounds 2T/16, Tr/16 and Tr/14 were performed in several
organic solvents as shown in Table 2. Gel formation of compounds 2T/16, Tr/16 and Tr/14 with
organic solvents was determined by the method “stable to inversion of the container” [35]. The
three compounds could gel organic solvents such as DMF, 1,4-dioxane and ethyl acetate. Scanning

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electron microscopy (SEM) was employed to investigate the morphologies of these xerogels (Fig.
5 and Fig. S10). The SEM image of the xerogel of dithiophene compound 2T/16 formed in ethyl
acetate showed entangled wrinkles (Fig. S10a). Whereas the SEM images of the xerogel of 2T/16
formed in 1,4-dioxane and DMF showed 1D nanobelts with a width of about 125 nm to 1000 nm
and with a length of more than several microns (Fig. 5a-b). Remarkably, triazole compounds
Tr/16 and Tr/14 could form gels with much more interesting morphologies (Fig. 5c-d and Fig.
S10b). The xerogels of both compounds Tr/16 and Tr/14 showed similar morphologies (Fig. 5 and
Fig.S10). For example, the SEM image of the xerogel of Tr/16 formed in ethyl acetate showed
flower-like morphology with diameter of more than 10 ꢀm (Fig. 5c). While the xerogel of Tr/16
obtained from 1,4-dioxane displayed entangled fibres with an average width of 125 nm to 500 nm
(Fig. S10b). Finally lotus leaf-like morphologies with a diameter of approximately 4.5 ꢀm to 16
ꢀm could be observed for the xerogel of Tr/16 obtained from DMF (Fig. 5d). The formation of
gels might be induced by the dipolar-dipolar interaction between polar solvents and heterocycles,
as well as other nonconvalent interactions, such as π-π interaction, hydrogen bonding etc. The
larger dipole moment of the triazole unit and the formation of H-bonds between triazole units and
the terminal amino groups (Fig. S11) might be the reason that the triazole based
4,6-diaminotriazine derivatives form gels with much more complex morphologies than
bisthiophene derivatives.
Table 2. Gelation test results of compounds 2T/16, Tr/16 and Tr/14.[a]
Solvent
Tr/14
Solvent
Tr/14
2T/16 Tr/16
2T/16
Tr/16
Ethyl acetate
Acetone
G
P
G
S
P
S
Chloroform
n-Hexane
S
P
S
G
P
P
G
P
G
P
P
P
G
P
G
S
P
S
P
P
P
G
P
P
S
P
S
G
P
P
DMF
Petroleum ether
1,4-Dioxane
Methanol
Toluene
Acetonitrile
Chloroform
Ethanol
[a]
G = gel; S = soluble; P = precipitation. Gelator concentration is 3.0 mg/mL. Gels formed at room temperature
(20 oC) .

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(b)
(a)
(c)
(d)
Fig. 5. SEM images of the xerogels (a) 2T/16 in 1,4-dioxane; (b) 2T/16 in DMF; (c) Tr/16 in ethyl acetate; (d)
Tr/16 in DMF. The inserts show photographs of gels formed by these compounds, respectively.
XRD mesurement was employed to investigate the assembled structures of the gels (Fig. 6 and
Fig. S12). The XRD parttens of xerogel formed by 2T/16 in DMF showed four small-angle
reflections at 7.70 (001), 2.59 (003), 1.96 (004) and 1.55 (005) nm, revealing that lamellar
structure was formed [36]. The calculated layer distance was 7.70 nm which was much larger than
one molecular length but smaller than two molecular length, indicating that bilayer structure was
formed. The XRD parttens of xerogels formed by 2T/16 in 1,4-dioxane and ethyl acetate (Fig.
S12a,b) as well as the XRD partten of xerogels formed by Tr/16 in DMF (Fig. 6b), 1,4-dioxane
and ethyl acetate (Fig. S12c,d) all indicated that bilayer structures were formed too.
(a)
(b)
Fig. 6. XRD parttens of xerogel of (a) 2T/16 and (b) Tr/16 obtained from DMF.

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It should be noted that although various triazine based LCs have been investigated, only few
organogels based on triazine derivatives have been reported [37,38,39,40,41], and complex gel
morphologies such as flower-like and lotus leaf-like ones have never been reported.
2.4. Chemosensor behaviour
The binding properties of the bisthiophene and triazole based 4,6-diaminotriazine derivatives
toward 10 equiv. of metal ions (such as Ag+, Cd2+, Co2+, Cu2+, Hg2+, K+, Li+, Mg2+, Ni2+, Pb2+,
Zn2+, Fe3+ and Al3+) were evaluated in the solvents of CH3CN : CH2Cl2 = 2 : 1 (v/v). After
addition of Pb2+ and Fe3+ ions, the fluorescence spectra of both 2T/12 and Tr/12 showed obvious
fluorescence quenching, indicating Pb2+ and Fe3+ can be recognized by both compounds 2T/12 and
Tr/12 (Fig. 7 and Fig. S13).
To get further insight into the binding response of 2T/12 and Tr/12 to Pb2+ and Fe3+, the
fluorescence titrations for Pb2+ and Fe3+ were carried out (Fig. S14). For compound 2T/12, with
increasing of Pb2+ (0 equiv. to 1 equiv.) and Fe3+ (0 equiv. to 2 equiv.), the emission peak at 496
nm was gradually decreased and a new emission peak appeared at 587 nm. Finally the emission
peak reached its fluorescence plateau at 1.0 equiv. For compound Tr/12, with increasing of Pb2+ (0
equiv. to 3.0 equiv.) and Fe3+ (0 equiv. to 2 equiv.), the emission peak at 400 nm was gradually
decreased, after addition of 3.0 equiv. of Pb2+ or 1 equiv. of Fe3+, the emission peak reached its
fluorescence quenching plateau (Fig. 7). The detection limits of these two compounds toward Pb2+
and Fe3+ were measured based on 3σ/k [42], the detection limits of 2T/12 to Pb2+ and Fe3+ were
3.70 × 10-6 mol L-1 and 2.87 × 10-6 mol L-1, respectively and those of Tr/12 to Pb2+and Fe3+ were
2.24 × 10-6 mol L-1and 4.63 × 10-6 mol L-1, respectively (Fig. S15). Additionally the fluorescence
Job's plot analysis [43] was analyzed, indicating that 2 : 1 complex can be formed after 2T/12 and
Tr/12 interacting with the recognized metal ions (Fig. S16).
(a)
(b)
Fig. 7. The fluorescence response of 2T/12 and Tr/12 (10-5 M, CH3CN : DCM = 2 : 1) upon adding 10 equiv. of
metal ions at pH = 7.0. (a) 2T/12 λex = 382 nm; (b) Tr/12 λex = 300 nm);
In order to further investigate the coordination sites, FT-IR experiments were performed (Fig.
S17). The FT-IR spectra of 2T/12 and Tr/12 exhibited characteristic peaks at 3464 cm-1 or 3456
cm-1, respectively, which were attributed to stretching vibration of N-H. The FT-IR spectra of
complexes 2T/12-Pb2+ and 2T/12-Fe3+ (Fig. S17a) showed slight blue shift from 3464 cm-1 to

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3434 cm-1 or 3439 cm-1, respectively. Compared with compound Tr/12, the FT-IR spectra of
complexes Tr/12-Pb2+ and Tr/12-Fe3+ also showed slight blue-shift (from 3436 cm-1 to 3423 cm-1
or 3425 cm-1, respectively), indicating that possible binding sites were the N atoms of amino (Fig.
S17b).
3. Conclusion
In conclusion, two series of bisthiophene and triazole based 4,6-diamino-1,3,5-triazine triblock
polyphiles ( 2T/n and Tr/n) with extremely long rigid cores have been obtained by replacing the
thiophene unit with bisthiophene or phenyltriazole units in the rigid cores of the previously
reported monothiophene derivatives (1T/n). Elongation of the rigid cores of the mesogens
enhanced their mesophase stability, therefore both the melting and isotropic temperatures of
longer core compounds 2T/n and Tr/n were higher than those of the previously reported shorter
core monothiophene compounds 1T/n. Simultaneously elongation of the rigid core minimized the
interface curvature, therefore both compounds 2T/12 and Tr/12 display Colhex/p6mm phases with
reduced interfacial curvature, whereas the previously reported shorter core monothiophene
compound T/12 displayed cubic phase with strong interfacial curvature. Most interesting,
although compounds 2T/n and Tr/n had the same core lengths, all compounds 2T/n self
assembled into Colhex/p6mm phases, whereas the higher triazole homologues Tr/14 and Tr/16
could self-assemble into CubI/ phases. The reason is that the more polar triazole units could
momentarily joined the H-bonding networks of the 4,6-diamino-1,3,5-triazine, leading to the
larger molecular fluctuations, reducing the incompatibility between aromatic core and
4,6-diamino-1,3,5-triazine to some extent. These effects resulted in a strong interface curvature
and the formation of micellar cubic phases for the long alkyl chain triazole homologues Tr/14 and
Tr/16. Therefore by combination of heterocycles which are polar and H-bonding groups, into the
rigid aromatic cores of 4,6-diamino-1,3,5-triazine triblock polyphiles, columnar and cubic
morphologies can still be realized in such 4,6-diamino-1,3,5-triazine triblock polyphiles with
extremely long rigid cores.
Additionally gelation and chemosensor properties of such 4,6-diamino-1,3,5-triazine triblock
polyphiles were firstly investigated. These compouds could form organogels in different solvents
with flower-like or lotus leaf-like morphologies. Therefore these compounds could be used as
chemosensors for metal ions.
Acknowledgment
This work was supported by National Natural Science Foundation of China (Nos. 21865038,
21664015, and 21602195) and program for Innovative Research Team (in Science and Technology)
in University of Yunnan Province for financial supports (2018FY001(-012)). We thank beamline
1W2A at Beijing Accelerator Laboratory and beamline BL16B1 at Shanghai Synchrotron
Radiation Facility (SSRF), China.
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Highlights
1) Bisthiophene/triazole diamino triazine triblock polyphiles have been synthesized.
2) They display Colhex/p6mm and Cub /
mesophases despite their long rigid cores.
Pm3n
I
3) These compounds can form organogels in organic solvents with different morphologies.
4) These compounds can act as chemosensor of metal ions.