Photoinduced color change and photomechanical effect of naphthalene diimides bearing alkylamine moieties in the solid state

Article abstract of DOI:10.1002/chem.201304849

Photoinduced color change of naphthalene diimides (NDIs) bearing alkylamine moieties has been observed in the solid state. The color change is attributed to the generation of a NDI radical-anion species, which may be formed through a photoinduced electron-transfer process from the alkylamine moiety to the NDI. The photosensitivity of NDIs is highly dependent on the structures of the alkylamine moieties. Crystallographic analysis, kinetic analysis, UV/Vis/NIR spectroscopic measurements, and analysis of the photoproduct suggested that a radical anion was formed through an irreversible process initiated by proton abstraction between an amine radical cation and the neutral amine moiety. The radical anions formed stacks including mixed-valence stacks and radical-anion stacks, as shown by the broad absorption bands in near-IR spectra. These photosensitive NDIs also showed crystal bending upon photoirradiation, which may be associated with a change in the intermolecular distance of the NDI stacks by the formation of monomeric radical anions, mixed-valence stacks, and radical-anion stacks.

Full text of DOI:10.1002/chem.201304849

DOI: 10.1002/chem.201304849
Full Paper
&
Photoresponsive Molecules
Photoinduced Color Change and Photomechanical Effect of
Naphthalene Diimides Bearing Alkylamine Moieties in the Solid
State
Yuki Matsunaga,[a, b] Kenta Goto,[a] Koji Kubono,[c] Katsuya Sako,[d] and Teruo Shinmyozu*[a]
Abstract: Photoinduced color change of naphthalene di-
imides (NDIs) bearing alkylamine moieties has been ob-
served in the solid state. The color change is attributed to
the generation of a NDI radical-anion species, which may be
formed through a photoinduced electron-transfer process
from the alkylamine moiety to the NDI. The photosensitivity
of NDIs is highly dependent on the structures of the alkyla-
mine moieties. Crystallographic analysis, kinetic analysis, UV/
Vis/NIR spectroscopic measurements, and analysis of the
photoproduct suggested that a radical anion was formed
through an irreversible process initiated by proton abstrac-
tion between an amine radical cation and the neutral amine
moiety. The radical anions formed stacks including mixed-va-
lence stacks and radical-anion stacks, as shown by the broad
absorption bands in near-IR spectra. These photosensitive
NDIs also showed crystal bending upon photoirradiation,
which may be associated with a change in the intermolecu-
lar distance of the NDI stacks by the formation of monomer-
ic radical anions, mixed-valence stacks, and radical-anion
stacks.
Introduction
formation of persistent radical species has been demonstrated
by various molecules, such as viologens,[4–6] tetrathiafulva-
lenes,[7] biindenylidenediones,[8] dibenzobarrelenes,[9] and a pyri-
dine/carboxylic acid complex,[10] in solution, as polymers, and
in the crystalline state, and the formed radical species induce
color changes, conductivity enhancement, and magnetism.
The aromatic diimide moiety is recognized as one of the
most promising n-type semiconductors and has been inten-
sively investigated for applications to optoelectronic devices.[11]
The aromatic diimide species undergoes two reversible chemi-
cal and electrochemical one-electron reductions to give rela-
tively stable radical anions and dianions,[12] and the radical
anions have a tendency to aggregate to form stacks.[13,14]
Besides chemical and electrochemical reductions, the aro-
matic diimide moiety also undergoes a photochemical one-
electron reduction to form a persistent radical anion through
a photoinduced electron transfer (PET) from electron donors,
such as triethylamines[15] and anions.[16] We have been interest-
ed in the intramolecular version of the photoinduced radical-
anion formation of aromatic diimides bearing electron-donat-
ing moieties and want to study their intramolecular PET
phenomena.[17]
Molecules that possess the ability to change their structural
and electronic properties in response to light have attracted
much interest.[1] Photochromic molecules represented by di-
arylethenes and azobenzenes are recognized as typical light-re-
sponsive molecules, which undergo a reversible color change
accompanied by a photochemical structural isomerization, and
their properties provide applications of these molecules to not
only optoelectronic devices, such as memories and switches,
but also to mechanical materials.[2,3] Besides the photochromic
molecules, molecules that can form persistent radicals or radi-
cal ions in response to light are fascinating because of the
unique optical, electrical, and magnetic properties based on
the unpaired spins of the radical species. The photoinduced
[a] Dr. Y. Matsunaga, Prof. Dr. K. Goto, Prof. Dr. T. Shinmyozu
Institute for Materials Chemistry and Engineering (IMCE)
Kyushu University
6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581 (Japan)
E-mail: shinmyo@ms.ifoc.kyushu-u.ac.jp
[b] Dr. Y. Matsunaga
Present address: Department of Chemistry
National Taiwan University
Taipei, 10617 (Taiwan)
During the course of this study, we unexpectedly observed
a photoinduced color change by simple naphthalene diimides
(NDIs)[18] bearing alkylamine moieties in the solid state (Fig-
ures 1, 2, and 5), which is due to the formation of the NDI radi-
cal anion. Furthermore, these photosensitive NDIs showed
crystal bending on photoirradiation. Herein, we report our in-
vestigation into the mechanism of color change and crystal
bending of these photosensitive NDIs.
[c] Prof. Dr. K. Kubono
Division of Natural Science
Osaka Kyoiku University, Asahigaoka 4-698-1
Kashiwara, Osaka 852-8582 (Japan)
[d] Prof. Dr. K. Sako
Department of Life and Materials Engineering
Nagoya Institute of Technology
Gokisocho, Showa-ku, Nagoya 466-8555 (Japan)
In our continuing study of the properties of the radical
anion of the aromatic diimide moiety, we previously demon-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201304849.
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Figure 1. Structures of NDIs 1–11 and the magnitude of the color change by
photoirradiation in the solid state. “Clear” and “Weak” denote clear and
weak color changes, respectively, whereas “No” indicates no color change.
Figure 3. a) UV/Vis/NIR diffuse reflectance spectra of 1 in air (dashed line)
and after irradiation (solid line; lmax =370 nm, 5 min). b) UV/Vis/NIR absorp-
tion spectra of 1 as the spin-coated film under vacuum before (dashed line)
and after (solid line) irradiation (lmax =370 nm, 3 min). Inset: spectra in the
region of l=300–900 nm.
Figure 2. Photoinduced color change of 1 in the solid state. Upon photoirra-
diation, the yellow microcrystalline solid turned black (lmax =370 nm, 3 min),
which reverted to yellow after being stored in the dark at room temperature
in air (48 h).
strated the generation of radical anions of the self-assembled
aggregate of pyromellitic diimide-based macrocycles[19] by
means of a chemical reaction in the solid state (this will be re-
ported elsewhere).[20]
diation under vacuum (Figure 3b), and these bands were as-
cribed to the formation of two different species, in which the
band at approximately l=1300 nm closely resembled the ab-
sorption of the NDI radical-anion stacks, whereas the other
band at approximately l=2300 nm was ascribed to the spe-
cies of the mixed-valence stacks between the NDI radical
anions and the neutral NDIs.[13] The formation of the NDI radi-
cal anion was also supported by electron-spin resonance (ESR)
spectrometric analysis. The broad and anisotropic ESR spec-
trum with g values of 2.0042–2.0023 was observed after photo-
irradiation of 1 in the solid state in air (Figure 4) in contrast to
the symmetric spectrum with a hyperfine structure in solu-
tion.[23] A similar ESR spectrum was reported for the NDIs con-
Results and Discussion
Photoinduced color change of NDI 1 in the solid state
When a microcrystalline solid of N,N’-bis[2-(dimethylamino)eth-
yl]-1,4,5,8-naphthalenetetracarboxylic 1,8:4,5-diimide (1)[21,22]
was irradiated with UV light (lmax =370 nm, 3 min) at room
temperature in air, 1 changed from yellow to black (Figure 2).
This color change of 1 was also observed even under room
light within 5–10 minutes. After discontinuation of the irradia-
tion of 1, the resultant black solid was stored in the dark and
reverted to yellow after 48 hours. The change from yellow to
black and black to yellow was repeatedly observed more than
20 times without any significant deterioration, whereas no
color change was observed when a degassed solution of 1 in
MeCN was irradiated (1ꢁ10ꢀ3 m; l>300 nm, 10 min).
To characterize the chemical species formed by the photoir-
radiation of 1, UV/Vis/near-infrared (NIR) diffuse reflectance
spectra were measured (Figure 3a). New absorption bands ap-
peared in the region of l=400–800 nm upon photoirradiation
(lmax =370 nm, 5 min) due to the monomeric NDI radical
anion.[23] In addition, significantly broad absorption bands ap-
peared in the region of l=800–2600 nm, which were more
clearly observed in the spin-coated film of 1 upon photoirra-
Figure 4. ESR spectra of 1 before (dashed line) and after irradiation (solid
line) in the crystalline state in air. Irradiation: lmax =370 nm, 5 min.
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taining the stacked NDI radical anions,[13] thus supporting the
formation of the radical-anion stacks in this system. The forma-
tion of the NDI radical anion was also confirmed by the IR
spectrum of 1 in a KBr pellet, which showed characteristic ab-
sorption bands of the NDI radical anion at n˜ =1627 and
1525 cmꢀ1 upon photoirradiation (see Figure S1 in the Sup-
porting Information).[13] In contrast to the photochemical for-
mation of the NDI radical anion in 1, NDI 11 without alkyla-
mine moieties showed no color change upon photoirradiation.
Therefore, the formation of the NDI radical anion in 1 is as-
cribed to a PET process from the dimethylamine moiety to the
NDI moiety. The conversion of neutral NDI 1 to a radical anion
was estimated to be approximately 4% after irradiation for
2 hours in the solid state on the basis of magnetic-susceptibili-
ty measurements (see the Supporting Information).
to that of 1 was observed. NDI 3 bearing N,N-diethylaminoeth-
yl groups also showed a similar clear color change, whereas
NDI 4 bearing a bulkier N,N-diisopropylaminoethyl groups ex-
hibited a weak color change, even after prolonged irradiation
(30 min) under vacuum. In the case of NDIs 5 and 6 with pyrro-
lidylethyl and pyrrolidylpropyl groups, respectively, 6 showed
a clear color change and 5 exhibited a weak color change,
even after prolonged irradiation (30 min) under vacuum.
Cyclic voltammograms of 1–6 in CH2Cl2 containing 0.1m
nBu4NPF6 showed no significant difference in the redox poten-
tials of these NDIs (see Figure S2 and Table S1 in the Support-
ing Information), thus suggesting that the difference in the
photosensitivity does not arise from the difference in the elec-
tronic properties of these NDIs. In the cases of NDIs 7–10 bear-
ing either N-methylphenylamine or diphenylamine moieties,
no color change was observed, even during spectroscopic
measurements under vacuum.
Effect of the structure of alkylamine moieties on the photo-
sensitivity of the NDIs
Insight into the mechanism of the radical-anion formation
The dependence of the photoinduced color change of the
NDIs on the structure of the amine moieties was examined
To obtain insight into the dependence of the photosensitivity
on the crystal structure of the NDIs, X-ray crystallographic stud-
ies of 1–6 were carried out (Figure 6).[24] The NDIs with clear
(Figure 5). When NDI
2 bearing N,N-dimethylaminopropyl
groups was irradiated in the solid state, a color change similar
Figure 5. Photographs and diffuse reflectance UV/Vis/NIR spectra of NDIs with various substituents before (left side in photographs and dashed line in spec-
tra) and after (right side in photographs and solid line in spectra) photoirradiation in air (lmax =370 nm, 5 min): a) 2, b) 3, c) 4, d) 5, and e) 6.
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far from each other (Figure 6 f). Crystal-structural analyses sug-
gest that proton abstraction from the amine radical cation by
the neighboring neutral amine moiety of the facing NDI may
be feasible in 1–3 and 6, but difficult in 4 and 5. Thus, the im-
portance of the proper arrangements of the alkylamine moiet-
ies in the solid state for the radical anion formation was
elucidated.
The possibility of the proton abstraction between the amine
radical cation and the neutral amine moiety, namely, an irrever-
sible mechanism of radical-anion formation, was also support-
ed by kinetic analysis of the formation of the NDI radical
anion. The generation of the NDI radical anion upon photoirra-
diation was evaluated by the following second-order
Equation (1):
kt ¼ 1=ðA ꢀAtÞꢀ1=ðA ꢀA0Þ
ð1Þ
1
1
where A0, A , and At are the observed absorption data that
1
correspond to l=765 nm at time zero, infinite time, and time
t of the reaction, respectively. The time-dependent change of
the UV/Vis/NIR spectrum of 1 upon photoirradiation and the
second-order plot are shown in Figure 7a,b, respectively. The
second-order plot showed a linear correlation. Evaluation of
the spin-coated film also showed linearity in the second-order
plot (see Figure S3 in the Supporting Information). These re-
sults indicate that the rate-determining step in the radical-
anion formation is bimolecular process, which does not conflict
with the hypothesis that proton abstraction occurs between
the amine radical cation and the neutral amine moiety.
Figure 6. Crystal structures of a) 1, b) 2, c) 3, d) 6, e) 4, and f) 5. Dashed lines
in (a)–(e) show the distances between the stacked NDIs, the imide carbon
and oxygen atoms, and the nitrogen atoms and the nearest methyl or meth-
ylene carbon atoms of neighboring alkylamine moieties. Another conforma-
tion observed as disorder in the amine moieties of 2 and the solvent mole-
cules in 5 are omitted for clarity.
color changes (i.e., 1–3 and 6) adopt similar p-stacked geome-
tries with interplanar distances of 3.28–3.34 ꢂ (Figure 6a–d),
which are shorter than that of graphite (3.35 ꢂ),[25] and the
imide carbonyl carbon and oxygen atoms of the stacked NDIs
are closely located each other (3.19–3.28 ꢂ). This close stacking
suggests significant p-electron delocalization over the continu-
ously stacked NDIs in the solid state (Figure 6a–d), which is
consistent with the observation of the broad and asymmetric
ESR spectrum (Figure 4) and the broad NIR absorption bands
(Figure 3) in 1 after irradiation.
It is well known that alkylamines, such as triethylamine and
triethanolamine, serve as sacrificial reagents in photocatalytic
reactions.[26] These reagents donate one electron to a photoca-
talyst through a PET process and the resultant radical cations
undergo irreversible reactions initiated by proton abstraction
by neutral amines around the radical cations.[27] A nitrogen
atom of an alkylamine moiety is located near the methyl or
methylene carbon atoms of the alkylamine moiety of the
neighboring molecule with distances of 3.73–4.43 ꢂ (Fig-
ure 6a–d). There is some void space around the alkylamine
moieties, which allows thermal rotation and/or vibration of the
amine moieties required for the reaction between the amine
moieties. In contrast, NDI 4 with a weak color change adopts
a more of a slipped-stack geometry along the long axis of the
molecule than those of 1–3 and 6, and amino nitrogen atoms
are surrounded by bulky isopropyl groups (Figure 6e). In the
case of 5 with a weak color change, the molecules are stacked
in columnar fashion, and the pyrrolidine moieties are located
Figure 7. a) Time-dependent change of the UV/Vis/NIR diffuse-reflectance
spectra of 1 upon photoirradiation (lmax =370 nm). b) Second-order kinetic
plot for change in absorbance at l=765 nm.
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formation), probably due to the
frozen thermal motions of the al-
kylamine moieties.
Based on the results described
above, we propose a plausible
mechanism for the photoin-
duced color change of the NDI
radical anion in the solid state
(Scheme 1). When NDI absorbs
a
photon, a charge-separated
state may be formed through
a PET process from the alkyla-
mine moiety to the NDI. The
proton abstraction from the re-
sultant amine radical cation by
a
neighboring neutral amine
moiety followed by decomposi-
tion of the resultant amine radi-
cal cation may lead to accumula-
tion of the NDI radical anion,
which induces a color change in
the solid state. Sensitivity to
Figure 8. 1H NMR spectra of 3 after photoirradiation (400 MHz, CDCl3).
photoirradiation is affected by
the ease of proton abstraction,
which is related to the arrange-
Furthermore, the irreversibility of the generation of the radi-
cal anion was supported by analysis of the photoproducts. The
decomposition pathway of the alkylamines in a photocatalytic
reaction is dealkylation.[26] Dealkylation of the alkylamine was
reported during electrochemical oxidation, in which proton ab-
straction from the resultant amine radical cation by the neutral
amine and subsequent irreversible reactions afford the dealky-
lated amine and aldehyde.[27] When NDI 3 was repeatedly irra-
diated in the solid state, the formation of NDIs bearing dealky-
lated amine moieties, namely, N-ethylaminoethyl groups, and
acetaldehyde were observed as major products by 1H NMR
spectroscopic analysis (see Figure 8 and Scheme S2 for the
dealkylation mechanism of 3). In addition, when NDI 1 was ir-
radiated at low temperature (in liquid N2), the color change
was drastically suppressed (see Figure S4 in the Supporting In-
ment of the reacting amine moieties in the solid state. The re-
version of the color may be caused by the one-electron oxida-
tion of the NDI radical anion by atmospheric oxygen to form
the neutral NDI. Although the possible existence of the long-
lived charge-separated species still cannot be completely ex-
cluded, the results presented herein support the irreversible
process for the generation of the NDI radical anion.
Formation of p-stacked radical anions
Time-dependent UV/Vis/NIR spectra of the spin-coated film of
1 were measured under vacuum (Figure 9). After irradiation for
30 seconds, new absorption bands due to the radical-anion
stacks and the mixed-valence stacks appeared at approximate-
ly l=1190 and 2300 nm, respectively (Figure 9a). As the irradi-
Scheme 1. A plausible mechanism for the radical-anion formation by photoirradiation.
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anthracenecarboxylic acid and
its derivatives.[32] In these sys-
tems, changes in the shape and
size of the molecules by photo-
isomerization cause stress in the
crystal, which leads to deforma-
tion.[28d] For the crystal bending
of 1, in contrast, drastic changes
in the molecular shape and size
is not expected between the
neutral NDI and NDI radical
anion according to theoretical
calculations (see Figure S6 in the
Supporting Information).
One possible reason for this
crystal bending is the change in
the
intermolecular
distance
caused by attractive or repulsive
interactions among the NDI radi-
cal anions. As described above,
the neutral NDIs are converted
into monomeric radical anions,
mixed-valence stacks, and radi-
cal-anion stacks upon photoirra-
Figure 9. a,b) Time-dependent change in the UV/Vis/NIR spectra for spin-coated 1 under vacuum upon irradiation
at a) lmax =370 nm and b) lmax =370 nm (5 min). c) Schematic representation of the formation and the intercon-
version of the NDI radical anion, the mixed-valence stacks, and the radical-anion stacks. Conversion of the mixed-
valence stacks into monomeric radical anions by oxygen is likely to occur, but not confirmed, therefore, it is de-
picted as (O2).
ation time increased, the intensity of the absorption band due
to the mixed-valence stacks decreased, whereas the intensity
of the band due to the radical-anion stacks increased with the
isosbestic point at approximately l=1800 nm. In sharp con-
trast, the intensity of the absorption band of the radical-anion
stacks gradually decreased after discontinuation of the photoir-
radiation (Figure 9b). Along with this behavior, the intensity of
the band due to mixed-valence stacks increased with the iso-
sbestic point at approximately l=1800 nm. These observa-
tions indicate an interconversion between radical-anion stacks
and mixed-valence stacks. Oxygen, which enters the evacuated
cell, may be responsible for the conversion of radical-anion
stacks into mixed-valance stacks.
diation. Considering the bending direction of the crystal, the ir-
radiated crystal surface is expected to be elongated along the
long axis of the crystal because of an increase in the intermo-
lecular distance of the NDIs relative to the neutral NDI species.
The monomeric radical anions are expected to show electro-
static repulsion among themselves, which may cause elonga-
tion of the irradiated crystal surface due to an increase in the
intermolecular distance of the NDI p planes relative to the neu-
tral NDI species. On the other hand, according to reports on
the mixed-valence dimer[33] and the p dimer[34] of the radical
anions, the intermolecular distances in the mixed-valence
stacks and the radical-anion stacks is expected to be shorter
than in the stacks of the neutral species, which may induce
the contraction of the irradiated crystal surface. In these elec-
tronic interactions, the repulsive interaction among the mono-
meric radical anions may be predominant for the observed
crystal bending. However, more detailed investigation is neces-
sary to elucidate the mechanism of the crystal bending ob-
served here.
Photomechanical bending of NDI crystals
When a rodlike crystal of 1 was irradiated, the crystal bent
away from the light accompanied by a change in the crystal
from yellow to dark brown (Figure 10a,b). When the dark-
brown crystal was kept in the dark, the crystal became almost
straight after 48 hours along with a change from dark brown
to yellow (Figure 10c). This photoinduced crystal bending was
observed more than three times. When the crystal of 1 was ir-
radiated with red light (lmax =580 nm), no change in the crystal
shape was observed due to the weak absorption of the light
at approximately l=580 nm. This observation eliminates any
thermal effect on the crystal bending. Therefore, the crystal
bending may be attributed to the behavior of the NDI radical
anions. Similar crystal bending was observed in NDIs 2, 3, and
6 with clear color changes (see Figure S5 in the Supporting In-
formation). A photomechanical effect in crystals has been re-
ported for several photochromic molecules, such as diaryl-
ethenes,[28] azobenzene,[29] salicylideneaniline,[30] fulgide,[31] and
Conclusion
A photoinduced color change of NDIs bearing alkylamine moi-
eties has been observed in the solid state. This color change
was attributed to NDI radical-anion formation through a PET
process, and the photosensitivity of the NDIs was highly de-
pendent on the structure of the alkylamine moieties. Crystallo-
graphic analysis, kinetic analysis, and analysis of the photo-
products suggest that a NDI radical anion was formed by de-
composition of the amine moiety, which was initiated by
proton abstraction between an amine radical cation and the
neutral amine moiety in the solid state. The generated mono-
meric radical anions may form stacks including mixed-valence
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Experimental Section
ESR measurement
A small amount of crystalline powder 1 was put into an ESR tube
(O.D.: 5 mm, I.D.: 4 mm). The tube was set in the cavity of the ESR
machine, and the machine was covered with a black-out curtain.
Photoirradiation was carried out through the window in the cavity.
X-ray crystallographic analysis
Crystals of 1–6 were obtained by recrystallization from solvents
(EtOH for 1, MeCN for 2–4, CHCl3/octane for 5 and 6). The struc-
tures were solved by using direct methods with SHELXS-97,[35]
SIR92,[36] or SIR2004[37] and refined by full-matrix least-squares pro-
cedures on F2 for all reflections with SHELXL-97.[35] The non-hydro-
gen atoms were refined anisotropically, and the hydrogen atoms
were refined isotropically.
Acknowledgements
We gratefully acknowledge the financial support from the
Grant-in-Aid for Scientific Research on Innovative Areas, Organ-
ic Synthesis Based on Reaction Integration (MEXT, Japan). This
work was supported by Management Express Grants for Na-
tional Universities Cooperation from MEXT (Japan). Y.M. is sin-
cerely thankful for financial support from the G-COE program,
Science for Future Molecular Systems, Kyushu University,
Japan. We are indebted to Prof. Noboru Koga and Assoc. Prof.
Satoru Karasawa of the Graduate School of Pharmaceutical Sci-
ences (Kyushu University) for the magnetic-susceptibility meas-
urements, Dr. Yasukazu Hirao of Osaka University for the ESR
spectroscopic measurement, Mr. Taisuke Matsumoto of the In-
stitute for Materials Chemistry and Engineering (Kyushu Uni-
versity) for the XRD measurements, and Takuya Kamimura of
the Graduate School of Sciences (Kyushu University) for X-ray
crystallographic studies. Y.M. thanks Dr. Ken-ichi Sakaguchi of
Toyo Gosei Co., Ltd., for helpful discussions and kind coopera-
tion throughout the research. The computation calculations
were mainly carried out by using the computer-center facilities
at the Research Institute for Information Technology (Kyushu
University, Japan).
Figure 10. Bending of a rodlike crystal (1.4 mmꢁ20 mmꢁ10 mm) of 1 upon
photoirradiation before irradiation (a), immediately after irradiation (b;
lmax =370 nm, 30 s), and after being kept in the dark at room temperature
in air for 48 h (c).
Keywords: arenes
photomechanical effect · radical ions
· electron transfer · photochemistry ·
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bands in NIR spectra. Crystal bending of these photosensitive
NDIs upon photoirradiation may be associated with a change
in the intermolecular distance of the NDI stacks by the forma-
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radical-anion stacks. Further investigation into the mechanism
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currently in progress, and the results will be reported
elsewhere.
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Received: December 11, 2013
Published online on && &&, 0000
&
&
Chem. Eur. J. 2014, 20, 1 – 9
www.chemeurj.org
8
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
Drastic change in the color of naphtha-
lene diimides (NDIs) bearing alkylamine
moieties in the solid state upon photoir-
radiation (see picture) is observed, and
the mechanism of this color change has
been elucidated. These photosensitive
NDIs also show crystal bending upon
photoirradiation.
&
Photoresponsive Molecules
Y. Matsunaga, K. Goto, K. Kubono,
K. Sako, T. Shinmyozu*
&& – &&
Photoinduced Color Change and
Photomechanical Effect of
Naphthalene Diimides Bearing
Alkylamine Moieties in the Solid State
Chem. Eur. J. 2014, 20, 1 – 9
www.chemeurj.org
9
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ