Adiabatic process of higher electronically excited states: luminescence from an excited state biradical generated by irradiation of benzophenone-substituted cyclopropanes

Article abstract of DOI:10.1002/poc.3636

Adiabatic photochemical reactions of cyclopropanes possessing a benzophenone moiety (trans- and cis-5), which generate a luminescent excited biradical ¹6^??*, were studied. Various photochemical and spectroscopic techniques were used for this purpose. Excitation (350 nm, n,π* band) of 5 at 77?K affords the lowest excited state ¹5* that undergoes intersystem crossing to form ³5*, which deactivates through phosphorescence. In contrast, 295-nm excitation (π,π* band) of 5 affords the higher electronically excited state ¹5**, which undergoes adiabatic C–C bond cleavage reaction to form the excited biradical ¹6^??* that luminesces at 630?nm. The results suggest that 5 follows 2 photoreaction modes depending on the excitation wavelength, a finding that disobeys Kasha's rule.

Full text of DOI:10.1002/poc.3636

Received: 27 June 2016
DOI 10.1002/poc.3636
Revised: 6 August 2016
Accepted: 9 August 2016
S P E C I A L I S S U E A R T I C L E
Adiabatic process of higher electronically excited states:
luminescence from an excited state biradical generated by
†
irradiation of benzophenone‐substituted cyclopropanes
1,2
1
1,2
1,2*
Yasunori Matsui | Toru Oishi | Eisuke Ohta | Hiroshi Ikeda
1
Department of Applied Chemistry, Graduate
Adiabatic photochemical reactions of cyclopropanes possessing a benzophenone
School of Engineering, Osaka Prefecture
1
••
University, Sakai, Osaka 599‐8531, Japan
moiety (trans‐ and cis‐5), which generate a luminescent excited biradical 6 *,
were studied. Various photochemical and spectroscopic techniques were used for
this purpose. Excitation (350nm, n,π* band) of 5 at 77 K affords the lowest excited
2
The Research Institute for Molecular Electronic
Devices (RIMED), Osaka Prefecture University,
Sakai, Osaka 599‐8531, Japan
1
3
state 5* that undergoes intersystem crossing to form 5*, which deactivates through
phosphorescence. In contrast, 295‐nm excitation (π,π* band) of 5 affords the higher
Correspondence
H. Ikeda, Department of Applied Chemistry,
Graduate School of Engineering, Osaka Prefecture
University, Sakai, Osaka 599‐8531, Japan.
Email: ikeda@chem.osakafu‐u.ac.jp
1
electronically excited state 5**, which undergoes adiabatic C–C bond cleavage
reaction to form the excited biradical 6 * that luminesces at 630 nm. The results
1 ••
suggest that 5 follows 2 photoreaction modes depending on the excitation
wavelength, a finding that disobeys Kasha's rule.
KEYWORDS
anti‐Kasha's rule, biradical, C–C bond cleavage reaction, higher excited state,
multiplicity
[
16–18]
1
|
INTRODUCTION
this photoreaction have been performed,
mechanism still remains unclear. In
the detailed
a
recent study,
[
1–3]
Photochemical homolytic bond cleavage reactions
that
we uncovered an adiabatic photoreaction of the
methylenecyclopropane derivative 3 possessing a benzophenone
[4]
generate ground state radical pairs are termed nonadiabatic
processes. On the other hand, similar bond cleavage reactions
that produce electronically excited states of radical pairs or
[3–5]
biradicals are referred to as adiabatic processes.
Observa-
tions of luminescence associated with adiabatic photochemi-
cal reactions have been described previously. Examples
of this phenomenon include fluorescence associated with
excited
azolylphenols
derivatives.
state
intramolecular
and chemiluminescence of 1,2‐dioxetane
proton
transfer
of
[
6–11]
[
12,13]
Photoreactions of 1,2‐diphenylcyclopropanes (1),
reported by Becker and Ramamurthy, also display “unusual”
luminescence behavior associated with excited state
biradical generation by photoinduced C–C bond cleavage
[
14,15]
(Scheme 1A).
Although many mechanistic studies of
†This article is published in Journal of Physical Organic Chemistry as a
special issue on the Symposium on Reactive Intermediates and Unusual
Molecules held at Pacifichem 2015.
SCHEME 1 “The excited state C–C bond cleavage‐luminescence” phenom-
ena of (A) 1a‐b, (B) 3, and (C) 5
J. Phys. Org. Chem. 2016; 1–8
wileyonlinelibrary.com/journal/poc
Copyright © 2016 John Wiley & Sons, Ltd.
1

2
MATSUI ET AL.
(BP) moiety (Scheme 1B) and demonstrated that emission in
this system is a result of triplet‐triplet fluorescence (575 nm)
3
•• [19–23]
of the excited (noted by *) biradical 4 *.
We refer to
this phenomenon as “excited state C–C bond cleavage‐lumi-
[
24,25]
nescence.”
Analyses of transient absorption and emis-
sion results, obtained using double laser flash photolysis
3
••
3
(
LFP), showed that 4 * is formed adiabatically from 3*,
which itself is generated by rapid intersystem crossing
1
(
ISC) in 3* owing to the presence of the BP moiety. This
observation suggests that introduction of 1 BP moiety
into the methylenecyclopropane system is sufficient to
enable ISC to be competitive with other undesirable reactions
1
[26–28]
of 3*.
In the current investigation, we used the enhanced ISC
[
29–31]
effect of a BP moiety on a diarylcyclopropane system
SCHEME 2 Routes used for synthesis of trans‐ and cis‐5. Reagents and con-
to control the nature of electronic excited states and lumines-
cence properties of biradicals generated by homolytic C–C
bond cleavage. For example, n,π*‐excitation (λEX = 355 nm)
of the BP moiety in trans‐ and cis‐1‐(4‐benzoylphenyl)‐2‐
phenylcyclopropane (5, Scheme 1C) should lead to
production of biradical‐derived luminescence, because it is
ditions: (i) H
2
NNHTs/methanol, rt; (ii) NaOCH
2
n
CH
2
OH/ethylene glycol/
n
hexane, reflux; (iii) hν/BP/styrene, rt; and (iv) BuLi/PhCON(CH
3
)
2
/THF
2.2 | Ultraviolet‐Visible absorption spectra
The ultraviolet‐visible absorption spectra of methylcyclohexane
solutions of trans‐ and cis‐5 (MCH, Figure 1, red and blue)
contain intense π,π* and weak n,π* bands at 280 and
3
expected that 5*, formed by rapid ISC, will undergo
adiabatic bond cleavage reaction to give excited biradical
3
40 nm, respectively. The π,π* bands of trans‐ and cis‐5
3
3
••
••
3
6
6
*. However, the results show that 5* does not produce
occur at longer wavelengths than that of BP (Figure 1,
black) as a result of electronic coupling between the aryl
ketone and phenylcyclopropane moieties.
* but rather it generates the ground state triplet
3
••
biradical 6 . In contrast, luminescence occurs from upon
π,π*‐excitation (λEX = 295 nm) of 5. In this case, the
higher excited state (denoted by **) 5** is generated that,
1
2
.3 | Matrix isolation experiments
contrary to Kasha's rule, undergoes adiabatic C–C bond
•
•
cleavage to form the excited biradical 6 *. The results of a
In a manner similar to BP, trans‐ and cis‐5 do not exhibit
photoluminescence in MCH at room temperature. Excitation
of BP in a degassed MCH matrix at 77 K with either 350
(n,π*, Figure 2A, black) or 295 nm (π,π*, Figure 2B, black)
light gives rise to a typical phosphorescence signal at
photochemical and spectroscopic investigation that led
•
•
to the observation of adiabatic formation of 6 * from
1
trans‐5** are described below.
4
7
19 nm. Excitation of trans‐5 in a degassed MCH matrix at
7 K by using 350‐nm light (n,π*) results in the formation
2
2
|
RESULTS AND DISCUSSION
of a relatively broad phosphorescence band (Figure 2A,
blue), which is associated with emission from BP*. In con-
trast, excitation of this substance at 295 nm (π,π* band)
results in formation of a broad emission band at 630 nm,
which is assignable to fluorescence of the singlet excited
biradical 6 * (Figure 2B, blue), together with phosphores-
cence from trans‐5*. The excitation spectrum of trans‐5
obtained monitoring emission at 419 nm (λDET) contains 2
3
.1 | Synthesis of trans‐ and cis‐5 bearing BP moieties
The trans‐ and cis‐ isomers of the BP moiety containing
a diarylcyclopropane 5 were synthesized starting with
4
Scheme 2. Condensation of 4‐bromobenzaldehyde and
tosylhydrazine in methanol gave 4‐bromobenzaldehyde
tosylhydrazone (7),
1
••
3
‐bromobenzaldehyde using the procedure shown in
[
32]
which upon treatment with
NaOCH CH OH generated 4‐bromophenyldiazomethane
2
2
(
8). Addition of the carbene, formed by photodeazetation
reaction of 7, to styrene yielded a mixture of trans‐ and
cis‐1‐(4‐bromophenyl)‐2‐phenylcyclopropane (trans‐ and
[
33,34]
cis‐9),
which were separated by using preparative
gel permeation chromatography (GPC). Independent
lithiation reactions of trans‐ and cis‐9 followed by
addition of N,N‐dimethylbenzamide produced trans‐ and
cis‐5.
FIGURE 1 Ultraviolet‐visible absorption spectra of (black) BP and (red)
trans‐ and (blue) cis‐5 (A, 0.01mM; B, 0.1mM) in MCH at room temperature

MATSUI ET AL.
3
The photostationary state ratio of the stereoisomers is
described by Equation 1,
½
trans‐5ꢀ
ε
× ΦROcis‐5
ꢁ
cis‐5
¼
α ×
(1)
½
cis‐5ꢀ
ε
× ΦROtrans‐5
ꢁ
trans‐5
where α, ε, and ΦRO are the ratio of branching trans‐5/
•
•
cis‐5 in the ring‐closing reaction of 6 , molar absorption
coefficients of the isomers of 5, and quantum yields for the
•
•
ring‐opening reaction of 5* to form 6 , respectively. Note
FIGURE 2 Emission spectra obtained by excitation at (A) λEX = 350 nm
and (B) λEX = 295 nm of (black) BP and (red) trans‐ and (blue) cis‐5
that no significant difference exists between εtrans‐5 and εcis‐5
(1mM) in the degassed MCH matrices at 77 K
(Figure 1B). The fact that [trans‐5]/[cis‐5] at the
photostationary state is almost unity (Figure 4) indicates that
α is ca 1, if ΦRO for trans‐5* (ΦROtrans‐5*) and cis‐5*
bands at 266 and 340 nm (Figure 3, black). In contrast, the
excitation spectrum of this substance obtained monitoring
emission at 630 nm contains a broad band centered at
(
ΦROcis‐5*) is the same.
Photoirradiation of a CH Cl solution of trans‐5 under an
2
2
2
79 nm (Figure 3, red). In the case of cis‐5 (Figure 2B,
air atmosphere for 20 hours produces keto‐aldehyde 11 in a
% yield and trace amounts of the carbonyl compounds 12
3
red), intense phosphorescence from cis‐5* (419 nm) and
4
1
••
relatively weak fluorescence from 6 * (630 nm) are also
observed. The only difference between the behaviors of
trans‐ and cis‐5 is the efficiencies of their primary photo-
chemical processes. The combined results indicate that
trans‐5 undergoes 2 photoreactions that occur via respective
to 14, together with recovered cis‐ and trans‐5 both in 24%
yields (Scheme 3). The products of this photoreaction origi-
[43]
nate from endoperoxide 10
that is the primary photoprod-
••
3
uct formed by trapping of 6 with molecular oxygen ( O ).
2
In accord with this proposal is the observation that transient
1
1
lower and higher energy trans‐5* and trans‐5**. In
••
absorption of 6 observed in the LFP experiment decays
addition, the results suggest that photochemical reaction of
faster in aerated relative to degassed CCl (see below).
4
1
••
trans‐5 to form the excited biradical 6 * takes place upon
excitation exclusively at 295 nm.
2
.5 | Transient absorption spectroscopy
To gain additional insight into the intermediates that partici-
pate in the photoisomerization reactions of trans‐ and cis‐5,
LFP (355 nm) studies were performed. LFP (355‐nm excita-
tion) of trans‐ and cis‐5 at room temperature in degassed ben-
zene or CH Cl does not give rise to formation of absorption
bands even after 50 ns even though the photoisomerization
reaction occurs under similar conditions. It is likely that the
reason for this is that C–C bond formation in the intermediate
biradical 6•• occurs rapidly in these solvents.
2
.4 | Cis‐Trans isomerization
Photoirradiation (350 nm) of trans‐ and cis‐5 (10mM) in
degassed CDCl at room temperature efficiently promotes
cis‐trans isomerization (Figure 4, Scheme 3).
process probably proceeds via biradical 6 (see below).
3
[35–42]
This
2
2
•
•
In contrast, LFP of trans‐ or cis‐5 in degassed CCl at
4
room temperature leads to production of a transient
FIGURE 3 Excitation spectra of trans‐5 (1mM, λDET = 419 [black] and
6
30 nm [red]) in the degassed MCH matrix at 77 K
FIGURE 4 Relative yields (determined by using proton nuclear magnetic
SCHEME 3 Products of photooxygenation reactions of trans‐ and cis‐5 in
resonance spectroscopy) as a function of time in the photoisomerization
2 2
aerated CH Cl solutions (isolated yields following 20‐hour irradiation
reactions of (A) trans‐ and (B) cis‐5 (10mM) in CDCl
3
periods)

4
MATSUI ET AL.
absorption band at 380 nm (Figure 5, decay time <90 μs),
•
•
which is assigned to 6 . The characteristics of this band cor-
1
••
3 ••
respond to the electronic transitions of 6 and/or 6
(
Figure 6) that are calculated by using time‐dependent density
[
44]
functional theory.
Decay of the 380‐nm transient absorp-
tion band, which takes place in a second‐order manner with
4
3 −1
2
rate constants of kDECAY = 1.1 × 10 and 1.6 × 10 s ,
is accelerated in the presence of air, possibly because of
•
•
3
trapping of 6 by O . The fact that no absorption band is
2
observed in the 530‐nm region, which is expected for
3
[45]
absorption by the BP* moiety,
suggests that rapid C–C
3
3 ••
bond cleavage of 5* occurs to form 6 at room tempera-
ture. The most likely reason for the observation made using
a CCl solution is kinetic and/or thermodynamic stabilization
4
3
••
of the triplet state 6 , which cannot afford the singlet
product 5 directly.
[
46]
FIGURE 7 Time‐resolved emission spectra and the corresponding time‐
profiles observed upon laser flash photolysis (355 nm) of (A and B) trans‐
2.6 | Analysis of time‐resolved emission
LFP (355 nm) of trans‐ and cis‐5 in degassed CCl at room
4
and (C and D) cis‐5 (2mM) in degassed CCl at room temperature
4
temperature gives rise to nearly identical weak fluorescence
1
••
bands at 666 nm arising in both cases from 6 * (Figure 7
A and C). Interestingly, this emission is not observed imme-
diately following (red) but rather 10 ns (orange) after the laser
pulse. The existence of this delay time strongly suggests that
••
6 * is generated via a 2‐photon process. The emission band
••
corresponding to 6 * arising from trans‐ or cis‐5 decays
with a single exponential function with a lifetime of ca
2
60 ns (Figure 7B and D). This finding indicates that lumi-
••
nescence from 6 * is fluorescence rather than
phosphorescence.
1
••
Insight into the proposal that formation of 6 * involves
a stepwise 2‐photon absorption process was gained by
determining the relationship between the intensity of
−
1
the excitation laser pulse (I /mJ pulse ) and that of emission
L
1
••
(
I , Figure 8A). If 6 * is generated via a 2‐photon process,
E
2
I should be proportional to I . However, the experimental
E
L
2
results demonstrate that I is dependent on both I and I
E
L
L
(Figure 8B, solid) in the following relationship:
2
IE ¼ 0:00213IL þ 0:00066IL
This finding indicates that a 1‐photon process directly
generating 6 * occurs concurrently with a 2‐photon
FIGURE 5 Transient absorption spectra obtained upon laser flash photoly-
1
••
sis (355 nm) of (A) trans‐ and (C) cis‐5 (2mM) in degassed CCl
temperature and their time‐dependent changes at 380 nm of (B) trans‐ and
D) cis‐5
4
at room
(
FIGURE 8 A, Emission spectra obtained upon laser flash photolysis
(
4 L
355 nm) of trans‐5 (2mM) in degassed CCl at room temperature when I
1
••
3
••
−1
FIGURE 6 Electronic transitions of (A) 6 and (B) 6 calculated at the
time‐dependent–UB3LYP/cc‐pVDZ level of theory
is 1, 3, 5, 8, 10, and 13 mJ pulse (from the bottom to the top). B, Rela-
tionship of I against the I
E L

MATSUI ET AL.
5
FIGURE 9 Energy diagrams for photoreactions of trans‐ and cis‐5. Energy levels are determined by using wavelengths of luminescence and the results of
1
••
density functional theory calculations [(U)B3LYP/cc‐pVDZ]. Pink and light blue correspond to the formation of 6 * via adiabatic and stepwise 2‐photon
pathways, respectively. ISC, intersystem crossing
−
1
process. When I is 10 mJ pulse , the ratio of the relative
Kasha's rule, which states that internal conversion from the
higher excited states to the lowest ones with the same multi-
L
contribution of the 1‐ and 2‐photon processes is calculated
to be 24/76. Note that the I value at 666 nm used in this
plicity should be faster than any other processes involving
E
1
••
[48,49]
calculation includes not only fluorescence of 6 * but also
light emissions.
Consequently, owing to conservation
3
the broad phosphorescence (Figure 8A) of 5*, which is also
of multiplicity, the luminescent biradical most likely is the
1
••
generated via a 1‐photon process. Thus, the actual contribu-
tion of the 2‐photon process in the 666‐nm band should be
greater than 76%.
excited singlet 6 * rather than its triplet counterpart.
1
The energy of trans‐5** is 4.14 eV, owing to its absorp-
tion wavelength of 295 nm, and is sufficiently high for adia-
••
batic and exergonic formation of 6 * (>3.25 eV). Analyses
of the excitation spectrum corresponding to the 630‐nm
emission band (Figure 3, blue) also support the conclusion
2.7 | Analysis of energy diagram
1
To analyze the energy changes occurring in photoreactions of
trans‐ and cis‐5, an energy diagram (Figure 9) was
constructed using luminescence wavelengths and the
energies obtained by using density functional theory
that anti‐Kasha behavior is taking place in that trans‐5** is
1
••
converted directly to 6 *. Although luminescence associ-
1
••
ated with 6 * occurs following 355‐nm LFP (Figure 8A),
formation of this excited singlet biradical from an energetic
viewpoint likely involves a stepwise 2‐photon process
(Figure 9, light blue). Note that the mechanism for the
luminescence phenomenon of cis‐5 is similar to that of
trans‐5, except for the fact that cis‐5 has a higher energy than
[(U)B3LYP/cc‐pVDZ] calculations. In this diagram, all
energies are given relative to that of trans‐5. The respective
1
3
energies of trans‐5* and trans‐5*, which are formed by
3
55‐nm excitation and ISC, respectively, are determined to
[47]
1 ••
be 3.28 and 2.96 eV, according to the literature.
the energies of 6 and 6 are computed to be 1.29 and
1
form 6 occur in a highly exergonic manner. Note that the
energy gap between 6 and 6 is negligibly small and,
as a result,
equilibrium.
Because
trans‐5 by 0.13 eV, and formation of 6 * from cis‐5 is less
1
••
3 ••
efficient than that from trans‐5, possibly as a consequence of
3
.28 eV, respectively, ring‐opening reactions of trans‐5* to
stereoelectronic factors (eg, differences in their ability to form
3
••
[50]
an intramolecular exciplex).
1
••
3 ••
1
••
3 ••
6
and
6
should be in rapid thermal
3 | CONCLUSIONS
1
••
Based on its fluorescence wavelength, biradical ( 6 *)
should have an energy of at least 3.25 eV. Thus, adiabatic
In the investigation described above, we elucidated the
mechanism for adiabatic photochemical reactions of trans‐
and cis‐5 by using photochemical (product analysis) and
photophysical (spectroscopic) techniques. The results sug-
3
3 ••
ring‐opening reaction of trans‐5* (2.96 eV) to form 6 *
1
••
(
and then 6 *) is energetically unfavorable. Therefore, to
1
••
explain its efficient formation, 6 * could be formed adia-
batically from a higher excited state, ie, trans‐5**
1
1 ••
gest that the excited biradical 6 * is not generated in an
(Figure 9, pink). Of course, this proposal is contrary to the
adiabatic reaction following n,π*‐excitation that forms the

6
MATSUI ET AL.
1
1 ••
lowest singlet excited state 5*. Rather, 6 * is produced
(ATR) ν = 814.8, 1006.7, 1068.4, 1182.2, 1372.1, 1487.8,
and 2044.2 cm .
−
1
by C–C bond cleavage in the upper singlet excited state
1
5
** formed by π,π*‐excitation. n,π*‐Excitation (350 nm)
3 1
of 5 affords 5* through ISC of 5* but it does not produce
4
.1.3 | Trans‐ and cis‐1‐(4‐bromophenyl)‐2‐phenylcyclopro‐
•
•
6
* owing to the existence of a reasonably high
pane (trans‐ and cis‐9)
energy gap.
Under Ar atmosphere, 8 (0.79 g, 4.0 mmol) and BP
Thus, the system probed in this effort has provided an
important example of a process that breaks Kasha's rule.
In contrast, 355‐nm (n,π*) excitation of 5 does generate
(4.0 g, 22.0 mL) in 20 mL of styrene were photoirradiated
[
1,2]
with Rayonet Lamp (50 W, λEX = 350 nm) for 12 hours.
The color of the solution turned yellow. After removal of
the excess amount of styrene under reduced pressure, puri-
fication using column chromatography (silica gel, toluene)
•
•
6
*, likely through a stepwise 2‐photon pathway. The
results of this effort demonstrate that exceptional stabilization
of biradicals, such as by incorporating them in a
trimethylenemethane moiety, is required to be able to
promote adiabatic hemolytic C–C bond cleavage reactions
from excited triplet states. It is significant that investigations
of adiabatic photoreactions, like those performed in this
study, contribute important information needed for the
development of a new field of photochemistry, which focuses
on photophysical and photochemical properties of higher
electronically excited states.
and preparative GPC afforded trans‐ (0.88 g, 3.21 mmol,
[48]
3
2%) and cis‐9 (0.42 g, 1.52 mmol, 11%)
as colorless
1
oil. trans‐9: H NMR (300 MHz, CDCl ) δ
1.38 to
3
ppm
1
4
.50 (m, 2H), 2.08 to 2.15 (m, 2H), 7.25 to 7.35 (m,
H), 7.40 to 7.43 (m, 5H). cis‐9: H NMR (300 MHz,
1
CDCl ) δ
1.25 to 1.40 (m, 2H), 2.35 to 2.55 (m,
3
ppm
2
2
H), 6.77 (d, J = 2.7 Hz, 2H), 6.90 (d, J = 2.7 Hz,
H), 7.02 to 7.40 (m, 5H).
4
.1.4 | Cis‐1‐(4‐benzoylphenyl)‐2‐phenylcyclopropane (cis‐5)
n
n
Under Ar atmosphere at −78°C, BuLi (2 M in hexane,
.14 mL, 2.3 mmol) was added dropwise to a 5.0 mL of
4
4
|
EXPERIMENTAL SECTION
1
THF solution containing cis‐9 (322 mg, 1.18 mmol). After
.1 | Preparation of substrates
stirring for 15 minutes, PhCON(CH ) (343 mg, 2.3 mmol)
3
2
in 5 mL of THF was added dropwise to the mixture. After
stirring for 3 hours, the mixture was allowed to warm to room
4
.1.1 | 4‐Bromobenzaldehyde tosylhydrazone (7)
mixture of H NNHTs (1.0 g, 5.5 mmol) and
2
‐bromobenzaldehyde (0.93 g, 5.0 mmol) in methanol was
A
4
temperature and quenched with aqueous NH Cl. The organic
4
layer was extracted with ether (30 mL × 3) and washed with
brine. After removal of the solvents, the residual mixture was
purified using column chromatography (silica gel, toluene)
and preparative GPC. Recrystallization of the resulting solid
from methanol afforded cis‐5 (139 mg, 0.47 mmol, 40%) as
stirred at room temperature for 2 hours. After removal of
the solvents, recrystallization of the resulting solid from
methanol afforded 7 (1.49 g, 23 mmol, 85%) as colorless
needles. 7: mp 171°C to 174°C; H NMR (300 MHz, CDCl )
δppm 2.42 (s, 3H), 7.33 (AA′XX′, J = 8.4 Hz, 2H), 7.45 (AA′
BB′, J = 8.7 Hz, 2H), 7.50 (AA′BB′, J = 8.7 Hz, 2H), 7.69
1
3
1
colorless powder. cis‐5: mp 42°C to 43°C; H NMR
(
300 MHz, CDCl ) δ
1.44 to 1.60 (m, 2H), 2.49 to 2.66
3
ppm
(s, 1H), 7.79 (s, 1H), 7.87 (AA′XX′, J = 8.4 Hz, 2H).
(
m, 2H), 6.98 to 7.20 (m, 7H), 7.40 to 7.46 (m, 2H), 7.52
13
to 7.57 (m, 1H), 7.67 to 7.70 (m, 4H); C NMR (75 MHz,
CDCl ) δ 12.2, 24.4, 25.7, 126.2, 128.1 (2C), 128.4
4
.1.2
|
4‐Bromophenyldiazomethane (8)
3
ππμ
(2C), 128.7, 129.5 (2C), 129.9 (2C) 130.1 (2C), 132.3 (2C),
Metallic sodium (0.210 g, 7.20 mmol) was slowly added to
0 mL of dry ethylene glycol to prepare a NaOCH CH OH
1
1
6
34.9, 137.7, 138.2, 144.6, 196.7; IR (KBr) 702, 1280,
1
2
2
−
1
603, and 1647 cm ; Anal. Calcd for C H O: C 88.56 H
22 18
solution. The substrate 7 (1.27 g, 3.60 mmol) was slowly
added to the solution and vigorously stirred. Ten milliliters
of hexane was added to the resultant solution, and the
.08 O 5.36; Found: C 88.60 H 6.14.
n
mixture was warmed with vigorous stirring for 5 minutes at
4.1.5
| Trans‐1‐(4‐benzoylphenyl)‐2‐phenylcyclopropane
(trans‐5)
7
0°C to 80°C. The organic layer was removed by pipette
n
n
n
and another 10 mL of hexane was added with continued
stirring. The procedure was repeated a total of 5 times. The
combined organic extracts were washed with aqueous NaOH
and brine. After filtration, the solvent was removed to afford
Under Ar atmosphere at −70°C, BuLi (1.6 M in hexane,
0.94 mL, 1.5 mmol) was added dropwise to a 5.0 mL of
THF solution containing trans‐9 (273 mg, 0.84 mmol). After
stirring for 15 minutes, PhCON(CH ) (224 mg, 1.5 mmol)
in 5 mL of THF was added dropwise to the mixture. After
stirring for 3 hours, the mixture was allowed to warm to room
3
2
[
51]
8
(0.553 g, 2.81 mmol, 78%) as red solid. Compound 8
slowly decomposes in organic solution with evolution of N2
1
at ambient temperature even in the dark. 8: H NMR
temperature and quenched with aqueous NH Cl. The organic
4
(
300 MHz, CDCl ) δ
4.90 (s, 1H), 6.78 (AA′XX′,
layer was extracted with ether (30 mL × 3) and washed with
brine. After removal of the solvents, the residual mixture was
3
ppm
J = 4.5 Hz, 2H), 7.38 (AA′XX′, J = 4.5 Hz, 2H); IR

MATSUI ET AL.
7
purified using column chromatography (silica gel, toluene)
and preparative GPC. Recrystallization of the resulting solid
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1
colorless powder. trans‐5 : mp 58°C to 59°C; H NMR
[
[
[
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(
300 MHz, CDCl ) δ
1.51 to 1.61 (m, 2H), 2.20 to 2.30
3
ppm
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3
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1
971, 1, 92.
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CDCl ) δ 19.2, 28.3, 29.3, 125.6 (2C), 126.0 (2C), 128.5
3
ππμ
[
[
(2C), 128.7 (2C), 130.2 (2C), 131.0 (2C), 132.4 (2C),
1
1
1
35.2, 138.2, 142.0, 148.2, 196.3; IR (KBr) 687.1, 752.1,
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−
1
C H O: C 88.56 H 6.08 O 5.36; Found: C 88.63 H 6.05.
2
2
18
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4
.1.6
|
Laser flash photolysis
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4
.1.7 | Quantum chemical calculations
[
[
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Tetrahedron 2011, 67, 7431.
Geometry optimizations were performed with the cc‐pVDZ
basis set, using the (U)B3LYP method. No imaginary
frequencies were found. Electronic transitions were
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the cc‐pVDZ basis set. All calculations were performed on
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[
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2
062.
Y.M. gratefully acknowledges Sasakawa Scientific Research
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1
SUPPORTING INFORMATION
Additional Supporting Information may be found online in
the supporting information tab for this article.
[
[
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CH
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How to cite this article: Matsui Y., Oishi T., Ohta E.,
and Ikeda H. (2016), Adiabatic process of higher elec-
tronically excited states: luminescence from an excited
state biradical generated by irradiation of benzophe-
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