A BODIPY-based highly emissive dye with thiophene-based branch harvesting the light

Article abstract of DOI:10.1080/15421406.2018.1467613

A novel BODIPY-based dye with highly emissive character was configured by Sonogashira coupling and routinely characterized by NMR and MS technology. The emission of dye was investigated in solution/film/solid and shows intensive emission. In solution, the emission peak appeared around 510?nm with little influence by the polar environment. The terthiophene plays an effective antenna effect, harvesting the light and transferring the energy to BODIPY. The pseudo Stoke's shift enlarged to ～170?nm in solution. In film, the emission peak shifted to 563?nm in polycarbonate matrix. And it shifted further to 585?nm in solid due to the highly twisted structure, which avoided closely regular-tight packing. The dye rendered an intense fluorescence, good optothermal stability, and high fluorescence quantum yield (0.55). The solid emission showed highly red emission with Commission Internationale de L'Eclairage (CIE) coordinates of (X = 0.69, Y = 0.31). Thus, the synthesized dye is idea candidate for emitting materials.

Full text of DOI:10.1080/15421406.2018.1467613

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
A BODIPY-based highly emissive dye with
thiophene-based branch harvesting the light
Xiaochuan Li, Yujie Han, Myeong Jin Kim & Young-A Son
To cite this article: Xiaochuan Li, Yujie Han, Myeong Jin Kim & Young-A Son (2018) A BODIPY-
based highly emissive dye with thiophene-based branch harvesting the light, Molecular Crystals
and Liquid Crystals, 662:1, 157-164, DOI: 10.1080/15421406.2018.1467613
To link to this article: https://doi.org/10.1080/15421406.2018.1467613
Published online: 04 Jun 2018.
Submit your article to this journal
Article views: 6
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=gmcl20

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
https://doi.org/./..
A BODIPY-based highly emissive dye with thiophene-based
branch harvesting the light
Xiaochuan Li a, Yujie Hana, Myeong Jin Kimb, and Young-A Sonb
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, Henan Normal University,
Xinxiang, Henan, P. R. China; bBK, Department of Advanced Organic Materials Engineering, Chungnam National
University, Daejeon, South Korea
ABSTRACT
KEYWORDS
BODIPY dye; CIE; pseudo
Stoke’s shift; solid emission;
terthiophene
A novel BODIPY-based dye with highly emissive character was con-
figured by Sonogashira coupling and routinely characterized by NMR
and MS technology. The emission of dye was investigated in solu-
tion/film/solid and shows intensive emission. In solution, the emission
peak appeared around 510 nm with little influence by the polar environ-
ment. The terthiophene plays an effective antenna effect, harvesting the
light and transferring the energy to BODIPY. The pseudo Stoke’s shift
enlarged to ∼170 nm in solution. In film, the emission peak shifted to
563 nm in polycarbonate matrix. And it shifted further to 585 nm in solid
due to the highly twisted structure, which avoided closely regular-tight
packing. The dye rendered an intense fluorescence, good optothermal
stability, and high fluorescence quantum yield (0.55). The solid emis-
sion showed highly red emission with Commission Internationale de
L’Eclairage (CIE) coordinates of (X = 0.69, Y = 0.31). Thus, the synthesized
dye is idea candidate for emitting materials.
Introduction
Organic π-conjugated fluorescent molecules with intense slid-state fluorescence are of signif-
icant in displaying devices including full-displays, which have attracted the interest of most
chemists and physicists in recent years. Applications related to the fluorescent materials were
found in organic light-emitting diodes (OLEDs), organic solid-state lasers (OSLs), sensors,
bio-images/-markers, and so on [1–7]. Wide applications require different demands on high
emission efficiency, light/thermal stability, white-light sources [8, 9]. In order to reach this
end, intensive efforts have been made and gain tremendous progress in configuration of vari-
ous fluorescence emission. In the visible region, many types of fluorescent molecular engi-
neer were made and the fluorescence spectra almost cover the whole visible region from
blue to deep-red. To this day, many types of emissive dye, such as coumarin, naphthalimide,
bisindolylmalimide, perylenediimides, rhodamine, and F-B complexes, are easy accessible
CONTACT Prof. Young-A Son
Chungnam National University,  Daehakro, Yuseong, Daejeon , South Korea; Prof. Xiaochuan Li
lixiaochuan@htu.edu.cn School of Chemistry and Chemical Engineering, Henan Normal University, East Jianshe Rd.
yason@cnu.ac.kr
Department of Advanced Organic Materials Engineering,
, Xinxiang, Henan , China.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
©  Taylor & Francis Group, LLC

158
X. LI ET AL.
and could be structurally modified as one expected due to the highly emissive character and
optothermal stability [10–18]. Additionally, the fluorescent dyes are desired to be high quan-
tum yield, structurally controllable emission [19, 20]. Among these materials four-coordinate
boron compounds have proven to be effective luminescent materials with wide usage
[21–24]. The molecular framework of boron-containing compounds could be modified for
the desired properties by altering ligands or substituents on the boron atoms. Red, green, and
blue emission has been realized by structural modification, and certain boron compounds
exhibit bright emission in the solid state. The structurally varies can not only enhance the
electron deficiency of the π-system through intramolecular electron delocalization but also
intensify the emission by constraining molecular rotations. The typical example of F-B com-
plexes is 4,4ꢀ-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY), which displays outstanding
stability and emission quantum yields. Continuous efforts are still underway to improve and
broaden its properties and application scope. 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 [25–28].
In this contribution, a branch based on thiophene ring was introduced to the framework of
BODIPY. The thiophene unit could harvest the UV light and the energy transfer to BODIPY
efficiently, thus radiation the energy by light (fluorescence). In this way, the Stoke’s shift of
BODIPY can be significant enlarged, avoiding re-absorbance. Detailed investigation about
the dye will be given in the following text.
Experimental
General procedures and materials
The solvents used in the reaction were carefully dried according to the standard procedure
˚
and stored over 4A molecular sieve. All the reagent-grade chemicals were purchased from
Sigma-Aldrich CO. LLC. (South Korea) and used without further purification. Melting points
were determined on a Mel-Temp IA9200 digital melting point apparatus in a glass capillary
®
and were uncorrected. All synthesized compounds were routinely characterized by TLC and
1H NMR. TLC was performed on aluminum-backed silica gel plates (Merck DC. Alufolien
Kieselgel 60 F254).
NMR spectroscopy and high resolution mass spectra (HRMS)
Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker AM-400 spectrome-
ter operating at frequencies of 400 MHz for proton in CDCl3. Proton chemical shifts (δ) are
relative to tetramethylsilane (TMS, δ = 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 spectrometer. High resolution mass spectra (HRMS)
were measured on a Bruker micrOTOF II Focus instrument.
UV-Vis and emission spectra
The absorption spectra were measured with a PERSEE TU-1900 and an Agilent 8453 spec-
trophotometer. Emission spectra were measured with Shimadzu RF-5301PC fluorescence
spectrophotometer. The solvents used in photochemical measurement were spectroscopic

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
159
Scheme . Synthesis of BT.
grade and were purified by distillation. The stock solution of compounds (2 × 10−3 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.
Preparation thin film
The solution for dye films was prepared by dissolving dye (2 mg) and polycarbonate (40 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 homogeneous dye solution.
The solution was then employed in the fabrication of films by using a spin coating tech-
nique. The quartz substrates (Ø = 20 mm) was fixed on the pallet of spin-coating instrument
(KW-4A). The solution is allowed to fall on rotating substrates 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.
Synthesis
The BODIPY dye was synthesized as depicted in Scheme 1. The thiophene-based branch
was synthesized according to the literature report [29]. Alkynyl was introduced by Sono-
gashira coupling reaction and yield 6. Subsequent desilicication could give 7. 10 was synthe-
sized according to the routine procedure as BODIPY. Finally, the target dye was coupled by
Sonogashira coupling between 7 and 10.
10-(3-((5,5ꢀꢀ-dimethyl-[2,2ꢀ:3ꢀ,2ꢀꢀ-terthiophen]-BODIPY (BT)
Under an atomosphere 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

160
X. LI ET AL.
Table . Optical data of BT in selected solvents.
UV-Vis
λabs (nm)
Fluorescence
Solvent
log εmax
λem (nm)
ꢀF
Stokes shift (nm)
Pseudo Stokes shift (nm)
Hexane
/
/
/
/
/
/
/
/
./.
./.
./.
./.
./.
./.
./.
./.






.
.
.
.
.
.
.
.
















Chloroform
Dioxane
THF
Ethyl Acetate
Acetonitrile
Ethanol


DMF
aFull width at half maximum is abbreviated as FWHM.
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 (50 mL). Then combined 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 50 mg (86%).
Mp: 183–186°C; 1H NMR (400 MHz, CDCl3): δ 7.69 (s, 2H), 7.62 (d, J = 6.5 Hz, 1H), 7.46
(s, 1H), 7.38 (s, 1H), 6.95 (d, J = 3.5 Hz, 1H), 6.86 (d, J = 3.5 Hz, 1H), 6.66 (d, J = 2.6 Hz, 2H),
5.99 (s, 2H), 2.56 (s, 6H), 2.46 (d, J = 6.3 Hz, 6H), 1.44 (s, 6H). 13C NMR (100 MHz, CDCl3):
δ 161.6, 153.3, 150.2, 146.3, 144.47, 143.7, 140.7, 139.4, 138.4, 137.1, 136.4, 135.5, 133.9, 129.9,
129.3, 128.6, 128.1, 127.4, 127.1, 126.1, 125.3, 123.3, 122.4, 120.0, 115.5, 93.8, 83.9, 16.8, 16.0,
14.4, 13.6, 13.4. HRMS calcd for C35H29BF2N2S3Na 645.1452, found 645.1459 [M+Na]+.
Results and discussion
The absorption behavior of BT was investigated in various polarities solvent, such as hex-
ane, chloroform, THF, dioxane, ethanol, DMF, etc. Due to the terthiophene’s substitution,
BT exhibits excellent solubility in organic medium with different polarity. Additionally, the
substitution of terthiophene does not induce any change of stability. Just as other BODIPY
analogues, BT is optothermal resistance. Even in DMF or DMSO, no degradation was found
after several days’ exposure of daylight. The fundamental absorption/emission peaks, absorp-
tion coefficient, quantum yields, and Stokes shifts are collected in Table 1. Figure 1 shows the
absorption spectra of BT in various solvents. The absorption spectra are of similar shape with
each other. There strong absorption band can be found around 500 nm and a shoulder band
(470 nm) at the shorter wavelength side. The molar absorption coefficients of BT are relatively
high and lie in the 4.90–5.03 (log ε) range. The absorption spectra are only barely affected by
solvent polarity with the maximum absorption value being slightly shifted hypsochromically
(∼3 nm) when the solvent is changed from nonpolar hexane to polar DMF, which is con-
sistent with the general behavior of BODIPY analogues [19]. It should be noted that there is
another absorption band at shorter wavelength side. This absorption could ascribe to the con-
tribution of terthiophene substitution. The longest maximum absorption could be ascribe to
S0→S1 transition 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 theS0→S2 tran-
sition. Absorption longer than 550 nm is almost optically transparent. Due to the appearance
of shorter wavelength absorption, a new option was opened for the fluorescence excitation.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
161
THF
Ethyl acetate
EtOH
Chloroform
Hexane
DMF
1.0
0.8
0.6
0.4
0.2
0.0
MeCN
Dioxane
350
400
450
500
550
600
Wavelength / nm
Figure . Absorption spectra of BT in selected solvents (. × − M).
Notably, BT exhibited intense fluorescence in most of the investigated organic solvents.
Their detailed emission parameters are listed in Table 1. Figure 2 presents the emission
profile in the selected solvents. BT shows the typical emission features of BODIPY analogues,
that is, strong green emission and narrow emission band. The emission maximum varied
around 510 nm with only several nanometers shift. Furthermore, the polar environment
does not induce emission shift. The emission profile is almost the mirror image of the
maximum absorption, which is in agreement with the Kasha’s rule. The quantum yields in the
selected solvents were determined ranging from 0.08 to 0.81 with reference to quinine sulfate
(ꢀ = 0.55, 0.1N H2SO4) as a standard. These values demonstrate BT is a green organic emit-
ter. Moreover, the tails of emission bands beyond 530 nm are very weak, which is important
for the purity of green emission. The Stokes shift (ꢁν), calculated from the wavelengths
of maximum intensity is only 12 nm, which is similar to the character of most BODIPY
derivatives. Shorter Stoke’s shift largely limited the application of BODIPY derivatives in
biotechnology and material science due to the excitation interference. The attaching of
Chloroform
DMF
300
EA
EtOH
Hexane
MeCN
THF
250
200
150
100
50
Dioxane
0
525
550
575
600
Wavelength / nm
Figure . Emission spectra of BT in selected solvents (. × − M). Emission and excitation slit widths were
set to be  nm.

162
X. LI ET AL.
Film
Solid
1.0
0.8
0.6
0.4
0.2
0.0
500
550
600
650
700
750
Wavelength (nm)
Figure . EmissionspectraofBT infilmatwt.%inpolycarbonateandinsolid-state.Emissionandexcitation
slit widths were set to be  nm.
terthiophene to BODIPY framework contributes a shorter wavelength absorption band at
340 nm. Therefore, the green emission could be realized upon 340 nm excitation, which can
significant enlarge the gap between excitation and emission. The pseudo Stoke’s shifts were
estimated to be ∼174 nm. It also demonstrates an efficient energy transfer from terthiophene
to BODIPY, giving great potential in material science and bio-technology application.
Organic materials with π-conjugated framework usually display red-shifted absorption
and emission spectra in condensed phases because of strong intermolecular interactions.
Figure 3 shows the emission of BT in film- and solid-state. In polycarbonate matrix, the
Figure . CIE  chromaticity coordinate of BT in solution/film/solid.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
163
dye molecules can be well separated in matrix and surrounded by the polymer chain. It
also avoided over-tight packing between dye molecules, which could lead to significant
fluorescence quench. In film, the emission peak was found at 563 nm, which shifted 49 nm
compared with those of the solution samples. The excited dye molecule is easy to dissipate
part of the absorbed energy through polymer matrix and fall into lower energy state (S1),
thus emit at longer wavelength side than that in solution. In addition, the polar environment
of polymer lattices also contributes to the film emission bathochromic shift. The solid
emission shifted furtherly 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 fluorescence. Tightly packing model in solid state enhanced the energy loss by
nonradiation transition through solid environment, in contrast to that in polycarbonate
film, leading to a further red-shift of fluorescence emission. The neat thin film and the
solid powders of BT are both brightly red-orange emissive. The solid-state fluorescence
quantum yield determined by an integrating sphere was 0.55. Additionally, the terthiophene
leads to highly twisted structure, which prevents the molecules from regular and close
approaching to its neighbors by the steric hindrance of terthiophene substituents on the
BODIPY framework. It also indicates that the emission in solid state mainly originate from
intermolecular interactions like π-stacking having a significant effect on the emission behav-
iors. The emission color in solution/film/solid was indicated by CIE chromaticity system
(Fig. 4). In solution, the CIE coordinates scattered all in green region. In film, the emission
color moves to green-yellow part (CIEx = 0.42, CIEy = 0.57) and it moved to red part
(CIEx = 0.69, CIEy = 0.31) furtherly. Therefore, the emitting character is of great potential
in configuration of emissive dyes in post-functionalization according to the emitting device
required.
Conclusions
In summary, a BODIPY-based dye with terthiophene attached was designed in this work and
full characterized by NMR and MS technology. The absorption and emission behavior were
investigated in solution, in film and in solid. Due to the terthiophene substitution, a shorter
absorption band appeared around 340 nm. It provides a selection to enlarge the Stoke’s shift.
Indeed, the pseudo Stoke’s shift can reach to more than 170 nm. Terthiophene play a func-
tion of antenna effect. All the emission color is indicated by CIE 1931 chromaticity system.
The highly efficient emission in solution and in solid phases with narrow bandwidths is of
great potential in material science and biotechnology. The present study not only provides
BODIPY-based materials with high emissive character, but also gives an indication of design
principles toward efficient energy transfer by attaching thiophene-based branch.
Funding
This work was supported by the National Natural Science Foundation of China (21772034), and
the Program for Innovative Research Team in University of Henan Province (15IRTSTHN003). This

164
X. LI ET AL.
study was supported by the Basic Science Research Pro-gram through the National Research Founda-
tion of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (Grant No. NRF-
2017R1E1A1A01074266).
ORCID
Xiaochuan Li http://orcid.org/0000-0002-6903-9574
References
[1] Figueira-Duarte, T. M., & Müllen, 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] Zhao, Y. S. et al. (2010). Acc. Chem. Res., 43, 409.
[6] Tatum, L. A., Su, X., & Aprahamian, I. (2014). Acc. Chem. Res., 47, 2141.
[7] Fukazawa, A., & Yamaguchi, S. (2009). Chem.-Asian J., 4, 1386.
[8] Kido, J., Kimura, M., & Nagai, K. (1995). Science, 267, 1332.
[9] Frient, R. H. et al. (1999). Nature, 397, 121.
[10] Oelgemoller, M., & Kramer, W. H. (2010). J. Photoch. Photobio. C, 11, 210.
[11] Wu, W.–C., Yeh, H.-C., Chan, L.–H., & Chen, C.–T. (2002). Adv. Mater., 14, 1072.
[12] Chen, C.-T. (2004). Chem. Mater., 16, 4389.
[13] Li, X., Xu, Y., Wang, B., & Son, Y.–A. (2012). Tetrahedron Lett., 53, 1098.
[14] Li, X., Zhao, N., Yu, L., & Son, Y.–A. (2015). Mol. Cryst. Liq. Cryst., 608, 273.
[15] Li, X., & Son, Y.–A. (2015). J. Nanosci. Nanotechnol., 15, 5370.
[16] Li, X., Zhang, J., & Son, Y.–A. (2015). J. Nanosci. Nanotechnol., 15, 5366.
[17] Ramanan, C., Kim, C. H., Marks, T. J., & Wasielewski, M. R. (2014). J. Phys. Chem., 118, 16941.
[18] Beija, M., Afonso, C. A. M., & Martinho, J. M. G. (2009). Chem. Soc. Rev., 38, 2410.
[19] Loudet, A., & Gurgess, K. (2007). Chem. Rev., 107, 4891.
[20] Li, X., Ji, G., J, J.–M., & Son, Y.-A. (2016). Mol. Cryst. Liq. Cryst., 636, 159.
[21] Ulrich, G., Goze, C., Guardigli, M., Roda, A., & Ziessel, R. (2005). Angew. Chem. Int. Ed., 44, 3694.
[22] Goze, C., Ulrich, G., & Ziessel, R. (2007). J. Org. Chem., 72, 313.
[23] Cheng, C. et al. (2015). Org. Lett., 17, 278.
[24] Jiao, L. et al. (2014). J. Org. Chem., 79, 1830.
[25] Frath, D., Massue, J., Ulrich, G., & Ziessel, R. (2014). Angew. Chem. Int. Ed., 53, 2290.
[26] Li, X., & Son, Y.-A. (2014). Dyes Pigm., 107, 1827.
[27] Chibani, S., Charaf-Eddin, A., Guennic, B. L., & Jacquemin, D. (2013). J. Chem. Theory Comput.,
9, 3127.
[28] Massue, J., Frath, D., Ulrich, G., Retailleau, P., & Ziessel, R. (2012). Org. Lett., 14, 230.
[29] Xia, C., Fan, X., Locklin, J., & Advincula, R. C. (2002). Org. Lett., 4, 2067.