Nondestructive photoluminescence read-out by intramolecular electron transfer in a perylene bisimide-diarylethene dyad

Article abstract of DOI:10.1002/chem.201201484

A novel, highly stable photochromic dyad 3 based on a perylene bisimide (PBI) fluorophore and a diarylethene (DAE) photochrome was synthesized and the optical and photophysical properties of this dyad were studied in detail by steady-state and time-resolved ultrafast spectroscopy. This photochromic dyad can be switched reversibly by UV-light irradiation of its ring-open form 3 o leading to the ring-closed form 3 c, and back reaction of 3 c to 3 o by irradiation with visible light. Solvent-dependent fluorescence studies revealed that the emission of ring-closed form 3 c is drastically quenched in solvents of medium (e.g., chloroform) to high (e.g., acetone) polarities, while the emission of the ring-open form 3 o is appreciably quenched only in highly polar solvents like DMF. The strong fluorescence quenching of 3 c is attributed to a photoinduced electron-transfer (PET) process from the excited PBI unit to ring-closed DAE moiety, as this process is thermodynamically highly favorable with a Gibbs free energy value of -0.34 eV in dichloromethane. The electron-transfer mechanism for the fluorescence quenching of ring-closed 3 c is substantiated by ultrafast transient measurements in dichloromethane and acetone, revealing stabilization of charge-separated states of 3 c in these solvents. Our results reported here show that the new photochromic dyad 3 has potential for nondestructive read-out in write/read/erase fluorescent memory systems. Copyright

Full text of DOI:10.1002/chem.201201484

FULL PAPER
DOI: 10.1002/chem.201201484
Nondestructive Photoluminescence Read-Out by Intramolecular Electron
Transfer in a Perylene Bisimide-DiACHTNUTRGNEUNGarylethene Dyad
Martin Berberich,[a] Mirco Natali,[b] Peter Spenst,[a] Claudio Chiorboli,[c]
Franco Scandola,*[b] and Frank Wꢀrthner*[a]
Dedicated to Professor Christoph Brꢀuchle and Professor Herbert Mayr on the occasion of their 65th birthdays
Abstract: A novel, highly stable photo-
chromic dyad 3 based on a perylene
ring-closed form 3c is drastically
quenched in solvents of medium (e.g.,
chloroform) to high (e.g., acetone) po-
larities, while the emission of the ring-
open form 3o is appreciably quenched
only in highly polar solvents like DMF.
The strong fluorescence quenching of
3c is attributed to a photoinduced elec-
tron-transfer (PET) process from the
excited PBI unit to ring-closed DAE
moiety, as this process is thermody-
namically highly favorable with
a
bis
N
a
Gibbs free energy value of ꢀ0.34 eV in
dichloromethane. The electron-transfer
mechanism for the fluorescence
quenching of ring-closed 3c is substan-
tiated by ultrafast transient measure-
ments in dichloromethane and acetone,
revealing stabilization of charge-sepa-
rated states of 3c in these solvents. Our
results reported here show that the
new photochromic dyad 3 has potential
for nondestructive read-out in write/
read/erase fluorescent memory systems.
diarylACHTUNGTRENNUNG
synthesized and the optical and photo-
physical properties of this dyad were
studied in detail by steady-state and
time-resolved ultrafast spectroscopy.
This photochromic dyad can be switch-
ed reversibly by UV-light irradiation of
its ring-open form 3o leading to the
ring-closed form 3c, and back reaction
of 3c to 3o by irradiation with visible
light. Solvent-dependent fluorescence
studies revealed that the emission of
Keywords: dyes/pigments · electron
transfer
· fluorescence · photo-
chromism · redox chemistry
Introduction
molecules, which are photoswitchable between two thermal-
ly stable isomers. This molecular property is known as pho-
tochromism and derived from the Greek words phos for
light and chroma for color; it was initially defined by Hirsh-
berg in the 1950s as “a reversible transformation of a chemi-
cal species induced in one or both directions by absorption
of electromagnetic radiation between two forms (isomers)
having different absorption spectra”.[1]
The demand for advanced data storage methods has in-
creased dramatically during the last decade. The develop-
ment of computer technologies and memory systems with
large data storage capacity and fast read–write efficiencies is
in a footrace with the increasing need for technologies, such
as high-resolution photography; high-definition (HD) film
techniques; and the miniaturization for laptops, tablet PCs,
and smartphones. An emerging data storage method that
has potential for high bit density is based on single organic
Contemporary photochromic compounds range from the
best-known azobenzenes,[2] which undergo photoinduced
cis–trans isomerization, to fulgides,[3] spiropyrans,[4] and di-
AHCTUNGTRENNUNG
arylethenes[5] that undergo six-p-electron pericyclic reactions
upon irradiation to give the respective so-called ring-closed
forms. While most of the known photochromic compounds
exhibit equilibrating thermal back reactions, diarylethene
(DAE) derivatives offer highly desirable thermal bistability
in both ring-open (denoted as DAEO) and ring-closed (de-
noted as DAEC) forms, making them unique among photo-
chromic molecular systems.[6] Another intriguing property of
DAEs is their excellent fatigue resistance toward repeated
switching cycles.[5a] DAEs, first introduced in 1988 by M. Irie
et al.,[7] are generally composed of two aromatic rings,
mainly thiophenes or benzo[b]thiophenes, that are connect-
ed by a carbon–carbon double-bond bridge, which is usually
a part of a five-membered ring like perfluorocyclopentene
or maleimide. While the open form of a diarylethene exhib-
its two rotamers, the so-called parallel and anti-parallel ro-
[a] M. Berberich, P. Spenst, Prof. Dr. F. Wꢀrthner
Universitꢁt Wꢀrzburg, Institut fꢀr Organische Chemie and
Center for Nanosystems Chemistry
Am Hubland, 97074 Wꢀrzburg (Germany)
Fax : (+49)931-31-84756
E-mail: wuerthner@chemie.uni-wuerzburg.de
[b] M. Natali, Prof. Dr. F. Scandola
Universitꢂ di Ferrara, Dipartimento di Chimica
Via L. Borsari 46, 44100 Ferrara (Italy)
Fax : (+39)0532-240-709
E-mail: snf@unife.it
[c] Dr. C. Chiorboli
ISOF-CNR, Sezione di Ferrara
Via L. Borsari 46, 44100 Ferrara (Italy)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201201484.
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
1
&
ÞÞ
These are not the final page numbers!

tamers, only the anti-parallel one may undergo the orbital-
controlled six-p-electron pericyclic isomerization upon irra-
diation to afford the ring-closed form (DAEC). Since the
open form isomer of DAE absorbs predominantly in the
short-wave spectral region, its ring closure can be initiated
by irradiation with UV light. The ring closure of DAE re-
sults in an extension of the p-system and thus the ring-
closed isomer possesses longer wavelength absorption
bands. Accordingly, the ring-opening reaction of the closed
form can be triggered by irradiation with visible light.
escent state can be obtained as the “read-out” signal, result-
ing in a binary emissive “1” and nonemissive “0” code. The
emission in this process is quenched by intramolecular Fçr-
ster resonance energy transfer (FRET) from the excited dye
to only one of the photochromic isomers. One detrimental
effect of the intramolecular fluorescence quenching by
FRET, however, is the concomitant excitation of the ring-
closed form of the photochromic dyad during the read-out
process, resulting in undesirable ring opening. Thus, energy
transfer may induce the photochromic back reaction of the
ring-closed form to the ring-open one during reading of the
fluorescence intensity, and such energy-transfer-based
memory systems lead to destructive read-outs.
Emission quenching based on intramolecular photoin-
duced electron transfer (PET)[21] may circumvent such a de-
structive read-out pathway. Some examples of electron-
transfer switching with different photochromic units have
been reported in the literature. However, such switching sys-
tems lack, so far, a thermally bistable photochrome or an ef-
ficient fluorophore to monitor electron transfer by fluores-
cence quenching.[22] An interesting system has been publish-
ed by Tsuchiya in which an electron-rich and an electron-
poor porphyrin are connected by an azobenzene bridge al-
lowing modulation of the donor–acceptor distance by photo-
induced cis–trans isomerization.[23] Only in the cis isomeric
form was electron transfer observed because of a markedly
reduced distance between the porphyrin units. One major
drawback, however, of azobenzene-based systems is the lack
of thermal stability of the cis and trans isomers.
The ease of photoswitching between thermally stable
ring-open and ring-closed DAE isomers has resulted in their
application in different optoelectronic devices.[2d,5b,8] More-
over, by implementing DAE chemistry, exciting concepts
such as reversible switching of conductance,[9] photopro-
ACHTUNGTRENNUNG
gramable, organic light-emitting diodes (OLEDs),[10] bulk
optical transistors,[11] integration in nanoparticles[12] and
quantum dots,[13] molecular logic devices,[14] anti-counterfeit-
ing technology,[15] and imaging of living cells by single-mole-
cule photoswitching[16] have recently been developed, and
more interestingly the photochromically controlled motion
of living organisms has been demonstrated.[17]
The high potential of photochromic systems for optical
data storage was convincingly demonstrated by Partheno-
poulos and Rentzepis in 1989 with a three-dimensional
memory system based on photochromic spirobenzopyran
embedded in a polymer matrix.[18] Followed by this seminal
work, several new photochromic systems have been devel-
oped for high-density data storage on a molecular level.[19]
In regard to our present work, one particularly relevant
photochromic dyad system consisting of a switchable DAE
unit and a fluorescent bis(phenylethynyl)anthracene dye
was reported by M. Irie, T. Fukaminato, and co-workers.[20]
In this particular system, emission of the dye unit could be
turned on and off repeatedly by isomerization of the photo-
chromic DAE unit upon irradiation with light of two differ-
ent wavelengths. With an additional third light source of a
different wavelength, the respective fluorescent or nonfluor-
A few years ago, nearly simultaneously our group[24] (see
dyad 1o in Scheme 1) and the group of Fukaminato and
Irie[25] proposed a concept for fluorescence photoswitching
by intramolecular electron transfer based on dyads of photo-
chromic diarylethene (DAE) and fluorescent perylene bisi-
mide (PBI) dye. The basic idea behind this concept is that
the ring-open and ring-closed isomers of the photochromic
DAE moiety exhibit different redox properties and the elec-
tron transfer from fluorescent PBI dye is thermodynamically
Scheme 1. Photochromic dyads 1o, 2o and 3o/3c, and reference compounds 4o and 5.
&
2
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Electron Transfer
FULL PAPER
favorable only to one of the two DAE isomers. We have
chosen perylene bisimides as emitters for photoswitching by
PET, because this class of dyes possess excellent photochem-
ical stability, high extinction coefficients, and outstanding
fluorescence quantum yields.[26] PBI chromophores are at-
tractive as electron donors or acceptors and their optical
and redox properties can easily be tuned over a wide range
by judicious alteration of substituents at the bay area
(1,6,7,12-positions).[26a,b,d,27] These desirable properties have
led to 1,7-di- and 1,6,7,12-tetraaryloxy-substituted PBIs, in
particular, being popular building blocks for the spectro-
scopic investigation of energy- or electron-transfer processes
in artificial light-harvesting arrays that are self-assembled in
solution or on surfaces.[28] Furthermore, the influences of
photochromic reaction on the aggregation behavior and op-
tical properties of PBIs have been investigated for systems
in which PBI is connected to a photochromic unit.[29]
nately, in dyad 2o this photochromic DAE unit is shown to
be unstable under irradiation with visible light (see next sec-
tion), and thus photoswitching properties of dyad 2o could
not be explored. Therefore, we have synthesized dyad 3o/
3c, containing a highly stable DAE photoswitch substituted
with two benzo[b]thiophene-1,1-dioxide subunits, for which
the ring-closed isomer is a considerably better electron ac-
ceptor than the ring-open isomer, and a highly fluorescent
tetraaryloxy-substituted PBI chromophore with a matched
oxidation potential to facilitate electron transfer to ring-
closed DAE. Here we report on the outstanding photo-
switching properties of the new dyad 3o/3c investigated in
detail by steady-state and time-resolved transient spectro-
scopy. This dyad allows writing, erasing, and reading of opti-
cal memory with light sources of different wavelengths with-
out destructive read-out.
Due to the fact that several DAE derivatives also show
electrochromic behavior, that is, ring-opening or ring-closure
of such photochromes, upon oxidation,[30] the DAE unit of a
photochromic donor–acceptor dyad may act as an electron
acceptor. One single example of DAE exhibiting electro-
chromic behavior upon reduction has also been reported.[31]
In an optimal case, electron transfer from a fluorescent PBI
dye to the DAE unit of a PBI–DAE dyad would be exer-
Results and Discussion
Synthesis: The synthetic routes to photochromic dyads 2o
and 3o/3c, and the reference diarylethene 4 containing two
benzo[b]thiophene-1,1-dioxide groups are illustrated in
Scheme 2.
The starting compound 6, which was prepared according
to a literature procedure,[32b] was reacted with lithiated 2-
bromo-3-methylbenzo[b]thiophene to afford photochromic
precursor 7, containing a pyrrole protecting group in 54%
yield. The pyrrole-protected amino group in 7 was depro-
tected by treatment with hydroxylamine under basic condi-
tions to obtain compound 8, which was further used for the
synthesis of reference diarylethene 4o and the target dyad
3o. The condensation reaction of 8 with phthalic anhydride
to the photochrome 9 and subsequent oxidation of the
sulfur atoms in 9 with Oxone (2ꢄKHSO5·KHSO4·K2SO4) in
a water–dichloromethane–acetone solvent mixture accord-
ing to a literature procedure reported for the oxidation of a
similar benzo[b]thiophene compound[35] afforded the refer-
ence DAE 4o in very high yield. We have used this mild
and neutral oxidation reagent Oxone instead of meta-chloro-
C
Cꢀ Cꢀ
gonic only for the PBI +–DAEC but not for PBI +–DAEO
C
charge-transfer (CT) state. The stabilization and, therefore,
the thermodynamically favored formation of a CT state can
be dramatically influenced by solvent polarity. With an ap-
propriately designed system, it would be then possible to
write, read, and erase optical memory without destructive
read-out by using light sources of three different wave-
lengths. However, all of reported photoswitching systems
based on this concept to date suffer from certain disadvan-
tages like low fluorescence quantum yield, photocyclization
by triplet-state population, small driving force for fluores-
cence-quenching PET, or low photostability.[24,25,32] For in-
stance, our previously reported DAE–PBI dyad 1o
(Scheme 1) has the disadvantage of low fluorescence quan-
tum yield (Ffl =14% in dichloromethane) and low photosta-
bility of the 1,7-dipyrrolidino-substituted PBI, leading to de-
composition of this moiety upon continuing irradiation.[24]
Therefore, since our initial communication,[24b] we have
made efforts to develop photoswitching systems with superi-
or properties by employing 1,6,7,12-tetraaryloxy PBI dyes.
These dyes are well-known for their outstanding photosta-
bility and fluorescence quantum yields close to 100%.[33]
However, their oxidation potential is higher and accordingly
a DAE derivative with stronger electron-acceptor character
was required to achieve the required driving force for PET.
In a first step, we synthesized the dyad 2o (Scheme 1),
which contains an unsymmetrically substituted DAE deriva-
tive bearing a benzo[b]thiophene-1,1-dioxide and a phenyl-
thiophene-1,1-dioxide subunit. This DAE derivate was also
used previously by Irie group in a photochromic dyad;[32]
however, such 3-methyl-5-phenylthiophene units were re-
ported to be not very stable upon irradiation.[34] Unfortu-
AHCTUNGTRENNUNG
peroxybenzoic acid (mCPBA),[36] which was often used for
the oxidation of sulfur atoms in diarylethene com-
pounds,[32,37] because the oxidation of DAE derivatives con-
taining sulfur heterocycles with acidic mCPBA leads to the
formation of increased amounts of side products.
Photochromic precursor 1-(3-methyl-5-phenylthiophen-2-
yl)-2-(2-methyl-6-amino-benzo[b]thiophen-3-yl)perfluorocy-
clopentene (11), bearing a phenylthiophene group, was syn-
thesized according to literature procedure.[32b] Imidization of
N-cyclohexyl-1,6,7,12-tetra(4-tert-butylphenoxy)-perylene-
3,4:9,10-tetracarboxylic acid 3,4-anhydride-9,10-imide (10)[38]
with amino-group-containing photochrome 11 in imidazole
gave the condensation product 12 in 73% yield. Compound
12 was then oxidized with Oxone yielding the unstable dyad
2o in only 11% yield, which decomposed continuously
during the purification step by column chromatography. It
was not possible to isolate pure closed form 2c after irradia-
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
3
&
ÞÞ
These are not the final page numbers!

F. Scandola, F. Wꢀrthner et al.
Scheme 2. Synthesis of photochromic dyads 2o and 3o/3c, and the reference photochrome 4o.
tion of a dichloromethane solution of 2o, because of its low
stability under ambient conditions.
range (see Figure S1a in the Supporting Information) result-
ing in a 53:47 ratio of 2o and 2c according to NMR analysis.
This visible-light-irradiated solution of 2o in dichlorome-
thane was stored for 15 h in the dark, and during this time
absorption in the UV region increased further with a hypso-
chromic shift of the maximum. Irradiation of this solution
with UV light (365 nm; this wavelength was also applied by
Fukaminato et al. to open the ring-closed form of this pho-
tochromic unit[32b]) did not recover the initial spectrum of
2o in the UV region (see Figure S1b in the Supporting In-
formation). This observation clearly indicates that UV-light
irradiation of ring-closed dyad 2c did not exclusively lead to
its ring-open form 2o or another photostationary state com-
posed of 2o and 2c, and thus the spectral changes observed
in the region between 300 and 400 nm upon irradiation with
UV light are rather due to decomposition of dyad 2o.
Therefore, no further investigations were performed with
dyad 2o.
Unlike dyad 2o, the ring closure of dyad 3o takes place
upon irradiation with UV light, and the closed form 3c can
be re-opened by visible light (>400 nm), which is the
common behavior for diarylethenes.[5a] Switching cycles of
3o in dichloromethane show the increased photostability of
this photochromic dyad compared to our previous systems
1o/1c[24b] and 2o/2c (Figure 1). Even after ten cycles, the
emission intensity, which can be switched between a high
emissive state (around 80% open form and 20% closed
form) and a less emissive state (around 25% open form and
75% closed form) equating around 38% of the intensity of
the higher emissive state, returns to the original value and
no decomposition occurs. The nondestructive read-out capa-
The condensation of the amino-group-containing photo-
chrome 8 with perylene monoanhydride monoimide 10 in
imidazole afforded the dyad precursor 13 and the subse-
quent oxidation of the latter with Oxone yielded our target
open-form dyad 3o in 67% yield. UV irradiation (350 nm)
of ring-open isomer 3o in dichloromethane led to the for-
mation of ring-closed isomer 3c. The closed form 3c could
be easily separated from the remaining open form by
column chromatography with silica gel under exclusion of
light and pure 3c was obtained in 69% yield, while 28% of
the open form 3o was re-isolated.
All new compounds, including the target dyads 2o and
3o/3c as well as reference 4o, were properly characterized
by 1H NMR spectroscopy and high-resolution mass spec-
trometry. The synthetic details and the characterization data
of new compounds 3o/3c, 4o, 7, 8, 9 and 13 are given in Ex-
perimental Section, those of 2o, 5, 10, 12 and 15 in the Sup-
porting Information.
UV/Vis absorption and fluorescence studies: We have
first performed UV/Vis investigations of dyad 2o, which
bears benzo[b]thiophene-1,1-dioxide and
a phenylthio-
phene-1,1-dioxide groups at the photochromic moiety. The
absorption spectrum of 2o in dichloromethane in the visible
region is very similar to that of the reference PBI dye 5. An
additional band is observed at 369 nm that can be attributed
to the open form of the photochromic moiety of this dyad.
Upon irradiation with visible light (>400 nm) for 80 min,
this band increases owing to the more pronounced absorp-
tion of the closed form of this DAE in this wavelength
&
4
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Electron Transfer
FULL PAPER
Figure 3. UV/Vis absorption spectra of dyads 3o (solid line) and 3c
(dotted line) and reference PBI dye 5 (dashed line) in dichloromethane
(1ꢄ10ꢀ5 m) at 258C and fluorescence emission spectrum of reference 5
(dashed line; lex =530 nm) in dichloromethane.
Figure 1. Switching cycles of 3o recorded by means of the fluorescence
intensity at 650 nm in dichloromethane upon alternating irradiation with
UV light (320 nm; ꢁ10 nm FWHM; xenon arc lamp 150 W) and visible
light (cut-off filter at 395 nm; xenon arc lamp 175 W).
Table 1. Optical properties of dyads 3o and 3c and reference compounds
5 and 4o in dichloromethane (1ꢄ10ꢀ5 m) at 258C.
labs [nm] (emax [mꢀ1 cmꢀ1])
lem
[nm][a]
Ffl
[%][a]
3o 265 (44900), 289 (47800), 455 (15600), 544
(26800), 582 (43900)
3c 265 (44900), 289 (44500), 368 (25000), 445
(16300), 586 (48000)
614
614
604
–
95
5
5
267 (39700), 287 (50600), 450 (16400), 537
(27200), 575 (43700)
96
–
4o 304 (7800), 318 (7800)
[a] Excitation wavelength 530 nm.
*
*
Figure 2. Fluorescence intensity at 650 nm of 3o ( ) and 3c ( ) in di-
chloromethane upon continuing excitation with monochromatic light at
600 nm (ꢁ10 nm FWHM; xenon short arc lamp 75 W; 6.9 mWcmꢀ2).
(Figure S2). Surprisingly, irradiation of a solution of 4o in
dichloromethane by UV light (254 nm) leads to a poor con-
version to the closed form 4c, a behavior that totally differs
from that of open-form dyad 3o as it converts nearly com-
pletely to the ring-closed form 3c upon UV (350 nm) irradi-
ation. These observations reveal that PBI chromophore has
a different impact on the photochromic behavior of diaryl-
bility was shown by enduring excitation of the fluorophore
unit of 3o and 3c at 600 nm in dichloromethane (Figure 2).
The emission intensity of 3o and 3c remained constant
over the time range of more than 3 h of intense irradiation
of the PBI fluorophore at 600 nm. This observation eviden-
ces that excitation of the PBI unit does not lead to decom-
position or an unfavorable ring-closure process of 3o or a
just as disadvantageous ring-opening of 3c.
Absorption spectra of 3o, 3c, and reference PBI dye 5
were measured in dichloromethane (Figure 3). The absorp-
tion maximum is bathochromically shifted by about 10 nm
for both ring-open (3o) and ring-closed (3c) dyads com-
pared to PBI 5 and the closed form exhibits a noticeable
higher extinction which is in accordance with our previous
observation.[24b] The emission maximum of PBI chromo-
phore (lem =604 nm) is likewise bathochromically shifted by
10 nm for 3o and 3c (see Table 1).
AHCTUNGTRENNUNG
similar absorption behavior in the visible region, solutions
of these dyads in dichloromethane exhibit distinctly differ-
ent color (Figure 4, top panel). The solution of the open
form appears pink, while that of the closed form appears
violet. Under UV light (365 nm), the solution of 3o is bright
red emissive and, in contrast, that of 3c is barely visible red
emissive. In accordance with these coloristic attributes, the
fluorescence quantum yields of open form 3o (95%) and
closed form 3c (5%) in dichloromethane are strikingly dif-
ferent (Figure 4, bottom panel). Thus, the pink color of 3o
solution arises from a combined effect of light absorption
(with complementary color violet) and red-light emission.
The fluorescence quantum yields of 3o and 3c were deter-
mined in several solvents of different polarity from tetra-
chloromethane (er =2.24) to dimethyl formamide (er =36.71)
and divided by the respective value of reference PBI 5 to
explore whether the fluorescence quenching behavior of
these dyads is dependent on the solvent polarity as expected
The closed form 3c exhibits a broad absorption band with
a maximum at 368 nm that extends into the visible range
and can be assigned to the diarylethene moiety. The absorp-
tion spectrum of the open form of reference diarylethene 4o
in dichloromethane shows absorption only in the UV range
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
5
&
ÞÞ
These are not the final page numbers!

F. Scandola, F. Wꢀrthner et al.
from the aryloxy substituents to the electron-poor PBI.[41]
A
far more pronounced solvent dependency is, however, ob-
served for closed form 3c. This isomer exhibits a fluores-
cence quantum yield of unity in tetrachloromethane that is
dramatically decreased to 11% in chloroform (er =4.89). In
more polar solvents, such as acetone (er =20.56), fluores-
cence of 3c is negligible. This tremendous on–off ratio of
fluorescence is a great advantage of our new photochromic
dyad 3 relative to other known PET-based, photochromic,
optical data storage systems. The observed increased lumi-
nescence quenching of 3c with increasing solvent polarity is
indicative of
a favored photoinduced electron-transfer
(PET) process, whereas a FRET-based process would not
show such solvent polarity dependence for fluorescence.
Cyclic voltammetry and determination of the PET driving
force: To calculate the driving force for the PET process of
dyad 3o/3c, the first oxidation potential of the electron
donor in dyad 3, that is, the PBI unit, and the first reduction
potential of the electron acceptor, that is, the diarylethene
switch, are required. Thus, the redox potentials of open and
closed form dyads 3o and 3c as well as reference PBI 5
were measured by cyclic voltammetry. The electrochemical
data are collected in Table 3 and the cyclic voltammograms
Figure 4. Top panel: Photographs of solutions of open form 3o and
closed form 3c in dichloromethane (1ꢄ10ꢀ5 m) under ambient laboratory
light (left) and under 365 nm (right). Bottom panel: Fluorescence quan-
tum yields of 3o and 3c (Ffl) divided by the quantum yield of reference
PBI 4 (Frflef) as a function of dielectric constants of solvents; open form
Table 3. Half-wave potentials of 3o and 3c and reference compounds 4o
and 5.[a]
red
ox
1=2
E
[V]
E
[V]
*
*
(
), closed form ( ).
1=2
4o
3o
3c
5
ꢀ1.37,[b,e] ꢀ1.62,[b,e] ꢀ1.92[b,e]
ꢀ1.24,[c] ꢀ1.41,[d,e] ꢀ1.83[b,e]
ꢀ0.97,[b] ꢀ1.17,[c] ꢀ1.32,[c] ꢀ1.76[b,e]
ꢀ1.27,[c] ꢀ1.41[c]
–
0.84[c]
0.89[c]
0.78[c]
Table 2. Fluorescence quantum yields of 3o, 3c and reference dye 5 in
different solvents.
[a] All measurements were carried out in dry dichloromethane (10ꢀ4 m)
using Fc/Fc+ as an internal standard and NBu4PF6 (0.1m) as supporting
electrolyte at a scan rate of 100 mVsꢀ1. [b] Values belonging to the DAE
unit. [c] Values attributed to the PBI unit. [d] Overlapped value of DAE
and PBI units. [e] Peak potential of irreversible reduction.
Solvent
er[a]
Ffl [%]
3c
3o
5
tetrachloromethane
di-n-butyl ether
chloroform
dichloromethane
1,2-dichloroethane
acetone
2.24
3.08
4.89
95ꢁ0.8
95ꢁ2.1
97ꢁ2.5
95ꢁ1.1
89ꢁ1.5
74ꢁ1.7
67ꢁ2.9
99ꢁ1.8
91ꢁ1.5
11ꢁ0.3
5ꢁ0.3
4ꢁ0.1
2ꢁ0.1
3ꢁ0.3
96ꢁ2.5
95ꢁ2.7
96[39]
96ꢁ1.1
96ꢁ1.2
88ꢁ4.0
87ꢁ2.9
8.93
10.36
20.56
36.71
are shown in the Supporting Information (Figure S7–S10).
According to the data shown in Table 3, an oxidation po-
tential between 0.8 and 0.9 V is observed for the PBI unit of
all of these compounds, irrespective of the attachment of an
open or close form DAE or a cyclohexane unit at the imide
nitrogen atoms. Likewise, the first reduction potential of the
PBI unit is found in a narrow range between ꢀ1.17 and
ꢀ1.27 V. Importantly, the first reduction potential of ring-
closed 3c at ꢀ0.97 V is significantly higher (less negative)
than that of ring open 3o (and reference diarylethene 4o as
well) and is accordingly attributable to the closed DAE sub-
unit. Unfortunately, the reduction waves of the open DAE
and PBI moieties overlap in the cyclic voltammogram of
open form 3o at a value of about ꢀ1.41 V. Thus, for the first
reduction potential of the open form we used the value of
ꢀ1.37 V observed for reference DAE 4o. The pronounced
difference of 0.40 V between the first reduction potentials of
open and closed form of photoswitch 3 indicates that the
DMF
[a] Solvent polarity values are taken from reference [40].
for a PET quenching mechanism. The fluorescence quantum
yields of 3o, 3c, and PBI 5 in different solvents are listed in
Table 2 and the values Ffl (%)/Frflef (%) as a function of sol-
vent polarities are shown in Figure 4 (bottom panel).
The open form dyad 3o shows a fluorescence quantum
yield of almost unity in solvents of low or intermediate po-
larity such as tetrachloromethane (er =2.24) and dichlorome-
thane (er =8.93). With increasing solvent polarity, the quan-
tum yield is decreased ultimately to 67% in dimethyl forma-
mide (er =36.71). Notably, the quantum yield of reference
dye 5 is decreased as well, from nearly unity in nonpolar en-
vironments to 87% in dimethyl formamide. For similar PBI
dyes this behavior has been attributed to charge transfer
&
6
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Electron Transfer
FULL PAPER
driving force for electron-transfer process should be much
more favorable for 3c than for 3o in dichloromethane or
other polar solvents, which is in accordance with the ob-
served strong fluorescence quenching for 3c in such solvents
(see Table 2). Accordingly, based on our cyclic voltammetry
analysis, the electron transfer from PBI donor to diaryl-
the fluorescence should not be significantly quenched, which
is indeed experimentally observed. In contrast, highly polar
solvents like dimethyl formamide should stabilize the
charge-transfer states and thus fluorescence quenching is ex-
pected even for the open form, which is also in accordance
with our observations (see Table 2).
ACHTUNGTRENNUNGethene acceptor should be thermodynamically favored for
the closed form over the open form.
Photophysical studies by time-resolved transient spectrosco-
py: To get an insight into the fluorescence-quenching proc-
ess of photoswitch 3, the fluorescence lifetimes of the open-
ring (3o) and closed-ring (3c) isomers as well as reference
fluorophore PBI 5 were determined in dichloromethane and
acetone by the time-correlated single-photon-counting (TC-
SPC) technique. The obtained results are summarized in
Table 4.
To quantify the thermodynamic driving force for the pho-
toinduced electron-transfer process of photochromic dyad 3,
we have applied the Rehm–Weller equation [Eq. (1)].[42]
e2
DG0 ¼ e½EoxðDÞ ꢀ EredðAÞꢂ ꢀ E00
ꢀ
4pe0esRCC
ð1Þ
e2
1
1
1
1
ꢀ
ð
þ
Þð ꢀ Þ
8pe0 rþ rꢀ eref es
Table 4. Fluorescence lifetime of 3o, 3c and PBI 5 measured by TC-
SPC.
The variables of Rehm–Weller equation are denoted as
Solvent
er
t [ns]
3o[a]
follows: Eox(D) and Ered(A) are the respective first oxidation
potential of the donor PBI and first reduction potential of
the acceptor DAE. The term E00 signifies the spectroscopic
excited state energy, while RCC is the distance between the
centers of the donor and acceptor moieties. The effective
ionic radii of the donor radical cation and acceptor radical
anion are labeled as r+ and rꢀ, respectively. The dielectric
constant of the reference solvent used in electrochemistry is
denoted as eref, while es is the dielectric constant of the re-
spective solvent applied in the spectroscopic investigation.
Since we have used dichloromethane in cyclic voltamme-
try and spectroscopy studies, the solvent related fourth term
in the Rehm-Weller equation can be neglected for dyad 3
for this particular environment. The reduction potentials of
the DAE acceptor units in the open and closed form are
ꢀ1.37 and ꢀ0.97 V, respectively, while the oxidation poten-
tials of the PBI unit in both forms are 0.84 and 0.89 V, re-
spectively. The excited state energy E00 was calculated from
the average value of the measured absorption maximum at
585 nm and emission maximum at 614 nm of the PBI moiety
in dyad 3, resulting in a value of 2.07 eV for both open and
closed forms. From the optimized structures of 3o and 3c at
the force-field level MM3* (MacroModel 9.8) center-to-
center distances RCC between the donor and acceptor units
of 3o and 3c are estimated as 1.27 nm.
5[a]
3c[a]
<0.25[b]
<0.25[b]
dichloromethane
acetone
8.93
20.56
6.6ꢁ0.03
6.9ꢁ0.03
6.5ꢁ0.03
5.3ꢁ0.03
[a] Excitation wavelength (lex) at 600 nm, analysis wavelength (lana) at
610 nm. [b] Lifetime below instrumental resolution.
As the data in Table 4 reveal, the lifetime of 3o is almost
identical to that of the reference PBI 5 in dichloromethane,
while a small (ca. 20%) decrease compared to the value for
5 is observed in acetone. This behavior, paralleled by the
fluorescence quantum yield data shown in Table 2, can be
explained by considering that photoinduced electron trans-
fer, with no driving force in dichloromethane may become
slightly exergonic in the more polar solvent acetone, provid-
ing a slow (time constant, ca. 20 ns) deactivation process for
the PBI excited state of 3o. Overall, the similar behavior of
3o and 5 indicates the absence of any major quenching of
the PBI excited state by the appended open form of the
photochromic DAE unit. By contrast, the lifetime of closed
form 3c is drastically decreased in both solvents compared
to those of 3o and PBI 5, revealing that the excited state of
the PBI unit is efficiently quenched in the closed form.
These lifetime results are in good agreement with fluores-
cence quantum yields (Table 2), which decrease dramatically
in both dichloromethane and acetone for 3c relative to
those for 3o. Moreover, in both solvents the lifetime of the
closed form 3c is too short (<0.25 ns) for an accurate deter-
mination by the single-photon-counting technique.
By applying these values in Equation (1), the Gibbs free
energy (DG8) for the formation of an intramolecular
charge-separated state in covalently bound donor–acceptor
system 3o/3c was calculated to be +0.01 eV for the open
3o and ꢀ0.34 eV for the closed form 3c. These values imply
that in moderately polar solvents like dichloromethane, elec-
tron transfer is thermodynamically highly favorable for the
To access the shorter timescale and to explore the mecha-
nism for fluorescence quenching of 3c, ultrafast transient
absorption spectroscopy measurements of 3c and, for com-
parison, of 3o and reference PBI 5 were performed by using
a femtosecond pump-probe setup (technical details are de-
scribed elsewhere).[43] The spectra are displayed in Figure 5.
Unless otherwise noted, the experiments were performed by
selective excitation of the PBI unit at its lowest singlet excit-
ring-closed form and hence the formation of PBI +–DAEC
C
Cꢀ
charge-transfer state and, on the other hand, electron trans-
fer should be disfavorable in ring-open form under similar
conditions. In less polar solvents like tetrachloromethane,
the formation of a charge-transfer state is expected to be en-
ergetically uphill for both open and closed forms, and thus
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
7
&
ÞÞ
These are not the final page numbers!

F. Scandola, F. Wꢀrthner et al.
ed state. The very similar tran-
sient spectral behavior of dyad
3o and reference PBI 5 con-
firms the conclusion inferred
from the emission measure-
ments that little, if any, inter-
component quenching of the
fluorophoric unit takes place in
the open form 3o.
The
transient
spectral
changes of the closed form 3c
in dichloromethane (Figure 5c),
on the other hand, exhibit a bi-
phasic spectral behavior entire-
ly different from that observed
for the open form 3o and refer-
ence 5. In the early time
window (ca. 1–35 ps, Figure 5c,
left panel) a complex decay of
the features associated with the
PBI excited state (ground-state
bleach centered at 590 nm,
stimulated emission in the 520–
680 nm range, excited-state ab-
sorption at longer wavelength)
is accompanied by the evident
formation of a positive absorp-
tion centered at 510 nm. In the
subsequent time window (ca.
35–160 ps,
Figure 5c,
right
panel) the transient spectrum
undergoes a clean decay to the
baseline, with isosbestic points
at DOD=0, 535, and 645 nm.
This biphasic behavior can be
assigned to the following se-
quence of charge separation
Figure 5. Ultrafast transient absorption spectra (lex =550 nm) of a) PBI model 5, b) open form dyad 3o and c)
closed form dyad 3c in dichloromethane. The arrows indicate spectral changes with increasing time.
ed state with pump light of 550 nm. The transient behavior
observed for the open form 3o in dichloromethane is very
similar to that exhibited by the reference dye 5 (Fig-
ure 5a,b). In both cases, the initial differential spectrum,
characteristic of the singlet excited state of the PBI unit, ex-
hibits a ground-state bleaching (mirroring the absorption
spectrum of PBI dye, Figure 3) at wavelengths shorter than
610 nm, an apparent bleach between 610 and 680 nm arising
from stimulated emission (mirroring the emission spectrum
of PBI dye, Figure 3), and a positive signal at wavelengths
longer than 680 nm due to excited-state absorption.
The observed spectral changes for reference PBI 5 and
dyad 3o consist of a fast process (time constant of 1.7 ps for
5 and 3.8 ps for 3o) involving a small decrease in ground-
state absorption bleach and a red-shift of the stimulated
emission (Figure 5a,b, left panels). Such fast process can be
very likely attributed to vibrational relaxation in the excited
state. The subsequent, slow decay of the whole transient
spectrum, consistent with the long emission lifetimes (shown
in Table 4), can be associated to the decay of the PBI excit-
[Eq. (2)] and charge recombination steps [Eq. (3)].
1
*
Cþ
PBI ꢀ DAEC ! PBI ꢀ DAEC
Cꢀ
ð2Þ
Cþ Cꢀ
PBI ꢀ DAEC ! PBI ꢀ DAEC
ð3Þ
This assignment is supported by the spectroelectrochemi-
cal (SEC) data of reference PBI 5 (Figure 6), showing that
one-electron oxidation of this chromophore is accompanied
by bleach in the region of the absorption maximum at
576 nm and by positive absorbance changes at both lower
(characteristic maximum at 486 nm) and higher wave-
lengths.[44] These SEC studies (Figure 6) permit an easy in-
terpretation of the transient spectral changes in Figure 5c.
The formation of the charge-separated state from the PBI
excited state (Figure 5c, left panel) is signaled by 1) an
asymmetric depletion of the bleach in ground-state maxi-
mum and 2) the build-up of the absorption maximum at
510 nm (formation of oxidized PBI). The decay of the
charge-separated state by charge recombination (Figure 5c,
&
8
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Electron Transfer
FULL PAPER
tively. In acetone (er =20.56) the values are 8.6 ps for charge
separation and 27 ps for recombination (Figure 7b). The ac-
celeration of the photoinduced electron transfer in the more
polar solvent complies with our expectations for a process in
the Marcus normal region as a consequence of the increased
driving force (by ca. 0.1 eV, estimated from a Weller-
type[42,45] calculation), whilst the concurrent slight accelera-
tion of the charge recombination points at a process in the
Marcus inverted region. The observed solvent effect on
quenching rate is in accordance with the strong fluorescence
quenching of 3c in polar solvents (Table 2).
For the purpose of comparison, ultrafast spectroscopy ex-
periments were also performed with the closed dyad 3c by
excitation at 400 nm. At this wavelength, light is absorbed
by both molecular components of the dyad in following pro-
portion: about 30% PBI unit and about 70% ring-closed
DAEC (Figure 3). The transient spectral behavior (Fig-
ure S14 in the Supporting Information) is practically the
same as observed upon excitation at 550 nm, with clear evi-
dence for photoinduced charge separation and recombina-
tion. The intensity of the transient signals, however, was def-
initely much larger than expected from the fraction of light
absorbed by the PBI unit, as determined by a comparison of
iso-absorbing 3c and 5 solutions. Thus, a sizeable fraction of
the light absorbed by the ring-closed DAEC unit apparently
contributes to the photophysical response from PBI unit.
This suggests the occurrence of excitation energy transfer as
shown in Equation (4).
Figure 6. UV/Vis absorption spectra of reference PBI 5 (only a section is
shown) as a function of applied voltage in dichloromethane (5.8ꢄ10ꢀ4 m,
0.1m Bu4NPF6); solid line: the neutral dye (0 mV) and dotted line: radi-
cal cation of 5 (1025 mV). The arrows indicate spectral changes with in-
creasing voltage. The whole spectral range is shown in the Supporting In-
formation (Figure S11).
right panel) nicely mirrors the spectral changes observed in
the spectroelectrochemical oxidation of reference PBI 5.
Ultrafast spectroscopy measurements performed in ace-
tone (Figure S13 in the Supplementary Information) showed
similar biphasic qualitative behavior as in dichloromethane
for the closed form 3c. The kinetics of charge separation
and recombination for 3c can be conveniently monitored at
+
C
the wavelengths of PBI absorption maximum at around
500 nm (Figure 7). In dichloromethane (Figure 7a), the ki-
netic analysis revealed values of 35 and 36 ps for the time
constants of charge separation and recombination, respec-
1
1
*
*
ð4Þ
PBI ꢀ DAEC ! PBI ꢀ DAEC
This hypothesis can be verified by measuring the excita-
tion spectrum of the weak PBI emission of 3c (Figure 8). As
a matter of fact, besides the two PBI bands at 590 and
Figure 8. Excitation spectrum of the PBI emission in dyad 3c (dotted
line), as compared with reference PBI 5 (solid line) in dichloromethane
(monitoring wavelength, 610 nm).
450 nm, a clear feature is observed at 365 nm, at which the
closed form of the DAE unit has its absorption maximum.
The lower intensity of this feature in the excitation
(Figure 8) relative to the absorption spectrum (Figure 3) in-
dicates that energy transfer is only partially (ca. 50%) effi-
Figure 7. Kinetics of formation and decay of the charge separated state
of 3c in a) dichloromethane and b) acetone.
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
9
&
ÞÞ
These are not the final page numbers!

F. Scandola, F. Wꢀrthner et al.
cient, implying a competition between the energy-transfer
process and other photoprocesses taking place in the excited
state of the ring-closed DAEC unit. The main photoprocess
expected from the excited state of the ring-closed DAEC
unit is the photochemical ring opening to DAEO [Eq. (5)].
1
*
ð5Þ
PBI ꢀ DAEC ! PBI ꢀ DAEO
Such processes are generally known to be ultrafast (typi-
cally, ps or fractions thereof),[46] proceeding via conical inter-
sections between the excited state and the ground state.[47]
In the early time window of the 400 nm ultrafast experi-
ment (Figure 9), the formation of the PBI excited state (as
monitored by the bleach of the ground-state absorption),
takes place promptly (within the excitation pulse width) for
reference 5, but clearly has a delayed component for dyad
3c. Within the accuracy limits of the experiment, the time
constant of the energy-transfer process from ring-closed
DAEC to PBI (and likewise for the competing ring-opening
reaction) can be estimated as about 1 ps. The observed
energy-transfer process competes in the excited state with
ring opening and is relevant to the efficiency of photo-
switching in 3c.
The photophysical/photochemical behavior of the 3c and
3o dyads discussed above is summarized in the energy-level
diagram of Figure 10. In this diagram, the energy-transfer
process [Eq. (4)] has been assumed to take place by means
of FRET to the second singlet excited state of the PBI unit
(maximum absorption at 445 nm), which is expected to give
a better spectral overlap than the lower energy one. The
triplet state of the DAE unit is not considered to be in-
volved in the photophysical behavior. Its energy is unknown,
but, based on comparisons with related systems,[32c] is ex-
pected to be out of reach of the lowest PBI excited singlet
state. The energy-transfer process from DAEO excited state
to the PBI fluorophore is simi-
Figure 9. Comparison of the formation kinetics of the PBI excited state
(as monitored by the bleach of ground-state absorption) following
400 nm excitation of a) dyad 3c and b) reference 5 in dichloromethane.
can be reversibly switched by UV irradiation of the open
form 3o and visible-light irradiation of closed form 3c with-
out significant decomposition. A rather complete characteri-
zation of the photoswitching mechanism of the system 3o/
3c has been achieved by ultrafast spectroscopic techniques.
From the design viewpoint of a fluorescent switch with non-
lar to that of the closed form
DAEC (Figure 10). The pres-
ence of such a process is sug-
gested, albeit less directly (for
spectral reasons) than for the
closed isomer, by excitation
spectra of the PBI fluorescence
in 3o (Figure S15 in the Sup-
porting Information).
Conclusion
The newly developed photo-
chromic dyad 3o/3c composed
of
a highly photostable and
emissive tetraaryloxy-substitut-
ed perylene bisimide (PBI)
chromophore (Ffl ca. 100%)
and a hitherto unknown diary-
Figure 10. Energy-level diagram and photophysical/chemical processes of dyad system 3o/3c in dichlorome-
lethene (DAE) photochrome thane.
&
10
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Electron Transfer
FULL PAPER
Fit Global Fluorescence Decay Analysis software. The time resolution of
the system after the deconvolution procedure is 250 ps.
destructive read-out, as sketched in the Introduction, the ex-
cited-state behavior of 3o and 3c is quite satisfactory and all
the main features sought for have been experimentally veri-
fied. These are: 1) pronounced difference in fluorescence
quenching efficiency of the PBI excited state by the open
and closed forms of the DAE unit of the present photo-
switching system, that is, the closed form 3c being most effi-
ciently quenched (Ffl <5%) and 2) efficient electron-trans-
fer-quenching mechanism. As compared to previous reports
on related perylene bisimide/diarylethene systems,[24b,25,32]
the experimental evidence for an electron-transfer mecha-
nism is very definite in the present case, with well-distin-
guished charge-separation and charge-recombination steps.
Also from a practical point of view, the determined fluores-
cence on/off ratio of up to 19:1 in dichloromethane (37:1 in
acetone) for 3o/3c and of 3:1 for the photostationary states
at 320/395 nm in dichloromethane facilitates excellent dis-
criminability between both states (see Figure 4). Thus, our
novel photochromic system satisfies the necessary require-
ments for nondestructive read-out in a write/read/erase fluo-
rescent memory device.
Femtosecond time-resolved studies: Femtosecond time-resolved experi-
ments were performed using a pump-probe setup based on the Spectra-
Physics Hurricane Ti:sapphire laser source and the Ultrafast Systems
Helios spectrometer. The 550 nm pump pulses were generated with a
Spectra Physics 800 OPA, while the 400 nm excitation wavelength was
achieved with a Spectra Physics SHG. Probe pulses were obtained by
continuum generation on a sapphire plate (useful spectral range: 450–
800 nm). Effective time resolution was about 300 fs, temporal chirp over
the white-light 450–750 nm range was about 200 fs, temporal window of
the optical delay stage was 0–2000 ps. The time-resolved spectral data
were analyzed with the Ultrafast Systems Surface Explorer Pro software.
Cyclic voltammetry: Cyclic voltammetry measurements performed on a
standard commercial electrochemical analyzer (EC epsilon; BAS Instru-
ments, UK) in a three electrode single-compartment cell under argon.
Dichloromethane (HPLC grade) was dried over calcium hydride under
argon and degassed prior to use. The supporting electrolyte tetrabutylam-
monium hexafluorophosphate (TBAHFP) was synthesized according to
literature,[49] recrystallized from ethanol/water and dried in high vacuum.
The measurements were carried out under exclusion of air and moisture
at a concentration of about 10ꢀ4 m with ferrocene as the internal standard
for the calibration of the potential. Working electrode: Pt disc; reference
electrode: Ag/AgCl; auxiliary electrode: Pt wire.
Spectroelectrochemistry: Spectroelectrochemistry measurements were
performed in a specially designed sample compartment consisting of a cy-
lindrical quartz cell, a platinum disc (ø=6 mm), a gold-covered metal
(V2A) plate as the auxiliary electrode and a Ag/AgCl pseudo-reference
electrode. All spectra were recorded in reflection mode and the optical
path length was varied by adjusting the vertical position of the working
electrode with a micrometer screw. The potential applied was varied in
steps of 25 or 50 mV with a potentiostat EG & G Princeton Applied re-
search Model 283. A JASCO V-670 spectrometer was used for UV/vis/
NIR absorption spectrum. The compounds were checked for reversibility
of the spectra.
Experimental Section
General: All solvents and reagents were purchased from commercial
sources and used as received without further purification, unless other-
wise stated. 2-Fluoro-1-{2’-methyl-6-(2,5-dimethylpyrrol-1-yl)-benzo[b]-
thiophen-3-yl}perfluorocyclopentene (6) was prepared according to liter-
ature procedure.[32b] 1,6,7,12-Tetrachloroperylene-3,4:9,10-tetracarboxylic
acid bisanhydride (14) was kindly provided by BASF SE, Ludwigshafen
(Germany). Column chromatography was performed using silica gel 60M
(0.04–0.063 mm) from Macherey–Nagel. Melting points were determined
on an Olympus BX41 polarization microscope and are uncorrected. 1H
and 13C NMR spectra were recorded on Bruker Avance 400 or Bruker
Avance DMX 600 and calibrated to the residual solvent peak. High-reso-
lution mass spectra (ESI) were recorded on an ESI MicrOTOF Focus
from Bruker Daltonics. MALDI-TOF mass spectra were recorded on an
Autoflex II from Bruker Daltonics. The UV irradiation was performed
by a Rayonet Photoreactor RPR-100 (Southern New England Ultraviolet
Company) with 16 UV lamps (each 24 Watt; lmax =350 nm). AL42 filter
from JASCO Corporation (L42.SP-08.08.03–0.1 mm cuvette) was used
for filtering irradiation below 400 nm.
1-(3-Methylbenzo[b]thiophen-2-yl)-2-{2-methyl-6-{2,5-dimethylpyrrol-1-
yl)benzo[b]thiophen-3-yl}perfluorocyclopentene (7): This compound was
synthesized according to the procedure reported for 1-(3-methyl-5-phe-
nylthiophen-2-yl)-2-{2-methyl-6-{2,5-dimethylpyrrole-1-yl)benzo[b]thio-
phen-3-yl}perfluorocyclopentene that contains one phenylthiophene
group.[32b]
A portion of 2-bromo-3-methylbenzo[b]thiophene (55 mg,
242 mmol) was dissolved in dry THF (5 mL) and cooled to ꢀ788C. n-Bu-
tyllithium (0.10 mL, 250 m mol; 2.5m in n-hexane) was added dropwise to
the solution and stirred for 30 min at ꢀ788C. Subsequently, compound 6
(102 mg, 235 mmol) in dry THF (2.5 mL) was added dropwise to the reac-
tion mixture and the resulting solution was stirred for additional 1 h at
ꢀ788C and 15 min at ambient temperature. The reaction mixture was
quenched with diluted hydrochloric acid and then extracted with diethyl
ether (4ꢄ15 mL). The combined organic layers were dried over sodium
sulfate and evaporated under reduced pressure. The crude product was
purified by column chromatography on silica gel (n-hexane/ethyl acetate
19:1 (v/v)) to yield a pale brownish solid (70.1 mg; 125 mmol; 54%).
1H NMR (400 MHz, CD2Cl2, 300 K): d=7.76–7.80 (m, 1H), 7.61–7.67 (m,
UV/Vis absorption and fluorescence spectroscopy: For all spectroscopic
measurements, spectroscopic grade solvents (Uvasol) from Merck (Ho-
henbrunn, Germany) were used. UV/Vis spectra were recorded on a
Perkin–Elmer UV/Vis spectrometer Lambda 35 and fluorescence as well
as excitation spectra with a PTI QM-4/2003 using conventional quartz
cells (light path: 1 cm). All fluorescence measurements were performed
under aerobic conditions and fluorescence spectra are corrected against
photomultiplier and lamp intensity. The fluorescence quantum yields
were determined as the average value for five different excitation wave-
lengths using N,N’-bis(2,6-diisopropylphenyl)-1,6,7,12-tetraphenoxypery-
lene-3,4:9,10-tetracarboxylic acid bisimide as reference (Ffl =0.96 in
chloroform) by applying the high dilution method (Abs.<0.05).[39,48]
2H), 7.57 (d, 4J
G
ACHTUNGTRENNUNG
3J(H,H)=8.5 Hz, 4J
ACHTUNGTRENNUNG
(s, 3H), 1.97 ppm (s, 6H); HRMS (ESI, pos. mode, acetonitrile/CHCl3
1:1): m/z calcd for C23H16F6NS2: 484.0628 [Mꢀ“protecting group”+H]+;
found: 484.06187; MS (MALDI, pos. mode, matrix DCTB 1:3 in CHCl3):
m/z calcd for C29H22F6NS2: 561.1019 [M+H]+; found: 561.100.
1-(3-Methylbenzo[b]thiophen-2-yl)-2-(2-methyl-6-aminobenzo[b]thio-
phen-3-yl)perfluorocyclopentene (8): This compound was synthesized ac-
cording to the procedure reported for 1-(3-methyl-5-phenylthiophen-2-
yl)-2-(2-methyl-6-amino-benzo[b]thiophen-3-yl)perfluorocyclopentene.[32b]
Emission lifetime measurements: Emission lifetimes were measured by
time-correlated single photon counting technique, using a TC-SPC appa-
ratus (PicoQuant Picoharp 300), equipped with subnanosecond LED
sources (280–600 nm range, 300–700 ps pulse width) powered with a Pico-
Quant PDL 800-B variable (2.5–40 MHz) pulsed power supply. The ex-
periments were performed using 600 nm LED (300 ps pulse width) as ex-
citation source. The decays were analyzed by means of PicoQuant Fluo-
A
mixture of compound 7 (64.0 mg, 114 mmol), hydroxylammonium
chloride (161 mg, 2.32 mmol), triethylamine (0.17 mL), ethanol (3 mL),
and water (0.6 mL) was stirred for 42 h at 958C. Water (25 mL) was
added to the solution, which was extracted with ethyl acetate (3ꢄ20 mL).
The combined organic layers were dried over sodium sulfate and evapo-
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
11
&
ÞÞ
These are not the final page numbers!

F. Scandola, F. Wꢀrthner et al.
rated under reduced pressure. The crude product was purified by column
chromatography on silica gel (ethyl acetate/n-hexane 7:3 (v/v)) to yield
an orange solid (51.1 mg; 91.0 mmol; 80%). 1H NMR (400 MHz, CD2Cl2,
HRMS (ESI, pos. mode, acetonitrile/CHCl3 1:1): m/z calcd for
C93H81F6N2O8S2: 1531.5336 [M+H]+; found: 1531.5338; MS (MALDI,
neg. mode, matrix DCTB 1:1 in CHCl3): m/z calcd for C93H80F6N2O8S2:
1530.5258 [M]ꢀ; found: 1530.553.
300 K): d=7.74–7.79 (m, 1H), 7.60–7.65 (m, 1H), 7.34–7.40 (m, 2H), 7.31
4
(dd, 3J
6.72 (dd, 3J
G
N
E
Oxidation of dyad 13 to open form dyad 3o: The oxidation was conduct-
ed according to a general procedure reported for benzo[b]thiophene de-
(H,H)=8.6, 4J
rivatives.[35]
A portion of Oxone (2 KHSO5·KHSO4·K2SO4; 152 mg,
3H), 2.09 ppm (s, 3H); HRMS (ESI, pos. mode, acetonitrile/CHCl3 1:1):
m/z calcd for C23H16F6NS2: 484.0628 [M+H]+; found: 484.06240; MS
(MALDI, pos. mode, matrix DCTB 1:3 in CHCl3): m/z calcd for
C23H15F6NS2: 483.0550 [M]+; found: 483.057.
247 mmol) was added carefully to a heterogeneous mixture of dyad 13
(34.1 mg, 21.8 mmol) and sodium bicarbonate (93.1 mg) in water
(1.5 mL), acetone (1.3 mL), and dichloromethane (1.4 mL). The mixture
was stirred vigorous for 7 d at room temperature. Water (20 mL) was
added to the mixture, which was then extracted with dichloromethane
(3ꢄ15 mL). The combined organic layers were dried over sodium sulfate
and evaporated under reduced pressure. The resulting residue was puri-
fied by column chromatography on silica gel (dichloromethane) to obtain
a red solid (23.5 mg; 14.7 mmol; 67%). M.p.: 286–2878C (from dioxane),
1H NMR (400 MHz, CD2Cl2, 300 K): d=8.18 (s, 2H), 8.12 (s, 2H), 7.69–
7.73 (m, 1H), 7.59–7.68 (m, 3H), 7.50–7.54 (m, 2H), 7.35–7.38 (m, 1H),
Diarylethene derivative 9: Compound 9 was synthesized according to the
procedure reported for a similar photochromic reference diarylethene.[32b]
A
mixture of compound 8 (62.0 mg, 128 mmol), phthalic anhydride
(38.0 mg, 256 mmol), dry quinoline (6.5 mL), and zinc acetate (6.9 mg)
was heated to 1558C for 20 h under an argon atmosphere. Hydrochloric
acid (1n) was added to the solution and the mixture was extracted with
dichloromethane (3ꢄ20 mL). The combined organic layers were evapo-
rated under reduced pressure. The resulting residue was purified by
column chromatography on silica gel (n-hexane/ethyl acetate 3:1 (v/v))
to obtain a yellowish solid (71.0 mg, 116.0 mmol, 90%). M.p.: 202–2048C
(from dichloromethane); 1H NMR (400 MHz, CD2Cl2, 300 K): d=7.93–
7.98 (m, 2H), 7.85–7.87 (m, 1H), 7.81–7.85 (m, 2H), 7.75–7.80 (m, 1H),
7.25–7.31 (m, 8H), 6.85 (d, 3J
ACTHNUTRGNEU(GN H,H)=8.0 Hz, 8H), 4.86–4.91 (m, 1H),
2.38–2.48 (m, 2H), 2.25 (s, 3H), 2.24 (s, 3H), 1.80–1.88 (m, 2H), 1.63–
1.71 (m, 3H), 1.34–1.45 (m, 3H), 1.31 (s, 18H), 1.28 ppm (s, 18H); UV/
Vis (CH2Cl2): lmax (emax)=265 (44900), 289 (47800), 455 (15600), 544
(26800), 582 nm (43900mꢀ1 cmꢀ1); fluorescence (CH2Cl2): lmax =614 nm
(lex =530 nm), Ffl =0.95; HRMS (ESI, pos. mode, acetonitrile/CHCl3
1:1): m/z calcd for C93H81F6N2O8S2: 1595.5133 [M+H]+; found:
1595.5141; MS (MALDI, pos. mode, matrix DCTB 1:3 in CHCl3): m/z
7.70 (dd, 3J
(dd, 3J(H,H)=8.6, 4J
ACHTUNGTRENNUNG
N
ACHTUNGTRENUN(NG H,H)=1.7 Hz, 1H), 7.63–7.67 (m, 1H), 7.45
U
3H), 2.17 ppm (s, 3H); HRMS (ESI, pos. mode, acetonitrile/CHCl3 1:1):
m/z calcd for C31H18F6NO2S2: 614.0683 [M+H]+; found: 614.06754; MS
(MALDI, pos. mode, matrix DCTB 1:3 in CHCl3): m/z calcd for
C31H17F6NO2S2: 613.0605 [M]+; found: 613.058.
calcd for C93H80F6N2O12S2: 1594.5055 [M]+; found: 1594.513; CV
red
(CH2Cl2, 0.1m TBAHFP, vs. Fc/Fc+, scan rate 100 mVsꢀ1): E (X2ꢀ
/
pp
red
red
ox
X
3ꢀ)=ꢀ1.83 V, E (Xꢀ/X2ꢀ)=ꢀ1.41 V, E (X/Xꢀ)=ꢀ1.24 V; E (X/
pp
pp
1=2
Reference diarylethene 4o: The oxidation of precursor 9 to diarylethene
4o was performed according to a general procedure described for ben-
X+)=0.84 V, E (X+/X2+)>1.10 V.
ox
1=2
Photolytic conversion of open form dyad 3o to closed form 3c: The com-
zo[b]thiophene
derivatives.[35]
A
portion
of
Oxone
pound was synthesized according to the procedure described for the
(2KHSO5·KHSO4·K2SO4; 920 mg ) was added carefully to a heterogene-
ous mixture of diarylethene 9 (142 mg, 231 mmol) and sodium bicarbon-
ate (563 mg) in water (9.2 mL), acetone (7.5 mL), and dichloromethane
(8.3 mL). The mixture was stirred vigorously for 3 h at room temperature
and then extracted with dichloromethane (3ꢄ20 mL). The combined or-
ganic layers were dried over sodium sulfate and evaporated under re-
duced pressure. The resulting residue was purified by column chromatog-
raphy on silica gel (chloroform/methanol 99.5/0.5 (v/v)) to obtain a
yellow solid (147 mg; 216 mmol; 94%). M.p.: 179–1818C (from dichloro-
methane); 1H NMR (400 MHz, CD2Cl2, 300 K): d=7.95–8.00 (m, 3H),
closed form of a 1,7-dipyrrolidinylperylene-diarylethene conjugate.[24b]
A
solution of the open form 3o (35.2 mg, 22.1 mmol) in dichloromethane
(200 mL) was irradiated in Rayonet Photoreactor with UV light
a
(350 nm) for 20 min under vigorous stirring. The solution was concentrat-
ed by rotary evaporation in the dark and the resultant precipitate was pu-
rified in the dark by column chromatography on silica gel (acetone/n-
hexane (1/4 v/v), dried at 10ꢀ3 mbar to yield 3c (24.1 mg, 15.1 mmol;
69%) as a dark red solid. A certain amount of the open form (9.9 mg,
1
6.2 mmol; 28%) was re-isolated as red solid. H NMR (600 MHz, CD2Cl2,
3
300 K): d=8.39 (d, J
G
7.83–7.88 (m, 2H), 7.80 (dd, 3J(H,H)=8.3 Hz, 4J
ACTHUNTGRNENUG ACHTUNTGERN(NUGN H,H)=2.0 Hz, 1H),
(d, 3J
3J
(m, 8H), 4.90 (tt, JACTHGUNTREN(NUNG H,H)=12.2 Hz, JACHTUNGTNER(NUGN H,H)=3.6 Hz, 1H), 2.39–2.46 (m,
(H,H)=8.0 Hz, 1H), 7.98 (d, 4J
ACHUTGTNRENNUG CAHTUNGTRENNUNG
7.70–7.75 (m, 1H), 7.61–7.68 (m, 2H), 7.52–7.56 (m, 1H), 7.37–7.41 (m,
1H), 2.28 (s, 3H), 2.25 ppm (s, 3H); UV/Vis (CH2Cl2): lmax (emax)=303
(7800), 318 nm (7800mꢀ1 cmꢀ1); HRMS (ESI, pos. mode, acetonitrile/
CHCl3 1:1): m/z calcd for C31H18F6NO6S2: 678.0479 [M+H]+; found:
678.04758; MS (MALDI, pos. mode, matrix DCTB 1:3 in CHCl3): m/z
AHCTUNGTRENNUNG
3
4
2H), 1.90 (s, 3H), 1.82–1.86 (m, 2H), 1.66–1.69 (m, 3H), 1.35–1.43 (m,
3H), 1.31 (s, 18H), 1.28 (s, 18H), 1.24 ppm (s, 3H); UV/Vis (CH2Cl2):
lmax (e)=265 (44900), 289 (44500), 368 (25000), 445 (16300), 546
(29200), 586 nm (48000mꢀ1 cmꢀ1); fluorescence (CH2Cl2): lmax =614 nm
(lex =530 nm), Ffl =0.05; HRMS (ESI, pos. mode, acetonitrile/CHCl3
calcd for C31H17F6NNaO6S2: 700.0299 [M+Na]+; found: 700.038; CV
red
pp
(CH2Cl2, 0.1m TBAHFP, vs. Fc/Fc+, scan rate 100 mVsꢀ1): E (X2ꢀ
/
red
red
X
3ꢀ)=ꢀ1.92 V, E (Xꢀ/X2ꢀ)=ꢀ1.62 V, E (X/Xꢀ)=ꢀ1.37 V.
1:1): m/z calcd for C93H80F6N2O12S2: 1595.5133 [M]+; found: 1595.5122;
pp
pp
red
pp
CV (CH2Cl2, 0.1m TBAHFP, vs. Fc/Fc+, scan rate 100 mVsꢀ1): E (X3ꢀ
/
Perylene bisimide/diarylethene dyad 13: This dyad was synthesized ac-
cording to the previously reported procedure for a photochromic dyad
bearing pyrrolidinyl-substituted perylene bisimide.[24b] A mixture of com-
pounds 8 (41.4 mg, 85.6 mmol), 10 (91.3 mg, 85.6 mmol), and imidazole
(2.0 g) was heated to 1108C for 14.5 h under an argon atmosphere. Etha-
nol (5 mL) was added to the hot solution, and after cooling to room tem-
perature 2n hydrochloric acid (20 mL) was added and the mixture was
then extracted with dichloromethane (3ꢄ15 mL). The combined organic
layers were evaporated under reduced pressure. The resulting residue
was purified by column chromatography on silica gel (dichloromethane/
n-hexane/acetic acid 500:500:3 (v/v/v)) to obtain a red solid (91.1 mg,
59.5 mmol, 69%). M.p.: 288–2908C (from dichloromethane); 1H NMR
(400 MHz, CD2Cl2, 300 K): d=8.18 (s, 2H), 8.12 (s, 2H), 7.75–7.80 (m,
1H), 7.62–7.71 (m, 3H), 7.34–7.39 (m, 2H), 7.23–7.30 (m, 9H), 6.85 (d,
red
red
red
X
4ꢀ)=ꢀ1.76 V, E
(X2ꢀ/X3ꢀ)=ꢀ1.32 V, E
(Xꢀ/X2ꢀ)=ꢀ1.17 V, E
1=2
1=2
1=2
ox
ox
(X/Xꢀ)=ꢀ0.97 V; E (X/X+)=0.89 V, E (X+/X2+)>1.20 V.
1=2
1=2
Acknowledgements
We thank Ana-Maria Krause and the group of Prof. Christoph Lambert
for their help with the spectroelectrochemistry studies.
[1] Y. Hirshberg, C. R. Hebd. Seances Acad. Sci.1950, 231, 903–904.
[2] a) H. Rau, Angew. Chem. 1973, 85, 248–258; Angew. Chem. Int. Ed.
Engl. 1973, 12, 224–235; b) F. Hamon, F. Djedaini-Pilard, F. Barbot,
C. Len, Tetrahedron 2009, 65, 10105–10123; c) R. Reuter, N. Hostet-
tler, M. Neuburger, H. A. Wegner, Chimia 2010, 64, 180–183;
3J
ACHTUNGTRENNUNG(H,H)=9.6 Hz, 8H), 4.86–4.91 (m, 1H), 2.37–2.49 (m, 2H), 2.40 (s,
3H), 2.14 (s, 3H), 1.90–1.94 (m, 2H), 1.83–1.86 (m, 3H), 1.34–1.45 (m,
3H), 1.31 (s, 18H), 1.28 ppm (s, 18H); UV/Vis (CH2Cl2): lmax (emax)=266
(62200), 287 (54500), 452 (16600), 539 (29100), 579 nm (47300mꢀ1 cmꢀ1);
&
12
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Electron Transfer
FULL PAPER
d) M.-M. Russew, S. Hecht, Adv. Mater. 2010, 22, 3348–3360;
e) A. A. Beharry, G. A. Woolley, Chem. Soc. Rev. 2011, 40, 4422–
4437.
derson, B. Albinsson, J. Andrꢅasson, Angew. Chem. 2010, 122,
1898–1901; Angew. Chem. Int. Ed. 2010, 49, 1854–1857; k) B. See-
feldt, K. Altenhoner, O. Tosic, T. Geisler, M. Sauer, J. Mattay, Pho-
tochem. Photobiol. Sci. 2011, 10, 1488–1495; l) T. Fukaminato, J.
Photochem. Photobiol., C 2011, 12, 177–208.
[3] Y. Yokoyama, Chem. Rev. 2000, 100, 1717–1740.
[4] G. Berkovic, V. Krongauz, V. Weiss, Chem. Rev. 2000, 100, 1741–
1754.
[5] a) M. Irie, Chem. Rev. 2000, 100, 1685–1716; b) H. Tian, S. Yang,
Chem. Soc. Rev. 2004, 33, 85–97.
[20] a) M. Irie, T. Fukaminato, T. Sasaki, N. Tamai, T. Kawai, Nature
2002, 420, 759–760; b) T. Fukaminato, T. Sasaki, T. Kawai, N.
Tamai, M. Irie, J. Am. Chem. Soc. 2004, 126, 14843–14849.
[6] M. Irie, T. Mrozek, J. Daub, A. Ajayaghosh, Y. Yokoyama, Molecu-
lar Switches (Ed.: B. L. Feringa), Wiley-VCH, Weinheim, 2001,
pp. 37–121.
[21] a) Supramolecular Photochemistry (Eds.: V. Balzani, F. Scandola),
Ellis Horwood, New York, 1991; b) Fundamentals of Photoinduced
Electron Transfer (Ed.: G. J. Kavarnos), VCH, Weinheim (Germa-
ny), 1993; c) Electron Transfer in Chemistry (Ed.: V. Balzani),
Wiley-VCH, Weinheim (Germany), 2001; d) N. Mataga, H. Chos-
rowjan, S. Taniguchi, J. Photochem. Photobiol. C 2005, 6, 37–79.
[22] a) J. M. Endtner, F. Effenberger, A. Hartschuh, H. Port, J. Am.
Chem. Soc. 2000, 122, 3037–3046; b) A. J. Myles, N. R. Branda, J.
Am. Chem. Soc. 2001, 123, 177–178; c) Y. Terazono, G. Kodis, J.
Andrꢅasson, G. Jeong, A. Brune, T. Hartmann, H. Dꢀrr, A. L.
Moore, T. A. Moore, D. Gust, J. Phys. Chem. B 2004, 108, 1812–
1814; A. L. Moore, T. A. Moore, D. Gust, J. Phys. Chem. B 2004,
108, 1812–1814; d) F. M. Raymo, M. Tomasulo, Chem. Soc. Rev.
2005, 34, 327–336.
[7] M. Irie, M. Mohri, J. Org. Chem. 1988, 53, 803–808.
[8] a) S. Kawata, Y. Kawata, Chem. Rev. 2000, 100, 1777–1788; b) B. L.
Feringa, J. Org. Chem. 2007, 72, 6635–6652; c) H. Tian, S. Wang,
Chem. Commun. 2007, 781–792; d) Molecular Devices and Ma-
chines-Concepts and Perspectives for the Nanoworld (Eds.: V. Balza-
ni, A. Credi, M. Venturi), Wiley-VCH, Weinheim (Germany), 2008;
e) H. Tian, Y. Feng, J. Mater. Chem. 2008, 18, 1617–1622; f) C. Yun,
J. You, J. Kim, J. Huh, E. Kim, J. Photochem. Photobiol. C 2009, 10,
111–129; g) U. Pischel, Aust. J. Chem. 2010, 63, 148–164; h) A.
Bianco, S. Perissinotto, M. Garbugli, G. Lanzani, C. Bertarelli, Laser
Photonics Rev. 2011, 5, 711–736; i) W. Zhu, Y. Yang, R. Mꢅtivier, Q.
Zhang, R. Guillot, Y. Xie, H. Tian, K. Nakatani, Angew. Chem.
2011, 123, 11178–11182; Angew. Chem. Int. Ed. 2011, 50, 10986–
10990; j) D. Gust, J. Andrꢅasson, U. Pischel, T. A. Moore, A. L.
Moore, Chem. Commun. 2012, 48, 1947–1957.
[9] a) N. Katsonis, T. Kudernac, M. Walko, S. J. van der Molen, B. J.
van Wees, B. L. Feringa, Adv. Mater. 2006, 18, 1397–1400;
b) M. T. W. Milder, J. Areephong, B. L. Feringa, W. R. Browne, J. L.
Herek, Chem. Phys. Lett. 2009, 479, 137–139.
[10] P. Zacharias, M. C. Gather, A. Kçhnen, N. Rehmann, K. Meerholz,
Angew. Chem. 2009, 121, 4098–4101; Angew. Chem. Int. Ed. 2009,
48, 4038–4041.
[23] S. Tsuchiya, J. Am. Chem. Soc. 1999, 121, 48–53.
[24] a) M. Berberich, Diploma Thesis, University of Wꢀrzburg, Wꢀrz-
burg (Germany), 2007; b) M. Berberich, A.-M. Krause, M. Orlandi,
F. Scandola, F. Wꢀrthner, Angew. Chem. 2008, 120, 6718–6721;
Angew. Chem. Int. Ed. 2008, 47, 6616–6619.
[25] Y. Odo, T. Fukaminato, M. Irie, Chem. Lett. 2007, 36, 240–241.
[26] a) H. Langhals, Heterocycles 1995, 40, 477–500; b) F. Wꢀrthner,
Chem. Commun. 2004, 1564–1579; c) T. Weil, T. Vosch, J. Hofkens,
K. Peneva, K. Mꢀllen, Angew. Chem. 2010, 122, 9252–9278; Angew.
Chem. Int. Ed. 2010, 49, 9068–9093; d) C. Huang, S. Barlow, S. R.
Marder, J. Org. Chem. 2011, 76, 2386–2407.
[11] M. Pꢁrs, C. C. Hofmann, K. Willinger, P. Bauer, M. Thelakkat, J.
Kçhler, Angew. Chem. 2011, 123, 11607–11610; Angew. Chem. Int.
Ed. 2011, 50, 11405–11408.
[12] J. Piard, R. Metivier, M. Giraud, A. Leaustic, P. Yu, K. Nakatani,
New J. Chem. 2009, 33, 1420–1426.
[27] a) Y. Avlasevich, C. Li, K. Mꢀllen, J. Mater. Chem. 2010, 20, 3814–
3826; b) X. Zhan, A. Facchetti, S. Barlow, T. J. Marks, M. A. Ratner,
M. R. Wasielewski, S. R. Marder, Adv. Mater. 2011, 23, 268–284;
S. R. Marder, Adv. Mater. 2011, 23, 268–284.
[28] a) A. Marcos Ramos, S. C. J. Meskers, E. H. A. Beckers, R. B.
Prince, L. Brunsveld, R. A. J. Janssen, J. Am. Chem. Soc. 2004, 126,
9630–9644; b) M. R. Wasielewski, J. Org. Chem. 2006, 71, 5051–
5066; c) E. E. Neuteboom, S. C. J. Meskers, E. H. A. Beckers, S.
Chopin, R. A. J. Janssen, J. Phys. Chem. A 2006, 110, 12363–12371;
d) J. Baggerman, D. C. Jagesar, R. A. L. Vallꢅe, J. Hofkens, F. C. De
Schryver, F. Schelhase, F. Vçgtle, A. M. Brouwer, Chem. Eur. J.
2007, 13, 1291–1299; e) E. Fron, R. Pilot, G. Schweitzer, J. Qu, A.
Herrmann, K. Mꢀllen, J. Hofkens, M. Van der Auweraer, F. C. De
Schryver, Photochem. Photobiol. Sci. 2008, 7, 597–604; f) M. R. Wa-
sielewski, Acc. Chem. Res. 2009, 42, 1910–1921; g) T. Vosch, E.
Fron, J.-i. Hotta, A. Deres, H. Uji-i, A. Idrissi, J. Yang, D. Kim, L.
Puhl, A. Haeuseler, K. Mꢀllen, F. C. De Schryver, M. Sliwa, J. Hofk-
ens, J. Phys. Chem. C 2009, 113, 11773–11782; h) M. Wolffs, N.
Delsuc, D. Veldman, N. V. Anh, R. M. Williams, S. C. J. Meskers,
R. A. J. Janssen, I. Huc, A. P. H. J. Schenning, J. Am. Chem. Soc.
2009, 131, 4819–4829; i) R. K. Dubey, A. Efimov, H. Lemmetyinen,
Chem. Mater. 2011, 23, 778–788; j) J. R. Siekierzycka, C. Hippius, F.
Wꢀrthner, R. M. Williams, A. M. Brouwer, J. Am. Chem. Soc. 2010,
132, 1240–1242; k) L. Flamigni, B. Ventura, A. Barbieri, H. Lang-
[13] Z. Erno, I. Yildiz, B. Gorodetsky, F. M. Raymo, N. R. Branda, Pho-
tochem. Photobiol. Sci. 2010, 9, 249–253.
[14] J. Andrꢅasson, U. Pischel, S. D. Straight, T. A. Moore, A. L. Moore,
D. Gust, J. Am. Chem. Soc. 2011, 133, 11641–11648.
[15] W. Tan, X. Li, J. Zhang, H. Tian, Dyes Pigm. 2011, 89, 260–265.
[16] a) J. Fçlling, V. Belov, R. Kunetsky, R. Medda, A. Schçnle, A.
Egner, C. Eggeling, M. Bossi, S. W. Hell, Angew. Chem. 2007, 119,
6382–6386; Angew. Chem. Int. Ed. 2007, 46, 6266–6270; b) Y. Zou,
T. Yi, S. Xiao, F. Li, C. Li, X. Gao, J. Wu, M. Yu, C. Huang, J. Am.
Chem. Soc. 2008, 130, 15750–15751.
[17] U. Al-Atar, R. Fernandes, B. Johnsen, D. Baillie, N. R. Branda, J.
Am. Chem. Soc. 2009, 131, 15966–15967.
[18] a) D. A. Parthenopoulos, P. M. Rentzepis, Science 1989, 245, 843–
845; b) F.-K. Bruder, R. Hagen, T. Rçlle, M.-S. Weiser, T. Fꢁcke,
Angew. Chem. 2011, 123, 4646–4668; Angew. Chem. Int. Ed. 2011,
50, 4552–4573.
[19] a) T. A. Golovkova, D. V. Kozlov, D. C. Neckers, J. Org. Chem.
2005, 70, 5545–5549; b) M. Bossi, V. Belov, S. Polyakova, S. W. Hell,
Angew. Chem. 2006, 118, 7623–7627; Angew. Chem. Int. Ed. 2006,
45, 7462–7465; c) G. Jiang, S. Wang, W. Yuan, L. Jiang, Y. Song, H.
Tian, D. Zhu, Chem. Mater. 2006, 18, 235–237; d) T. Fukaminato, T.
Umemoto, Y. Iwata, S. Yokojima, M. Yoneyama, S. Nakamura, M.
Irie, J. Am. Chem. Soc. 2007, 129, 5932–5938; e) J. H. Hurenkamp,
J. J. D. de Jong, W. R. Browne, J. H. van Esch, B. L. Feringa, Org.
Biomol. Chem. 2008, 6, 1268–1277; f) S. F. Yan, V. N. Belov, M. L.
Bossi, S. W. Hell, Eur. J. Org. Chem. 2008, 2531–2538; g) J. Fçlling,
S. Polyakova, V. Belov, A. van Blaaderen, M. L. Bossi, S. W. Hell,
Small 2008, 4, 134–142; h) J. Cusido, E. Deniz, F. M. Raymo, Eur. J.
Org. Chem. 2009, 2031–2045; i) R. Mꢅtivier, S. Badrꢅ, R. Mꢅallet-
Renault, P. Yu, R. B. Pansu, K. Nakatani, J. Phys. Chem. C 2009,
113, 11916–11926; j) J. Kꢁrnbratt, M. Hammarson, S. Li, H. L. An-
AHCTUNGERTGhNNUN als, F. Wetzel, K. Fuchs, A. Walter, Chem. Eur. J. 2010, 16, 13406–
13416; l) A. J. Jimꢅnez, B. Grimm, V. L. Gunderson, M. T. Vagnini,
S. Krick Calderon, M. S. Rodrꢆguez-Morgade, M. R. Wasielewski,
D. M. Guldi, T. Torres, Chem. Eur. J. 2011, 17, 5024–5032.
[29] a) T. Fukaminato, M. Irie, Adv. Mater. 2006, 18, 3225–3228; b) L.
Ma, Q. Wang, G. Lu, R. Chen, X. Sun, Langmuir 2010, 26, 6702–
6707; c) J. Wang, A. Kulago, W. R. Browne, B. L. Feringa, J. Am.
Chem. Soc. 2010, 132, 4191–4196.
[30] a) A. Peters, N. R. Branda, J. Am. Chem. Soc. 2003, 125, 3404–3405;
b) A. Peters, N. R. Branda, Chem. Commun. 2003, 954–955;
c) W. R. Browne, J. J. D. de Jong, T. Kudernac, M. Walko, L. N.
Lucas, K. Uchida, J. H. van Esch, B. L. Feringa, Chem. Eur. J. 2005,
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
13
&
ÞÞ
These are not the final page numbers!

F. Scandola, F. Wꢀrthner et al.
11, 6414–6429; d) W. R. Browne, J. J. D. de Jong, T. Kudernac, M.
Walko, L. N. Lucas, K. Uchida, J. H. van Esch, B. L. Feringa, Chem.
Eur. J. 2005, 11, 6430–6441; e) Y. Moriyama, K. Matsuda, N. Tanifu-
ji, S. Irie, M. Irie, Org. Lett. 2005, 7, 3315–3318; f) G. Guirado, C.
Coudret, M. Hliwa, J.-P. Launay, J. Phys. Chem. B 2005, 109, 17445–
17459.
[39] R. Gvishi, R. Reisfeld, Z. Burshstein, Chem. Phys. Lett. 1993, 213,
338–344.
[40] C. Reichardt, Solvents and Solvent Effects in Organic Chemistry, 3rd
ed., Wiley-VCH, Weinheim (Germany), 2003.
[41] E. Fron, G. Schweitzer, P. Osswald, F. Wꢀrthner, P. Marsal, D. Bel-
jonne, K. Mꢀllen, F. C. De Schryver, M. Van der Auweraer, Photo-
chem. Photobiol. Sci. 2008, 7, 1509–1521.
[42] A. Z. Weller, Z. Phys. Chem. 1982, 133, 93–98.
[43] C. Chiorboli, M. A. J. Rodgers, F. Scandola, J. Am. Chem. Soc. 2003,
125, 483–491.
[31] B. Gorodetsky, H. D. Samachetty, R. L. Donkers, M. S. Workentin,
N. R. Branda, Angew. Chem. 2004, 116, 2872–2875; Angew. Chem.
Int. Ed. 2004, 43, 2812–2815.
[32] a) T. Fukaminato, T. Doi, M. Tanaka, M. Irie, J. Phys. Chem. C
2009, 113, 11623–11627; b) T. Fukaminato, M. Tanaka, T. Doi, N.
Tamaoki, T. Katayama, A. Mallick, Y. Ishibashi, H. Miyasaka, M.
Irie, Photochem. Photobiol. Sci. 2010, 9, 181–187; c) T. Fukaminato,
T. Doi, N. Tamaoki, K. Okuno, Y. Ishibashi, H. Miyasaka, M. Irie, J.
Am. Chem. Soc. 2011, 133, 4984–4990.
[33] G. Seybold, G. Wagenblast, Dyes Pigm. 1989, 11, 303–317.
[34] M. Irie, T. Lifka, K. Uchida, S. Kobatake, Y. Shindo, Chem.
Commun. 1999, 747–750.
[35] D. Enders, G. Del Signore, Heterocycles 2004, 64, 101–120.
[36] W. Adam, C.-G. Zhao, C. R. Saha-Mçller, K. Jakka, Oxidation of
Organic Compounds by Dioxiranes, Wiley, Hoboken (New Jersey,
USA), 2009.
[44] F. Wꢀrthner, A. Sautter, D. Schmid, P. J. A. Weber, Chem. Eur. J.
2001, 7, 894–902.
[45] D. Rehm, A. Weller, Ber. Bunsen-Ges. 1969, 73, 834–839.
[46] N. Tamai, H. Miyasaka, Chem. Rev. 2000, 100, 1875–1890.
[47] M. Boggio-Pasqua, M. Ravaglia, M. J. Bearpark, M. Garavelli,
M. A. Robb, J. Phys. Chem. A 2003, 107, 11139–11152.
[48] Principles of Fluorescence Spectroscopy, 2nd ed. (Ed.: J. R. Lako-
witz), Kluwer Academic/Plenum, New York (USA), 1999, pp. 52–
55.
[49] A. J. Fry, Laboratory Techniques in Electroanalytical Chemistry, 2nd
ed. (Eds.: P. T. Kessing, W. R. Heinemann), Dekker, New York
(USA), 1996, p. 481.
[37] Y.-C. Jeong, S. I. Yang, K.-H. Ahn, E. Kim, Chem. Commun. 2005,
2503–2505.
Received: April 30, 2012
[38] For the synthesis of 10, see Supporting Information.
Published online: && &&, 0000
&
14
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Electron Transfer
FULL PAPER
Electron Transfer
M. Berberich, M. Natali, P. Spenst,
C. Chiorboli, F. Scandola,*
F. Wꢁrthner* .................. &&&& — &&&&
Nondestructive Photoluminescence
Read-Out by Intramolecular Electron
Transfer in a Perylene Bisimide-Di-
Tuning fluorescence: A novel, highly
stable, photochromic dyad based on a
perylene bisimide fluorophore and a
diarylethene photochrome was synthe-
sized and its optical and photophysical
properties were studied in detail by
steady-state and time-resolved ultrafast
spectroscopy (see figure; o=open
form, c= closed form). Solvent-
dependent fluorescence studies
revealed that the emission of the ring-
closed form is drastically quenched in
solvents of medium-to-high polarities.
AHCTUNGTREGaNNUN rylethene Dyad
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
15
&
ÞÞ
These are not the final page numbers!