Selective photoinduced single or double electron reduction of perylenebisimides

Article abstract of DOI:10.1016/j.jphotochem.2012.01.008

Selective single and double electron reduction of two soluble perylenebisimides was performed by irradiating these compounds in benzonitrile solutions containing triethylamine 10^-2 M. Lamp irradiation in the absence of oxygen generates, consecutively, the corresponding radical anion and dianion as persistent species, depending of the irradiation time. These negative PBI species were persistent long enough to be characterized by optical and EPR spectroscopies. Laser flash photolysis determines that the kinetics of PBI reduction follows two first order processes assigned to the presence of two different populations of solvated electrons in the medium. The fastest reduction takes place in tens of microseconds and the slowest occurs with a lifetime longer than hundred microseconds.

Full text of DOI:10.1016/j.jphotochem.2012.01.008

Journal of Photochemistry and Photobiology A: Chemistry 231 (2012) 28–32
Contents lists available at SciVerse ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Selective photoinduced single or double electron reduction of perylenebisimides
Maykel de Miguela, Mercedes Álvaroa, Hermenegildo Garcíaa,∗, F. Javier Céspedes-Guiraob,
Fernando Fernández-Lázarob, Ángela Sastre-Santosb
a Instituto de Tecnología Química CSIC-UPV and Departamento de Química, Av. De los Naranjos S/N, 46022 Valencia, Spain
b División de Química Orgánica, Instituto de Bioingeniería, Universidad Miguel Hernández, Elche 03202 (Alicante), Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Selective single and double electron reduction of two soluble perylenebisimides was performed by irra-
diating these compounds in benzonitrile solutions containing triethylamine 10−2 M. Lamp irradiation in
the absence of oxygen generates, consecutively, the corresponding radical anion and dianion as persis-
tent species, depending of the irradiation time. These negative PBI species were persistent long enough
to be characterized by optical and EPR spectroscopies. Laser flash photolysis determines that the kinetics
of PBI reduction follows two first order processes assigned to the presence of two different populations
of solvated electrons in the medium. The fastest reduction takes place in tens of microseconds and the
slowest occurs with a lifetime longer than hundred microseconds.
Received 6 November 2011
Received in revised form 8 January 2012
Accepted 12 January 2012
Available online 21 January 2012
Keywords:
Photoinduced electron transfer
Perylenebisimide
Persistent radical anion
Perylene dianion
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
by the steric congestion of the aryloxyl groups should also
modify the electronic states and electron acceptor proper-
Perylenebisimides (PBIs) [1] have attracted considerable atten-
tion due to their remarkable photochemical properties that
allow their use as sensors [2], in single photon sources [3],
in photoinduced energy/electron transfer systems [4] and as
active components in organic field-effect transistors [5], organic
light-emitting displays [6], photovoltaic cells [7] and fluorescent
biolabels [8], for example.
PBIs can act as electron acceptor molecules giving rise to the
corresponding anions [9]. In the present study we report the gen-
eration of the corresponding mono- and dianions of two PBIs (see
Chart 1) by photolysing them in benzonitrile solutions containing
triethylamine.
ties of these compound respect to unsubstituted conventional
PBIs.
The difference between PBI 1 and 2 is the nature of substituents
located at the N atom of the imide groups. Thus, compound 1 con-
tains imidazolium units while in the case of compound 2 there
are one 2-ethylhexyl and one 2-hydroxyethyl groups. The ratio-
nale behind the selection of these substituents on the imide N
atoms is to compare the electron acceptor properties of a PBI
having supposedly inert aliphatic substituent (PBI 2) with that
of another PBI containing positively-charged aromatic heterocy-
cles (PBI 1) that could exert a stronger influence on the molecular
properties of PBI. In fact, PBI 1 has been used as precursor to
anchor a PBI moiety onto carbon nanotubes through generation
of a nitrogen-heterocycle carbene that undergoes dipolar cycload-
dition to the nanotube walls, while PBI 2 was utilized to bind PBIs
to carbon nanotubes through ester linkages [10]. Therefore, char-
acterization of the photochemical properties of soluble PBI 1 and 2
would allow determining the common behavior of the PBI core as
electron acceptor and assessing whether peripheral substituents
on the nitrogen atoms exert any influence on the photochemical
properties.
The structure of the two PBIs under study (compounds
1
and 2) has in common the presence of four 1,1,3,3-
tetramethylbutylphenoxy substituents located at the bay
positions of the PBI core leading to distortion in the
a
perylene skeleton due to the steric congestion present in the
bay region. These alkylphenoxy groups have been introduced
to increase the solubility of PBIs 1 and 2 in common organic
solvents by reducing the strong ␲–␲ stacking interactions
that are generally present in perylene compounds causing a
considerable decrease of their solubility [11]. In addition to
an increased solubility, distortion of the perylene ring caused
2. Results and discussion
Preliminary nanosecond laser flash photolysis studies of PBI 1
and 2 in acetonitrile either at 355 or 532 nm did not allow detecting
any transient decaying in the microsecond time scale.
∗
Corresponding author.
E-mail addresses: hgarcia@qim.upv.es (H. García), asastre@umh.es
(Á. Sastre-Santos).
1010-6030/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2012.01.008

M. de Miguel et al. / Journal of Photochemistry and Photobiology A: Chemistry 231 (2012) 28–32
29
N
PF6
N
OH
O
O
N
O
O
O
N
N
O
O
O
O
O
O
O
O
O
N
N
O
O
N
2
1
PF6
Chart 1. Chemical structure of the two PBIs under investigation.
In order to generate transient anions from PBI 1 and 2 and con-
sidering that PBIs can act as electron acceptors, we envisioned an
indirect system in which laser excitation of the solvent would lead
to charge separation with generation of solvated electrons. These
solvated electrons could be trapped by PBIs and, in this way, the
corresponding anions would be formed. Considering the solubility
of the PBIs under study, the system that we used for that pho-
toinduced generation of electrons was a solution of triethylamine
(10−2 M) in benzonitrile. PBIs 1 and 2 were highly soluble in ace-
tonitrile and benzonitrile. Benzonitrile was, however, the solvent
of choice because it can be photochemically excited by irradiating
the phenyl ring chromophore. As the preliminary experiments have
shown that the irradiation of PBI 1 and 2 in acetonitrile at 355 nm
does not generate any transient, and also taking into account that
benzonitrile has still a weak absorption at 355 nm, we selected this
wavelength for excitation of the triethylamine/benzonitrile solu-
tion.
conditions but in absence of triethylamine. The differences between
these two transient spectra is attributable to the generation of sol-
vated electrons arising from photoinduced electron transfer from
triethylamine as electron donor to benzonitrile in its electronic
excited state as acceptor as indicated in Eq. (1). NEt3•+ radical cation
appearing in Eq. (1) does not exhibit any characteristic absorption
band in the visible region. Our proposal is compatible with prece-
dents in the literature showing that triethylamine is a good electron
donor in many photoinduced electron transfer processes [12,13].
Attempts to record the optical spectrum of solvated electrons in
PhCN by dissolving sodium metal in PhCN were unsuccessful and
only a broad continuous band from 350 to 600 nm was recorded.
In these experiments using steady-state UV–vis absorption spec-
troscopy the spectral zone below 350 nm was not accessible due to
the absorption of PhCN.
hv
PhC N−→ PhC N∗
(1)
Fig. 1 shows the transient spectrum recorded upon 355 nm
excitation of a 10−2 M solution of triethylamine in benzonitrile
compared to the transient spectrum recorded under the same
−
N(Et)3 + PhC N∗ → N(Et)3 + + PhC N•
•
2.1. Lamp irradiation
0.06
Photochemical generation of electrons in benzonitrile can serve
to promote photoinduced reductions of probe molecules. In par-
ticular, these electrons could be trapped by PBIs generating the
corresponding anions. Alternatively, direct photo excitation of
PBIs leading to the generation of the corresponding electronically
excited states can lead also to a photoinduced electron transfer
from NEt3 as donor and PBI excited state as acceptor leading to the
formation of the PBI anions. These assumptions were confirmed
by performing lamp irradiation of benzonitrile solutions of PBIs
containing triethylamine in the absence of oxygen and recording
the spectral changes by conventional steady-state optical spec-
troscopy.
b
0.06
0.04
0.02
0
0.03
0.00
a
0
50
μs
Time /
Upon lamp irradiation of benzonitrile solutions of PBI 1 and 2
(absorbance at 355 nm 0.03, concentration 4.5 ␮M) in the presence
of triethylamine (10−2 M), disappearance of the absorption band
corresponding to the neutral PBI concomitantly with the appear-
ance of an absorption beyond 800 nm (the maximum wavelength
monitored in our system) was observed. This new absorption spec-
trum (see Fig. 2) was attributed to the PBI radical anion+ [5e,9b]
generated by electron trapping by PBI.
300
400
500
600
700
Wavelength / nm
Fig. 1. UV–vis transient absorption spectra of a N2 purged neat benzonitrile (ꢀ)
and a N2 purged benzonitrile solution of triethylamine (10−2 M) (ꢁ) recorded 1.2 ␮s
after 355 nm laser excitation. The inset shows the decays of benzonitrile (a) and
benzonitrile–triethylamine (b) solutions monitored at 340 nm.

30
M. de Miguel et al. / Journal of Photochemistry and Photobiology A: Chemistry 231 (2012) 28–32
0.05
0.04
0.03
0.02
0.01
0.00
-0.01
0.010
0.005
0.000
-0.005
-0.010
-0.015
0.6
0.4
0.2
0
0
100
Time / μs
200
300
400
500
600
700
800
300
400
500
600
700
800
Wavelength / nm
Wavelength / nm
Fig. 2. UV–vis absorption spectra of benzonitrile–triethylamine (10−2 M) solution of
PBI 1 (absorbance at 355 nm 0.03, 4.5 ␮M) before (ꢀ) and after 10 min (ꢁ) or 20 min
(᭹) irradiation with quasi-monochromatic UV lamp at 350 nm. (For interpretation
of the references to color in text, the reader is referred to the web version of the
article.)
Fig. 4. UV–vis transient absorption spectra of a N2 purged benzonitrile–
triethylamine (0.01 M) solution of PBI 1 (absorbance at 355 nm 0.03, 4.5 ␮M)
recorded at 7 (ꢀ) and 319 (ꢁ) ␮s after a 355 nm laser pulse of 10 mJ. The inset shows
the signal monitored at 590 nm.
PhC N•− + PBI− → PhC N + PBI2−
(3)
This assignment of the photochemical products is supported by
EPR spectroscopy, where the growth of a signal at 0.6 G with hyper-
fine coupling 0.658 for N and 0.572 for H was observed (Fig. 3).
The experimental EPR spectra agree reasonably well with that cal-
culated for PBI 1 or 2 radical anions (8H, hpc 0.572 Hz, 2N, hpa
0.658 Hz).
The above experiments were carried out under inert atmo-
sphere in the absence of oxygen. Under these conditions, the
photogenerated PBIs•− and PBI2− were persistent for minutes.
However, if oxygen is admitted into the solutions, then the changes
were fully reversible and both PBI•− and PBI2− return back to the
original PBI neutral state. The decay of PBI mono- and dianion back
to the parent neutral compound in the presence of oxygen is due to
single or double electron transfer from the organic anions to oxy-
gen acting as the terminal electron acceptor according to Eqs. (4)
and (5).
Upon continued irradiation of PBIs 1 and 2, a complete trans-
formation of PBI into PBI•− is achieved. Moreover, if the irradiation
is prolonged further, then also PBI•− disappears and a concomi-
tant increase of a new band at about 690 nm with a shoulder in the
blue side of the band is observed (see Fig. 2). These changes in the
optical spectrum are accompanied by simultaneous disappearance
of the signal in EPR spectroscopy indicating that the new species
formed has a closed shell configuration. Based on the data reported
in the literature obtained by spectroelectrochemistry, we assigned
the new species to PBI2− [5e]. The excellent match between the
spectra peaking at 690 nm in Fig. 2 with the spectra reported in the
literature for the PBI2− dianion provides experimental support to
the previous assignments. Eqs. (2) and (3) summarize the species
that are generated by consecutive single electron transfer from the
medium to PBIs.
PBI•− + O2 → PBI + O2
PBI2− + O2 → PBI•− + O2
(4)
(5)
−
•
−
•
The photochemical process of PBI•− and PBI2− generation and
their quenching by oxygen is fully reversible and no photoproducts
are formed in significant amounts to affect it, as it could be repeated
four times without observing any fatigue. In agreement with their
high chemical stability, PBIs appear to be stable compounds against
•−
the attack of O2 generated in the medium.
−
PhC N•− + PBI → PhC N + PBI•
(2)
2.2. Laser flash photolysis
Using 355 nm laser excitation in benzonitrile containing tri-
ethylamine (10−2 M) it is possible to photochemically generate
electrons in the medium that could be subsequently trapped by
PBIs acting as electron acceptors according to Eqs. (1)–(3). The
kinetics of the electron capture by PBI can be adequately followed
by nanosecond transient spectroscopy. Fig. 4 shows the transient
spectra recorded at different delay times after excitation of ben-
zonitrile and triethylamine containing PBI 1. As it can be seen there,
the transient spectra are characterized by a peak at 340 nm due to
the solvent (compare to Fig. 1) as well as a bleaching of the signal
at 590 nm and a peak beyond 780 nm. The bleaching at 590 nm is
related to the disappearance of PBI 1 by accepting electrons and
being transformed into PBI•− characterized by the absorption with
apparent ꢀmax at 780 nm. The temporal profile of the signal mon-
itored at 590 nm is shown also in Fig. 4 and can be fitted to a two
consecutive first order decays with lifetimes of 15.8 and 126.6 ␮s
and relative proportion 30 and 70%, respectively. We suggest that
this kinetics reflects the presence in the medium of two main types
of electrons, the slowest process corresponding to the trapping of
Fig. 3. EPR of a benzonitrile–triethylamine (0.01 M) solution of PBI 1 (absorbance at
355 nm 0.03, 4.5 ␮M, black line) and the corresponding simulation for PBI 1 radical
anion (red line). (For interpretation of the references to color in this figure legend,
the reader is referred to the web version of the article.)

M. de Miguel et al. / Journal of Photochemistry and Photobiology A: Chemistry 231 (2012) 28–32
31
0.06
0.04
0.02
0
0.03
0.02
0.06
0.04
0.02
0.00
-0.02
a
0.01
0
0.01
0.01
0.01
0.01
0.01
-0.02
-0.04
-0.06
b
0.00
0
10
20
30
0
13
Time /
μs
Power / mJ
400
500
600
700
800
400
500
600
700
800
Wavelength /nm
Wavelength / nm
Fig. 5. UV–vis transient absorption spectra of
a N2 purged benzonitrile–
Fig. 6. UV–vis transient absorption spectra of
a N2 purged benzonitrile–
triethylamine (0.01 M) solution of PBI 1 (absorbance at 355 nm 0.03, 4.5 ␮M)
recorded at 0.64 (ꢀ), 5.15 (ꢁ) and 32.35 (ꢂ) ␮s after excitation with a 355 nm laser
pulse of 15 mJ. The left inset shows the power dependence of the signal monitored
at 690 nm and the right inset shows the temporal profile of the signals monitored
at 590 (a), multiplied by −1, and 690 (b) nm under N2 atmosphere.
triethylamine (0.01 M) solution of PBI•− (absorbance at 355 nm 0.03, 4.5 ␮M)
recorded after 355 nm laser excitation with a pulse of 15 mJ.
the kinetics of the single electron reduction of PBI•−. The transient
spectra recorded under these conditions are shown in Fig. 6, where
the growth of a band from 550 to 730 nm peaking at 650 and 690 nm
is clearly observed accompanied by some bleaching at 760 nm due
to the photolysis of PBI•−. The results presented in Fig. 6 for PBI 1
were very similar to those recorded for PBI 2.
In addition, lamp irradiation also provides the opportunity to
prepare a persistent solution of PBI2−. These solutions were sub-
jected to laser flash photolysis under the same conditions, showing
that even in a medium rich on solvated electrons, photolysis of
PBI2− gives an instantaneous bleaching of PBI2− and formation of
PBI•−. This instantaneous bleaching is followed by a slower recov-
ery of the PBI2−. These results can be interpreted considering that
photoexcitation of electron rich PBI2− gives rise to an instanta-
neous electron photoejection that, due to the present of solvated
electrons, leads to a recovery of PBI2− from PBI•− (Eqs. (3) and (6)).
the electrons that are located in deeper traps, probably in the nitrile
group of benzonitrile. The bleaching of PBI is accompanied by a con-
comitant increase of the signal due to PBI•− at 780 nm. The location
of the latter band in the far red end of our multiplier makes the sig-
nal at this long wavelength noisy, rendering kinetic measurements
less accurate than when monitoring the signal at 590 nm.
The previous transient spectra and signal kinetics were very
similar for PBI 1 and PBI 2 indicating that the electron trapping
occurs at the PBI core and that the imide nitrogen substituent is
not involved in the process.
We observed that the transient spectrum for the irradiation of
PBIs in benzonitrile containing triethylamine varies depending on
the laser power. When the laser power increases in the range from
8 to 18 mJ, a gradual decrease of the intensity of the 780 nm band,
accompanied by the growth of a new band at 680 nm is observed
(see Fig. 5). We attribute these changes to the occurrence of two
consecutive electron transfers from the medium to PBI that even-
tually form the PBI2− dianion. In fact, the intensity of the transient
signal monitored at 690 nm does not follow a linear relationship
(see left inset in Fig. 5) but can be adequately fitted to two lines
having higher slope at higher laser fluencies. This interpretation is
in agreement with the observation of a decrease of the peak corre-
sponding to PBI•− as the intensity of the peak due to PBI2− increases.
In fact the temporal profiles of PBI ground state bleaching and the
growth of the 690 nm band characteristic of the PBI2−, although not
exactly coincident, are very similar suggesting that almost all the
PBI is rapidly converted into PBI dianion under these conditions.
Both PBI 1 and PBI 2 exhibit identical behavior and dependence
with the laser power.
hv
PBI2−−→ PBI•− + esolvated
(6)
3. Conclusions
Photolysis of a solution of benzonitrile containing triethylamine
is a convenient mean to effect the photoinduced reduction of PBIs.
The process can take places in two separate steps using conven-
tional lamps or pulsed lasers at low powers or can be performed as
an apparent single event at high laser fluencies. The formation of
negatively charged PBI species is reversible and the corresponding
negative species exhibit high persistence in the absence of oxygen.
These conditions have allowed determining the kinetics of elec-
tron trapping by PBI that in this medium takes places following
two first order kinetics that have been associated to the presence
of two types of electrons in this medium, one more reactive and
a second more relaxed type of electron. The presence of these two
types of electrons would originate two kinetics for the generation of
negative PBI species, one of them typically in tens of microseconds
and a second one more prevalent occurring at longer time scales
on hundreds of microseconds.
The ready transformation of PBI•− into PBI2− was confirmed by
an independent experiment in which PBI•− was subjected to pho-
tolysis under the same conditions as those of neutral PBI (355 nm
laser excitation of benzonitrile containing 10−2 M triethylamine).
As we have commented earlier when presenting the results of
lamp irradiation, it is possible to obtain a solution of PBI•− start-
ing from PBI by adjusting the irradiation time. We have already
mentioned that the persistence of this radical anion under these
conditions is sufficiently long to allow studying the photophysical
properties of PBI•−. In this way, starting from a PBI solution and
by means of lamp irradiation, we converted PBI into PBI•− quan-
titatively as confirmed by optical spectroscopy. At this moment,
the solution was exposed to laser flash photolysis to determine
4. Experimental
PBIs 1 and 2 where synthesized as reported elsewhere [10].
UV–vis absorption spectra were recorded with a Perkin-Elmer ꢀ35
spectrophotometer.

32
M. de Miguel et al. / Journal of Photochemistry and Photobiology A: Chemistry 231 (2012) 28–32
EPR spectra were recorded in a Bruker EMX-12 spectrometer,
(d) M.S. Rodríguez-Morgade, T. Torres, C. Atienza-Castellanos, D.M. Guldi, J.
Am. Chem. Soc. 128 (2006) 15145–15154;
operating at X-band, with a modulation frequency of 100 kHz and
modulation amplitude of 1.0 G, and irradiating with a UV lamp.
Solutions of PBI (ABS = 0.3 at 355 nm, 4.5 ␮M) in
benzonitrile–triethylamine (0.01 mM) contained on a Suprasil
quartz cuvette (0.7 × 0.7) capped with septa were purged with N2
and irradiated for 10, 20 and 30 min inside a Luzchem multilamp
photoreactor with eight 8 W lamps (Hitachi FL8BL-B) emitting
mainly at 350 nm.
Laser flash photolysis experiments were carried out in a
Luzchem ns laser flash system using the third (355 nm) harmonic
of a Q-switched Nd:YAG laser (pulse 10 ns) as the excitation source.
The PBIs solution in benzonitrile–triethylamine contained on a
Suprasil quartz cuvette (0.7 × 0.7 cm2) capped with septa were
purged with a N2 or O2 flow at least 15 min before irradiation
experiments.
(e) S. Fukuzumi, K. Ohkubo, J. Ortiz, A.M. Gutiérrez, F. Fernández-Lázaro, Á.
Sastre-Santos, J. Phys. Chem. A 112 (2008) 10744–10752;
(f) R.V.D. Gómez, R. Blanco, C. Seoane, J.L. Segura, R.A.J. Janssen, Macro-
molecules 40 (2007) 2760–2772;
(g) A.J. Jiménez, F. Spänig, M.S. Rodríguez-Morgade, K. Ohkubo, S. Fukuzumi,
D.M. Guldi, T. Torres, Org. Lett. 9 (2007) 2481–2484;
(h) F.J. Céspedes-Guirao, L. Martín-Gomis, K. Ohkubo, S. Fukuzumi,
F. Fernández-Lázaro, Á. Sastre-Santos, Chem. Eur. J. 17 (2011)
9153–9163;
(i) F.J. Céspedes-Guirao, K. Ohkubo, S. Fukuzumi, F. Fernández-Lázaro, Á.
Sastre-Santos, Chem. Asian J. 6 (2011) 3110–3121.
[5] (a) F. Würthner, M. Stolte, Chem. Commun. 47 (2011) 5109–5115;
(b) B.A. Jones, M.J. Ahrens, M.-H. Yoon, A. Facchetti, T.J. Marks, M.R. Wasielewski,
Angew. Chem. Int. Ed. 43 (2004) 6363–6366;
(c) X. Zhan, Z. Tan, B. Domercq, Z. An, X. Zhang, S. Barlow, Y. Li, D. Zhu, B. Kip-
pelen, S.R. Marder, J. Am. Chem. Soc. 129 (2007) 7246–7247;
(d) A.L. Briseno, S.C.B. Mannsfeld, C. Reese, J.M. Hancock, Y. Xiong, S.A. Jenekhe,
Z. Bao, Y. Xia, Nano Lett. 7 (2007) 2847–2853;
(e) F. Würthner, A. Sautter, D. Schmid, P.J.A. Weber, Chem. Eur. J. 7 (2001)
894–902.
[6] (a) R.D. Costa, F.J. Céspedes-Guirao, H.J. Bolink, J. Gierschner, E. Ortí, F.
Fernández-Lázaro, Á. Sastre-Santos, Chem. Commun. (2009) 3886–3888;
(b) F.J. Céspedes-Guirao, S. García-Santamaría, F. Fernández-Lázaro, Á. Sastre-
Santos, H.J. Bolink, J. Phys. D: Appl. Phys. 42 (2009) 105106;
(c) R.D. Costa, F.J. Céspedes-Guirao, H.J. Bolink, F. Fernández-Lázaro, Á. Sastre-
Santos, E. Ortí, J. Gierschner, J. Phys. Chem. C 113 (2009) 19292–19297.
[7] (a) L. Schmidt-Mende, A. Fechtenkötter, K. Müllen, E. Moons, R.H. Friend, J.D.
MacKenzie, Science 293 (2001) 1119–1122;
Acknowledgments
Financial support by Spanish MICINN (CTQ2009-11583,
CTQ2010-20349, and Consolider-Ingenio 2010 Project HOPE CSD
2007-00007) is gratefully acknowledged. FJC also thanks the
Spanish Ministry of Education for a postgraduate scholarship.
(b) Y. Shibano, T. Umeyama, Y. Matano, H. Imahori, Org. Lett.
1971–1974;
9 (2007)
(c) M. Planells, F.J. Céspedes-Guirao, A. Forneli, Á. Sastre-Santos, F. Fernández-
Lázaro, E. Palomares, J. Mater. Chem. 18 (2008) 5802–5808;
References
(d) M. Planells, F.J. Céspedes-Guirao, L. Gonc¸ alves, Á. Sastre-Santos, F.
Fernández- Lázaro, E. Palomares, J. Mater. Chem. 19 (2009) 5818–5825.
[8] (a) K. Peneva, G. Mihov, A. Herrmann, N. Zarrabi, M. Börsch, T.M. Duncan, K.
Müllen, J. Am. Chem. Soc. 130 (2008) 53298–55399;
[1] (a) F. Würthner, Chem. Commun. 10 (2004) 1564–1579;
(b) H. Langhals, Helv. Chim. Acta 88 (2005) 1309–1343;
(c) M.R. Wasielewski, J. Org. Chem. 71 (2006) 5051–5066;
(d) A. Herrmann, K. Müllen, Chem. Lett. 35 (2006) 978–985.
[2] X. Zhang, S. Rehm, M.M. Safont-Sempere, F. Würthner, Nat. Chem. 1 (2009) 623.
[3] (a) M. Sliwa, C. Flors, I. Oesterling, J. Hotta, K. Mullen, F.C. De Schryver, J. Hofkens,
J. Phys.: Condens. Matter (2007) 19;
(b) P. Tinnefeld, K.D. Weston, T. Vosch, M. Cotlet, T. Weil, J. Hofkens, K. Mullen,
F.C. De Schryver, M. Sauer, J. Am. Chem. Soc. 124 (2002) 14310–14311;
(c) B. Lounis, M. Orrit, Rep. Prog. Phys. 68 (2005) 1129–1179.
[4] (a) A. Prodi, C. Chiorboli, F. Scandola, E. Iengo, E. Alessio, R. Dobrawa, F.
Würthner, J. Am. Chem. Soc. 127 (2005) 1454–1462;
(b) F.J. Céspedes-Guirao, A.B. Ropero, E. Font-Sanchis, A. Nadal,
F. Fernández-Lázaro, Á. Sastre-Santos, Chem. Commun. 47 (2011)
8307–8309.
[9] (a) D. Gosztola, M.P. Niemczyk, W. Svec, A.S. Lukas, M.R. Wasielewski, J. Phys.
Chem. A 104 (2000) 6545;
(b) F.J. Céspedes-Guirao, K. Ohkubo, S. Fukuzumi, Á. Sastre-Santos, F.
Fernández-Lázaro, J. Org. Chem. 74 (2009) 5871–5880.
[10] R. Martín, F.J. Céspedes-Guirao, M. de Miguel, F. Fernández-Lázaro, H. García,
Á. Sastre-Santos, Chem. Sci. 3 (2012) 470–475, doi:10.1039/C1SC00609F.
[11] F. Wurthner, Pure Appl. Chem. 78 (2006) 2341–2349.
(b) S. Fukuzumi, K. Ohkubo, J. Ortiz, A.M. Gutiérrez, F. Fernández-Lázaro, A.
Sastre-Santos, Chem. Commun. (2005) 3814–3816;
(c) R.F. Kelley, M.J. Tauber, M.R. Wasielewski, J. Am. Chem. Soc. 128 (2006)
4779–4791;
[12] J.C. Scaiano, M. Barra, R. Sinta, Chem. Mater. 8 (1996) 161–166.
[13] W. Xu, X.M. Zhang, P.S. Mariano, J. Am. Chem. Soc. 113 (1991) 8863–8878.