A Direct S0→Tn Transition in the Photoreaction of Heavy-Atom-Containing Molecules

Article abstract of DOI:10.1002/anie.201915181

According to the Grotthuss–Draper law, light must be absorbed by a substrate to initiate a photoreaction. There have been several reports, however, on the promotion of photoreactions using hypervalent iodine during irradiation with light from a non-absorbing region. This contradiction gave rise to a mystery regarding photoreactions involving hypervalent iodine. We demonstrated that the photoactivation of hypervalent iodine with light from the apparently non-absorbing region proceeds via a direct S₀→T_n transition, which has been considered a forbidden process. Spectroscopic, computational, and synthetic experimental results support this conclusion. Moreover, the photoactivation mode could be extended to monovalent iodine and bromine, as well as bismuth(III)-containing molecules, providing new possibilities for studying photoreactions that involve heavy-atom-containing molecules.

Full text of DOI:10.1002/anie.201915181

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: Direct S0→Tn Transition in the Photoreaction of Heavy-Atom-
Containing Molecules
Authors: Masaya Nakajima, Sho Nagasawa, Koki Matsumoto, Takahito
Kuribara, Atsuya Muranaka, Masanobu Uchiyama, and
Tetsuhiro Nemoto
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201915181
Angew. Chem. 10.1002/ange.201915181
Link to VoR: http://dx.doi.org/10.1002/anie.201915181
http://dx.doi.org/10.1002/ange.201915181

10.1002/anie.201915181
Angewandte Chemie International Edition
RESEARCH ARTICLE
Direct S0→Tn Transition in the Photoreaction of Heavy-Atom-
Containing Molecules
Masaya Nakajima,*[a],[b] Sho Nagasawa,[a] Koki Matsumoto,[a] Takahito Kuribara,[a] Atsuya Muranaka,[b]
Masanobu Uchiyama,[b],[c] Tetsuhiro Nemoto*[a]
Abstract: According to the Grotthuss–Draper law, light must be
absorbed by a substrate to initiate a photoreaction. There have been
several reports, however, on the promotion of photoreactions using
hypervalent iodine during irradiation with light from a non-absorbing
absorption spectra of these hypervalent iodine compounds,
however, includes no apparent absorption bands in this
wavelength region (Figure 1b). This contradiction gave rise to a
“mystery” regarding photoreactions using hypervalent iodine.
Conventionally, triplet photoreactions in organic chemistry are
developed based on the S0→Sn→S1→T1 transition (Figure 1c).
Despite reports of the spectroscopic detection of S0→Tn
absorption transitions in the 1960s,[6] these findings have never
been widely accepted by organic chemists, probably because of
the significantly unfavored property of the S0→Tn transition
compared with the S1→T1 transition. Because the energy level is
lower in the triplet excited state than in the singlet excited state,
S0→Tn absorption bands are observed in a longer wavelength
region than that of the S0→Sn transition bands, leading us to
hypothesize that a direct S0→Tn transition, which has been
considered a forbidden process, could be the key to unraveling
the mystery of hypervalent iodine photoreactions.
region. This contradiction gave rise to
a “mystery” regarding
photoreactions involving hypervalent iodine. We demonstrated that
the photoactivation of hypervalent iodine with light from the apparently
non-absorbing region proceeds via a direct S0→Tn transition, which
has been considered
a
forbidden process. Spectroscopic,
computational, and synthetic experimental results support this
conclusion. Moreover, the photoactivation mode could be extended to
monovalent iodine and bromine, as well as bismuth(III)-containing
molecules, providing new possibilities for studying photoreactions that
involve heavy-atom-containing molecules.
Introduction
Due to the increased development of light-emitting diodes (LEDs)
in the 21st century, visible light is taking the place of ultraviolet
(UV) light as an energy source for photoreactions in organic
chemistry. The emergence of photoredox catalysis has also
strongly boosted the use of visible light in this field.[1] Hypervalent
iodine has long attracted the attention of organic chemists.[2]
Photoactivation of hypervalent iodine initiates radical reactions via
homolysis of the three-center, four-electron bond. Studies of
photoreactions using hypervalent iodine under UV irradiation
began in the 1980s.[3] Until recently, however, the development of
photoreactions using hypervalent iodine has progressed
slowly.[4,5] Maruoka et al. recently reported the difluoromethylation
of heteroaromatic compounds using hypervalent iodine I (Figure
1a) under irradiation with violet light (400 nm).[5f] Wang et al. also
reported a radical cyclization with in-situ-generated hypervalent
iodine II (Figure 1a) with blue LED (450 nm) irradiation.[5d]
According to the Grotthuss–Draper law, light must be absorbed
by a substrate or catalyst to initiate a photoreaction. The
a)
Maruoka et al.
I(O2CCF2H)2
O
N
O
N
N
N
N
N
I
R
N
N
CF2H
O
O
CDCl3, h! (400 nm)
up to 56% yield
Wang et al.
O
O
O
Ph
Ph
O
O
Ph
I
O
Ph
O
II
O
O
O
KPF6, toluene
h! (Blue LED, 450 nm)
74% yield
b)
Absorption of PhI(O2CCF2H) (I)
O
O
O
Ph
I
O
Absorption of
(II)
O
Why did a photoreaction proceed?
400 nm
450 nm
[a]
Prof. Dr. M. Nakajima, S. Nagasawa, K. Matsumoto, T. Kuribara,
Prof. Dr. T. Nemoto
c)
Sn
S1
Graduate School of Pharmaceutical Sciences
Chiba University
1-8-1, Inohana, Chuo-ku, Chiba 260-8675, Japan.
E-mail: m.nakajima@chiba-u.jp (MN), tnemoto@faculty.chiba-u.jp
(TN)
Prof. Dr. M. Nakajima, Dr A. Muranaka, Prof. Dr. M. Uchiyama
Cluster for Pioneering Research (CPR)
Advanced Elements Chemistry Laboratory, RIKEN
2-1, Hirosawa, Wako, Saitama 351-0198, Japan.
Prof. Dr. M. Uchiyama
Tn
T1
Radical
reaction
Usual S0 →Sn
transition
Forbidden
S0 → Tn transition
[b]
[c]
UV (< 300 nm)
Our hypothesis: Really forbidden in
photoreactions using hypervalent iodine?
S0
Graduate School of Pharmaceutical Sciences
The University of Tokyo
7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Figure 1. Hypervalent iodine reactivity and absorptivity. (a) Examples of
mysterious photoreactions using hypervalent iodine under irradiation by light
from a non-absorbing region of the electromagnetic spectrum. (b) Absorption
spectra of hypervalent iodine compounds I and II. (c) Jablonski diagram
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/anie.201915181
Angewandte Chemie International Edition
RESEARCH ARTICLE
illustrating a general pathway for molecular excitation and our hypothesis. Ph:
phenyl
heavy-atom effect of iodine, enabling the “forbidden” transition of
hypervalent iodine compounds.
Results and Discussion
a)
II
To test our hypothesis, we first conducted spectroscopic
experiments on the optical properties of hypervalent iodine. We
chose hypervalent iodine II as a benchmark substrate, and its
absorption, emission, and phosphorescence spectra were
measured (Figure 2a). Emission was observed by excitation at
240 nm. The delayed emission spectrum revealed that the
emission at 260–350 nm is a fluorescent component, and the
peaks at wavelengths greater than 350 nm are phosphorescent
components. The excitation light required for phosphorescent
emission at 550 nm ranged from 230 to 410 nm, despite the fact
that almost no absorption band was observed at wavelengths
greater than 320 nm. In practice, phosphorescence was observed
by irradiation at 360 nm (Figure S1),[7] indicating that direct
excitation to the triplet excited state occurred under these
conditions. The obtained spectroscopic information suggests that
weak absorption bands corresponding to the S0→Tn transitions
should be present in this region. Thus, we measured the
absorption spectra of highly concentrated solutions of II using a
cell with a long optical path length to observe the S0 → Tn
absorption (Figure 2b). As a result, we could observe the
absorption in the skirt of spectra extending up to 410 nm under
the conditions of c (concentration)・l (optical path length) = 1
mM・100 mm. Since this absorption coincided with the excitation
spectrum for phosphorescence emission at 550 nm, it was proved
that the spectra at 330–410 nm having a molar extinction
coefficient (e) up to 30 correspond to the absorption of the direct
S0→Tn transition. In addition, similar absorption spectra were
obtained under the measurement conditions between c・l = 1
mM・1 mm and c・l = 0.01 mM・100 mm. Hence, the weak
absorption observed using the 1 mM solution was not caused by
the formation of aggregated compounds.
b)
S0→Sn absorption
S0→Tn absorption
Figure 2. (a) Absorption and emission properties of hypervalent iodine
compound II; the vertical axis is normalized. (b) Absorption spectra of II under
various conditions.
1
3a
3e
2a
3b
3f
2b
3c
4
2c
3d
The absorption spectra of various hypervalent iodine compounds
revealed no apparent absorption bands in the region above 360
nm (Figure 1b and 3a). On the other hand, similar spectroscopic
profiles to those of II were also obtained using highly concentrated
solutions of typical hypervalent iodine reagents 1, 2a, and 3d,[7]
supporting the hypothesis of direct generation of the triplet excited
state from the ground state using hypervalent iodine compounds.
Spin-forbidden direct singlet-triplet absorption rarely occurs in
organic compounds because the e of S0→Tn absorption is very
small; for example, the emax of anthracene for S0→Sn absorption
is ~104, and the emax for S0→Tn absorption is ~10-4, which means
that S0 → Tn absorption is 108 times weaker than S0 → Sn
X
CF3
O
O
I(O2CR)2
3a (R = CH3)
3b (R = i-Pr)
3c (R = CH2-p-tolyl)
3d (R = adamantyl)
3e (R = CH2CF3)
3f (R = CF3)
I
I
I
O
O
O
2a (X = CF3)
2b (X = Cl)
2c (X = N3)
1
4
Figure 3. Absorption spectra of hypervalent iodine compounds; the
wavelengths of light used for the chemical reactions in Scheme 1 are also
indicated.
absorption.[8] In contrast, there was only
a three-order-of-
magnitude difference in e between these two transitions in the
case of II; ε for the S0→Tn absorption at 350 nm was 21, and ε for
the S0→Sn absorptions at 230 and 285 nm were 13215 and 1881,
respectively. The existence of internal or external heavy atoms
facilitates spin-forbidden S1→T1 and S0→Tn intersystem crossing
due to strong spin orbit coupling.[8] Therefore, we reasoned that
the spin-forbidden transition was relaxed due to the internal
After the direct transition to the triplet excited state was
demonstrated spectroscopically, we next performed quantum
calculations to predict the S0 → Tn absorption wavelength for
hypervalent iodine using the Gaussian 16 software. After
structural optimizations using density functional theory (DFT) with
the MN15 functional and the basis sets SDD (for I) and cc-pVTZ
(for the other atoms), time-dependent DFT (TD-DFT) calculations
This article is protected by copyright. All rights reserved.

10.1002/anie.201915181
Angewandte Chemie International Edition
RESEARCH ARTICLE
were performed using various functionals with the same basis
sets.[9] The calculated values of the longest absorption
wavelengths for the S0→T1 transitions of various hypervalent
iodine compounds are shown in Table 1. The direct S0 → Tn
absorption bands of these hypervalent iodine compounds were
estimated to range between 350 and 400 nm. These were utilized
as an index for setting the conditions of the corresponding photo-
induced reactions.
were irradiated with 365-nm or 385-nm light in the presence of the
2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPO) radical, affording the
corresponding O-alkylated products 5a–f (Scheme 1a) in 7%–
87% yields. No reaction occurred under light-shielding conditions
(Scheme 1a). Dichlorination of
6 using 2b (Scheme 1b)
proceeded at room temperature by irradiation with 400-nm light to
obtain compound 7 in 61% yield, and a high temperature was
required to promote the reaction in the dark. Spectroscopic
analyses of a mixed solution of 6 and 2b revealed that no
electron-donor-acceptor complex formed in this reaction,[7]
indicating that solely the S0→Tn transition of 2b initiated this
radical process. A radical-clock experiment using 2b and 8
afforded compound 9 with a 36% yield [73% yield based on the
recovered starting material (brsm) method], suggesting that
homolysis of the chlorine–iodine bond occurred to give a chlorine
radical via a direct S0→Tn transition (Scheme 1b). C–H azidation
of 10 using 2c was examined by irradiation with 400-nm light at
room temperature; product 11 was obtained in 40% yield (73%
brsm yield), providing a rational explanation for the progress of
the curious background reaction in the absence of a photocatalyst
as reported by Wang et al. (Scheme 1c).[4c] Iodylbenzene 4 has a
low alcohol-oxidizing ability. In fact, oxidation of 12 and 13 did not
proceed in the dark. In striking contrast, the oxidation reactions
proceeded smoothly under light irradiation at 400 nm, producing
compounds 14 and 15 in excellent yields. The use of blue light
(450 nm) or green light (510 nm) also promoted the reaction
(Scheme 1d).
MN15
418
323
328
325
346
351
324
325
331
325
326
327
374
cam-B3LYP
416
mPW1PW91
446
ωB97XD
413
329
335
330
355
374
331
331
337
332
333
334
376
II
1
345
352
348
360
375
348
348
353
348
349
350
383
347
353
351
377
387
350
350
357
351
353
354
393
2a
3d
2b
2c
3a
3b
3c
3e
I
3f
4
(nm)
Table 1. S0→T1 absorption wavelengths for hypervalent iodine compounds
predicted by TD-DFT calculations. Structural optimization: MN15/SDD (I) and
cc-pVTZ (others). Basis sets for TD-DFT calculation: SDD (I) and cc-pVTZ
(others).
To confirm that radical species are generated from hypervalent
iodine compounds via a direct S0→Tn transition, radical-capture
experiments were first undertaken. Compounds 1, 2a, and 3a–f
a)
CF3
I(O2CR)2
TEMPO (2 equiv)
5a (R = CH3) : 7%
5b (R = i-Pr) : 36%
5c (R = CH2-p-tolyl) : 52%
5d (R = adamantyl) : 20%
5e (R = CH2CF3) : 39%
5f (R = CF3) : 87%
TEMPO (1 equiv)
I
h! (385 nm)
CDCl3
–50 ºC, 24 h
O
h! (365 nm)
N
5f
OR
CDCl3, 24 h
X
3a–f
5a–f
1 (X = Me2)
2a (X = O)
From 1: 17% (rt)
From 2a: 36% (–50 ºC)
No reaction occurred in the dark at rt.
b)
Cl
I
Cl
I
Cl
Cl
Cl
O
2b
O
2b
Cl
(2.2 equiv)
(2.2 equiv)
O
O
N
N
Ts
Ts
h! (400 nm), dioxane, rt, 24 h
h! (400 nm)
dioxane, rt, 24 h, 61%
6
7
8
9
36% (73% brsm)
No reaction occurred in the dark at rt. (33% yield at 60° C)
No reaction occurred in the dark at rt.
d)
c)
OH
O
O
O
I
N3
Ph
12
or
Ph
14
or
I
4
O
CO2Me
NPhth
2c
(2 equiv)
CO2Me
NPhth
(1.5 - 2 equiv)
OH
O
O
h!, solvent, rt, 17 h
h! (450 nm)
hexafluoroisopropanol
N3
11
10
13
15
rt, 24 h, 40% (73% brsm)
For 14 (in CDCl3): h! (400 nm): 97%, h! (450 nm): 97%, h! (510 nm): 9%
For 15 (in CH2Cl2): h! (400 nm): 81%, h! (450 nm): 24%, h! (510 nm): 8%
No reaction occurred in the dark at rt.
No reaction occurred in the dark at rt.
This article is protected by copyright. All rights reserved.

10.1002/anie.201915181
Angewandte Chemie International Edition
RESEARCH ARTICLE
Scheme 1. Photoreactions using hypervalent iodine via a direct S0→Tn transition. Ts: tosyl, NPhth: phthalimide
We also synthesized a novel hypervalent iodine with an acridine
skeleton 16, which was designed to absorb light of a longer
wavelength than that generally absorbed by hypervalent iodine
compounds.[7] The absorption, emission, and phosphorescence
spectra of 16 are shown in Figure 4a. Strong absorption bands
were observed at wavelengths up to 410 nm, and weak
absorption bands were observed at wavelengths up to 550 nm.
Phosphorescence was observed upon irradiation at 450 nm,
indicating that the weak absorption between 410 to 550 nm was
S0 → Tn absorption. Oxidation of 12 was examined using 16
(Figure 4b). No reaction occurred under light-shielding conditions;
in contrast, visible light irradiation promoted the reaction. It is
worth emphasizing that although the absorbance at 400 nm was
much higher than that at 450 or 510 nm, oxidation proceeded
more efficiently under irradiation with 450- or 510-nm light
compared with that under 400-nm light. These results indicate that
the generation of a triplet excited state via a direct S0 → Tn
transition is more efficient than that via S0→S1→T1 intersystem
crossing.
indicating the existence of absorption bands for direct S0→Tn
transition between these wavelengths. In practice, we could
observe weak absorption at 380–500 nm under the conditions of
c・l = 1 mM・100 mm, and phosphorescence was also observed
by irradiation at 400 nm (Figure 5a). With these spectroscopic
data in hand, radical-mediated reduction of 17a using Bu3SnH
was examined in the absence of a radical initiator. The target
reaction proceeded under irradiation with 400- or 450-nm light,
providing naphthalene 18 in excellent yield. A control experiment
was performed in the dark, demonstrating the positive effect of
visible light irradiation on this experiment. The same phenomenon
was also observed when using bromonaphthalene 17b, and no
reaction occurred in the dark (Figure 5b).
a)
I
17a
a)
S0→Sn absorption
S0→Tn absorption
X
H
b)
nBu3SnH (4 equiv)
MeCN
X = I: 98%
X = Br: 89%
h! (400 or 450 nm)
18
rt, 24 h
17a (X = I)
17b (X = Br)
17a: Reaction in the dark at rt gave 18 in 12% yield.
17b: No reaction occurred in the dark at rt.
Ph
b)
Figure 5. (a) Absorption and emission properties of 17a; the vertical axis is
normalized. (b) Photo-induced reduction of 17 via a direct S0→Tn transition.
No reaction occurred
in the dark at rt.
16
N
(1.5 equiv)
h! (400 nm): 22%
h! (450 nm): 80%
h! (510 nm): 41%
I
O
O
Furthermore, the same activation mode could be applied to
organobismuth compounds. Spectroscopic analyses of
triphenylbismuthine(III) 19 revealed the existence of an
absorption band with an upper wavelength limit at 320 nm and
that the excitation light for phosphorescence emission at 500 nm
ranged up to 470 nm, indicating that light between 310 and 455
nm will trigger a direct S0 → Tn transition (Figure 6a). The
calculated prediction of the S0→T1 transition for 19 is 346 nm, and
the energy of the T1 state of 19 was calculated to be 54.0 kcal/mol
higher than that of the S0 state. On the other hand, the bond
dissociation energy of the bismuth–carbon bond in 19 was
calculated to be 56.0 kcal/mol, indicating that a phenyl radical can
be generated via a direct S0→Tn transition (Figure 6b). As shown
in Figure 6c, when 19 was irradiated with 365- and 400-nm light
in the presence of bis(pinacolato)diboron, 53% and 74% yields of
phenyl pinacolborane 20 were synthesized, respectively,
12
14
h!, PhCl, rt, 5 h
Figure 4. (a) Absorption and emission properties of hypervalent iodine 16; the
vertical axis is normalized. (b) Photo-induced oxidation of 12 using hypervalent
iodine 16 via a direct S0→Tn transition.
If a direct S0→Tn transition of hypervalent iodine occurs due to the
internal heavy-atom effect of iodine, it should be possible to
extend this reaction mode to the visible light activation of general
heavy-atom-containing molecules. As a proof-of-concept study,
we examined photoreactions of monovalent iodine- or bromine-
containing
molecules. Spectroscopic
analyses
of 1-
iodonaphthalene 17a revealed that, despite the observation of an
absorption band at wavelengths up to 310 nm, the excitation light
for phosphorescence emission at 600 nm ranged up to 490 nm,
This article is protected by copyright. All rights reserved.

10.1002/anie.201915181
Angewandte Chemie International Edition
RESEARCH ARTICLE
validating
bis(pinacolato)diboron,
our
hypothesis.
19 was
In
addition,
slowly oxidized
without
by
wavelength region proceeded via a direct S0→Tn transition, which
has been, until now, considered
a
forbidden process.
dichloromethane to give triphenylbismuth dichloride(V) 21 in 42%
yield. These results strongly suggest that the participation of a
direct S0 → Tn transition in photoreactions will be broadly
applicable to heavy-atom-containing molecules.
Spectroscopic and experimental measurements support our
conclusion. Moreover, proof-of-concept studies involving photo-
induced
radical
reactions
of
halonaphthalenes
and
triphenylbismuthine revealed that this reaction mode could extend
to monovalent iodine and bromine, as well as bismuth(III)-
containing molecules. These findings present new possibilities for
the study of photoreactions involving heavy-atom-containing
molecules. Further studies on the generality and applicability of
this photoactivation mode are in progress.
a)
Supporting Information. Experimental procedures and spectral data
(PDF). This material is available free of charge via the Internet.
Bi
19
Acknowledgements
S0→Tn
S0→Sn
Allotment of computational resource (Project G18008) from
HOKUSAI GreatWave (RIKEN) is gratefully acknowledged. We
acknowledged Dr. K. Miyamoto (The University of Tokyo) for his
helpful discussions. This work was supported by Institute of
Global Prominent Research, Chiba University.
b)
(kcal/mol)
*
•
+
Bi
•
Bi
19c
Keywords: hypervalent iodine • heavy-atom-containing
molecule • photoreaction • S0→Tn transitions
19b
∆H = 56.0
19a (T1)
∆H = 54.0
[1]
a) A. Bauer, F. Westkämper, S. Grimme, T. Bach, Nature 2005, 436,
1139; b) D. A. Nicewicz, D. W. C. MacMillan, Science 2008, 322, 77; c)
M. A. Ischay, M. E. Anzovino, J. Du, T. P. Yoon, J. Am. Chem. Soc. 2008,
130, 12886; d) J. M. R. Narayanam, J. W. Tucker, C. R. J. Stephenson,
J. Am. Chem. Soc. 2009, 131, 8756; e) M. T. Pirnot, D. A. Rankic, D. B.
C. Martin, D. W. C. MacMillan, Science 2013, 339, 1593; f) R. Brimioulle,
T. Bach, Science 2013, 342, 840; g) Z. Zuo, D. T. Ahneman, L. Chu, J.
A. Terrett, A. G. Doyle, D. W. C. MacMillan, Science 2014, 345, 437; h)
T. R. Blum, Z. D. Miller, D. M. Bates, I. A. Guzei, T. P. Yoon, Science
2016, 354, 1391; i) M. H. Shaw, J. Twilton, D. W. C. MacMillan, J. Org.
Chem. 2016, 81, 6898; j) M. S. Oderinde, N. H. Jones, A. Juneau, M.
Frenette, B. Aquila, S. Tentarelli, D. W. Robbins, J. W. Johannes, Angew.
Chem. Int. Ed. 2016, 55, 13219; k) M. Jiang, H. Li, H. Yang, H. Fu, Angew.
Chem. Int. Ed. 2017, 56, 874; l) H. Yue, C. Zhu, M. Rueping, Angew.
Chem. Int. Ed. 2018, 57, 1371; m) L. Pitzer, F. Sandfort, F. Strieth-
Kalthoff, F. Glorius, J. Am. Chem. Soc. 2017, 139, 13652; n) X. Huang,
T. R. Quinn, K. Harms, R. D. Webster, L. Zhang, O. Wiest, E. Meggers,
J. Am. Chem. Soc. 2017, 139, 9120; o) K. Shimomaki, K. Murata, R.
Martin, N. Iwasawa, J. Am. Chem. Soc. 2017, 139, 9467; p) M. J. James,
J. L. Schwarz, F. Strieth-Kalthoff, B. Wibbeling, F. Glorius, J. Am. Chem.
Soc. 2018, 140, 8624; q) L.-L. Liao, G.-M. Cao, J.-H. Ye, G.-Q. Sun, W.-
J. Zhou, Y.-Y. Gui, S.-S. Yan, G. Shen, D.-G. Yu, J. Am. Chem. Soc.
2018, 140, 17338; r) T. Morack, C. Mück-Lichtenfeld, R. Gilmour, Angew.
Chem. Int. Ed. 2019, 58, 1208; s) X. Bao, Q. Wang, J. Zhu, Angew. Chem.
Int. Ed. 2019, 58, 2139; t) X. Jiang, M.-M. Zhang, W. Xiong, L.-Q. Lu, W.-
J. Xiao, Angew. Chem. Int. Ed. 2019, 58, 2402; u) M. Zhu, C. Zheng, X.
Zhang, S.-L. You, J. Am. Chem. Soc. 2019, 141, 2636; v) C. Theunissen,
M. A. Ashley, T. Rovis, J. Am. Chem. Soc. 2019, 141, 6791: w) T. Patra,
S. Mukherjee, J. Ma, F. Strieth-Kalthoff, F. Glorius, Angew. Chem. Int.
Ed. 2019, 58, 10514; x) S. I. Faßbender, J. J. Molloy, C. Mück-Lichtenfeld,
R. Gilmour, Angew. Chem. 2019, 131, 18792; y) C. Kerzig, O. S. Wenger,
Chem. Sci. 2019, 10, 11023; z) D. Rombach, H. -A. Wagenknecht,
Angew. Chem. Int. Ed. 2020, 59, 300
direct S0→Tn
transition
Bond Dissociation
Energy
Bi
19 (S0)
∆H = 0.0
(Bpin)2
(10 equiv)
h!
CH2Cl2
rt, 24 h
c)
O
B
BiPh3
19
h! (365 nm)
O
BiPh3Cl2
CH2Cl2
rt, 24 h
20
21
53% (365 nm)
74% (400 nm)
42%
No reaction occurred in the dark at rt.
Figure 6. (a) Absorption and emission properties of triphenylbismuthine(III) 19;
the vertical axis is normalized. (b) Energy diagram of triplet state and bond
dissociation of 19. Calculations were performed with mPW1PW91/SDD (for Bi)
and cc-pVTZ (for the other atoms). (c) Radical reactions of 19 via a direct S0→
Tn transition. (BPin)2: Bis(pinacolato)diboron
Conclusion
In summary, we have demonstrated that photoactivation of
hypervalent iodine with light of an apparently non-absorbing
This article is protected by copyright. All rights reserved.

10.1002/anie.201915181
Angewandte Chemie International Edition
RESEARCH ARTICLE
[2]
a) Y. Kita, H. Tohma, K. Kikuchi, M. Inagaki, T. Yakura, J. Org. Chem.
1991, 56, 435; b) Y. Kita, H. Tohma, K. Hatanaka, T. Takada, S. Fujita,
S. Mitoh, H. Sakurai, S. Oka, J. Am. Chem. Soc. 1994, 116, 3684; c) V.
V. Zhdankin, A. P. Krasutsky, C. J. Kuehl, A. J. Simonsen, J. K.
Woodward, B. Mismash, J. T. Bolz, J. Am. Chem. Soc. 1996, 118, 5192;
d) D. Macikenas, E. Skrzypczak-Jankun, J. D. Protasiewicz, J. Am.
Chem. Soc. 1999, 121, 7164; e) U. H. Hirt, B. Spingler, T. Wirth, J. Org.
Chem. 1998, 63, 7674; f) K. C. Nicolaou, T. Montagnon, P. S. Baran, Y.-
L. Zhong, J. Am. Chem. Soc. 2002, 124, 2245; g) P. Eisenberger, S.
Gischig, A. Togni, Chem. Eur. J. 2006, 12, 2579; h) I. Kieltsch, P.
Eisenberger, A. Togni, Angew. Chem. Int. Ed. 2007, 46, 754; i) R. J.
Phipps, M. J. Gaunt, Science 2009, 323, 1593; j) J. P. Brand, J. Waser,
Angew. Chem. Int. Ed. 2010, 49, 7304; k) S. M. Banik, J. W. Medley, E.
N. Jacobsen, Science 2016, 353, 51; l) A. Yoshimura, V. V. Zhdankin,
Chem. Rev. 2016, 116, 3328.
[3]
[4]
a) F. Mininsci, E. Vismara, F. Fontana, M. C. N. Barbosa, Tetrahedron
Lett. 1989, 30, 4569; b) H. Togo, M. Aoki, M. Yokoyama, Tetrahedron
Lett. 1991, 32, 6559; c) H. Togo, M. Aoki, M. Yokoyama, Chem. Lett.
1992, 21, 2169; d) H. Togo, M. Aoki, M. Yokoyama, Tetrahedron 1993,
49, 8241; e) H. Togo, R. Taguchi, K. Yamaguchi, M. Yokoyama, J. Chem.
Soc. Perkin Trans. I 1995, 2135.
a) J. Xie, P. Xu, H. Li, Q. Xue, H. Jin, Y. Cheng, C. Zhu, Chem. Commun.
2013, 49, 5672; b) Z. He, M. Bae, J. Wu, T. F. Jamison, Angew. Chem.
Int. Ed. 2014, 53, 14451; c) Y. Wang, G.-X. Li, G. Yang, G. He, G. Chen,
Chem. Sci. 2016, 7, 2679; d) P. Becker, T. Duhamel, C. J. Stein, M.
Reiher, K. Muñiz, Angew. Chem. Int. Ed. 2017, 56, 8004; e) H. Zhang, K.
Muñiz, ACS Catal. 2017, 7, 4122; f) Z. Wang, A. G. Herraiz, A. M. del
Hoyo, M. G. Suero, Nature 2018, 554, 86; g) Y. Liang, X. Zhang, D. W.
C. MacMillan, Nature 2018, 559, 83; h) J. Genovino, Y. Lian, Y. Zhang,
T. O. Hope, A. Juneau, Y. Gagné, G. Ingle, M. Frenette, Org. Lett. 2018,
20, 3229; i) T. Duhamel, K. Muñiz, Chem. Commun. 2019, 55, 933.
a) S. A. Moteki, A. Usui, S. Selvakumar, T. Zhang, K. Maruoka, Angew.
Chem. Int. Ed. 2014, 53, 11060; b) H. Tan, H. Li, W. Ji, L. Wang, Angew.
Chem. Int. Ed. 2015, 54, 8374; c) W. Ji, H. Tan, M. Wang, P. Li, L. Wang,
Chem. Commun. 2016, 52, 1462; d) S. Yang, H. Tan, W. Ji, X. Zhang, P.
Li, L. Wang, Adv. Synth. Catal. 2017, 359, 443; e) S. Selvakumar, R.
Sakamoto, K. Maruoka, Chem. Eur. J. 2016, 22, 6552; f) R. Sakamoto,
H. Kashiwagi, K. Maruoka, Org. Lett. 2017, 19, 5126; g) Y. Kobayashi, S.
Masakado, Y. Takemoto, Angew. Chem. Int. Ed. 2018, 57, 693; h) X. Wu,
H. Zhang, N. Tang, Z. Wu, D. Wang, M. Ji, Y. Xu, M. Wang, C. Zhu, Nat.
Commun. 2018, 9, 3343; i) C. F. Meyer, S. M. Hell, A. Misale, A. A.
Trabanco, V. Gouverneur, Angew. Chem. Int. Ed. 2019, 58, 8829.
a) Y. Kanda, H. Kaseda, T. Matumura, Spectrochim. Acta 1964, 20,
1387; b) D. R. Kearns, W. A. Case, J. Am. Chem. Soc. 1966, 88, 5087;
c) A. P. Marchetti, D. R. Kearns, J. Am. Chem. Soc. 1967, 89, 768.
See the Supporting Information for details.
[5]
[6]
[7]
[8]
N. J. Turro, V. Ramamurthy, J. C. Scaiano, Principles of Molecular
Photochemistry – An Introduction, University Science Books, Sausalito,
CA, 2009.
[9]
a) T. H. Dunning Jr., J. Chem. Phys. 1989, 90, 1007; b) M. Dolg, U.
Wedig, H. Stoll, H. Preuß, J. Chem. Phys. 1987, 86, 866; c) D. Andrae,
U. Haüßermann, M. Dolg, H. Stoll, H. Preuß, Theor. Chim. Acta 1990,
77, 123; d) A. Bergner, M. Dolg, W. Kuchle, H. Stoll, H. Preuß, Mol. Phys.
1993, 80, 1431; e) H. S. Yu, X. He, S. L. Li, D. G. Truhlar, Chem. Sci.
2016, 7, 5032; f) K. Matsumoto, M. Nakajima, T. Nemoto, J. Phys. Org.
Chem. 2019, 32, e3961.
This article is protected by copyright. All rights reserved.

10.1002/anie.201915181
Angewandte Chemie International Edition
RESEARCH ARTICLE
Entry for the Table of Contents (Please choose one layout)
Layout 1:
RESEARCH ARTICLE
R
I
R
Ar
I
h! (365, 400, 450 nm)
Direct S0
→
Tn transition:
Ar
Radical reaction
Masaya Nakajima*, Sho
Nagasawa, Koki Matsumoto,
Takahito Kuribara, Atsuya
Muranaka, Masanobu
Uchiyama, Tetsuhiro
Nemoto*
Ar Br
Bi Ph3
Spectroscopic experiments
revealed that photoreactions
of heavy-atom-containing
molecules with light from the
apparently non-absorbing
region proceed via a
Forbidden direct
S0→Tn transition!
Sn
S1
Tn
T1
Radical
reaction
S0
Page No. – Page No.
forbidden direct S0→Tn
transition. This phenomenon
occurs in the photoreaction
of aryl iodides (I, III, and V),
aryl bromide, and
Direct S0
→
Tn Transition
Sheds Light on the
Mystery of Photoreaction
of Heavy-Atom-Containing
Molecules
bismuth(III)-containing
Layout 2:
RESEARCH ARTICLE
Author(s), Corresponding Author(s)*
((Insert TOC Graphic here. Note: Please provide a legible image, 11×2.5 cm (w×h),
Page No. – Page No.
min. font size 6-7 pt.))
Title
Text for Table of Contents, 450 characters with spaces.
This article is protected by copyright. All rights reserved.