Thiophene Modulated BODIPY Dye as a Light Harvester

Article abstract of DOI:10.1080/15421406.2019.1597557

A new BODIPY dye with terthiophene branched is configured by Sonogashira coupling and fully characterized by NMR and MS. In general organic solvents, it emits typical green fluorescence ranging in 513-518 nm, like most BODIPY analogues. The terthiophene substitution is greatly improved and the emission peak does not sensitive to the polarity environment. More importantly, the terthiophene plays the role of antenna, harvesting the 340 nm’s excitation energy and transferring the energy to BODIPY efficiently. Even though the molar extinction coefficient in 340 nm is lower than that of maximum absorption, it can enlarge the pseudo Stoke’s shift to ～170 nm, well separating the excitation and emission. In film, the emission shifted to 562 nm due to the polymer chain dissipation part of the energy. It shifted further to 585 nm in solid. The branched terthiophene configures a twisted molecular conformation, which avoids the dye regular packing. Highly emission, excellent solubility and stability constitute the general character of the thiophene attached BIDIPY dye.

Full text of DOI:10.1080/15421406.2019.1597557

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: https://www.tandfonline.com/loi/gmcl20
Thiophene Modulated BODIPY Dye as a Light
Harvester
Xiaochuan Li, Meifei Liao, Jia Sun, Gisu Heo & Young-A Son
To cite this article: Xiaochuan Li, Meifei Liao, Jia Sun, Gisu Heo & Young-A Son (2019)
Thiophene Modulated BODIPY Dye as a Light Harvester, Molecular Crystals and Liquid Crystals,
679:1, 127-136, DOI: 10.1080/15421406.2019.1597557
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
2019, VOL. 679, NO. 1, 127–136
https://doi.org/10.1080/15421406.2019.1597557
Thiophene Modulated BODIPY Dye as a Light Harvester
Xiaochuan Lia,b, Meifei Liaoa, Jia Suna, Gisu Heoc, and Young-A Sonc
aHenan Key Laboratory of Organic Functional Molecule and Drug Innovation, Collaborative Inovation
Center of Henan Province for Green Manufacturing of Fine Chemicals, Key Laboratory of Green
Chemical Media and Reactions, Ministry of Education, School of Chemistry and Chemical Engineering,
b
Henan Normal University, Xianxiang, Henan, P. R. China; Jiangxi Key Laboratory of Organic Chemistry,
c
Jiangxi Science & Technology Normal University, Nanchang 330013, P. R. China; Chungnam National
University, Department of Advanced Organic Materials Engineering, Daejeon 305-764, S. Korea
KEY WORDS
ABSTRACT
BODIPY dye; Stoke’s shift;
fluorescence emission;
thiophene
A new BODIPY dye with terthiophene branched is configured by
Sonogashira coupling and fully characterized by NMR and MS. In
general organic solvents, it emits typical green fluorescence ranging
in 513-518 nm, like most BODIPY analogues. The terthiophene substi-
tution is greatly improved and the emission peak does not sensitive
to the polarity environment. More importantly, the terthiophene
plays the role of antenna, harvesting the 340nm’s excitation energy
and transferring the energy to BODIPY efficiently. Even though the
molar extinction coefficient in 340nm is lower than that of max-
imum absorption, it can enlarge the pseudo Stoke’s shift to
ꢀ170 nm, well separating the excitation and emission. In film, the
emission shifted to 562nm due to the polymer chain dissipation
part of the energy. It shifted further to 585nm in solid. The
branched terthiophene configures a twisted molecular conformation,
which avoids the dye regular packing. Highly emission, excellent
solubility and stability constitute the general character of the thio-
phene attached BIDIPY dye.
1. Introduction
Organic fluorescence dyes could emit single or multi-color light in doping to polymer
or in solid state are of great potential in advanced material design and biological explor-
ation. And the design and synthesis of various types of fluorescent dyes have been put
forward with meticulous effort by the chemists and physicists. Documentation related
to fluorescent materials and devices increase progressively with years in organic light-
emitting diodes (OLEDs), organic solid-state lasers (OSLs), probes, dye sensitized solar
cell, molecular rotors, and so on [1–8]. Further application based on fluorescent dyes
requires higher emission efficiency, multi-emission, single molecule white-light emis-
sion, and super stability [9–14]. In order to reach this end, intensive efforts have been
made and tremendous progresses in dye molecular configuration have been obtained. In
the visible region, many types of fluorescent dyes are fully developed and the fluores-
cence spectra covers whole visible region, including near infrared and part far infrared
region. To this day, the typical emissive dyes, such as coumarin, naphthalimide,
CONTACT X. Li
lixiaochuan@henannu.edu.cn; Y.-A. Son
yason@cnu.ac.kr
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
ß 2019 Taylor & Francis Group, LLC

128
X. LI ET AL.
bisindolymalimide, perylenediimides, rhodamine, and F-B complexes, have been widely
accepted and structurally modified as the materials required in emissive character and
optothermal stability [15–24]. Recently, scientists have been testified the newly observed
aggregation induced emission (AIE) and vibration induced emission (VIE) mechanisms,
which opens a new area to fluorescent dyes [8, 25–27]. Among various fluorescent dyes,
fluorine-boron containing compounds have been proved to be effective luminescent
materials in many fields [28–33]. The F-B containing compounds could be structural
modified for the desired properties by ligands or substituents alteration. Red and far red
emissive molecular structures have been configured and exhibits intensive fluorescence
in various micro-environment. The structurally varies can not only enhance the electron
deficiency of the p-system through intramolecular electron delocalization but also inten-
sify the emission by constraining molecular rotations. BODIPY (4,4’-difluoro-4-bora-
3a,4a-diaza-s-indacene) derivatives is the typical F-B complex. Additionally, different
chelating modes were also developed to expand the F-B family including ditopic
(N ꢀ C, C ꢀ C, C ꢀ O, O ꢀ O) or tritopic boron complexes [12, 29, 34].
In this contribution, a thiophene unit configured branch is attached to the framework
of BODIPY. Harvesting UV light and transferring the energy to the BODIPY could sig-
nificantly extends the Stoke’s shift and avoids the overlap between excitation and emis-
sion. Detailed investigation about the dye will be given in the following text.
2. Experiment
2.1. General Procedures and Materials
The solvents used in the reaction were carefully dried according to the standard proced-
ure and stored over 4Å molecular sieve. All the reagent-grade chemicals were purchased
from Sigma-Aldrich CO. LLC. (South Korea) and used without further purification. All
1
synthesized compounds were routinely characterized by TLC and H NMR. TLC was
performed on aluminum-backed silica gel plates (Merck DC. Alufolien Kieselgel
60 F254).
2.2. NMR spectroscopy and High Resolution Mass spectra (HRMS)
Nuclear magnetic resonance (NMR) spectra were recorded on a Brucker AM-400 spec-
trometer operating at frequencies of 400 MHz for proton in CDCl3. Proton chemical
shifts (d) are relative to tetramethylsilane (TMS, d ¼ 0) as internal standard and
expressed in parts per million. Spin multiplicities are given as s (singlet), d (doublet), t
(triplet), and m (multiplet) as well as b (broad). Coupling constants (J) are given in
Hertz. The mass spectra measured on a LC-MS (Waters UPLC-TQD) mass spectrom-
eter. High resolution mass spectra (HRMS) were measured on a Brucker micrOTOF II
Focus instrument.
2.3. UV-Vis, Emission spectra, Emission decay, and Quantum yield
The absorption spectra were measured with a PERSEE TU-1900 and an Agilent 8453
spectrophotometer. Emission spectra were measured with Shimadzu RF-5301PC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
129
fluorescence spectrophotometer. The solvents used in photochemical measurement were
spectroscopic grade and were purified by distillation. The stock solution of compounds
(2 ꢁ 10ꢂ3 M) was prepared and a fixed amount of these concentrated solutions were
added to each experimental solution. All the experiments were done repeatedly, and
reproducible results were obtained. Prior to the spectroscopic measurements, solutions
were deoxygenated by bubbling nitrogen through them. Emission decay was determined
on FLS980 and absolute fluorescence quantum yields by using a calibrated integrating
sphere system on FLS980.
2.4. Preparation thin film
The solution for dye films was prepared by dissolving dye (3 mg) and polycarbonate
(120 mg) in 3 mL chloroform. The result solution were stirred with a micro magnetic
bar for 20 h and aged at room temperature for 20 h, in order to yield a clear and homo-
geneous dye solution. The solution was then employed in the fabrication of films by
using a spin coating technique. The quartz substrates (Ø ¼ 20 mm) was fixed on the pal-
let of spin-coating instrument (KW-4A). The solution is allowed to fall on rotating sub-
strates from microsyringe. The spin speed was set to be 500 rpm for 30 s, and then
accelerated to 2000 rpm for 120 s. The produced uniform thin film was used in emission
measurement.
3. Synthesis
The target dye is synthesized as shown in Scheme 1. Thiophene branch is synthesized
according to the literature report [35]. Alkynyl was introduced by Sonogashira coupling
reaction, yielding 6. Subsequent desilicication gives 7. 10 is obtained by routinely syn-
thetic procedure for BODIPY. Finally, 7 is coupled with 10 by Sonogashira coupling to
yield the target dye.
3.1. 10-(3-((5,500-dimethyl-[2,20:30,200-terthiophen]-BODIPY (BYT)
Under an atmosphere of dry argon, 10 (50.6 mg, 0.15 mmol), 7 (66.3 mg, 0.165 mmol),
Pd(PPh3)4 (5.2 mg, 0.005 mmol), CuI (4.3 mg, 0.023 mmol) was mixed with THF (5 mL)
in a flame dried Schlenk tube. After stirring for 15 min, Et3N (4 mL) was added and the
mixture was stirred at room temperature for 5 h. After 10 and 7 were full reacted, as
confirmed by TLC, the mixture was poured to cool water 50 mL. The organic phase was
separated and the water phase was extracted with dichloromethane (50mL). Then com-
bined organic phase was dried over Mg2SO4. After the solvent was removed, the residue
was loaded to the column (200–300 mesh) and eluted by hexane:dichloromethane (2:1)
to give yellow powder 74.4 mg (80%).
1H NMR (400 MHz, CDCl3): d 7.65 (d, J ¼ 8.3 Hz, 2H), 7.30 (s, 1H), 7.28 (s, 2H),
6.97 (d, J ¼ 3.5 Hz, 1H), 6.88 (d, J ¼ 3.4 Hz, 1H), 6.68 (d, J ¼ 2.6 Hz, 2H), 6.00 (s, 2H),
2.56 (s, 6H), 2.48 (d, J ¼ 5.5 Hz, 6H), 1.43 (s, 6H). 13C NMR (100 MHz, CDCl3): 160.2,
154.6, 150.1, 149.8, 147.8, 146.3, 142.3, 137.9, 137.2, 137.8, 136.6, 135.5, 132.9, 130.8,
129.4, 128.1, 127.1, 126.2, 125.8, 122.5, 123.4, 123.0, 122.4, 115.5, 95.1, 83.4, 16.6, 16.0,

130
X. LI ET AL.
Scheme 1. Synthesis of BYT.
Figure 1. Absorption spectra of BYT and BODIPY in selected solvents (1.0 ꢁ 10ꢂ5 M).
14.7, 13.8, 13.4. HRMS (ESI): [M þ H]þ C35H30BF2N2S3 requires 623.1632, found
[M þ H]þ 623.1636.
4. Result and discussion
The absorption behavior of BYT is investigated in the selected organic solvents, includ-
ing chloroform, 1,4-dioxane, tetrahydrofuran (THF), and acetonitrile,(Figure 1). Due to
the terthiophene’s attachment, BYT exhibits excellent solubility not only in the above
organic medium but also in the weak polar solvent, such as hexane and toluene. Also,
terthiophene’s attachment does not induce obvious change in stability. Similar to most
of BODIPY analogues, BYT is optothermal resistance. Even after several days’ exposure
of room light, no degradation could be found. The fundamental absorption/emission

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
131
Table 1. Optical data of BYT in selected solvents.
UV-Vis
Fluorescence
ET Efficiency
(%)
Stokes shift
(nm)
Pseudo Stokes
shift (nm)
Solvent
kabs (nm)
log emax
kem (nm)
UF
FWHMa
chloroform
dioxane
THF
344/504
342/502
341/502
338/499
4.57/5.03
4.53/5.02
4.53/5.02
4.49/4.96
518
513
516
513
0.58
0.51
0.46
0.23
26
26
26
27
0.97
0.96
0.95
0.95
14
11
14
14
174
171
175
175
acetonitrile
aFull width at half maximum is abbreviated as FWHM.
Figure 2. Emission spectra of BYT in selected solvents (1ꢁ 10ꢂ5 M). Insert: CIE 1931 chromaticity dia-
gram of the emissions of BYT in solution.
peaks, absorption coefficient, quantum yields, and Stokes shifts are collected in Table 1.
Figure 1 shows the absorption profile of BYT and BODIPY. The absorption profiles are
of similar shape. The maximum absorption band around 500 nm can be observed with
a shoulder band around 470 nm at the shorter wavelength side. In absorption, BYT
inherits the character of BODIPY analogues with high absorption coefficient (log e:
4.96 ꢀ 5.03) and almost identical absorption band. The absorption profile is barely
affected by the polar environment even though the solvent polarity changed from
chloroform to acetonitrile (hypsochromic shift about 5 nm), demonstrating its insensi-
tivity toward polarity [15]. Another significant absorption character is medium absorp-
tion (440 nm) at shorter wavelength side, which could ascribe to the contribution of
terthiophene moiety. The longest maximum absorption could be ascribe to S0!S1 tran-
sition with the bands on the high- and low-energy side corresponding to 0–1 and 0–0
vibration transition, respectively. 400 nm’s absorption can be identified as the S0!S2
transition [14, 15]. Absorption longer than 550 nm is almost optically transparent. The
shorter wavelength side absorption, contributed by terthiophene, provides an alterna-
tively fluorescence excitation.
BYT inherits the highly emissive character of BODIPY and emits intense green fluor-
escence in the organic solvents. Their detailed emission parameters are listed in Table 1.
Figure 2 shows the emission profile in the selected solvents. The maximum emission
band is same to the BODIPY core, locating around 510 nm with only several

132
X. LI ET AL.
nanometers shift. Furthermore, the polar environment does not induce significant shift.
The emission profile is almost the mirror image of the maximum absorption band,
which is in agreement with the Kasha’s rule. Absolute fluorescence quantum yields of
BYT in the selected solvents are estimated in the range of 0.23-0.58 by calibrated inte-
grating sphere, which is slightly lower than the parent BODIPY (0.62 in methanol) [15].
Moreover, the tails of emission bands beyond 530 nm is very weak, demonstrating a
pure green emission. The Stoke’s shift (Dꢀ), calculated form the wavelength of max-
imum intensity is only 26 nm, similar to the character of most BODIPY analogues. Due
to the shorter Stoke’s shift set limitation in biological application and materials require-
ment due to the excitation interference. However, the attaching of terthiophene to
BODIPY framework added a new absorption band at the shorter wavelength side
(340 nm), which is well separated from the BODIPY’s excitation. Even though the molar
extinction coefficient is lower than that of BODIPY, the BODIPY’s green emission
could be realized upon shorter wavelength excitation and enlarge the gap between exci-
tation and emission. The pseudo Stoke’s shifts are estimated to be ꢀ170 nm. The reason
behind this phenomenon is the efficient energy transfer from terthiophene to BODIPY,
giving great potential in biological design and device fabrication. Generally, terthio-
phene, the energy donor, has no emission in the range of 475-600 nm, where the
BODIPY unit exhibits fluorescence. When excited with 340 nm that terthiophene
absorbed, negligible fluorescence emission was observed in 400-475 nm, supporting the
energy transfer to the acceptor BODIPY unit. Whether excited at 340 or 500 nm, only
the BODIPY’s emission can be detected. Consistent with the absorption spectra, slightly
emission shift of BYT indicates a very weak electronic coupling between the terthio-
phene and BODIPY units. The energy transfer efficiency, E, can be calculated with the
following equation with I and I0 represented the fluorescence intensity of the donor in
the presence and absence of the acceptor [36]. In BYT, the energy transfer efficiency
was estimated to be 95-97%.
I
E ¼ 1ꢂ
I0
€
Within the framework of the Forster formulation, an effective interaction radius (R0,
the distance at which transfer efficiency is 50%) can be calculated form the steady-state
spectra and the fluorescence quantum yield of the donor chromophore (/D) with the
following equation where j2 is a constant depending on donor-acceptor orientation
(ranging from 0.77 for parallel to 0.69 for perpendicular orientation), /D is the donor
fluorescence quantum yield (/terthiophene ¼ 0.15), n is the refractive index of the solvent,
and J is the spectral overlap integral [37, 38]. Based on the fluorescence (terthiophene)
and absorption spectra (BODIPY), the overlap integral, J, give the critical radius
R0 ¼ 36 Å.
j2/DJ
n4
R0 ¼ 8:875 ꢁ 10ꢂ5
Å
Generally, dye molecule with larger p-conjugate system red-shift its absorption and
emission spectra in condensed phase due to intermolecular interactions and energy level
interference [39]. Figure 3 shows the emission of BYT in film- and solid-state. In poly-
carbonate matrix, the dye molecules can be well separated in matrix. Surrounding by
the polymer matrix, the energy dissipation through polymer chain lower the energy
level of S1 in the excited state and leads the emission red-shifting to longer wavelength.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
133
Figure 3. Emission spectra of BYT in film at 5 wt.%in polycarbonate and in solid-state. Emission and
excitation slit widths were set to be 3 nm. Insert: CIE 1931 chromaticity diagram of the emissions of
BYT in film and solid.
In film, the emission peak is estimated to be 562 nm, shifting 49 nm in comparison with
the solution samples. The excited dye molecule dissipate part of the excitation energy
by vibrational relaxation through the polymer chain, thus emit at longer wavelength
side. In addition, the polar environment of polymer lattices also contributes to the film
emission bathochromic shift. Unlike film, the solid emission shifted fatherly to 585 nm.
Obviously, the emission energy in solid was lowered by dissipating part of the energy in
nonradiation way. The solid powder is obtained by evaporation of dye sample in
chloroform. Therefore, the solid powder is of microcrystalline morphology, in which
the dye molecules were packed more tightly than that in film. The stronger interaction
between dye molecules dissipate more energy to adjacent dye molecules efficiently, and
then return to ground state by radiation transition, emitting more lower energy fluores-
cence. The aggregation state in solid is of great influence in energy loss by nonradiation
transition by micro-environment, in contrast to that in film, leading to a further red-
shift of fluorescence emission. The neat thin film and the solid powders of BYT are
both brightly red-orange emissive. The solid-state fluorescence quantum yield is deter-
mined to be 0.58. More importantly, the terthiophene unit is a twisted conformation,
which prevents the molecules from regular and closely approaching to its neighbors.
Steric hindrance derived from terthiophene on BODIPY enhances the barrier of energy
dissipation and inhibits the aggregate induced fluorescence quench. However, the
vibronic levels of S1 in excited state must increase in some degree when the molecular
packing changing from loosening to tight. It can be deduced from the broadened
FWHM of emission spectra in film and sold. FWHM are determined as 40 and 53 nm
for film and solid emission, respectively. The emission color in film/solid was indicated
by CIE chromaticity system (Fig. 4). In solution, the emission color gathers in green
region (Fig. 2 insert). In film, the emission color moves to yellow-green part (x ¼ 0.42,
y ¼ 0.57) and it moves to orange part in solid furtherly (x ¼ 0.54, y ¼ 0.46)
(Fig. 3 insert).

134
X. LI ET AL.
Figure 4. Time-correlated single photon-counting fluorescence decay curves of BYT in film and sold.
(Excitation wavelength: 404 nm, pulse width:100 ns).
Because the radiative and nonradiative deactivation rates are key factors emission
character, lifetimes are also useful tool to get insight of the excited state dynamics.
Time-resolved fluorescence measurements were carried out with a time-correlated sin-
gle-photon counting (TCSPC) spectrometer using pulsed 404 nm laser light. The emis-
sion decay of BYT both in film and solid determines to be mono-exponential decay
function. The fluorescence lifetime were estimated to be 4.33 and 5.62 ns. The mono-
exponential decay function indicates that the energy levels of excited dye molecules do
not to be interfered significantly by the aggregation sate, which could leads to larger
FWHM or multiemission behavior. Therefore, the emitting character is of great poten-
tial in configuration of single- or multi-color combination light sources.
5. Conclusions
In summary, a terthiophene attached BODIPY derivative is configured in this contribu-
tion and routinely characterized by NMR and MS technology. Absorption and emission
behavior are investigated in selected organic solvents. Due to the attachment of terthio-
phene, a newly absorption band around 340 nm at the shorter wavelength side is found.
Excitation at this band could well avoid the emission band. The pseudo Stoke’s shift
estimates to be about 170 nm, which is larger than that of the most BODIPY analogues.
Terthiophene plays the role of antenna, absorbing excitation energy and transferring to
BODIPY efficiently. All the emission color is characterized by CIE 1931 chromaticity
system. The green emission is almost same to the BODIPY. The highly emission behav-
ior in film and solid state with FWHM around 40 and 53 nm is promising in material
science and bio-application. The above investigation not only provides a clue in dye
configuration, but also directs the next step in post-function.
Acknowledgement
This research work was supported by the National Natural Science Foundation of China (Grant
no. 21772034, 21877027) and the Program for Innovative Research Team in University of Henan

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
135
Province (Grant No. 19IRTSTHN023). This study was supported by the Basic Science Research
Pro-gram through the National Research Foundation of Korea (NRF) funded by the Ministry of
Science, ICT and Future Planning (Grant No. NRF-2017R1E1A1A01074266).
References
[1] Figueira-Duarte, T. M., & Mu€llen, K. (2011). Chem. Rev., 111, 7260.
[2] Anthony, J. E. (2006). Chem. Rev., 106, 5028.
[3] Saragi, T. P. I., Spehr, T., Siebert, A., Fuhrmann-Lieker, T., & Salbeck, J. (2007). Chem.
Rev., 107, 1011.
[4] Hudson, Z. M., &Wang, S. (2009). Acc. Chem. Res., 42, 1584.
[5] Zhang, Z., Chen, C.-L., Chen, Y.-A., Wei, Y.-C., Su, J., Tian, H., & Chou, P.-T. (2018).
Angew. Chem. Int. Ed., 57, 9880.
[6] Lin, T.-Z., Sarma, M., Chen, Y.-T., Liu, S.-H., Lin, K.-T., Chiang, P. Y., Chuang, W.-T.,
Hsu, H.-F., Hung, W.-Y., Tang, W.-C., Wong, K.-T., & Chou, P.-T. (2018). Nature
Commun., 9, 3111.
[7] Vendrell, M., Zhai, D., Er, J. C., & Chang, Y.-T. (2012). Chem. Rev., 112, 4391.
[8] Mei, J., Hong, Y., Lam, J. W. Y., Qin, A., Tang, Y., & Tang, B. Z. (2014). Adv. Mater., 26,
5429.
[9] Li, X., Han, Y., Min, K., & Son, Y.-A. (2018). Mol. Cryst. Liq. Cryst., 660, 10.
[10] Li, D., Hu, W., Wang, J., Zhang, Q., Cao, X.-M., Ma, X., & Tian, H. (2018). Chem. Sci., 9,
5709.
[11] Li, X., Sun, S., Kim, I. J., & Son, Y.-A. (2017). Mol. Cryst. Liq. Cryst., 654, 139.
[12] Li, X., & Son, Y.-A. (2014). Dyes Pigm., 107, 182.
[13] Schiphorst, J., Kendhale, A. M., Debije, M. G., Menelaou, C., Herz, L. M., & Schenning,
A. P. H. J. (2014). Chem. Mater., 26, 3876.
[14] Li, X., Ji, G., & Son, Y.-A. (2016). Dyes Pigm., 124, 232.
[15] Loudet, A., & Burgess, K. (2007). Chem. Rev., 107, 4891.
[16] Li, X., Ji, G., Jung, J.-M., & Son, Y.-A. (2016). Mol. Cryst. Liq. Cryst., 636, 159.
[17] Chen, X., Pradhan, T., Wang, F., Kim, J. S., & Yoon, J. (2012). Chem. Rev., 112, 1910.
[18] Li, X., Li, A., Jiang, W., & Son, Y.-A. (2017). Mol. Cryst. Liq. Cryst., 645, 1.
[19] Slberti, D., Grang, C., Prota, S., Aime, S., Tei, L., & Crich, S. G. (2018). ACS Omeg, 3, 8097.
ꢀ
[20] Zhang, Q.-W., Li, D., Li, X., White, P. B., Mecinovic, J., Ma, X., Ågren, H., Nolte,
R. J. M., & Tian, H. (2016). J. Am. Chem. Soc., 138, 13541.
[21] He, L., Yang, X., Xu, K., Yang, Y., & Li, W. (2017). Chem. Commun., 53, 13168.
€
[22] Wu€thner, F., Saha-Moller, C. R., Fimmel, B., Ogi, S., Leowanawat, P., & Schmidt, D.
(2016). Chem. Rev., 116, 962.
[23] Beija, M., Afonso, C. A. M., & Martinho, J. M. G. (2009). Chem. Soc. Rev., 38, 2410.
[24] Fu, Y., Han, H.-H., Zhang, J., He, X.-P., Feringa, B. L., & Tian, H. (2018). J. Am. Chem.
Soc., 140, 8671.
[25] Zhange, Y., Wu, Y.-S., Tang, K.-C., Chen, C.- L., Ho, J.-W., Su, J., Tian, H., & Chou, P.-
T. (2015). J. Am. Chem. Soc., 137, 8509.
[26] Hu, R., Leung, N. L. C., & Tang, B. Z. (2014). Chem. Soc. Rev., 443, 4494.
[27] Ding, D., Li, K., Liu, B., & Tang, B. Z. (2013). Acc. Chem. Res., 46, 2441.
[28] Ulrich, G., Ziessel, R., & Harriman, A. (2008). Angew. Chem. Int. Ed., 47, 1184.
[29] Frath, D., Massue, J., Ulrich, G., & Ziessel, R. (2014). Angew. Chem. Int. Ed., 53, 2290.
[30] Li, X., Sun, S., Kim, I. J., & Son, Y.-A. (2017). Mol. Cryst. Liq. Cryst., 654, 131.
[31] Ulrich, G., Goze, C., Guardigli, M., Roda, A., & Ziessel, R. (2005). Angew. Chem. Int. Ed.,
44, 3694.
[32] Goze, C., Ulrich, G., & Ziessel, R. (2007). J. Org. Chem., 72, 313.
[33] Sheng, W., Wu, Y., Yu, C., Bobadova-Parvanova, P., Hao, E., & Jiao, L. (2018). Org. Lett.,
20, 2620.

136
X. LI ET AL.
[34] Lakshmi, V., Haketa, Y., Yamakado, R., Yasuda, N., & Maeda, H. (2017). Chem.
Commun., 53, 3834.
[35] Xia, C., Fan, X., Locklin, J., & Advincula, R. C. (2002). Org. Lett., 4, 2067.
[36] Lantzsch, G., Binder, H., & Heerklotz, H. (1994). J. Fluores., 4, 339.
[37] Cerullo, G., Stagira, S., Zavelani-Rossi, M., De Silverstri, S., Virgili, T., Lidzey, D. G., &
Bradly, D. D. C. (2001). Chem. Physics Lett., 335, 27.
[38] Maus, M., R. De, M. Lor, T. Weil, S. Mitra, U.-M. Wieslere, A. Herrmann, J. Hofkens, T.
Vosch, K. Mu€llen, & F. C. De Schryver, (2001). J. Am. Chem. Soc. 123, 7668.
[39] Zhou, Y., Xiao, Y., Chi, S., & Qian, Y. (2008). Org. Lett., 10, 633.