Development of Solid-State Emissive Materials Based on Multifunctional o-Carborane-Pyrene Dyads

Article abstract of DOI:10.1021/acs.orglett.6b01920

The molecular design based on o-carborane dyads is described for preparing multifunctional luminescent molecules such as dual emissions, aggregation and crystallization-induced emission enhancements, and luminescent color changes. The pyrene-substituted o-carborane dyads were synthesized via the insertion reaction between decaborane and 1-ethynylpyrene in the presence of Lewis base in a good yield. Finally, extremely bright luminescent compounds with solid-state emission properties (φ_PL > 0.99) were obtained.

Full text of DOI:10.1021/acs.orglett.6b01920

Letter
pubs.acs.org/OrgLett
Development of Solid-State Emissive Materials Based on
Multifunctional o‑Carborane−Pyrene Dyads
Kenta Nishino, Hideki Yamamoto, Kazuo Tanaka,* and Yoshiki Chujo*
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
S
* Supporting Information
ABSTRACT: The molecular design based on o-carborane dyads is described for
preparing multifunctional luminescent molecules such as dual emissions, aggregation and
crystallization-induced emission enhancements, and luminescent color changes. The
pyrene-substituted o-carborane dyads were synthesized via the insertion reaction between
decaborane and 1-ethynylpyrene in the presence of Lewis base in a good yield. Finally,
extremely bright luminescent compounds with solid-state emission properties (ΦPL
0.99) were obtained.
>
olid-state emissive compounds composed of conjugated
molecules have attracted much attention as a versatile
donor−acceptor interaction should be significantly enhanced at
the perpendicular conformation between the C−C bond in o-
carborane and the conjugated plane involving the directly
connected aromatic unit to o-carborane.9 It can be said that
such structural anisotropy should be unique characteristics of o-
carborane-based electronic acceptors.
S
platform for realizing advanced optically functional materials
and organic light-emitting devices. To receive highly functional
devices, the development of key building blocks which can
induce solid-state emission is a topic with high relevance. One
of the crucial difficulties to be solved in the development of
solid-state emissive molecules is aggregation-caused quenching
(ACQ) which is generally observed as a critical annihilation
process in the condensed state. Contrary to conventional
organic dyes showing ACQ, it was found that some classes of
organic dyes1 and recently organoboron complexes2 can
present bright emission only in the aggregation state. These
phenomena are called aggregation-induced emission (AIE) or
AIE enhancement (AIEE). Since the application of solid-state
emission from AIE-active molecules to the material design
should be a valid strategy to overcome ACQ, new AIE-active
molecules and comprehension of photochemical mechanism
for their emissions are of great significance to receive highly
efficient solid-state emissive materials.3
o-Carborane is a class of boron cluster compounds composed
of two carbon and ten boron atoms (1,2-dicarba-closo-
dodecaborane) and has been focused as an optically functional
“element-block”4 which is defined as a functional heteroatom-
containing building block.5 In particular, since the first report
on the AIE-active o-carborane polymers, o-carborane is
recognized as an AIE-inducible “element block”.6 o-Carborane
works as an electron-withdrawing group because of the
electron-deficient characteristics of skeletal electrons delocal-
ized via the 3-center-2-electron bonds.7 Therefore, by
combination with the electron-donating groups or aromatic
units, robust electronic conjugation can be constructed via the
σ*−π* conjugation, leading to large emission bands from the
intramolecular charge transfer (ICT) transition.8 The vibration
at the C−C bond in o-carborane consumed excitation energy,
resulting in the annihilation in the solution state.6a In contrast,
strong emission can be recovered in the solid state by
suppressing this intramolecular motion. Thus, AIE properties
can be obtained. Moreover, it was proposed that the degree of
Herein, we report the molecular design based on o-carborane
dyads for preparing multifunctional luminescent molecules such
as dual emissions, AIEE, crystallization-induced emission
enhancement (CIEE), luminescent chromism, and highly
efficient solid-state emissions. Initially, the pyrene-substituted
o-carborane dyad was synthesized, and dual emissions were
observed in the solution state. It was revealed that these
emissions were assigned as locally excited (LE) and ICT
emission bands. Additionally, it was clarified that the dyad had
an AIEE property attributable to the ICT emission band.
Furthermore, in the aggregation and crystalline states, large
emission efficiencies were obtained (ΦPL = 0.40 and 0.80,
respectively). It was suggested that the rotation at the
carborane moiety could occur even in the solid state, leading
to the twisted intramolecular charge transfer (TICT)
emission.10 On the basis of this speculation, to confirm the
TICT mechanism and to improve the solid-state emissive
abilities by completely suppressing molecular motions, the
methyl and TMS-substituted carborane dyads were prepared.
Finally, extremely bright luminescent compounds with solid-
state emission properties (ΦPL > 0.99) were obtained. This
manuscript presents the feasible “element block” as an optically
multifunctional unit based on o-carborane.
The synthesis of o-carborane dyads was performed according
to Scheme 1. 1-(Trimethylsilyl)ethnylpyrene was obtained
from 1-bromopyrene through the Sonogashira−Hagihara
coupling reaction with PdCl2(PPh3)2 as a catalyst. Then the
trimethylsilyl (TMS) group was removed in the presence of
tetrabutylammonium fluoride. Finally, CBP-H having orange
Received: July 5, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.6b01920
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Letter
the eq (Figure 1b).11 It was indicated that the slope of the
approximate line prepared from the emission band around 400
nm was almost zero. On the other hand, the significant keen
slope was obtained from the plots with the peak positions
observed around 600 nm. These data indicate that the
luminescent bands around 400 and 600 nm should be assigned
to the LE state of the pyrene moiety and the ICT state,
respectively. Usually, the emission band from the LE state can
be observed only under frozen or structurally restricted
environmental conditions.12 The intramolecular rotation
could be disturbed even in the solution state. Additionally,
the transition dipole moment was estimated as 10.73 D
according to the Lippert−Mataga equation. This value is
relatively larger than those of previous luminescent dyes with
ICT emission properties.11 It is suggested that structural
alteration could proceed in the excited state.
To examine the possibility of the structural alteration during
the ICT process, PL spectra were monitored with variable
temperatures from 10 to 50 °C (Figure S12). Accordingly, it
was indicated that the ratios between the magnitude of the CT
emission and that of the LE emission increased by increasing
the detection temperature. This behavior was often observed in
the emission from the TICT mechanism.13 Furthermore, from
the PL spectrum recorded at 77 K, only the LE emission was
obtained (Figure S13). These data strongly support that the
dual-emission properties of CBP-H should be from the LE and
TICT states.
Scheme 1. Synthesis of o-Carborane−Pyrene Dyads
emission was obtained by the insertion reaction of 1-
ethynylpyrene into decaborane (Figure S21). By introducing
methyl and TMS groups at another carbon in o-carborane,
CBP-Me and CBP-TMS possessing green and yellow
emissions were obtained, respectively (Figures S22 and S23).
1
The product was characterized by H, 11B, and 13C NMR and
mass measurements and an elemental analysis. The product
showed good stability toward air and light under ambient
conditions. From these data, we concluded that the product
possessed the designed structure and stability high enough for
the optical measurements.
Initially, optical properties were evaluated in the diluted
solution for examining the intrinsic electronic properties of the
dyad. Figure 1a shows the photoluminescence (PL) spectra of
To estimate the relationship between the dihedral angle
which is defined as the directional difference between the C−C
bond in the o-carborane moiety and the pyrene group and
optical properties, quantum calculation was performed by using
density functional theory (DFT) and time-dependent DFT
(TD-DFT). As mentioned in the introduction, the degree of
electronic interaction should be enhanced in the perpendicular
conformation between the C−C bond in the o-carborane
moiety and the aryl group. On this basis, electronic structures
were investigated with two types of conformations including
parallel and perpendicular distributions (Figure 2). The
Figure 1. (a) PL spectra of pyrene (dashed line) and CBP-H (solid
line). All samples were measured in THF (1.0 × 10−5 M) and excited
at 351 nm. All spectra were normalized at λmax. (b) Lippert−Mataga
plots of CBP-H. Gray and black dots represent emission peaks in
shorter and longer wavelength regions, respectively. (c) PL spectra of
CBP-H in the THF solution (solid line), water suspension (dotted
line), and crystalline state (dashed line).
CBP-H and pyrene as the model compound in THF. Pyrene
showed the vibrational emission peaks around 400 nm.
Correspondingly, CBP-H also presented a similar spectral
pattern around the same region. Interestingly, the broad
emission band with a peak around 600 nm was obtained. The
emission intensity of this broad emission band in the longer
wavelength region was much larger than that in the shorter
wavelength region. According to the kinetic data as listed in
Table S2, these emissions should be fluorescent. Moreover,
phosphorescence was hardly observed from any compounds.
To investigate the emission mechanism from CBP-H, the
changes in absorption and PL spectra were monitored with
variable solvents such as hexane, benzene, dichloromethane,
chloroform, acetone, and acetonitrile (Figures S10 and S11).
Significant peak shifts were hardly observed in the absorption
spectra. In contrast, drastic peak shifts were shown from the
broad emission band in the longer wavelength region in the PL
spectra. By increasing solvent polarity, red-shifted emissions
were obtained. To analyze the solvatochromic luminescence,
the Lippert−Mataga plots were prepared with the values of the
Stokes shift against the solvent polarizability, Δf, according to
Figure 2. Calculated structure and molecular orbitals of CBP-H in the
ground (left) and excited states. ψ values mean a dihedral angle
between pyrene and the C−C bond in o-carborane. The differences of
total energy (ΔE) and energy levels of each orbital were calculated at
the B3LYP/6-31G(d) level by DFT and the B3LYP/6-31+G(d) level
by TD-DFT.
difference between them was represented as the dihedral
angle (ψ) between the pyrene moiety and the C−C bond in o-
carborane. In the parallel distribution, it was shown that both
the highest occupied molecular orbital (HOMO) and the
lowest unoccupied molecular orbital (LUMO) were localized at
the pyrene moiety. In contrast, LUMO in the perpendicular
distribution was delocalized over the whole molecule through
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σ*−π* conjugation. Therefore, the LE and ICT states were
attributable to the parallel and perpendicular distributions,
respectively. Next, the energy levels of each state were
calculated (Table S1). Five hydrogens on the o-carborane
moiety are located around the pyrene-connecting bond.
Therefore, the pyrene moiety should have the steric repulsion
with these hydrogens. Hence, it is difficult to have completely
planar and perpendicular conformations (0° and 90°) toward
the C−C bond in the o-carborane. Indeed, in the ground state,
the parallel distributions (ψ = 26.6° and 180.0°) were
energetically more stable than the perpendicular distribution
(ψ = 103.4°). In contrary, the perpendicular distribution (ψ =
97.3°) was much favorable compared to the parallel
distributions (ψ = 19.3° or 179.9°) in the excited state. From
these data, the TICT process should be responsible for the
emission of the o-carborane−pyrene dyads.
of this idea, CBP-Me and CBP-TMS with strong emissions
(Figures S22 and S23) were synthesized by the conversion
from the lithiated CBP-H with methyl iodide and trimethylsilyl
chloride, respectively (Scheme 1). Similarly to CBP-H, the
1
characterizations of the products were executed with H, 11B,
and 13C NMR spectroscopies, mass measurements, and
elemental analyses. The products presented good stability
toward air and light under ambient conditions. Thus, we
concluded that the desired dyads can be obtained.
From the PL measurements in the crystalline state, the broad
emission bands were observed in the regions similar to that of
the TICT emission of CBP-H (Figures S15 and S16). It should
be emphasized that both dyads showed extremely high
quantum efficiencies (ΦPL > 0.99) in the crystal state (Table
1). From the PL spectra at 77 K, contrary to CBP-H, CBP-Me
and CBP-TMS presented not vibrational emission bands but
broad large ones attributable to the ICT emissions at 547 and
578 nm, respectively (Figures S17 and S18). It is likely that the
intramolecular rotation should be prohibited because of steric
hindrances of the substituents in o-carborane. The correspond-
ing energy levels were obtained from the computer calculations
(Figures S19 and S20). From these data, it can be said that o-
carborane should be a versatile “element-block” not only for
realizing multifunctional materials but also for designing highly
efficient solid-state luminescent dyes.
Next, solid-state emission properties of CBP-H were
evaluated. To the solution of THF was added water (water/
THF v/v = 99/1), and the change in emission intensity was
monitored (Figure 1c, Table 1). Apparently, white turbidity
Table 1. Summary of Emission Properties of the Dyads
THF
λem (nm)
water
λem (nm)
crystal
λem (nm) ΦPL
a
a
a
R
ΦPL
ΦPL
H
401, 631
611
0.16
0.41
0.19
596
584
599
0.40
0.60
0.73
618
545
579
0.80
0.99
0.99
Me
TMS
401, 632
It should be mentioned that the o-carborane dyads
demonstrated luminescent chromism toward various external
stimuli. Solvatochromic luminescence was induced owing to
both the intrinsic sensitivity of the ICT state to the
environmental polarity and the intensity ratios between the
LE and ICT emissions.11 CBP-H presented clear thermo-
chromism by cooling. By regulating the rotation efficiency of
the o-carborane moiety by temperature changes, the intensity
ratio between the LE and TICT emissions can be tuned,
leading to luminescent chromism. Finally, phase transition
induced luminescent chromism with the o-carborane dyads. By
aggregation and crystallization, the peak shifts of the emission
bands were observed. In the condensed state, the molecules
should be placed under hydrophobic conditions, and then the
blue shifts of the ICT emission from each o-carborane dyad
could be obtained by phase changes.
In conclusion, we present the validity of the o-carborane unit
for constructing multifunctional emissive materials. On the
basis of variable degrees of electronic interaction between o-
carborane and pyrene depending on the dihedral angle, bright
ICT was observed. From the solution sample, it was also
proposed that the intramolecular rotation could be disturbed in
the excited state, leading to the dual-emissive property.
Additionally, it was shown that because of the sphere structural
feature of o-carborane, the molecular rotation can proceed even
in the solid state. Then AIEE and CIEE were obtained.
Moreover, ACQ could be efficiently suppressed. As a result, the
solid-state emission was observed. Finally, in this study, by
significantly suppressing the molecular rotation in the dyads
with large substituents, an extremely highly efficient solid-state
emission could be detected. From these data, we can say that o-
carborane-based dyads should be facile “element block”
advance emission devices and bioprobes.
a
Determined as an absolute value with an integration sphere.
appeared, indicating the formation of the aggregation.
Correspondingly, the intense broad emission band around
600 nm attributable to the TICT emission was obtained with
the larger emission efficiency. Moreover, the large emission
efficiency was observed from the crystalline sample prepared by
recrystallization than those from the aggregation as well as the
THF solution. These data involve two significant issues.
According to the larger values of emission efficiencies in both
aggregation and crystalline samples than that in the solution, it
is clearly indicated that CBP-H possesses not only AIEE but
also CIEE properties.6a,14 Furthermore, it was suggested that
CBP-H should be capable of presenting the TICT emission in
the solid state. In the PL spectrum of the crystalline sample
with CBP-H at 77 K (Figure S14), new emission bands were
detected with the peaks around 400 and 450 nm. In particular,
the emission band around 400 and 450 nm can be assigned to
emissions from the LE state and the excimer as observed in the
solution at 77 K, respectively. These results demonstrate that
CBP-H can provide significant emission from the TICT state.
In other words, the intramolecular rotation at the o-carborane
moiety can be preserved even in the crystalline state. Because of
the sphere structural feature of o-carborane, the ACQ should be
suppressed. As a result, solid-state emission can be obtained via
the TICT transition. The emission band around 450 nm which
appeared in the water suspension could be originated from the
excimer. It is likely that pyrene moieties should be condensed,
leading to the excimer formation.
Based on the solid-state TICT emission from CBP-H, CBP-
Me and CBP-TMS were designed for further enhancement to
the solid-state emission efficiencies. The substituent at another
carbon atom in o-carborane can effectively inhibit rotation at
the pyrene unit. Therefore, much stronger emission could be
expected from the crystalline samples. To confirm the validity
C
DOI: 10.1021/acs.orglett.6b01920
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Chem., Int. Ed. 2012, 51, 2677. (e) Harder, R. A.; MacBride, J. A. H.;
Rivers, G. P.; Yufit, D.; Goeta, A. E.; Howard, J. A. K.; Wade, K.; Fox,
M. A. Tetrahedron 2014, 70, 5182. (f) Kahlert, J.; Stammler, H.-G.;
Neumann, B.; Harder, R. A.; Weber, L.; Fox, M. A. Angew. Chem., Int.
Ed. 2014, 53, 3702. (g) Mukherjee, S.; Thilagar, P. Chem. Commun.
2016, 52, 1070.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.6b01920.
■
S
(6) (a) Kokado, K.; Chujo, Y. Macromolecules 2009, 42, 1418.
(b) Naito, H.; Morisaki, Y.; Chujo, Y. Angew. Chem., Int. Ed. 2015, 54,
5084. (c) Tominaga, M.; Naito, H.; Morisaki, Y.; Chujo, Y. New J.
Chem. 2014, 38, 5686. (d) Tominaga, M.; Naito, H.; Morisaki, Y.;
Chujo, Y. Asian J. Org. Chem. 2014, 3, 624. (e) Inagi, S.; Hosoi, K.;
Kubo, T.; Shida, N.; Fuchigami, T. Electrochemistry 2013, 81, 368.
(f) Kokado, K.; Nagai, A.; Chujo, Y. Tetrahedron Lett. 2011, 52, 293.
(g) Kokado, K.; Nagai, A.; Chujo, Y. Macromolecules 2010, 43, 6463.
(h) Bae, H. J.; Kim, H.; Lee, K. M.; Kim, T.; Lee, Y. S.; Do, Y.; Lee, M.
H. Dalton Trans. 2014, 43, 4978. (i) Choi, B. H.; Lee, J. H.; Hwang,
H.; Lee, K. M.; Park, M. H. Organometallics 2016, 35, 1771.
(7) (a) Tsuboya, N.; Lamrani, M.; Hamasaki, R.; Ito, M.; Mitsuishi,
M.; Miyashita, T.; Yamamoto, Y. J. Mater. Chem. 2002, 12, 2701.
(b) Huh, J. O.; Kim, H.; Lee, K. M.; Lee, Y. S.; Do, Y.; Lee, M. H.
Chem. Commun. 2010, 46, 1138. (c) Lee, K. M.; Huh, J. O.; Kim, T.;
Do, Y.; Lee, M. H. Dalton Trans. 2011, 40, 11758.
Synthetic procedures, NMR data, optical spectra, and
calculation results (PDF)
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: kazuo123@chujo.synchem.kyoto-u.ac.jp.
*E-mail: chujo@chujo.synchem.kyoto-u.ac.jp.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was partially supported by a Grant-in-Aid for
Scientific Research on Innovative Areas “New Polymeric
Materials Based on Element-Blocks (No.2401)” (JSPS
KAKENHI Grant No. JP24102013).
(8) (a) Kokado, K.; Chujo, Y. Dalton Trans. 2011, 40, 1919.
(b) Kokado, K.; Chujo, Y. J. Org. Chem. 2011, 76, 316. (c) Boyd, L. A.;
Clegg, W.; Copley, R. C. B.; Davidson, M. G.; Fox, M. A.; Hibbert, T.
G.; Howard, J. A. K.; Mackinnon, A.; Peace, R. J.; Wade, K. Dalton
Trans. 2004, 2786. (d) Kwon, S.; Wee, K.-R.; Cho, Y.-J.; Kang, S. O.
Chem. - Eur. J. 2014, 20, 5953.
REFERENCES
■
(1) (a) Luo, J.; Xie, Z.; Lam, J. W. Y.; Cheng, L.; Chen, H.; Qiu, C.;
Kwok, H. S.; Zhan, X.; Liu, Y.; Zhu, D.; Tang, B. Z. Chem. Commun.
(9) (a) Weber, L.; Kahlert, J.; Brockhinke, R.; Bohling, L.;
̈
2001, 1740. (b) Tong, H.; Hong, Y.; Dong, Y.; Haußler, M.; Lam, J.
̈
Brockhinke, A.; Stammler, J.-G.; Neumann, B.; Harder, R. A.; Fox,
M. A. Chem. - Eur. J. 2012, 18, 8347. (b) Kim, S.-Y.; Lee, A.-R.; Jin, G.
F.; Cho, Y.-J.; Son, H.-J.; Han, W.-S.; Kang, S. O. J. Org. Chem. 2015,
W. Y.; Li, Z.; Guo, Z.; Guo, Z.; Tang, B. Z. Chem. Commun. 2006,
3705. (c) An, B.-K.; Kwon, S.-K.; Jung, S.-D.; Park, S. Y. J. Am. Chem.
Soc. 2002, 124, 14410.
80, 4573. (c) Weber, L.; Kahlert, J.; Bohling, L.; Brockhinke, A.;
̈
(2) (a) Yoshii, R.; Nagai, A.; Tanaka, K.; Chujo, Y. Chem. - Eur. J.
2013, 19, 4506. (b) Kumbhar, H. S.; Deshpande, S. S.; Shankarling, G.
S. Dyes Pigm. 2016, 127, 161. (c) Liu, Q.; Wang, X.; Yan, H.; Wu, Y.;
Li, Z.; Gong, S.; Liu, P.; Liu, Z. J. Mater. Chem. C 2015, 3, 2953.
(d) Kubota, Y.; Kasatani, K.; Takai, H.; Funabiki, K.; Matsui, M.
Dalton Trans. 2015, 44, 3326. (e) Wang, X.; Wu, Y.; Liu, Q.; Li, Z.;
Yan, H.; Ji, C.; Duan, J.; Liu, Z. Chem. Commun. 2015, 51, 784.
(f) Zheng, J.; Huang, F.; Li, Y.; Xu, T.; Xu, H.; Jia, J.; Ye, Q.; Gao, J.
Dyes Pigm. 2015, 113, 502. (g) Mukherjee, S.; Thilagar, P. Chem. - Eur.
J. 2014, 20, 9052. (h) Li, Z.; Lv, X.; Chen, Y.; Fu, W.-F. Dyes Pigm.
2014, 105, 157. (i) Perumal, K.; Garg, J. A.; Blacque, O.; Saiganesh, R.;
Kabilan, S.; Balasubramanian, K. K.; Venkatesan, K. Chem. - Asian J.
2012, 7, 2670. (i) Quan, L.; Chen, Y.; Lv, X.-J.; Fu, W.-F. Chem. - Eur.
J. 2012, 18, 14599.
(3) (a) Yoshii, R.; Suenaga, K.; Tanaka, K.; Chujo, Y. Chem. - Eur. J.
2015, 21, 7231. (b) Butler, T.; Morris, W. A.; Samonina-Kosicka, J.;
Fraser, C. L. ACS Appl. Mater. Interfaces 2016, 8, 1242. (c) Wu, D.;
Shao, L.; Li, Y.; Hu, Q.; Huang, F.; Yu, G.; Tang, G. Chem. Commun.
2016, 52, 541. (d) Shimizu, S.; Murayama, A.; Haruyama, T.; Iino, T.;
Mori, S.; Furuta, H.; Kobayashi, N. Chem. - Eur. J. 2015, 21, 12996.
(e) Dai, C.; Yang, D.; Zhang, W.; Fu, X.; Chen, Q.; Zhu, C.; Cheng,
Y.; Wang, L. J. Mater. Chem. B 2015, 3, 7030. (f) Gong, S.; Liu, Q.;
Wang, X.; Xia, B.; Liu, Z.; He, W. Dalton Trans. 2015, 44, 14063.
(g) Fu, Y.; Qiu, F.; Zhang, F.; Mai, Y.; Wang, Y.; Fu, S.; Tang, R.;
Zhuang, X.; Feng, X. Chem. Commun. 2015, 51, 5298. (h) Butler, W.
A.; Morris, T.; Samonina-Kosicka, J.; Fraser, C. L. Chem. Commun.
2015, 51, 3359. (i) Wang, L.; Zhang, Z.; Cheng, X.; Ye, K.; Li, F.;
Wang, Y.; Zhang, H. J. Mater. Chem. C 2015, 3, 499. (j) Yan, W.; Long,
G.; Yang, X.; Chen, Y. New J. Chem. 2014, 38, 6088.
Stammler, H. G.; Neumann, B.; Harder, R. A.; Low, P. J.; Fox, M. A.
Dalton. Trans. 2013, 42, 2266. (d) Weber, L.; Kahlert, J.; Brockhinke,
R.; Bohling, L.; Halama, J.; Brockhinke, A.; Stammler, H. G.;
̈
Neumann, B.; Nervi, C.; Harder, R. A.; Low, P. J.; Fox, M. A. Dalton.
Trans. 2013, 42, 10982. (e) Park, J.; Lee, Y. H.; Ryu, J. Y.; Lee, J.; Lee,
M. H. Dalton Trans. 2016, 45, 5667−5675. (f) Wee, K.-R.; Cho, Y.-J.;
Song, J. K.; Kang, S. O. Angew. Chem., Int. Ed. 2013, 52, 9682.
(10) Dong, H.; Wei, Y.; Zhang, W.; Wei, C.; Zhang, C.; Yao, J.; Zhao,
Y. S. J. Am. Chem. Soc. 2016, 138, 1118.
(11) Valeur, B. Molecular Fluorescence; Wiley-VCH: Weinheim, 2002.
(12) (a) Okamoto, A.; Tainaka, K.; Nishiza, K.; Saito, I. J. Am. Chem.
Soc. 2005, 127, 13128. (b) Tanaka, K.; Jeon, J.-H.; Inafuku, K.; Chujo,
Y. Bioorg. Med. Chem. 2012, 20, 915.
(13) (a) Cao, C.; Liu, X.; Qiao, Q.; Zhao, M.; Yin, W.; Mao, D.;
Zhang, H.; Xu, Z. Chem. Commun. 2014, 50, 15811. (b) Hu, R.; Lager,
E.; Aguilar-Aguilar, A.; Liu, J.; Lam, J. W. Y.; Sung, H. H. Y.; Williams,
I. D.; Zhong, Y.; Wong, K. S.; Pena-Cabrera, E.; Tang, B. Z. J. Phys.
̃
Chem. C 2009, 113, 15845. (c) Ito, A.; Ishizaka, S.; Kitamura, N. Phys.
Chem. Chem. Phys. 2010, 12, 6641. (d) Grabowski, Z. R.; Rotkiewicz,
K.; Rettig, W. Chem. Rev. 2003, 103, 3899.
(14) (a) Yoshii, R.; Hirose, A.; Tanaka, K.; Chujo, Y. Chem. - Eur. J.
2014, 20, 8320. (b) Yoshii, R.; Hirose, A.; Tanaka, K.; Chujo, Y. J. Am.
Chem. Soc. 2014, 136, 18131.
(4) Chujo, Y.; Tanaka, K. Bull. Chem. Soc. Jpn. 2015, 88, 633.
(5) (a) Peterson, J. J.; Werre, M.; Simon, Y. C.; Coughlin, E. B.;
Carter, K. R. Macromolecules 2009, 42, 8594. (b) Lerouge, F.; Ferrer-
Ugalde, A.; Vinas, C.; Teixidor, F.; Sillanpaa, R.; Abreu, A.; Xochitiotzi,
̃
̈
̈
E.; Farfan, N.; Santillan, R.; Nunez, R. Dalton Trans. 2011, 40, 7541.
́
́
̃
(c) Dash, B. P.; Satapathy, R.; Gaillard, E. R.; Norton, K. M.; Maguire,
J. A.; Chug, N.; Hosmane, N. S. Inorg. Chem. 2011, 50, 5485. (d) Wee,
K.-R.; Han, W.-S.; Cho, D. W.; Kwon, S.; Pac, C.; Kang, S. O. Angew.
D
DOI: 10.1021/acs.orglett.6b01920
Org. Lett. XXXX, XXX, XXX−XXX