Twisted Bodipy Derivative as a Heavy-Atom-Free Triplet Photosensitizer Showing Strong Absorption of Yellow Light, Intersystem Crossing, and a High-Energy Long-Lived Triplet State

Article abstract of DOI:10.1021/acs.orglett.0c01903

A Bodipy derivative with twisted π-conjugation system is demonstrated that shows efficient intersystem crossing (ISC) (singlet oxygen quantum yield φΔ = 55%) and a long-lived triplet state (τT = 197.5 μs) with high energy (ET1 = 1.44-1.53 eV). This is superior to the conventional heavy-atom-enhanced ISC in a reference Bodipy compound, which results in much shorter triplet state lifetime (3.3 μs) and lower triplet-state energy (1.2 eV).

Full text of DOI:10.1021/acs.orglett.0c01903

pubs.acs.org/OrgLett
Letter
Twisted Bodipy Derivative as a Heavy-Atom-Free Triplet
Photosensitizer Showing Strong Absorption of Yellow Light,
Intersystem Crossing, and a High-Energy Long-Lived Triplet State
Yu Dong, Bernhard Dick, and Jianzhang Zhao*
Cite This: https://dx.doi.org/10.1021/acs.orglett.0c01903
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: A Bodipy derivative with twisted π-conjugation system
is demonstrated that shows efficient intersystem crossing (ISC)
(singlet oxygen quantum yield ΦΔ = 55%) and a long-lived triplet
state (τT = 197.5 μs) with high energy (ET = 1.44−1.53 eV). This is
1
superior to the conventional heavy-atom-enhanced ISC in a reference
Bodipy compound, which results in much shorter triplet state lifetime
(3.3 μs) and lower triplet-state energy (1.2 eV).
riplet photosensitizers (PSs) feature strong visible-light
harvesting, efficient intersystem crossing (ISC), and long-
Another novel yet not fully investigated method for
enhancing ISC is twisted π-conjugation-induced ISC. Pre-
viously, ISC was observed for perylenebis(imide) (PBI)
chromophores with twisted structures12 as well as for twisted
hydrocarbons.13 It was confirmed that the deviation of the π-
conjugation framework from planarity enhances the SOC for
helicene derivatives and π-conjugated polymers.14 However,
helicenes usually show weak absorption of visible light and are
difficult to derivatize. Some porphyrins with twisted structures
also show ISC,15 but their synthesis is challenging. The
photophysical properties of some Bodipy derivatives with
twisted structures have been reported, and such derivatives
have been used as fluorescent bioimaging agents.16 However,
the ISC ability of twisted Bodipy PSs has rarely been studied.17
Therefore, novel heavy-atom-free compounds with twisted π-
conjugation frameworks and simple and feasibly derivatizable
molecular structures that show high ISC efficiency and strong
visible-light harvesting ability are highly desired.
T
lived triplet states. Triplet PSs are widely used in photo-
catalysis,1 photon upconversion,2 photodynamic therapy
(PDT),3 photovoltaics,4 etc. The most important photo-
physical process of triplet PSs is ISC.5 ISC mostly occurs via
spin−orbit coupling (SOC). SOC can be enhanced by the
heavy-atom effect due to transition metal atoms (Ir, Pt, Ru,
etc.) or bromine and iodine atoms.6 However, triplet PSs
invoking the heavy-atom effect have disadvantages, e.g., high
toxicity, poor photo- or chemical stability (due to labile
coordination or C−halogen bonds), and shortened triplet-state
lifetimes, since the heavy-atom effect may enhance both S1 →
T1 and T1 → S0 processes.
To address these challenges, recently heavy-atom-free triplet
PSs have attracted much attention. Concerning this aspect,
n−π* ↔ π−π* transitions (El Sayed’s rule),7 electron spin
converters,8 and exciton coupling9 have been used to enhance
ISC. However, these methods suffer from the drawbacks of
complicated synthesis, etc. Charge-recombination-induced ISC
via radical-pair ISC (RP ISC) in electron donor/acceptor
dyads with a long and rigid linker between the two parts has
been known for decades.10 Unfortunately, RP ISC is inhibited
in compact electron donor/acceptor dyads because of the large
In order to address the above challenges, herein we report
the efficient ISC of a Bodipy derivative, BDP-1 (Scheme 1).
The compound was reported previously,16a and single-crystal
X-ray diffraction showed that the torsion angles between the
1
3
Received: June 6, 2020
energy gap between the CT and CT states caused by the
higher electron exchange energy. Recently, efficient ISC was
observed for compact electron donor/acceptor dyads adopting
an orthogonal geometry via spin−orbit charge transfer ISC
(SOCT-ISC),11 but the application of these triplet PSs may be
complicated by the solvent-polarity dependence of the ISC.
https://dx.doi.org/10.1021/acs.orglett.0c01903
© XXXX American Chemical Society
Org. Lett. XXXX, XXX, XXX−XXX
A

Organic Letters
pubs.acs.org/OrgLett
Letter
BDP-1, for instance in photocatalysis1b,c or PDT.3a,20 In
comparison, BDP-3 shows a slightly weaker absorption band
centered at 638 nm (ε = 8.50 × 104 M−1 cm−1).21 Compound
BDP-2 shows an absorption band at 593 nm (Figure 1),
similar to that of BDP-1 but slightly weaker (ε = 9.10 × 104
M−1 cm−1 at 593 nm).
Scheme 1. Molecular Structures of Twisted Bodipy BDP-1
and the Reference Compounds Used in These Studies
The triplet-state properties of BDP-1 were studied with
nanosecond transient absorption (ns TA) spectroscopy
(Figure 2). Upon pulsed laser excitation at 550 nm, a
peripheral phenyl moieties and the Bodipy core are 17° and
−17°, respectively. Also important was the observation of
moderate fluorescence of BDP-1 (ΦF = 54% in hexane).16a We
envisaged that ISC would be possible for BDP-1 because other
nonradiative decay pathways of the S1 state should be
nonefficient for this rigid molecule.12,13,14b BDP-218 and 2,6-
diiodobis(styryl)Bodipy (BDP-3)1c containing heavy atoms
and native Bodipy (BDP) were used as references in these
studies.
The UV−vis absorption spectra of the compounds were
studied (Figure 1). A strong absorption band centered at 564
Figure 2. (a) Nanosecond transient absorption spectra of BDP-1 in
deaerated DCM. (b) Decay trace at 560 nm. λex = 550 nm, c = 1.0 ×
10−5 M, 20 °C. τT is the intrinsic lifetime obtained by fitting of the
data with a TTA-based kinetic model.26
ground-state blenching (GSB) band at ca. 560 nm was
observed along with excited-state absorption (ESA) bands in
the range of 300−700 nm (superimposed with the GSB band).
These ESA bands are different from typical BDP triplet-state
ESA bands centered at ca. 420 and 675 nm.22 These results
indicate that the T1 → Tn transitions of BDP-1 are different
from those of the native BDP triplet state. TD-DFT
calculations were performed to assign the ESA bands (Figure
S8). For BDP-1, the ESA band at 610 nm is attributed to the
T1 → T4 transition, whereas the ESA band in the region of
300−500 nm is attributed to T1 → Tn (n = 7−17) transitions.
The molecular orbitals involved in these transitions are
delocalized over the entire molecule (Figure S8).15b
The apparent triplet-state lifetime (τT) was determined to be
94.3 μs (in DCM). However, because of the high ISC
efficiency (ΦΔ = 55.0%; Table 1), strong absorption of
excitation light, and long-lived triplet state, triplet−triplet
annihilation (TTA) should be significant, and the apparent τT
must be shorter than the intrinsic τT. Therefore, the intrinsic
Figure 1. UV−vis absorption spectra of the compounds. c = 1.0 ×
10−5 M in DCM, 20 °C.
nm was observed for BDP-1 (molar absorption coefficient ε =
1.21 × 105 M−1 cm−1; Table 1), which is red-shifted by 2238
cm−1 compared with BDP (ε = 7.80 × 104 M−1 cm−1 at 500
nm). This red-shifted absorption is attributed to the extended
π-conjugation of the molecule.19 The strong visible-light-
harvesting ability is clearly beneficial for further applications of
Table 1. Photophysical Properties of Compounds
a
b
c
d
e
f
g
solvent
λabs (ε )
λF
ΦF
ΦΔ
ΦT
τT
h
h
h
h
BDP-1
BDP-2
BDP-3
HEX
TOL
DCM
ACN
HEX
TOL
DCM
ACN
DCM
562 (1.46)
566 (1.31)
564 (1.21)
557 (1.13)
594 (1.00)
600 (0.99)
593 (0.91)
589 (0.89)
638 (0.85)
568
575
572
568
610
621
617
619
657
0.37
0.47
0.31
0.36
0.16
0.14
0.13
0.14
0.10
0.17
0.26
0.55
0.41
0.20
0.46
0.57
0.55
0.62
0.41
0.41
0.56
0.39
246.6
336.7
197.5
217.2
3.9
i
j
−
i
j
−
3.8
3.3
i
j
−
i
j
−
3.3
1.8
k
k
k
j
k
−
a
b
c
d
c = 1.0 × 10−5 M, in nm. Molar absorption coefficient, in 105 M−1 cm−1. Fluorescence emission maximum, in nm. Absolute fluorescence
e
quantum yield determined; determination error = 0.01. Singlet oxygen quantum yield with 2,6-diiodobodipy (ΦΔ = 0.85 in toluene) as the
f
standard; determination error = 0.03. Triplet quantum yield with 2,6-diiodoBodipy (ΦT = 0.88 in toluene) as the standard. Determined with the
g
h
ground state bleaching method. Triplet state lifetime, in μs. Intrinsic triplet state lifetime obtained by fitting experimental curves with a TTA-
based kinetic model.26 Methylene blue (ΦΔ = 0.57 in DCM) was used as the standard. Not determined. Literature value.21
i
j
k
B
https://dx.doi.org/10.1021/acs.orglett.0c01903
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Figure 3. (a) TTA upconversion with BDP-1 as the triplet PS and 9-(2-phenylethynyl)-10-[2-(trimethylsilyl)ethynyl]anthracene (A-1) (Scheme
S1) as the acceptor. (b) CIE coordinates of the luminescence of BDP-1 alone and the upconversion. (c) Photographs of the emission of BDP-1
alone and the upconversion. Upconversion was performed upon excitation of the solution with a 561 nm cw laser (power density = 76.8 mW/cm2).
The luminescence spectra and photographs were recorded with a bandpass filter (transparent in the range of 390−520 nm). c(BDP-1) = 1.0 × 10−5
M and c(A-1) = 7.0 × 10−5 M in deaerated DCM, 20 °C.
lifetime was determined by fitting the decay traces (Figure 2b)
with a kinetic model with the TTA self-quenching effect
considered.23 The obtained intrinsic τT (197.5 μs) is much
longer than the apparent lifetime (94.3 μs). It is worth noting
that the TTA quenching effect is frequently not considered in
the determination of τT.22,24 Also, it is noteworthy that the τT
of BDP-1 (197.5 μs) is much longer than those of Bodipy
derivatives showing absorption bands at similar wavelengths.
For instance, some polybrominated Bodipy derivatives show τT
in the range of 26−43 μs (heavy-atom-effect-induced ISC).25
For BDP-2 with iodine atoms, τT is much shorter (3.3 μs;
Table 1 and Figure S7). BDP-3 shows a τT of 1.8 μs.1c A long-
lived triplet state is useful for PDT, especially in the hypoxic
microenvironment of tumor tissues.11c,20b
The highest ΦT value of BDP-1 was determined to be 56%
in DCM, and the ΦT values in other solvents are also
satisfactory (Table 1). The ISC ability in both nonpolar and
polar solvents is actually an advantage. In the previously
reported heavy-atom-free triplet PSs based on charge-
recombination-induced ISC,11 the ISC efficiency is highly
dependent on the solvent polarity, which may complicate the
application of the triplet PS. For the ISC induced by the
twisted π-conjugation framework, however, the ISC is not
enhanced by charge separation and charge recombination but
instead is induced by the reduced symmetry of the molecule
and correspondingly the increased SOC magnitude.14,17
Recently, benzo[a]phenanthrene-fused Bodipy, with a twisted
π-conjugation framework, was reported to show an ISC yield
of 63% (in DCM), based on sensitized singlet oxygen
phosphorescence, but the absorption is weaker (ε = 4.93 ×
104 M−1 cm−1).27
observed in the presence of 4 equiv of BDP-1 (Figure S11d),
which indicates that ET of BDP-1 is higher than 1.44 eV.
1
Furthermore, perylene (1.53 eV) was used as the quencher
in TTET.29 No shortening of τT of BDP-1 (145.0 vs 142.0 μs)
was observed in the presence of 4 equiv of perylene (Figure
S11h), indicating that ET of BDP-1 is lower than 1.53 eV.
1
Therefore, ET of BDP-1 is in the range of 1.44−1.53 eV,
1
which is slightly lower than that of 2,6-diiodoBodipy (1.61
eV)30 but higher than those of BDP-2 (1.25 eV) and BDP-3
(1.13 eV).21 The high energy of the T1 state is important for
applications of triplet PSs.
TTA upconversion was performed using BDP-1 as the
triplet PS and A-1 (Scheme S1) as the energy acceptor (Figure
3). For BDP-1 alone, no fluorescence was observed upon
excitation with a 561 nm continuous wave (cw) laser
(measured with a bandpass filter that was transparent over
the range of 390−520 nm; Figure 3a). After addition of 7 equiv
of A-1, an emission band at ca. 460 nm was observed, which is
the upconverted emission of A-1 (Figure 3a). The
upconversion quantum yield was determined to be 3.1%.
The achieved anti-Stokes shift of 3913 cm−1 is larger than that
previously reported for the 2,6-diiodoBodipy/perylene system
(ca. 3380 cm−1).10 Large anti-Stokes shifts are important for
TTA upconversion.31 The upconverted emission is visible to
unaided eyes (Figure 3c). With BDP-2 and BDP-3, no
upconversion emission was observed (Figure S13). We
attribute this to the lower ET and the short τT. To the best
1
of our knowledge, reports of the use of a twisted Bodipy
derivative as a triplet PS are rare.17
In summary, efficient intersystem crossing (singlet oxygen
quantum yield ΦΔ = 55%) was observed for a heavy-atom-free
Bodipy derivative with a twisted π-conjugation framework. The
derivative shows strong visible-light absorption (ε = 1.21 × 105
M−1 cm−1 at 564 nm) and an exceptionally long lived triplet
state (intrinsic triplet state lifetime τT = 197.5 μs) with a high
triplet state energy (ca. 1.4 eV). One of the advantages of using
the twisted π-conjugation framework to enhance ISC, instead
of the typical heavy-atom effect, is demonstrated by the
comparison with 2,6-diiodostyrylBodipy, which shows a similar
absorption wavelength but has a much shorter triplet state
lifetime (3.3 μs). The Bodipy derivative with the twisted π-
conjugation framework was used as a triplet PS in triplet−
triplet annihilation upconversion. A large anti-Stokes shift
(3913 cm−1) and satisfactory upconversion quantum yield
(3.1%) were observed. Our results indicate that chromophores
Since no phosphorescence was observed for BDP-1, triplet−
triplet energy transfer (TTET) was used to determine the
energy of the T1 state (ET ) (Figure S9). 1-Chloro-9,10-bis(2-
1
phenylethynyl)anthracene (CBPEA) (Scheme S1), for which
ET = 1.20 eV, was used as the triplet-state energy acceptor
1
(quencher).22 The apparent τT of BDP-1 (146.0 μs) was
reduced to 10.5 μs in the presence of 4 equiv of CBPEA.
Moreover, evolution-associated decay spectra (EADS) were
obtained by global fitting of the ns TA data with a sequential
model (Figure S10). We conclude that ET of BDP-1 is higher
1
than 1.20 eV. Next, methylene blue (MB) (ET = 1.44 eV)28
1
was used as the sensitizer and BDP-1 as the quencher (Figure
S11). No reduction of the τT of MB (194.6 vs 209.2 μs) was
C
https://dx.doi.org/10.1021/acs.orglett.0c01903
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
(8) Wu, W.; Zhao, J.; Sun, J.; Guo, S. J. Org. Chem. 2012, 77, 5305−
with a twisted π-conjugation structure may become a novel
molecular structure motif for heavy-atom-free triplet photo-
sensitizers.
5312.
̈
̈
̈
(9) Broring, M.; Kruger, R.; Link, S.; Kleeberg, C.; Kohler, S.; Xie,
X.; Ventura, B.; Flamigni, L. Chem. - Eur. J. 2008, 14, 2976−2983.
(10) (a) Wiederrecht, G. P.; Svec, W. A.; Wasielewski, M. R.; Galili,
T.; Levanon, H. J. Am. Chem. Soc. 1999, 121, 7726−7727.
(b) Verhoeven, J. W.; van Ramesdonk, H. J.; Groeneveld, M. M.;
Benniston, A. C.; Harriman, A. ChemPhysChem 2005, 6, 2251−2260.
(c) Ziessel, R.; Allen, B. D.; Rewinska, D. B.; Harriman, A. Chem. -
Eur. J. 2009, 15, 7382−7393.
ASSOCIATED CONTENT
* Supporting Information
■
sı
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c01903.
Experimental procedures, characterization data, and
spectroscopic data (PDF)
(11) (a) van Willigen, H.; Jones, G.; Farahat, M. S. J. Phys. Chem.
1996, 100, 3312−3316. (b) Dance, Z. E. X.; Mickley, S. M.; Wilson,
T. M.; Ricks, A. B.; Scott, A. M.; Ratner, M. A.; Wasielewski, M. R. J.
Phys. Chem. A 2008, 112, 4194−4201. (c) Hou, Y.; Liu, Q.; Zhao, J.
Chem. Commun. 2020, 56, 1721−1724. (d) Filatov, M. A.;
Karuthedath, S.; Polestshuk, P. M.; Savoie, H.; Flanagan, K. J.; Sy,
C.; Sitte, E.; Telitchko, M.; Laquai, F.; Boyle, R. W.; Senge, M. O. J.
Am. Chem. Soc. 2017, 139, 6282−6285.
AUTHOR INFORMATION
Corresponding Author
■
Jianzhang Zhao − State Key Laboratory of Fine Chemicals,
School of Chemical Engineering, Dalian University of
Technology, Dalian 116024, P. R. China; orcid.org/0000-
0002-5405-6398; Email: zhaojzh@dlut.edu.cn
(12) (a) Wu, Y.; Zhen, Y.; Ma, Y.; Zheng, R.; Wang, Z.; Fu, H. J. J.
Phys. Chem. Lett. 2010, 1, 2499−2502. (b) Nagarajan, K.; Mallia, A.
R.; Reddy, V. S.; Hariharan, M. J. Phys. Chem. C 2016, 120, 8443−
8450. (c) Nagarajan, K.; Mallia, A. R.; Muraleedharan, K.; Hariharan,
M. Chem. Sci. 2017, 8, 1776−1782.
Authors
Yu Dong − State Key Laboratory of Fine Chemicals, School of
Chemical Engineering, Dalian University of Technology, Dalian
116024, P. R. China; orcid.org/0000-0001-6191-7857
̀
(13) Salla, C. A. M.; Farias, G.; Rouzieres, M.; Dechambenoit, P.;
Durola, F.; Bock, H.; de Souza, B.; Bechtold, I. H. Angew. Chem., Int.
Ed. 2019, 58, 6982−6986.
Bernhard Dick − Lehrstuhl fu
̈
r Physikalische Chemie, Institut
(14) (a) Sapir, M.; Donckt, E. V. Chem. Phys. Lett. 1975, 36, 108−
110. (b) Schmidt, K.; Brovelli, S.; Coropceanu, V.; Beljonne, D.;
Cornil, J.; Bazzini, C.; Caronna, T.; Tubino, R.; Meinardi, F.; Shuai,
̈
̈
fur Physikalische und Theoretische Chemie, Universitat
Regensburg, D-93053 Regensburg, Germany; orcid.org/
́
Z.; Bredas, J.-L. J. Phys. Chem. A 2007, 111, 10490−10499.
0000-0002-9693-5243
(15) (a) Hong, Y.; Oh, J.; Sung, Y. M.; Tanaka, Y.; Osuka, A.; Kim,
D. Angew. Chem., Int. Ed. 2017, 56, 2932−2936. (b) Ema, F.; Tanabe,
M.; Saito, S.; Yoneda, T.; Sugisaki, K.; Tachikawa, T.; Akimoto, S.;
Yamauchi, S.; Sato, K.; Osuka, A.; Takui, T.; Kobori, Y. J. Phys. Chem.
Lett. 2018, 9, 2685−2690.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c01903
Notes
(16) (a) Wang, Y.-W.; Descalzo, A. B.; Shen, Z.; You, X.-Z.; Rurack,
K. Chem. - Eur. J. 2010, 16, 2887−2903. (b) Ni, Y.; Zeng, W.; Huang,
K.-W.; Wu, J. Chem. Commun. 2013, 49, 1217−1219.
(17) Wang, Z.; Huang, L.; Yan, Y.; El-Zohry, A. M.; Toffoletti, A.;
Zhao, J.; Barbon, A.; Dick, B.; Mohammed, O. F.; Han, G. Angew.
Chem., Int. Ed. 2020, DOI: 10.1002/anie.202005269.
(18) Zhang, C.; Zhao, J.; Cui, X.; Wu, X. J. Org. Chem. 2015, 80,
5674−5686.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
J.Z. thank the National Natural Science Foundation of China
for financial support (21673031, 21761142005, and
21911530095). B.D. thanks the Dalian University of
Technology for support through a HaiTian Professorship.
(19) (a) Ziessel, R.; Harriman, A. Chem. Commun. 2011, 47, 611−
631. (b) Lu, H.; Mack, J.; Yang, Y.; Shen, Z. Chem. Soc. Rev. 2014, 43,
4778−4823.
REFERENCES
■
̈
(1) (a) Hari, D. P.; Konig, B. Angew. Chem., Int. Ed. 2013, 52, 4734−
(20) (a) Li, X.; Kolemen, S.; Yoon, J.; Akkaya, E. U. Adv. Funct.
Mater. 2017, 27, 1604053. (b) Lincoln, R.; Kohler, L.; Monro, S.; Yin,
H.; Stephenson, M.; Zong, R.; Chouai, A.; Dorsey, C.; Hennigar, R.;
Thummel, R. P.; McFarland, S. A. J. Am. Chem. Soc. 2013, 135,
17161−17175.
4743. (b) Fukuzumi, S.; Ohkubo, K. Chem. Sci. 2013, 4, 561−574.
(c) Huang, L.; Zhao, J.; Guo, S.; Zhang, C.; Ma, J. J. Org. Chem. 2013,
78, 5627−5637.
(2) (a) Singh-Rachford, T. N.; Castellano, F. N. Coord. Chem. Rev.
2010, 254, 2560−2573. (b) Zhao, J.; Ji, S.; Guo, H. RSC Adv. 2011, 1,
937−950.
(21) Ma, J.; Yuan, X.; Kucu̧ koz, B.; Li, S.; Zhang, C.; Majumdar, P.;
̈ ̈
̈
Karatay, A.; Li, X.; Gul Yaglioglu, H.; Elmali, A.; Zhao, J.; Hayvali, M.
J. Mater. Chem. C 2014, 2, 3900−3913.
(3) (a) Kamkaew, A.; Lim, S. H.; Lee, H. B.; Kiew, L. V.; Chung, L.
Y.; Burgess, K. Chem. Soc. Rev. 2013, 42, 77−88. (b) Jiang, X.-J.; Lau,
J. T. F.; Wang, Q.; Ng, D. K. P.; Lo, P.-C. Chem. - Eur. J. 2016, 22,
8273−8281.
(22) Wu, W.; Guo, H.; Wu, W.; Ji, S.; Zhao, J. J. Org. Chem. 2011,
76, 7056−7064.
(23) Lou, Z.; Hou, Y.; Chen, K.; Zhao, J.; Ji, S.; Zhong, F.; Dede, Y.;
Dick, B. J. Phys. Chem. C 2018, 122, 185−193.
(4) (a) Guo, F.; Kim, Y.-G.; Reynolds, J. R.; Schanze, K. S. Chem.
Commun. 2006, 1887−1889. (b) Wu, Y.; Zhu, W. Chem. Soc. Rev.
2013, 42, 2039−2058.
(24) (a) Adarsh, N.; Shanmugasundaram, M.; Avirah, R. R.;
Ramaiah, D. Chem. - Eur. J. 2012, 18, 12655−12662. (b) Maligaspe,
E.; Pundsack, T. J.; Albert, L. M.; Zatsikha, Y. V.; Solntsev, P. V.;
Blank, D. A.; Nemykin, V. N. Inorg. Chem. 2015, 54, 4167−4174.
(25) Zhang, X.-F.; Yang, X. J. Phys. Chem. B 2013, 117, 5533−5539.
(26) Dong, Y.; Sukhanov, A. A.; Zhao, J.; Elmali, A.; Li, X.; Dick, B.;
Karatay, A.; Voronkova, V. K. J. Phys. Chem. C 2019, 123, 22793−
22811.
(5) Zhao, J.; Wu, W.; Sun, J.; Guo, S. Chem. Soc. Rev. 2013, 42,
5323−5351.
(6) (a) Yogo, T.; Urano, Y.; Ishitsuka, Y.; Maniwa, F.; Nagano, T. J.
̈
Am. Chem. Soc. 2005, 127, 12162−12163. (b) Lanoe, P.-H.; Fillaut, J.-
L.; Toupet, L.; Williams, J. A. G.; Bozec, H. L.; Guerchais, V. Chem.
Commun. 2008, 4333−4335.
(7) (a) Parker, C. A.; Joyce, T. A. Chem. Commun. 1968, 749−750.
(b) Zhao, N.; Xuan, S.; Zhou, Z.; Fronczek, F. R.; Smith, K. M.;
Vicente, M. G. H. J. Org. Chem. 2017, 82, 9744−9750.
(27) Ito, H.; Sakai, H.; Suzuki, Y.; Kawamata, J.; Hasobe, T. Chem. -
Eur. J. 2020, 26, 316−325.
D
https://dx.doi.org/10.1021/acs.orglett.0c01903
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
(28) Kearns, D. R.; Hollins, R. A.; Khan, A. U.; Chambers, R. W.;
Radlick, P. J. Am. Chem. Soc. 1967, 89, 5455−5456.
(29) Cui, X.; El-Zohry, A. M.; Wang, Z.; Zhao, J.; Mohammed, O. F.
J. Phys. Chem. C 2017, 121, 16182−16192.
(30) Zhang, T.; Ma, X.; Tian, H. Chem. Sci. 2020, 11, 482−487.
(31) (a) Amemori, S.; Sasaki, Y.; Yanai, N.; Kimizuka, N. J. Am.
Chem. Soc. 2016, 138, 8702−8705. (b) Wei, Y.; Zheng, M.; Chen, L.;
Zhou, X.; Liu, S. Dalton Trans 2019, 48, 11763−11771.
E
https://dx.doi.org/10.1021/acs.orglett.0c01903
Org. Lett. XXXX, XXX, XXX−XXX