Flavin core as electron acceptor component in a zinc(II)-phthalocyanine- based dyad

Article abstract of DOI:10.1071/CH08006

A zinc(ii)-phthalocyanine-flavin dyad has been synthesized by Heck-type cross-coupling between a flavin that bears a p-iodophenyl group and a phthalocyanine functionalized with a vinyl moiety. Electrochemical experiments reveal that no significant interaction occurs at the ground state between the two electroactive subunits. However, the occurrence of a photoinduced electron transfer in this donor?acceptor conjugate is observed in transient absorption experiments. Charge-separation (i.e., 4.0 × 10¹¹ s ^-1) and charge-recombination dynamics in benzonitrile (2.2 × 10¹⁰ s^-1) reveal a remarkable stabilization of the radical ion pair in this solvent. CSIRO 2008.

Full text of DOI:10.1071/CH08006

RESEARCH FRONT
Full Paper
CSIRO PUBLISHING
Aust. J. Chem. 2008, 61, 256–261
www.publish.csiro.au/journals/ajc
Flavin Core as Electron Acceptor Component
in a Zinc(II)-Phthalocyanine-Based Dyad
Andreas Gouloumis,A,D G. M. Aminur Rahman,B Julia Abel,C
Gema de la Torre,A Purificación Vázquez,A Luis Echegoyen,C,E
Dirk M. Guldi,B,E and Tomas TorresA,E
ADepartamento de Química Orgánica, Facultad de Ciencias, Universidad Autónoma
de Madrid, Cantoblanco, 28049-Madrid, Spain.
BDepartment of Chemistry and Pharmacy, Interdisciplinary Center for Molecular Materials (ICMM),
Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstrasse 3, 91058 Erlangen, Germany.
CDepartment of Chemistry, Clemson University, Clemson, SC 29634, USA.
DDepartamento de Química Orgánica I, Facultad de Química, Universidad Complutense
de Madrid, 28040-Madrid, Spain.
ECorresponding authors. Email: tomas.torres@uam.es, dirk.guldi@chemie.uni-erlangen.de,
luis@clemson.edu
A zinc(ii)-phthalocyanine-flavin dyad has been synthesized by Heck-type cross-coupling between a flavin that bears a
p-iodophenyl group and a phthalocyanine functionalized with a vinyl moiety. Electrochemical experiments reveal that no
significant interaction occurs at the ground state between the two electroactive subunits. However, the occurrence of a
photoinduced electron transfer in this donor–acceptor conjugate is observed in transient absorption experiments. Charge-
separation (i.e., 4.0 × 1011 s−1) and charge-recombination dynamics in benzonitrile (2.2 × 1010
s
−1) reveal a remarkable
stabilization of the radical ion pair in this solvent.
Manuscript received: 10 January 2008.
Final version: 6 March 2008.
Introduction
single-walled nanotubes,[12] and ruthenium-trisbipyridine
complexes[13] – have been combined with Pcs. In most of the
resulting electron-donor–acceptor ensembles, Pcs perform as
donor moieties, especially when ZnII is complexed in the central
cavity of the macrocycle.
The induction and control of many important biological pro-
cesses rely on light signals that are collected and mediated
by chromophores, which are known to subsequently trigger
cascades of electron and/or energy transfer events. Thus, photo-
induced electron transfer is a basic process in biology, but also
in chemistry and materials science. For chemists, it has become
a fascinating challenge to design and tailor synthetic electron-
donor–acceptor systems[1] that contain a variety of electron-
donor and electron-acceptor moieties,[2] separated by a proper
spacer, to gain control over light energy conversion processes.
Phthalocyanines (Pcs)[3] are synthetic tetrabenzotetraazapor-
phyrins that have drawn considerable attention as molecular
materials. It is mainly their outstanding electronic and optical
properties that drive this development.[4] In particular, they are
perfectly suited as integrated components for light energy con-
version systems; they exhibit very high extinction coefficients
around 700 nm – a range where the maximum of the solar pho-
ton flux occurs – for efficient photon harvesting and rich redox
chemistry. For this reason, Pcs have been used as chromophores
in plastic solar cells[5] and for the sensitization of nanocrys-
talline, mesoporous TiO2 films.[6] With the goal of understand-
ing the basic processes of photoinduced electron and energy
transfer in photoactive Pc-containing ensembles and poten-
tial applications in molecular photovoltaics, different electro-
active systems – which include porphyrin,[7] fullerene (C60),[8]
anthraquinone,[9] perylendiimide,[10] subphthalocyanine,[11]
Natural chromophores that contain isoalloxazine rings are
called flavins, and flavin-containing proteins are known as
flavoproteins,[14] which play an essential role in oxidoreduc-
tion reactions,[15] and as blue-light sensitive photoreceptors.[16]
Flavins bear electron-accepting character and, for that reason,
electron-donor–acceptor ensembles based on isoalloxazine dyes
covalently linked to electron-donor dyes have emerged as artifi-
cial model systems for their biological counterparts. To this end,
artificial systems that contain phenothiazine-flavin as a donor–
acceptor redox unit and pyrene as antenna have been constructed
to model photoinduced energy and electron transfer processes
of natural blue-light photoreceptors.[17] Porphyrin-flavin dyads
have also been prepared and examined in the context of deter-
mining energy- and electron-transfer processes between the two
moieties.[18]
With the goal of testing new donor–acceptor models, we
aimed to synthesize a ZnPc-flavin dyad 1 (Scheme 1), where
the two electroactive subunits were covalently linked through
a styryl spacer that connected nitrogen-10 of flavin and
the periphery of the Pc, and to explore the electrochemi-
cal and photoinduced electron-transfer properties in this novel
system.
© CSIRO 2008
10.1071/CH08006
0004-9425/08/040256

RESEARCH FRONT
Flavin Core as Electron Acceptor Component
257
Results and Discussion
exhibits two one-electron cathodic peaks, one of them reversible
(ꢀEp1 = 63 mV) (ν = 20–600 mV s−1) at around −1.02V and
another one chemically irreversible at around −1.55V (Fig. 2).
Vinylphthalocyanine 5 is electrochemically active in both anodic
and cathodic sweep directions between +1.2 and −2.0V.
On the cathodic scan (Fig. 2) compound 5 exhibits three
one-electron quasi-irreversible cathodic peaks (ꢀEp1 = 55 mV,
The methodology for the preparation of N(10)-substituted
flavins has been previously described by Yoneda et al.[19] In
particular, we aimed to prepare flavin 4 (Scheme 2), which
bears a p-iodophenyl group at position 10, as a precursor for
a subsequent Heck-type cross-coupling with phthalocyanine 5
functionalized with a vinyl moiety and three solubilizing tert-
butyl groups at the periphery of the macrocycle (Scheme 3). The
reaction between 6-chloro-3-methyluracile (2)[20] and commer-
cially available 4-iodoaniline in a mixture of diethylaniline and
acetic acid afforded 6-(4-iodoanilinyl)-3-methyluracile (3). The
condensation of the latter with nitrosobenzene in a Ac2O/AcOH
mixture led to flavin 4 as a yellow solid in 38% overall yield.
The synthesis of ZnPc-flavin 1 was carried out by a
cross-coupling Heck-type reaction between the unsymmetrically
substituted ZnII-vinylphthalocyanine 5[21] and flavin 4 using
Jeffery’s protocol (see Scheme 3).[22] The product was isolated
from the reaction mixture by column chromatography as a green
fluorescent solid in 52% yield. The 1H NMR spectrum of ZnPc-
flavin 1 shows broadened aromatic and vinylic signals owing to
the presence of several positional isomers, although it is easy to
assign the flavin’s methyl group (3.5 ppm) and tert-butyl groups
(1.9–1.6 ppm). The UV-vis spectrum of ZnPc-flavin 1 (Fig. 1)
displays both the Soret band at 350 nm and a slightly split Q-band
at around 692 nm, which corresponds to the Pc core.The Q-band
is shifted by 13 nm relative to that seen in the vinylphthalocya-
nine 5 (Fig. 1). The spectrum of ZnPc-flavin 1 also shows a
continuous band between 400 and 500 nm as part of the flavin
subunit.
ꢀEp2 = 120 mV, and ꢀEp3 = 102 mV) (ν = 20–600 mV s−1) at
around −1.04, −1.27, and −1.49V, respectively. In the anodic
scan, this phthalocyanine shows a two-electron oxidation peak
at around 0.59V.
C(CH3)3
O
N
N
N
N
Zn
N
CH3
N
N
N
N
N
(H3C)3C
؉
O
N
N
I
C(CH3)3
4
5
(CH3CN)2PdCl2
LiCl/Bu4NϩBrϪ
TEA
1
Electrochemical Measurements
The electrochemical behaviour of Pc-flavin dyad 1 and reference
compounds 4 and 5 were studied using cyclic voltammetry (CV)
and the results are summarized in Fig. 2. The potential data are
collected in Table 1.
The CV shows that flavin 4 is electrochemically active
in the cathodic sweep direction between 0 and −2.0V. It
Scheme 3. Synthesis of ZnPc-flavin 1.
1
0.8
0.6
0.4
0.2
0
C(CH3)3
N
N
N
Zn
N
N
N
(H3C)3C
N
N
N
N
O
N
O
N
C(CH3)3
300
400
500
600
700
800
CH3
Wavelength [nm]
1
Fig. 1. Absorption spectra of vinylphthalocyanine 5 (dashed line) and
ZnPc-flavin 1 (black line) in THF.
Scheme 1.
O
N
O
O
NO
I
NH2
CH3
CH3
CH3
N
N
N
N
Cl
HN
I
N
H
N
H
O
O
N
O
DEAN/AcOH
Ac2O/AcOH
I
2
3
4
Scheme 2. Synthesis of flavin 4.

RESEARCH FRONT
258
A. Gouloumis et al.
The CV of dyad 1 (Fig. 2) shows three reduction processes
on the cathodic scan sweep (ꢀEp1 = 63 mV, ꢀEp2 = 70 mV, and
fluorescence spectrum that exhibits a strong *0–0 transition at
678 nm followed by vibrational fine structure (i.e., *0–1, *0–2,
etc.) at lower energies. Important is a small Stokes shift, that is,
the energetic difference between the long-wavelength absorption
and short-wavelength fluorescence of only 5 nm, which speaks
for the structural rigidity of the Pc. The quantum yields for the
radiative pathway are 0.3 with an underlying lifetime – measured
in time-resolved measurements – of 3.9 ns. In relation to the ref-
erence ZnPc, the corresponding values for ZnPc-flavin 1 are
changed (Fig. 3). First, the *0–0 transition is shifted to the red,
which is similar to what has been concluded for the ground state
absorption. Second, the quantum yields are much lower with
values, for example, 0.03 in tetrahydrofuran (THF) and 0.009 in
benzonitrile. From this we derive quenching factors of 10 and
37 in THF and benzonitrile, respectively. Finally, the fluores-
cence lifetimes are as short as 0.254 ns in THF. In particular,
the solvent dependence of the excited state deactivation points
to a charge transfer that evolves between the photoexcited ZnPc
chromophore and the electron accepting flavin. From electro-
chemical experiments we estimate that the energy of this radical
ion pair state is 1.61 eV, which is 0.18 eV lower than that of the
ZnPc singlet excited state.
To gather spectroscopic support for this charge-transfer pos-
tulate we turned to time-resolved differential absorption mea-
surements following photoexcitation at 670 nm. However, let’s
first turn to the reference ZnPc, whose transients are collected in
Fig. 4. Here, we see the instantaneous formation (i.e., >1 ps)
of the ZnPc singlet excited state. Spectroscopic attributes of
this transient are minima around 608 and 670 nm, which are
a good reflection of the ground state bleaching, and maxima at
490 nm and in the range between 750 and 1000 nm.This transient
was found to be metastable, since it decays rather slowly (i.e.,
3.2 × 108 s−1, Fig. 4) by intersystem crossing to the energeti-
cally lower lying triplet excited state. A quantum yield of ∼70%
has been derived for the triplet formation. The latter is oxygen
sensitive to singlet oxygen with nearly diffusion-controlled rate
constants (i.e., 109 m−1 s−1). In the absence of molecular oxygen
the lifetime of the ZnII-Pc triplet excited state is ∼100 ms.
Quite different are the changes upon photoexciting ZnPc-
flavin 1. Although initially the singlet–singlet features of the
ꢀEp3 = 95 mV) (ν = 100–600 mV s−1) at around −1.03, −1.29,
and −1.59V, which can be assigned as follows: the first one
probably corresponds to the overlapped first reduction waves of
both Pc and flavin subunits, the second peak to the second Pc-
based reduction wave, and the third one to the overlap of the third
Pc-based reduction wave with the second flavin reduction peak.
On the anodic scan one can observe the unresolved Pc-based
two-electron oxidation process at around 0.58V.
The results presented above indicate that there are very small
potential differences observed for the subunits of dyad 1 when
compared with those observed for the model compounds 4 and
5, which indicates a negligible interaction between the moieties
in the ground state.
Photophysical Experiments
Insight into electron-donor–acceptor interactions between the
ZnII-Pcandtheflavinsubunitscamefromfluorescencemeasure-
ments. In light of the different contributions in the absorption
spectrum (i.e., flavin component in the blue and ZnPc com-
ponent unit in the red, Fig. 1) we decided to focus on the
exclusive excitation in the 600 to 700 nm range, where merely
the ZnPc component has been shown to absorb. In the steady
state measurements with reference Pc (ZnPc),∗ we recorded a
50
40
1
30
20
10
4
5
0
Ϫ10
1000
500
0
Ϫ500
Ϫ1000 Ϫ1500 Ϫ2000
60000
40000
20000
0
Potential [mV]
Fig. 2. Cyclic voltammograms (sweep rate 0.1V s−1) for 1, 4, and 5 in
o-DCB that contained n-Bu4NPF6 at room temperature.
Table 1. Electrochemical data [V v. Ag/AgCl] for the redox pro-
cesses of compounds 1, 4, and 5 obtained by CV in o-DCB solutions
(0.1 M n-Bu4NPF6) at room temperature under identical experimental
conditions
A
B
Compound
E1red
E2red
E3red
Eox
1
4
5
−1.03
−1.02
−1.04
−1.29
−1.55C
−1.27
−1.59
−1.49
0.58
600
650
700
750
800
Wavelength [nm]
0.59
AFirst Pc and flavin potentials are overlapped.
BThird Pc and second flavin potentials are overlapped.
CChemically irreversible.
Fig. 3. Fluorescence spectra of reference ZnPc (dashed line) and
ZnPc-flavin 1 inTHF (black line) and benzonitrile (dotted line) upon 608 nm
photoexcitation.
∗ ZnPc (reference Pc, ZincII 2,9,16,23-tetra-tert-butylphthalocyanine) is commercially available and has an absorption spectrum in THF, which resembles
that of vinylphthalocyanine 5.

RESEARCH FRONT
Flavin Core as Electron Acceptor Component
259
0.008
0.006
0.004
0.002
0
0.01
0.005
0
Ϫ0.005
Ϫ0.002
400
600
800
1000
1200
1400
400
600
800
1000
1200
1400
Wavelength [nm]
Wavelength [nm]
0.004
0.008
0.006
0.004
0.002
0
0.002
0
Ϫ0.002
Ϫ0.004
Ϫ0.006
Ϫ0.008
Ϫ0.002
Ϫ0.004
0
500
1000
1500
2000
2500
3000
0
50
100
150
200
Time [ps]
Time [ps]
Fig. 4. Upper part: differential absorption spectra (visible and
near-infrared) obtained upon femtosecond flash photolysis (670 nm) of ref-
erence ZnPc in argon-saturated benzonitrile with several time delays at
room temperature. Lower part: time–absorption profiles of the spectra shown
above at 620 (i.e., open cicles) and 740 nm (i.e., closed circles), monitoring
the intersystem crossing.
Fig. 5. Upper part: differential absorption spectra (visible and
near-infrared) obtained upon femtosecond flash photolysis (670 nm) of
ZnPc-flavin 1 in argon-saturated benzonitrile with several time delays at
room temperature. Lower part: time–absorption profiles of the spectra
shown above at 618 nm (i.e., closed circles) and 845 nm (i.e., open cicles),
monitoring the charge separation and charge recombination.
ZnPc component are discernable, these transform rather rapidly
(i.e., 4.0 × 1011
s
−1) in benzonitrile to a new photoproduct.
In benzonitrile, the rate constant for charge recombination is
2.2 × 1010
s
−1, which decreases inTHF, a solvent of lower polar-
Figure 5 underlines this transformation spectroscopically and
kinetically.An important spectroscopic feature of the new photo-
product, which assists in assigning it to a radical ion pair state, is
a maximum around 845 nm. Numerous electrochemical, radio-
lytic, and photolytic investigations have demonstrated that this
is a clear fingerprint of the one electron oxidized radical cation
of the ZnPc core.[6] Also the transient maximum in the visible
region (i.e., 505 nm) is part of this radical cation spectrum. To
gather evidence for the one electron reduction of flavin is ren-
dered more difficult. In this context, a pulse radiolytic study,
which focussed on the reduction of flavin with hydrated elec-
trons, is particularly helpful. In this work[23] it has been shown
that (flavin)•− gives rise to a maximum at 370 nm, which is,
however, outside of the spectroscopic window of our experi-
mental set-up.This maximum is followed by a somewhat weaker
shoulder/maximum at 440 nm. A close inspection of the 400 to
500 nmrangehelpstoidentifyfeaturesthatarereminiscentofthe
pulse radiolytic data: a shoulder/maximum at 440 nm. In turn,
the listed spectroscopic signatures corroborate the formation
of the (ZnPc)•+–(flavin)•− radical ion pair state. Figure 5
also demonstrates that the (ZnPc)•+–(flavin)•− radical ion pair
state decays on a time scale of several tens of picoseconds.
ity, to 2.7 × 109 s−1. In both solvents charge recombination
leads to a quantitative recovery of the singlet ground state –
no involvement of any triplet excited state (i.e., ZnPc or flavin)
is noted.
Conclusions
We have prepared for the first time a ZnPc-flavin dyad 1
using a Pd-catalyzed cross coupling methodology between
appropriately functionalized flavin and Pc chromophores. This
donor–acceptor conjugate has been electrochemically and
photophysically characterized. Although the two components
do not notably interact in the ground state, we have been able
to demonstrate photoinduced charge transfer from the Pc to
the flavin unit. Remarkable is the fact that the radical ion
pair state lifetimes, although short, are still longer than in a
recently published ZnPc-C60 donor–acceptor conjugate[24] (i.e.,
benzonitrile: 3.3 × 1010
s
−1; THF: 8.3 × 109 s−1). This fact can
be rationalized by taking into account that (flavin)•− gains some
stabilization based on its polarizability, which is also believed to
contribute to retarding a fast charge recombination.[25]

RESEARCH FRONT
260
A. Gouloumis et al.
Experimental
10-(4-Iodophenyl)-3-methylisoalloxazine 4
General Methods and Materials
In a mixture of Ac2O and AcOH (4:1, 2 mL), nitrosobenzene
(0.32 g, 3 mmol) and 6-(4-iodoanilinyl)-3-methyluracile (3)
(0.343 g, 1 mmol) were added. The mixture was heated at
140◦C for 30 min and the solvent was eliminated under reduced
pressure. Ethanol was added to the crude product and the pre-
cipitate was filtered off. After flash column chromatography
(SiO2, AcOEt/CHCl3 1:9) 4 was obtained as a yellow solid.
Yield: 236 mg (55%), mp >300◦C. (Found: C 47.19, H 2.69,
N 12.86%. Calc. for C17H11IN4O2: C 47.19, H 2.69, N 12.86%.)
νmax (KBr)/cm−1 1713, 1672, 1551, 1281, 1173, 984, 750. δH
(300 MHz, CDCl3) 8.35 (dd, J 8.6, Jꢀ 1.62, 1H, flavin 6-H), 8.01
(d, AAꢀXXꢀ J 8.6, 2H, ArH), 7.75–7.55 (m, 2H, flavin 7-H, 8-H)
7.06 (d, AAꢀXXꢀ J 8.6, 2H, ArH), 6.93 (dd, J 8.6, Jꢀ 1.62, 1H,
flavin 9-H), 3.49 (s, 3H, CH3). m/z (ES) 430 [M+].
Chemicals were purchased from commercial suppliers and used
without further purification. Column chromatography was car-
ried out on silica gel Merck-60 (230–400 mesh, 60 Å), and TLC
on aluminum sheets precoated with silica gel 60 F254 (E. Merck).
PTFE filters (pore size 0.45 µm) were used. IR spectra were
recorded on a Bruker Vector 22 spectrophotometer using KBr
disks. Matrix-assisted laser desorpton–ionization time-of-flight
mass spectrometry (MALDI-TOF-MS) spectra were determined
on a BRUKER REFLEX III instrument equipped with a nitrogen
laser operating at 337 nm. NMR spectra were recorded with a
Bruker AC-300 instrument. UV/Vis spectra were recorded with
a Hewlett–Packard 8453 instrument.
Tri-tert-butyl-[(E)-2-(3-methylisoalloxazinyl)-10-styryl]-
phthalocyanine ZnII 1
Photophysics
Femtosecond transient absorption studies were performed with
670 nm laser pulses (1 kHz, 150 fs pulse width) from an ampli-
fied Ti:sapphire laser system (Clark-MXR, Inc.). Fluorescence
lifetimes were measured with a Laser Strobe Fluorescence
Lifetime Spectrometer (Photon Technology International) with
337 nm laser pulses from a nitrogen laser fibre-coupled to
a lens-based T-formal sample compartment equipped with a
stroboscopic detector. Details of the Laser Strobe systems
are described on the manufacture’s website (http://www.pti-
nj.com/LaserStrobe/; verified 28 March 2008). Emission spectra
were recorded by using a FluoroMax-3 (Horiba Co.). The
experiments were performed at 20◦C.
A mixture of vinylphthalocyanine 5 (92 mg, 0.12 mmol), 10-
(4-iodophenyl)-3-methylisoalloxazine (4) (50 mg, 0.12 mmol),
LiCl (3 mg, 0.072 mmol), (MeCN)2PdCl2 (2 mg, 76 µmol),
tetrabutylammonium bromide (40 mg, 0.12 mmol), and triethyl-
amine (0.1 mL) in N,N-dimethylformamide (DMF, 4 mL) was
heated under argon at 100◦C during 48 h. The solvent was
removed under reduced pressure and the crude was triturated
with methanol and then filtered off. After flash column chro-
matography (SiO2, THF/hexane, 1/3), 1 was obtained as a green
fluorescent solid. Yield 68 mg (52%), mp >300◦C. (Found:
C 69.82, H 4.75, N 15.36%. Calc. for C63H52N12O2Zn: C 70.42,
H 4.88, N 15.64%.) νmax (KBr)/cm−1 2956, 1716, 1665, 1615,
1586, 1489, 1317, 1275, 1084, 1046, 921, 806, 748. λmax/nm
(log ε) 690 (5.15), 676 (5.10), 348 (4.90). δH (300 MHz, CDCl3)
9.0–7.0 (m, 22H, ArH, flavin, vinylic), 3.5 (br s, 3H, NCH3),
1.9–1.6 (m, 27H, C(CH3)3). m/z (MALDI-TOF) 1072–1080
[M+].
Electrochemistry
CV was performed on a Windows-driven BAS 100w electro-
chemical analyzer at room temperature with a three-electrode
configuration in o-dichlorobenzene (o-DCB) solution that con-
tained the substrate (typically ∼1 mmol dm−3) and the support-
ing electrolyte. A glassy carbon (φ 3 mm) disc was used as the
working electrode, a platinum wire (φ 1 mm), and a commercial
Ag/AgClelectrodewerethecounterandthereferenceelectrodes,
respectively. Both the counter and the reference electrodes were
directly immersed in the electrolyte solution. Tetrabutylammo-
nium hexafluorophosphate (n-Bu4NPF6) was employed as the
supporting electrolyte at a concentration of 0.1 mol dm−3. Solu-
tions were stirred and deaerated by bubbling argon for a few
minutes before each voltammetric measurement.
Acknowledgements
The authors are grateful to the financial support of MEC (CTQ2005–
08933/BQU), Comunidad de Madrid (S-0505/PPQ/000225), ESF-MEC
(Sohyd project), SFB 583, DFG (GU 517/4–1), FCI, and the Office of Basic
Energy Sciences of the USA Department of Energy, and the National Science
Foundation AJA and LE (Grant number CHE-0509989).
References
[1] (a) S. Fukuzumi, in Functional Organic Materials (Eds T. J. J. Müller,
U. H. F. Bunz) 2007, p. 465 (Wiley-VCH: Weinheim).
(b) F. D’Souza, O. Ito, Coord. Chem. Rev. 2005, 249, 1410.
doi:10.1016/J.CCR.2005.01.002
[2] N. Martin, Chem. Commun. 2006, 2093. doi:10.1039/B601582B
[3] G. de la Torre, C. G. Claessens, T. Torres, Chem. Commun. 2007,
2000. doi:10.1039/B614234F
[4] (a) K. M. Kadish, K. M. Smith, R. Guilard, (Eds), The Porphyrin
Handbook 2003, Vols. 15–20 (Academic Press: San Diego, CA).
(b) G. de la Torre, M. Nicolau, T. Torres, in Supramolecular Photo-
sensitive and Electroactive Materials (Ed. H. Nalwa) 2001, pp. 1–111
(Academic Press: New York, NY).
(c) G. de la Torre, P. Vázquez, F. Agulló-López, T. Torres, Chem. Rev.
2004, 104, 3723. doi:10.1021/CR030206T
[5] (a) J. G. Xue, S. Uchida, B. P. Ran, S. R. Forrest, Appl. Phys. Lett.
2004, 84, 3013. doi:10.1063/1.1713036
(b) J. G. Xue, S. Uchida, B. P. Rand, S. R. Forrest, Appl. Phys. Lett.
2004, 85, 5757. doi:10.1063/1.1829776
[6] (a) E. Palomares, M. V. Martínez-Díaz, S. A. Haque, T. Torres,
J. R. Durrant, Chem. Commun. 2004, 2112. doi:10.1039/B407860H
6-(4-Iodoanilinyl)-3-methyluracile 3
4-Iodoaniline (0.46 g, 2.1 mmol) and 6-chloro-3-methyluracile
(2) (0.34 g, 2.1 mmol) were added to a mixture of N,N-
diethylaniline (1 mL) and acetic acid (0.1 mL). After heating at
190◦C for 30 min, ether was added to the cold mixture and the
precipitate was filtered off. Crystallization from ethanol afforded
3 as brownish needles.Yield: 0.49 g (68%), mp >300◦C. (Found:
C 38.27, H 2.89, N 12.08%. Calc. for C11H9IN3O2: C 38.51,
H 2.94, N 12.25%.) νmax (KBr)/cm−1 3390, 1725, 1692, 1556,
1290, 1182, 980, 752. δH (300 MHz, (D6)DMSO) 8.41 (br s, 1H,
ArNH), 7.68 (d, AAꢀXXꢀ J 7.2, 2H, ArH), 7.01 (d, AAꢀXXꢀ Jꢀ
7.2, 2H, ArH), 4.88 (s, 1H, CH), 3.05 (s, 3H, CH3). δC (75 MHz,
(D6)DMSO) 202.1 (C=O), 168.5 (C=O), 150.6 (C-7), 137.7
(C-9), 129.9 (C-5), 123.5 (C-6), 118.1 (C-8), 85.7 (C-10), 28.0
(CH3). m/z (EI) 343 [M+], 216 [(M − I+)].

RESEARCH FRONT
Flavin Core as Electron Acceptor Component
261
(b)A. Morandeira, I. Lopez-Duarte, M.V. Martínez-Díaz, B. O’Regan,
C. Shuttle, N. A. Haji-Zainulabidin, T. Torres, E. Palomares,
J. R. Durrant, J. Am. Chem. Soc. 2007, 129, 9250. doi:10.1021/
JA0722980
(c) J.-J. Cid, J.-H. Yum, S.-R. Jang, Md. K. Nazeeruddin,
E. Martínez-Ferrero, E. Palomares, J. Ko, M. Grätzel, T. Torres,
Angew. Chem. Int. Ed. 2007, 46, 8358. doi:10.1002/ANIE.200703106
(d) P. Y. Reddy, L. Giribabu, C. Lyness, H. J. Snaith, C. Vijaykumar,
M. Chandrasekharam, M. Lakshmikantam, J.-H. Yum, K. Kalyana-
sundaram, M. Grätzel, M. K. Nazeeruddin, Angew. Chem. Int. Ed.
2007, 46, 373. doi:10.1002/ANIE.200603098
[11] D. González-Rodríguez, C. G. Claessens, T. Torres, S. Liu,
L. Echegoyen, N. Vila, S. Nonell, Chem. Eur. J. 2005, 11, 3881.
doi:10.1002/CHEM.200400779
[12] (a) B. Ballesteros, S. Campidelli, G. de la Torre, C. Ehli, D. M. Guldi,
M. Prato, T. Torres, Chem. Commun. 2007, 2950. doi:10.1039/
B702819A
(b) B. Ballesteros, G. de la Torre, C. Ehli, G. M. Aminur Rahman,
F. Agulló-Rueda, D. M. Guldi, T. Torres, J. Am. Chem. Soc. 2007, 129,
5061. doi:10.1021/JA068240N
[13] A. González-Cabello, P. Vázquez, T. Torres, D. M. Guldi, J. Org.
Chem. 2003, 68, 8635. doi:10.1021/JO0341968
(e) B. C. O’Regan, I. Lopez-Duarte, M. V. Martinez-Diaz, A. Forneli,
J.Albero,A. Morandeira, E. Palomares, T. Torres, J. R. Durrant, J.Am.
Chem. Soc. 2008, 130, 2906. doi:10.1021/JA078045O
[7] (a) J. P. C. Tomé, A. M. V. M. Pereira, C. M. A. Alonso,
M. G. P. M. S. Neves, A. C. Tomé, A. M. S. Silva, J. A. S. Cavaleiro,
M. V. Martínez-Díaz, T. Torres, G. M. Aminur Rahman, J. Ramey,
D. M. Guldi, Eur. J. Org. Chem. 2006, 257. doi:10.1002/EJOC.
200500558
[14] A. Koziol, M. M. Szafran, P. F. Heelis, in Flavins and Flavoproteins
(Eds D. E. Edmondson, D. B. Mccormick) 1987, pp. 287–290
(Gruyter: Berlin).
[15] F. Müller (Ed.), Chemistry and Photochemistry of Flavoenzymes
1991–1992, Vols. 1–3 (CRC Press: Boca Raton, FL).
[16] A. Sancar, Annu. Rev. Biochem. 2000, 69, 31. doi:10.1146/
ANNUREV.BIOCHEM.69.1.31
[17] (a) Z. Shen, J. Strauss, J. Daub, Chem. Commun. 2002, 460.
doi:10.1039/B109151D
(b) Z. Shen, R. Procházka, J. Daub, N. Fritz, N. Acar, S. Schneider,
Phys. Chem. Chem. Phys. 2003, 5, 3257. doi:10.1039/B301279D
[18] (a) J. Takeda, S. Ohta, M. Hirobe, J. Am. Chem. Soc. 1987, 109, 7677.
doi:10.1021/JA00259A017
(b) S. Tannert, E. A. Ermilov, J. O. Vogel, M. T. M. Choi, D. K. P. Ng,
B. Röder, J. Phys. Chem. B 2007, 111, 8053. doi:10.1021/JP0724222
(c) Y. Bian, X. Chen, D. Wang, C.-F. Choi, Y. Zhou, P. Zhu,
D. K. P. Ng, J. Jiang, Y. Weng, X. Li, Chem. Eur. J. 2007, 13, 4169.
doi:10.1002/CHEM.200601668
[8] (a) D. M. Guldi, J. Ramey, M. V. Martínez-Díaz, A. de la Escosura,
T. Torres, T. Da Ros, M. Prato, Chem. Commun. 2002, 2774.
doi:10.1039/B208516J
(b) P. Nayar, A. M. Brun, A. Harriman, T. P. Begley, Chem. Commun.
1992, 395.
(c) K. Hasharoni, H. Levanon, J. Gätschmann, H. Schubert,
H. Kurreck, K. Möbius, J. Phys. Chem. 1995, 99, 7514.
doi:10.1021/J100019A037
(d) D. T. Hermann, A. C. Schindler, K. Polborn, R. Gompper,
S. Stark, A. B. J. Parusel, G. Grabner, G. Köhler, Chem. Eur. J. 1999,
5, 3208. doi:10.1002/(SICI)1521-3765(19991105)5:11<3208::AID-
CHEM3208>3.0.CO;2-O
(b) D. M. Guldi, I. Zilbermann, A. Gouloumis, P. Vázquez, T. Torres,
J. Phys. Chem. B 2004, 108, 18485. doi:10.1021/JP047105Z
(c) K. N. Kim, C. S. Choi, K.-Y. Kay,Tetrahedron Lett. 2005, 46, 6791.
doi:10.1016/J.TETLET.2005.08.038
(d) A. de la Escosura, M. V. Martínez-Díaz, D. M. Guldi, T. Torres,
J. Am. Chem. Soc. 2006, 128, 4112. doi:10.1021/JA058123C
(e) B. Ballesteros, G. de la Torre, T. Torres, G. L. Hug,
G. M. Aminur Rahman, D. M. Guldi, Tetrahedron 2006, 62, 2097.
doi:10.1016/J.TET.2005.08.126
(f) A. Gouloumis, A. de la Escosura, P. Vázquez, T. Torres, A. Kahnt,
D. M. Guldi, H. Neugebauer, C. Winder, M. Drees, N. Serdar, Sari-
ciftci, Org. Lett. 2006, 8, 5187. doi:10.1021/OL061723B
(g)T.Torres,A. Gouloumis, D. Sánchez-García, J. Jayawickramarajah,
W. Seitz, D. M. Guldi, J. L. Sessler, Chem. Commun. 2007, 292.
doi:10.1039/B613086K
[19] F. Yoneda, K. Shinozuka, K. Tsukuda, A. Koshiro, J. Heterocycl.
Chem. 1979, 16, 1365.
[20] G. Nübel, W. Pfleiderer, Chem. Ber. 1962, 95, 1605. doi:10.1002/
CBER.19620950706
[21] A. Gouloumis, S.-G. Liu, A. Sastre, P. Vázquez, L. Echegoyen, T. Tor-
res, Chem. Eur. J. 2000, 6, 3600. doi:10.1002/1521-3765(20001002)6:
19<3600::AID-CHEM3600>3.3.CO;2-S
[22] T. Jeffery, Tetrahedron Lett. 1985, 26, 2667. doi:10.1016/S0040-4039
(00)98131-0
(h) G. Bottari, D. Olea, C. Gómez-Navarro, F. Zamora, J. Gómez-
Herrero,T.Torres,Angew. Chem. Int. Ed. 2008, 47, 2026 doi:10.1002/
ANIE.200705260
[23] P. F. Heelis, B. J. Parsons, J. Chem. Soc., Chem. Commun. 1994, 793.
doi:10.1039/C39940000793
[24] M. Quintiliani, A. Kahnt, T. Wölfle, W. Hieringer, P. Vázquez,
A. Görling, D. M. Guldi, T. Torres, Chem. Eur. J., in press.
doi:10.1002/CHEM.200701700
[9] A. Gouloumis, D. González-Rodriguez, P. Vázquez, T. Torres, S. Liu,
L. Echegoyen, J. Ramey, G. L. Hug, D. M. Guldi, J. Am. Chem. Soc.
2006, 128, 12674. doi:10.1021/JA055344+
[25] E. C. Breinlinger, C. J. Keenan,V. M. Rotello, J.Am. Chem. Soc. 1998,
120, 8606. doi:10.1021/JA9809556
[10] M. S. Rodríguez-Morgade, T. Torres, C. Atienza-Castellanos,
D. M. Guldi, J. Am. Chem. Soc. 2006, 128, 15145. doi:10.1021/
JA0622195