Ground and Excited State Electronic Interactions in a Bis(phenanthroline) Copper(I) Complex Sandwiched between Two Fullerene Subunits

Article abstract of DOI:10.1021/ic035146o

A new fullerene-substituted phenanthroline ligand has been obtained by reaction of a phenanthroline derivative bearing a 1,3-phenylenebis(methylene)-tethered bis-malonate with C₆₀ in a double Bingel cyclopropanation. The relative position of the two cyclopropane rings in the resulting bis-methanofullerene derivatives has been determined on the basis of the molecular symmetry (C_s) deduced from the ¹H and ¹³C NMR spectra. The corresponding Cu(I) complex F-Cu-F has been prepared in good yields by treatment of the ligand with Cu(CH₃CN)₄BF₄. In the resulting multicomponent system, both C₆₀ moieties are in a tangential orientation relative to their bridging phenyl ring, and the central bis(phenanthroline)Cu(I) core is sandwiched between the two carbon spheres. The electrochemical properties of F-Cu-F suggest the existence of ground-state electronic interactions in this multicomponent array based on the mutual effects exerted by the fullerene units to the bis(2,9-diphenyl-1,10-phenanthroline)Cu(I) complex and vice versa. Close vicinity and electronic interactions between the inorganic core and the peripheral fullerene units are also suggested by increased electronic absorption around 430 nm. The distance between the two moieties is estimated to be 4.3 A by molecular modeling studies. The excited-state properties of F-Cu-F have also been investigated. Photoinduced electron transfer from the central chromophore to the external fullerene units occurs but, surprisingly, only following population of the excited states of the central inorganic unit and not of the external carbon spheres. This is mainly attributed to kinetic factors related to the different nature of the two types of excited states involved, namely charge transfer (excitation on the metal-complexed moiety) vs a localized state (excitation on the fullerene units).

Full text of DOI:10.1021/ic035146o

Inorg. Chem. 2003, 42, 8783−8793
Ground and Excited State Electronic Interactions in a
Bis(phenanthroline) Copper(I) Complex Sandwiched between Two
Fullerene Subunits
Yannick Rio, Ge´rald Enderlin, Cyril Bourgogne, and Jean-Franc¸ois Nierengarten*
Groupe de Chimie des Fullere`nes et des Syste`mes Conjugue´s, Ecole Europe´enne de Chimie,
Polyme`res et Mate´riaux (ECPM), UniVersite´ Louis Pasteur et CNRS, UMR 7504 (IPCMS),
25 Rue Becquerel, 67087 Strasbourg Cedex 2, France
Jean-Paul Gisselbrecht and Maurice Gross
Laboratoire d’Electrochimie et de Chimie Physique du Corps Solide, UniVersite´ Louis Pasteur et
CNRS (UMR 7512), 4 Rue Blaise Pascal, 67070 Strasbourg Cedex, France
Gianluca Accorsi and Nicola Armaroli*
Istituto per la Sintesi Organica e la FotoreattiVita`, Laboratorio di Fotochimica,
Consiglio Nazionale della Ricerche, Via Gobetti 101, 40129 Bologna, Italy
Received October 2, 2003
A new fullerene-substituted phenanthroline ligand has been obtained by reaction of a phenanthroline derivative
bearing a 1,3-phenylenebis(methylene)-tethered bis-malonate with C in a double Bingel cyclopropanation. The
60
relative position of the two cyclopropane rings in the resulting bis-methanofullerene derivatives has been determined
on the basis of the molecular symmetry (C ) deduced from the 1H and 13C NMR spectra. The corresponding Cu(I)
s
complex F−Cu−F has been prepared in good yields by treatment of the ligand with Cu(CH CN)4BF . In the resulting
3
4
multicomponent system, both C moieties are in a tangential orientation relative to their bridging phenyl ring, and
60
the central bis(phenanthroline)Cu(I) core is sandwiched between the two carbon spheres. The electrochemical
properties of F−Cu−F suggest the existence of ground-state electronic interactions in this multicomponent array
based on the mutual effects exerted by the fullerene units to the bis(2,9-diphenyl-1,10-phenanthroline)Cu(I) complex
and vice versa. Close vicinity and electronic interactions between the inorganic core and the peripheral fullerene
units are also suggested by increased electronic absorption around 430 nm. The distance between the two moieties
is estimated to be 4.3 Å by molecular modeling studies. The excited-state properties of F−Cu−F have also been
investigated. Photoinduced electron transfer from the central chromophore to the external fullerene units occurs
but, surprisingly, only following population of the excited states of the central inorganic unit and not of the external
carbon spheres. This is mainly attributed to kinetic factors related to the different nature of the two types of excited
states involved, namely charge transfer (excitation on the metal-complexed moiety) vs a localized state (excitation
on the fullerene units).
Introduction
gain insight into the dynamics and mechanism of intra-
molecular photoinduced energy and electron transfer proc-
esses.1,2 In particular, several hybrid systems involving
inorganic and organic molecular subunits have been prepared
In the last two decades, many covalently linked multi-
component arrays containing metal complexes have been
synthesized. They have proven to be of great importance to
(1) Scandola, F.; Chiorboli, C.; Indelli, M. T.; Rampi, M. A. In Electron
Transfer in Chemistry; Balzani, V., Ed.; Wiley-VCH: Weinheim,
2001; Vol. 3, p 337.
* Corresponding authors. E-mail: jfnierengarten@chimie.u-strasbg.fr
(J.-F.N.). Phone: + 33 390 242645 (J.-F.N.). Fax: + 33 390 242706
(J.-F.N.). E-mail: armaroli@isof.cnr.it.
(2) Barigelletti, F.; Flamigni, L. Chem. Soc. ReV. 2000, 29, 1.
10.1021/ic035146o CCC: $25.00 © 2003 American Chemical Society
Published on Web 11/27/2003
Inorganic Chemistry, Vol. 42, No. 26, 2003 8783

Rio et al.
Figure 1. Compound F-Cu-F and the corresponding model compounds Cu and F.
in which the inorganic moiety is a coordination compound
of d6 metal ions [Ru(II), Os(II), Re(I)] that can act as light
absorbing unit (chromophore), capable of starting up photo-
induced processes.3 Depending on the electronic properties
of the organic counterpart(s), two classes of such arrays have
been singled out, which are conventionally called “chro-
mophore-quencher” and “chromophore-sensitizer”.1,3 In the
former case, the organic quencher is typically an electron
donor or acceptor with no chromophoric character; in the
latter case, the organic sensitizer is a chromophore itself and
may transfer its excitation energy to the inorganic chro-
mophoric counterpart.1,3
Recent developments in the synthesis of functionalized
fullerenes have allowed the preparation of new families of
organic-inorganic (hybrid) arrays, where the organic sub-
units are C60 fullerenes, while the inorganic chromophores
can be Ru(II),4-6 Cu(I),7,8 or Re(I)6 complexes.9 Fullerenes
absorb light throughout the UV-vis spectral region, possess
low-lying ππ* singlet and triplet states, and are excellent
electron acceptors. Such concomitant features are rather
unique for organic molecules; thus, when one uses the above-
mentioned classification for organic-inorganic hybrids
containing fullerenes, one has to keep in mind that the roles
of chromophore and quenchers/sensitizer can be exchanged
between the organic and the inorganic units. Addressing light
excitation to a given molecular component, i.e., choosing
the chromophore, enables the assignment of the specific role
of each partner.
Herein we describe the synthesis, the electrochemical, and
the photophysical properties of a new organic-inorganic
array F-Cu-F made of a Cu(I)-bisphenanthroline complex
(6) Armaroli, N.; Accorsi, G.; Felder, D.; Nierengarten, J. F. Chem. Eur.
J. 2002, 8, 2314.
(7) Armaroli, N.; Diederich, F.; Dietrich-Buchecker, C. O.; Flamigni, L.;
Marconi, G.; Nierengarten, J. F.; Sauvage, J. P. Chem. Eur. J. 1998,
4, 406.
(8) Armaroli, N.; Boudon, C.; Felder, D.; Gisselbrecht, J. P.; Gross, M.;
Marconi, G.; Nicoud, J. F.; Nierengarten, J. F.; Vicinelli, V. Angew.
Chem., Int. Ed. 1999, 38, 3730.
(3) Photoinduced Electron Transfer in Metal-Organic Dyads; Schanze,
K. S., Walters, K. A., Eds.; Marcel Dekker: New York, 1998.
(4) Maggini, M.; Guldi, D. M.; Mondini, S.; Scorrano, G.; Paolucci, F.;
Ceroni, P.; Roffia, S. Chem. Eur. J. 1998, 4, 1992.
(5) Guldi, D. M.; Maggini, M.; Menna, E.; Scorrano, G.; Ceroni, P.;
Marcaccio, M.; Paolucci, F.; Roffia, S. Chem. Eur. J. 2001, 7, 1597.
(9) Meijer, M. D.; van Klink, G. P. M.; van Koten, G. Coord. Chem.
ReV. 2002, 230, 141.
8784 Inorganic Chemistry, Vol. 42, No. 26, 2003

Fullerene-Phenanthroline Cu(I) Complexes
Scheme 1. Preparation of Diol 6a
a Reagents and conditions: (a) t-BuLi, THF, -78 to 0 °C, 3 h, then 1,10-phenanthroline, 0 °C, 3 h, then H2O, then MnO2 (78%); (b) TIPSCl, imidazole,
DMF, 0 °C, 48 h (93%); (c) t-BuLi, THF, -78 to 0 °C, 3 h, then 2, 0 °C, 5 h, then H2O, then MnO2 (75%); (d) TBAF, THF, 0 °C, 30 min (quantitative).
(Cu) sandwiched between two fullerene subunits (F) (Figure
1). Interestingly, owing to the unique structural features of
F-Cu-F, ground-state electronic interactions between the
two types of subunits are observed. The excited-state
properties of F-Cu-F have also been investigated and
compared to those of the corresponding model compounds
F and Cu (Figure 1). When the Cu-complexed core is
excited, F-Cu-F exhibits photoinduced electron transfer
from the inorganic to the organic moieties. In contrast,
excitation of the carbon spheres does not bring about any
photoinduced processes. Thus, although both the inorganic
and the organic units can start up electron transfer, only the
former moiety turns out to be an effective chromophore in
triggering the excited state interaction.
in a double Bingel12 cyclopropanation. To this end, a phen-
anthroline derivative substituted with a 1,3-phenylenebis-
(methylene)-tethered bis-malonate was prepared by an es-
terification reaction between diol 6 and a malonic acid mono-
ester derivative. The synthesis of the key intermediate 6 is
depicted in Scheme 1. Treatment of 1-bromo-3,4-didodecyl-
oxybenzene (1) with t-BuLi followed by reaction of the
resulting 1-lithio-3,4-didodecyloxybenzene with 1,10-phenan-
throline under the conditions developed by Sauvage and co-
workers13 gave 2 in 78% yield. Treatment of diol 314 with
triisopropylsilyl chloride (TIPSCl) in the presence of imid-
azole afforded the protected derivative 4 in 93% yield.
Halogen-lithium exchange was achieved by reaction of 4
with t-BuLi. Subsequent addition of the resulting organo-
lithium derivative to 2 followed by hydrolysis and rearoma-
tization with MnO2 gave 5 in 75% yield. Diol 6 was then
obtained in a quantitative yield by treatment with tetra-n-
butylammonium fluoride (TBAF) in THF at 0 °C.
Results and Discussion
Synthesis. In order to control the distance and the
orientation of the different components in F-Cu-F, it was
decided to connect one of the phenyl groups of both
phenanthroline ligands to two points of the surface of their
fullerene substituent. In this way, both C60 moieties are in a
tangential orientation relative to their bridging phenyl ring
and the central bis(phenanthroline)Cu(I) core is thus sand-
wiched between the two carbon spheres. The phenanthroline
ligand precursor of F-Cu-F was obtained by taking
advantage of the versatile regioselective reaction developed
in the group of Diederich10,11 which led to C60 bis-adducts
by a cyclization reaction at the C sphere with bis-malonates
Reaction of diol 6 with malonic acid mono-ester 715 under
esterification conditions using N,N′-dicyclohexylcarbodiimide
(DCC) and 4-(dimethylamino)pyridine (DMAP) in CH2Cl2
gave bis-malonate 8 in 73% yield. Finally, reaction of 8 with
(11) Nierengarten, J. F.; Habicher, T.; Kessinger, R.; Cardullo, F.; Diederich,
F.; Gramlich, V.; Gisselbrecht, J. P.; Boudon, C.; Gross, M. HelV.
Chim. Acta 1997, 80, 2238.
(12) Bingel, C. Chem. Ber. 1993, 126, 1957.
(13) Marnot, P. A.; Dietrich-Buchecker, C. O.; Sauvage, J. P. Tetrahedron
Lett. 1982, 23, 5291.
(14) Sherrod, S. A.; da Costa, R. L.; Barnes, R. A.; Boekelheide, V. J.
Am. Chem. Soc. 1974, 96, 1565.
(15) Felder, D.; Nava, M. G.; Carreon, M. D.; Eckert, J. F.; Luccisano,
M.; Schall, C.; Masson, P.; Gallani, J. L.; Heinrich, B.; Guillon, D.;
Nierengarten, J. F. HelV. Chim. Acta 2002, 85, 288.
(10) Nierengarten, J. F.; Gramlich, V.; Cardullo, F.; Diederich, F. Angew.
Chem., Int. Ed. Engl. 1996, 35, 2101.
Inorganic Chemistry, Vol. 42, No. 26, 2003 8785

Rio et al.
Scheme 2. Preparation of Ligand 9a
a Reagents and conditions: (a) 6, DCC, DMAP, CH2Cl2, 0 °C to room temperature, 72 h (73%); (b) C60, I2, DBU, toluene, rt, 12 h (38%); (c) Cu(CH3CN)4BF4,
CH3CN, CH2Cl2, rt, 1 h (92%).
Figure 2. 1H NMR spectrum (CDCl3, 400 MHz) of the fullerene-functionalized phenanthroline derivative 9.
C60, I2, and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in
toluene at room temperature afforded the desired cyclization
product 9 in 38% yield (Scheme 2).
Compound 9 was characterized by 1H and 13C NMR, UV-
vis, and IR spectroscopies. In addition, the structure of 9
was confirmed by FAB mass spectrometry. The relative
position of the two cyclopropane rings in 9 on the C60 surface
was determined on the basis of the molecular symmetry (Cs)
deduced from the H and 13C NMR spectra. The H NMR
spectrum of 9 is depicted in Figure 2. Unambiguous
assignment was achieved on the basis of 2D-COSY and
NOESY spectra recorded at room temperature in CDCl3. The
spectrum of 9 shows all the characteristic features of Cs
symmetrical 1,3-phenylenebis(methylene)-tethered fullerene
1
1
8786 Inorganic Chemistry, Vol. 42, No. 26, 2003

Fullerene-Phenanthroline Cu(I) Complexes
cis-2 bis-adduct derivatives.15-18 Effectively, two sets of AB
quartets are observed for the diastereotopic benzylic CH2
groups (HA-B and HC-D) and an A2X system is revealed for
the aromatic protons of the 1,3,5-trisubstituted bridging
phenyl ring (Hd and He). The spectrum is also characterized
by three sets of AB quartets in the aromatic region in a
typical pattern for a disymmetrical 2,9-disubstituted-1,10-
phenanthroline (H3-4, H5-6, and H7-8), an AMX system for
the aromatic protons of the 3,4-didodecyloxyphenyl unit (Ha,
Hb, and Hc), and an A2X system for the aromatic protons of
the 3,5-didodecyloxyphenyl rings (Hf and Hg).
The color and, accordingly, the absorption spectrum of a
C
60 bis-adduct are highly dependent on the addition pattern
Figure 3. MALDI-TOF mass spectrum of F-Cu-F.
and characteristic for each of the regioisomers.10,11,15 The
orange color and the UV-vis spectrum of 9 are indeed fully
consistent with those of previously reported analogous cis-2
bis-adducts.10,11,15-18
Table 1. Electrochemical Properties Determined by CV on a Glassy
Carbon Working Electrode in CH2Cl2 + 0.1 M nBu4NPF6 Solutions at
Room Temperature
reduction
oxidation
E1
The Cu(I) model complex Cu (Figure 1) was obtained in
96% yield by treatment of ligand 5 with Cu(CH3CN)4BF4
in CH2Cl2/CH3CN at room temperature. The coordination
of 5 to the Cu(I) cation was easily observed by apparition
of the metal-to-ligand charge transfer (MLCT) band char-
acteristic of bis(2,9-diphenyl-1,10-phenanthroline)Cu(I) de-
compd
Cu
E3
E2
E1
-2.15a
-1.13a
-1.06a,c
+0.37a
9
-1.95b
-1.51b
F-Cu-F
-1.91b,c
-1.41b,c
+0.44a
a Values for (Epa + Epc)/2 in V vs Fc/Fc+ at a scan rate of 0.1 V s-1
b Irreversible process, Epc value reported. c Dielectronic process.
.
1
rivatives (see below). Furthermore, the H NMR spectrum
of Cu provided also good evidence for its formation.
Effectively, as a result of the ring current effect of one
phenanthroline subunit on the 2,9-substituents of the second
one in the complex, the signals of the protons belonging to
the phenyl rings attached to the phenanthroline core are
shielded about 1.0-1.5 ppm in Cu when compared to the
corresponding signals in ligand 5. This particular behavior
is specific to such copper(I) complexes.19
Compound F-Cu-F was also obtained by treatment of
the corresponding ligand (9) with Cu(CH3CN)4BF4. The 1H
NMR spectrum of complex F-Cu-F is consistent with the
proposed structure. As observed for Cu, the resonances of
the protons belonging to the phenyl rings attached to the
phenanthroline unit are shielded about 1.0-1.5 ppm in the
1H NMR spectrum of F-Cu-F when compared to the
corresponding signals in the spectrum of 9. In addition, it
can be noted that compound F-Cu-F is C2 symmetric and
therefore chiral. As a result, the two equivalent fullerene cis-2
bis-adduct moieties have lost their plane of symmetry. For
this reason, some of the protons that were equivalent in ligand
9 are not equivalent any longer in the complex and give rise
to two sets of signals (Hd, HA, HB, HC, HD, Hf, and Hg, see
Figure 2 for the assignment). The structure of F-Cu-F was
also confirmed by mass spectrometry. As shown in Figure
3, the MALDI-TOF mass spectrum of F-Cu-F displays a
singly charged ion peak at m/z 5198.6 which can be assigned
to the Cu(I) complex F-Cu-F after loss of the tetra-
fluoroborate counteranion ([M - BF4]+, calculated for
C356H352O28N4Cu: 5198.3). Two characteristic fragments are
also observed. The first one at m/z 2568.2 corresponds to
the free protonated ligand ([9 + H]+) and the second one at
m/z 2630.7 to the ligand coordinating a Cu(I) cation
([9 + Cu]+). It can be noted that this fragmentation pattern
is typically observed for such Cu(I) complexes.20 How-
ever, when compared to mass spectra recorded under much
harsher FAB conditions, the intensity of these two fragmen-
tation peaks is very small in the MALDI-TOF mass
spectrum, thus showing that the latter technique is an ideal
tool for the characterization of such high molecular weight
compounds.
Electrochemistry. The electrochemical properties of Cu,
9, and F-Cu-F were investigated by cyclic voltammetry
(CV) in CH2Cl2 + 0.1 M nBu4NPF6 solutions. The results
are summarized in Table 1.
In the anodic region, the copper(I) complex F-Cu-F
shows a reversible one-electron process at +0.44 V vs Fc/
Fc+ assigned to the oxidation of the metal center.8,21-23
Interestingly, the Cu-based oxidation appears to be signifi-
cantly more anodic (∆E ) 70 mV) with respect to the
corresponding model compound Cu. The oxidation of Cu(I)
to Cu(II) is accompanied by rearrangement from nearly
tetrahedral to distorted square planar geometry.24 However,
(16) Nierengarten, J. F.; Schall, C.; Nicoud, J. F. Angew. Chem., Int. Ed.
1998, 37, 1934.
(17) Nierengarten, J. F.; Eckert, J. F.; Felder, D.; Nicoud, J. F.; Armaroli,
N.; Marconi, G.; Vicinelli, V.; Boudon, C.; Gisselbrecht, J. P.; Gross,
M.; Hadziioannou, G.; Krasnikov, V.; Ouali, L.; Echegoyen, L.; Liu,
S. G. Carbon 2000, 38, 1587.
(20) Moucheron, C.; Dietrich-Buchecker, C. O.; Sauvage, J. P.; Van
Dorsselaer, A. J. Chem. Soc., Dalton Trans. 1994, 885.
(21) Dietrich-Buchecker, C. O.; Sauvage, J. P.; Kern, J. M. J. Am. Chem.
Soc. 1989, 111, 7791.
(22) Federlin, P.; Kern, J. M.; Rastegar, A.; Dietrich-Buchecker, C.; Marnot,
P. A.; Sauvage, J. P. New J. Chem. 1990, 14, 9.
(18) Nierengarten, J. F.; Oswald, L.; Nicoud, J. F. Chem. Commun. 1998,
1545.
(19) Dietrich-Buchecker, C. O.; Marnot, P. A.; Sauvage, J.-P.; Kintzinger,
J.-P. NouV. J. Chem. 1984, 8, 573.
(23) Dietrich-Buchecker, C. O.; Nierengarten, J. F.; Sauvage, J. P.;
Armaroli, N.; Balzani, V.; De Cola, L. J. Am. Chem. Soc. 1993, 115,
11237.
(24) Armaroli, N. Chem. Soc. ReV. 2001, 30, 113.
Inorganic Chemistry, Vol. 42, No. 26, 2003 8787

Rio et al.
Figure 5. Absorption spectrum of F-Cu-F in CH2Cl2 (s) and benzo-
nitrile (- - -), compared to the sum spectrum of 2F + Cu (‚‚‚) in CH2Cl2;
the profile obtained by subtracting the sum spectrum to the experimental
one is (-‚-‚-). Inset: emission spectra in CH2Cl2; fullerene fluorescence
Figure 4. Snapshot of the theoretical structure of F-Cu-F at 300 K
obtained from a Molecular Dynamics calculation showing the fullerene-
phenyl-phenanthroline-phenyl stacking (the dodecyloxy groups have been
replaced by methoxy substituents for clarity). The shortest distance between
the fullerene sphere and its bridging phenyl ring (blue line) is 4.3 Å; the
distance from the center of the phenyl ring of one ligand to the center of
the central six-membered ring of the phenanthroline of the other ligand
(yellow line) is 3.9 Å.
and MLCT band (left), sensitized singlet oxygen luminescence (right), λexc
)
600 nm, A ) 0.190 for all samples, light partitioning in F-Cu-F is 0.5:
1:0.5. The emission properties of F are the same as for 9.
from the oxidation potential of the metal center. Effectively,
the reduction potentials are expected at a more negative value
in such a case. However, one has to consider the proximity
of the positively charged Cu(I) cation. Actually, Diederich
and Echegoyen have reported positive shifts in the fullerene
reduction potential (∆E ) 90 mV) of a C60-dibenzo-18-
crown-6 conjugate upon complexation of a potassium cation
due to the electrostatic effect of K+ bound in close proximity
to the carbon sphere.27,28 Similarly, the positive shift in
potential observed for the reduction of F-Cu-F relative to
the uncomplexed compound 9 is attributed to an electrostatic
effect able to counterbalance the electronic interactions
between the bis(2,9-diphenyl-1,10-phenanthroline)Cu(I) core
and the C60 units that tend to negatively shift the reduction
potentials.
Photophysical Properties. The electronic absorption
spectrum of F-Cu-F in CH2Cl2 is reported in Figure 5.
Good matching with the profile obtained by summing the
spectra of the model compounds Cu and F (1:2 ratio) is
observed everywhere but in the region around 430 nm. Upon
subtraction, the band depicted in Figure 5 is obtained. This
can be attributed to electronic donor-acceptor interactions,
as observed for some fullerene host-guest complexes29 and
in fullerodendrimers where the external branches wrap the
central carbon sphere.30-32 The increased band intensity in
polar benzonitrile (Figure 5) corroborates this assignment.33
Notably, donor-acceptor multicomponent arrays containing
this process is not expected to be strongly affected by bulky
substituents, when they are not directly attached to the
phenanthroline ligand.25 The observed potential shift is thus
attributed to the strong electron-withdrawing effect of the
fullerene units which destabilizes the Cu(II) state of the
complex, as previously seen for C60-porphyrin conjugates
bearing similar cis-2 fullerene bis-adduct substituents.17,18
This hypothesis is corroborated by the photophysical mea-
surements which revealed the existence of sizable intramo-
lecular electronic interactions in F-Cu-F (vide infra).
Notably, molecular modeling studies show that the fullerene
units are in tight vicinity to the bis(2,9-diphenyl-1,10-
phenanthroline)Cu(I) complex (Figure 4). Effectively, the
distance of the fullerene sphere to the center of its bridging
phenyl ring is estimated to be 4.3 Å showing that they are
close to being at the van der Waals contact. Therefore, it
appears reasonable to ascribe the observed shift for the metal
centered oxidation in F-Cu-F to electronic interactions
between the bis(2,9-diphenyl-1,10-phenanthroline)Cu(I) core
and the fullerene units.
As far as the reduction potential is concerned, F-Cu-F
and model compound 9 show a similar behavior totally
consistent with previously reported data for fullerene cis-2
bis-adducts.17,18,26 It can be noted that the two fullerene
subunits in F-Cu-F behave as independent redox centers.
Surprisingly, the reduction potentials are shifted to more
positive values for F-Cu-F (∆E ) 70 mV for the first
reduction) when compared to fullerene derivative 9. The
latter observation seems to be in contradiction with the
electronic interactions between the bis(2,9-diphenyl-1,10-
phenanthroline)Cu(I) core and the fullerene units deduced
(27) Bourgeois, J. P.; Seiler, P.; Fibbioli, M.; Pretsch, E.; Diederich, F.;
Echegoyen, L. HelV. Chim. Acta 1999, 82, 1572.
(28) Bourgeois, J. P.; Echegoyen, L.; Fibbioli, M.; Pretsch, E.; Diederich,
F. Angew. Chem., Int. Ed. 1998, 37, 2118.
(29) Eckert, J. F.; Byrne, D.; Nicoud, J. F.; Oswald, L.; Nierengarten, J.
F.; Numata, M.; Ikeda, A.; Shinkai, S.; Armaroli, N. New J. Chem.
2000, 24, 749.
(30) Rio, Y.; Accorsi, G.; Nierengarten, E.; Rehspringer, J.-L.; Ho¨nerlage,
B.; Kopitkovas, G.; Chugreev, A.; Van Dorsselaer, A.; Armaroli, N.;
Nierengarten, J. F. New J. Chem. 2002, 26, 1146.
(31) Murata, Y.; Ito, M.; Komatsu, K. J. Mater. Chem. 2002, 12, 2009.
(32) Rio, Y.; Accorsi, G.; Nierengarten, H.; Bourgogne, C.; Strub, J.-M.;
Van Dorsselaer, A.; Armaroli, N.; Nierengarten, J.-F. Tetrahedron
2003, 59, 3833.
(25) Armaroli, N.; Accorsi, G.; Gisselbrecht, J. P.; Gross, M.; Eckert, J.
F.; Nierengarten, J. F. New J. Chem. 2003, 27, 1470.
(26) Cardullo, F.; Seiler, P.; Isaacs, L.; Nierengarten, J. F.; Haldimann, R.
F.; Diederich, F.; MordasiniDenti, T.; Thiel, W.; Boudon, C.;
Gisselbrecht, J. P.; Gross, M. HelV. Chim. Acta 1997, 80, 343.
8788 Inorganic Chemistry, Vol. 42, No. 26, 2003

Fullerene-Phenanthroline Cu(I) Complexes
fullerenes rarely present high-energy30,31 or low-energy33-35
CT absorption bands, and this happens only when a contact
distance between donor-acceptor partners is possible. Thus,
our results are in good agreement with the molecular
modeling studies showing that the fullerene units are in tight
vicinity to the central Cu(I) complex in F-Cu-F (Figure
4).
eV)8 is evidenced, the quenching of the Cu-complexed
moiety must be attributed to quantitative photoinduced
electron-transfer process occurring from the lowest MLCT
manifold, located at about 1.63 eV, to a lower-lying charge
separated Cu+-F- localized at 1.50 eV, as estimated from
the one-electron redox potentials39 (Table 1). Unfortunately,
we are unable to detect the charge recombination step since
our current transient absorption apparatus has no spectral
sensitivity above 1000 nm, where the fullerene radical anion
diagnostic peak is located. On the other hand, the oxidized
metal center is not expected to give observable absorption
features, also considering that at 355 and 532 nm (Nd:YAG
laser harmonics) most of the light (>60%) is absorbed by
the fullerene chromophores, which are unable to trigger
electron transfer and exhibit very strong singlet and triplet
transient absorption features.
An energy level diagram reporting all the relevant
electronic and charge separated states, as determined by
luminescence and electrochemical potentials,39 is reported
in Figure 6. A certain degree of Coulombic interaction within
the charge separated system may be present due to the short
intercomponent distance and the medium-level polarity of
CH2Cl2.40 A quantitative estimation of this effect is subject
to severe approximations,41 and we prefer to neglect such
contribution, keeping in mind that some stabilization of the
charge separated state may occur with respect to what is
indicated in Figure 6. For the Cu-complexed moiety, both
the singlet and triplet state are reported; they are in thermal
equilibration at room temperature, the population of the triplet
being predominant.38
Both kind of molecular subunits of F-Cu-F are lumi-
nescent. At 298 K, Cu exhibits an emission band (λmax
)
726 nm, τ ) 199 ns, and Φem ) 8.5 × 10-4 in air-free
CH2Cl2 solution) originating from the deactivation of a
thermally equilibrated manifold of the lowest singlet and
triplet metal-to-ligand charge-transfer states (1MLCT and
3MLCT), separated by about 1500 cm-1.24,36,37 At 77 K, the
emission band, red shifted and very weak (λmax ) 760 nm,
τ ) 1.6 µs), is attributed to the 3MLCT level.37,38 At 298 K,
dimethanofullerene F exhibits a structured fluorescence band
with the highest energy feature peaking at 706 nm (τ ) 1.5
ns, Φem ) 3.0 × 10-4, CH2Cl2), substantially unmodified at
77 K.8
The characteristic luminescence properties of the two
reference compounds can conveniently signal the occurrence
of intercomponent excited-state interactions in the F-Cu-F
assembly. In Figure 5 are displayed the emission spectra of
Cu, F, and F-Cu-F at λexc ) 600 nm (isoabsorbing
samples, A ) 0.190), where light partitioning among the Cu
and F chromophores in F-Cu-F is 0.5:1:0.5. Quenching
of the MLCT-type emission band of the Cu(I)-complexed
moiety is evidenced. On the contrary, the amount of light
directly exciting the fullerene moieties (50%) gives rise to a
fluorescence band exhibiting the same parameters as F (see
above). The yield of fullerene triplet formation of F-Cu-F
relative to F has been indirectly measured via the singlet
oxygen method described earlier.6 Taking into account the
1:1 light sharing among the two types of chromophores, the
yield of fullerene triplet formation is the same for F-Cu-F
and F (Figure 5, inset); also the triplet lifetime is identical,
i.e., 18.0 µs and 650 ns in air-free and air-equilibrated
CH2Cl2, respectively. Taken together, the above results show
that (i) excitation of the Cu(I)-complexed core results in
quenching of the MLCT excited states not followed by
sensitization of the fullerene electronic levels; (ii) excitation
of the external carbon spheres brings about regular deactiva-
tion of the C60 excited states, unmodified relative to F. The
quenched lifetime of the MLCT level of F-Cu-F is
determined to be 600 ps by time correlated single photon
counting spectrometry, thus kq) 1.7 × 109 s-1. Since no
sensitization of the lower lying fullerene triplet state (1.40
The electron-transfer rate constant, according to the
classical model of Marcus and Sutin, can be expressed as
follows:42
∆Gq
RT
k ) ν κ exp
(1)
(
)
el
N
where νΝ is the nuclear frequency factor of the reaction,
which can be expressed as a weighted mean of the frequen-
cies of the various nuclear modes involved in the reaction
coordinate, K is the transmission coefficient of the reaction
which describes the probability that the reactants, once they
reach the geometry of the crossing point between potential
energy surfaces, convert into products; ∆Gq is the activation
energy of the electron-transfer process.
According to electrochemical data and absorption spectra
and in light of the short interchromophoric distance (4.3 Å),
the electronic interaction between the metal center and the
fullerene units in F-Cu-F is relatively high. Therefore,
electron transfer can be expected to occur in the in the so-
called adiabatic regime in which the rate determining step
is the nuclear motion that leads to the transition-state
geometry and the electronic transmission coefficient of the
(33) Armaroli, N.; Marconi, G.; Echegoyen, L.; Bourgeois, J. P.; Diederich,
F. Chem. Eur. J. 2000, 6, 1629.
(34) Simonsen, K. B.; Konovalov, V. V.; Konovalova, T. A.; Kawai, T.;
Cava, M. P.; Kispert, L. D.; Metzger, R. M.; Becher, J. J. Chem. Soc.,
Perkin Trans. 2 1999, 657.
(35) Imahori, H.; Tkachenko, N. V.; Vehmanen, V.; Tamaki, K.; Lem-
metyinen, H.; Sakata, Y.; Fukuzumi, S. J. Phys. Chem. A 2001, 105,
1750.
(36) Everly, R. M.; McMillin, D. R. J. Phys. Chem. 1991, 95, 9071.
(37) Felder, D.; Nierengarten, J. F.; Barigelletti, F.; Ventura, B.; Armaroli,
N. J. Am. Chem. Soc. 2001, 123, 6291.
(39) Balzani, V.; Scandola, F. Supramolecular Photochemistry; Ellis
Horwood: Chichester, U.K., 1991; p 44.
(40) Kavarnos, G. J.; Turro, N. J. Chem. ReV. 1986, 86, 401.
(41) Koeberg, M.; de Groot, M.; Verhoeven, J. W.; Lokan, N. R.; Shephard,
M. J.; Paddon-Row, M. N. J. Phys. Chem. A 2001, 105, 3417.
(42) Marcus, R. A.; Sutin, N. Biochim. Biophys. Acta 1985, 811, 265.
(38) Kirchhoff, J. R.; Gamache, R. E.; Blaskie, M. W.; Del Paggio, A. A.;
Lengel, R. K.; McMillin, D. R. Inorg. Chem. 1983, 22, 2380.
Inorganic Chemistry, Vol. 42, No. 26, 2003 8789

Rio et al.
Figure 6. Energy level diagram for F-Cu-F and related photoinduced
processes upon excitation of both chromophores. In the shorthand notations,
only one F unit is indicated for F-Cu-F because under our experimental
conditions, i.e., light intensity, only one F unit can be excited. The excited
state energies of 3CuMLCT-F and Cu-1F are estimated from the 77 K
emission band maxima of Cu and F, respectively, that of 1CuMLCT-F is
located 1500 cm-1 above 3CuMLCT-F (ref 38), and that of Cu-3F from
theoretical calculations (ref 8). The position of the CS state is obtained
from the electrochemical data.
Figure 7. Schematic representation of the photoinduced processes observed
in F-Cu-F.
reaction (K) is virtually unity.40 ∆Gq is related to the
related to molecular internal rearrangements following
electron transfer. In fact, Cu(I)-phenanthroline complexes
are known to undergo extensive structural rearrangements
upon oxidation of Cu(I) to Cu(II),24 due to the different
coordination geometry of the two ions. All these effects on
the total reorganization energy of a Marcus “normal region”
electron-transfer process (-∆G°<λ) contribute to lower the
activation barrier ∆Gq toward the formation of Cu+-F-,
when preliminary formation of a MLCT state is ac-
complished. On the contrary, when the carbon sphere is the
chromophore and a localized 1ππ* state is generated, electron
transfer is comparably disfavored and fast internal deactiva-
tion prevails. Interestingly, enhancement of electron-transfer
rate between two distant porphyrin units, separated by a
[Cu(phen)2]+-type chromophore acting as primary electron
acceptor, has been documented very recently.44
thermodynamic driving force according to eq 242
λ
4
∆G° 2
λ
∆Gq ) 1 +
(2)
(
)
where λ is the reorganization energy, a term comprising two
contributions, namely inner (bond length and angles) and
outer (solvent orientation) nuclear rearrangements of the
reacting pair.
From the energy diagram in Figure 6, it is evident that
electron transfer occurring from Cu-1F and 3CuMLCT-F are
both moderately exergonic (∆G° ) -0.25 and -0.13 eV).
In both cases, electron transfer can be safely located in the
normal region of the Marcus parabola, even if some
stabilization of the charge-separated state due to Coulombic
interactions is present (see above); for example, compact
hybrid fullerene-porphyrin arrays exhibit a λ value as large
as 0.86 eV.43 Thus a faster electron-transfer process from
the fullerene singlet than form the MLCT state should occur,
which is not the case. Indeed the longer lifetime of the MLCT
manifold (199 ns) relative to the fullerene singlet (1.5 ns)
should favor competitive deactivation pathways, such as
electron transfer, versus internal deactivation. However the
lifetime effect alone is not expected to play a crucial role,
since the rate of electron-transfer deactivation of the MLCT
state is 2.5 times faster than the rate of intrinsic decay of
the fullerene singlet so, in principle, it is fast enough to expect
substantial electron-transfer deactivation from the latter level,
too.
Although in the adiabatic regime the intercomponent
electronic coupling is not expected to play a significant role
in determining the electron-transfer rate, it must be empha-
sized that the formation of the MLCT state prior to the final
charge separation may contribute to yield a better electronic
interaction between the two chromophores. In fact, the
formation of the MLCT state implies redistribution of
negative charge on the phenyl-phenanthroline ligand,45 i.e.,
in the direction of the attached C60 electron acceptor. This
makes the donor-acceptor distance effectively smaller,
certainly not disfavoring the reaction kinetics. Similar
electronic effects on the rate of photoinduced electron transfer
have been recently observed for organic46 and hybrid47
donor-acceptor arrays. The electron-transfer process occur-
ring in F-Cu-F upon excitation of the Cu(I)-complexed
chromophore is schematized in Figure 7.
We believe that the main reason for the observed asym-
metric electron-transfer behavior may lie in the different
nature of the two excited states, i.e., charge transfer vs
localized. In particular, the preliminary formation of the
MLCT state lowers the external reorganization energy
demand, related to solvent repolarization around newly
formed charged species. Even more importantly, one can
expect a favorable impact on internal reorganization energy,
(44) Andersson, M.; Linke, M.; Chambron, J. C.; Davidsson, J.; Heitz, V.;
Hammarstro¨m, L.; Sauvage, J. P. J. Am. Chem. Soc. 2002, 124, 4347.
(45) Gordon, C. K.; McGarvey, J. J. Inorg. Chem. 1991, 30, 2986.
(46) Lukas, A. S.; Zhao, Y. Y.; Miller, S. E.; Wasielewski, M. R. J. Phys.
Chem. B 2002, 106, 1299.
(47) Flamigni, L.; Marconi, G.; Dixon, I. M.; Collin, J. P.; Sauvage, J. P.
J. Phys. Chem. B 2002, 106, 6663.
(43) Guldi, D. M. Chem. Soc. ReV. 2002, 31, 22.
8790 Inorganic Chemistry, Vol. 42, No. 26, 2003

Fullerene-Phenanthroline Cu(I) Complexes
It must also be noted that the fullerene singlet state might
be quenched by energy transfer to the 3MLCT excited level
(Figure 6), but this process is not observed. Such singlet-
triplet energy transfer should occur via the double electron-
exchange mechanism,48 which is expected to be controlled
by similar factors as electron transfer,49 and thus disfavored
as well. The present case interestingly compares to a Cu(I)-
phenanthroline rotaxane bearing two fullerene stoppers,
where quenching of the fullerene singlet state by energy
transfer to the 3MLCT level of the Cu(I)-complexed moiety
was observed.7 The different behavior of the two systems
may be attributed to substantial variations of interchro-
mophoric distance, possibly affecting the ground- and
excited-state distortion (and electronic properties) of the
central metal chromophore.24 Also, the electronic properties
(e.g., absorption and emission spectra) of methanofullerenes
and bismethanofullerenes are somewhat different.
As evidenced by the lack of singlet oxygen sensitization,
the CS state of F-Cu-F is deactivated to the ground state
and not to the fullerene triplet level, as found instead in
fullerene dyads with Ru2+ or Re+ coordination compounds.6
This suggests that fullerene/Cu(I)-phenanthroline dyads
might be more promising candidates for the construction of
photochemical devices for charge separation, since they are
not suffering from the wasting sink effect of the fullerene
triplet.6
electron transfer from the central metal-complexed chro-
mophore to the external fullerene units may occur, in
principle, by excitation of both moieties, but it is observed
only following population of the excited states of the
inorganic core. Photoexcitation of the peripheral carbon
spheres is followed by “trivial” internal deactivation. The
extensive internal and external (solvent) rearrangements that
characterize the formation of MLCT excited states in Cu(I)-
phenanthrolines are able to lead the reaction coordinates to
favorable values so that electron transfer may proceed
quickly. This effect is particularly favorable in F-Cu-F
where the electronic interaction is not negligible and the gain
of a suitable reaction geometry is crucial to promote electron
transfer (adiabatic regime). These results show that hybrid
organic-inorganic multicomponent arrays,52 due to profound
differences in the nature of excited states, are particularly
promising for the design of optoelectronic devices in which
excitation of a given subunit triggers a specific and selective
response.
Experimental Section
General Methods. Reagents and solvents were purchased as
reagent grade and used without further purification. Compounds
F,15 1,53 3,14 and 715 were prepared according to previously reported
procedures. All reactions were performed in standard glassware
under an inert Ar atmosphere. Evaporation and concentration were
done at water aspirator pressure and drying in vacuo at 10-2 Torr.
Column chromatography: silica gel 60 (230-400 mesh, 0.040-
0.063 mm) was purchased from E. Merck. Thin layer chromatog-
raphy (TLC) was performed on glass sheets coated with silica gel
60 F254 purchased from E. Merck, visualization by UV light. IR
spectra (cm-1) were measured on an ATI Mattson Genesis Series
FTIR instrument. NMR spectra were recorded on a Bruker AC 200
(200 MHz) or a Bruker AM 400 (400 MHz) with solvent peaks as
reference. FAB-mass spectra (m/z; % relative intensity) were taken
on a ZA HF instrument with 4-nitrobenzyl alcohol as matrix. Mass
measurement were carried out on a Bruker BIFLEX matrix-assisted
laser desorption time-of-flight mass spectrometer (MALDI-TOF)
equipped with SCOUT high-resolution optics, an X-Y multisample
probe, and a gridless reflector. Ionization is accomplished with the
337 nm beam from a nitrogen laser with a repetition rate of 3 Hz.
All data were acquired at a maximum accelerating potential of 20
kV in the linear positive ion mode. The output signal from the
detector was digitized at a sampling rate of 1 GHz. A saturated
solution of 1,8,9-trihydroxyanthracene (dithranol Aldrich EC: 214-
538-0) in CH2Cl2 was used as a matrix. Typically, a 1/1 mixture
of the sample solution in CH2Cl2 was mixed with the matrix
solution, and 0.5 µL of the resulting mixture was deposited on the
probe tip. Calibration was performed in the external mode with
insulin (5734.6 Da) and ACTH (2465.2 Da). Elemental analyses
were performed by the analytical service at the Institut Charles
Sadron (Strasbourg, France).
Conclusion
A new fullerene-substituted phenanthroline ligand has been
obtained by reaction of a phenanthroline derivative bearing
a 1,3-phenylenebis(methylene)-tethered bis-malonate with
C60 in a double Bingel cyclopropanation. The corresponding
Cu(I) complex F-Cu-F has been prepared in good yields
by treatment of the ligand with a Cu(I) salt. In this
multicomponent system, both C60 moieties are in a tangential
orientation relative to their bridging phenyl rings, and the
central bis(phenanthroline)Cu(I) core is sandwiched between
the two carbon spheres. Therefore, structural parameters such
as the distance and the orientation of the different compo-
nents in F-Cu-F are well defined. The electrochemical
properties of F-Cu-F suggest the existence of ground-state
donor-acceptor interactions in this multicomponent array
based on the mutual effects exerted by the fullerene units to
the bis(2,9-diphenyl-1,10-phenanthroline)Cu(I) complex and
vice versa. The presence of a new absorption band in the
UV-vis spectrum of F-Cu-F strengthens the hypothesis
of strong electronic interactions between the inorganic core
and the peripheral organic units, which is also supported by
the short intercomponent distance derived by molecular
modeling (4.3 Å). Electronic intramolecular interactions have
been found in fullerene-metal cluster complexes50 but are
extremely rare in fullerene multicomponent arrays with
nonplanar metal complexes.9,51 In F-Cu-F, photoinduced
Compound 2. A 1.7 M t-BuLi solution in pentane (7.9 mL, 13.4
mmol) was added by syringe to an argon-flushed, stirred solution
of 1 (3.20 g, 6.1 mmol) in dry THF (60 mL) at -78 °C. After 2 h,
the resulting yellow solution was allowed to warm to 0 °C (over 1
(48) Gilbert, A.; Baggott, J. Essentials of Molecular Photochemistry;
Blackwell Scientific Publications: Oxford, U.K., 1991; p 176.
(49) Piotrowiak, P. In Electron Transfer in Chemistry; Balzani, V., Ed.;
Wiley-VCH: Weinheim, 2001; Vol. 1, p 215.
(51) Armaroli, N. Photochem. Photobiol. Sci. 2003, 2, 73.
(52) Liu, Y.; Li, Y.; Schanze, K. S. J. Photochem. Photobiol., C 2002, 3,
1.
(53) Yatabe, T.; Harbison, M. A.; Brand, J. D.; Wagner, M.; Mullen, K.;
Samori, P.; Rabe, J. P. J. Mater. Chem. 2000, 10, 1519.
(50) Lee, K.; Song, H.; Park, J. T. Acc. Chem. Res. 2003, 36, 78.
Inorganic Chemistry, Vol. 42, No. 26, 2003 8791

Rio et al.
h), and then added under argon to a degassed solution of 1,10-
phenanthroline (0.88 g, 4.9 mmol) in dry THF (20 mL) cooled to
0 °C (ice-water bath). The resulting dark red mixture was stirred
for 3 h, and then hydrolyzed with water. CH2Cl2 was added, and
the bright yellow organic layer decanted. The aqueous layer was
extracted with CH2Cl2 (3×), and the combined organic layers were
thereafter rearomatized by addition of MnO2 (30 g), dried (MgSO4),
and filtered; the filtrate was then evaporated to dryness. Column
chromatography on SiO2 (CH2Cl2) yielded 2 (2.38 g, 78%) as a
H), 1.10-1.60 (m, 36 H), 1.85 (m, 4 H), 2.21 (t, J ) 6 Hz, 2 H),
4.09 (t, J ) 6 Hz, 2 H), 4.25 (t, J ) 6 Hz, 2 H), 4.81 (d, J ) 6 Hz,
4 H), 7.04 (d, J ) 8 Hz, 1 H), 7.46 (t, J ) 2 Hz, 1 H), 7.76 (s, 2
H), 7.90 (dd, J ) 8 and 2 Hz, 1 H), 8.06 (d, J ) 8 Hz, 1 H), 8.11
(d, J ) 2 Hz, 1 H), 8.13 (d, J ) 8 Hz, 1 H), 8.25 (d, J ) 8 Hz, 1
H), 8.29 (d, J ) 8 Hz, 1 H), 8.35 (d, J ) 2 Hz, 2 H). 13C NMR (50
MHz, CDCl3): 14.1, 22.7, 26.1, 26.2, 29.4, 29.5, 29.7, 65.3, 69.2,
69.6, 113.3, 113.7, 119.9, 120.9, 125.3, 125.5, 126.2, 126.4, 127.5,
128.1, 132.4, 136.7, 139.9, 139.8, 141.8, 159.9, 149.4, 150.9, 156.1,
156.9. Anal. Calcd for C50H68O4N2: C 78.89, H 9.01, N 3.68, O
8.41. Found: C 78.70, H 9.13, N 3.64, O 8.71.
1
colorless glassy product. H NMR (200 MHz, CDCl3): 0.89 (t, J
) 6 Hz, 6 H), 1.10-1.50 (m, 36 H), 1.86 (m, 4 H), 4.09 (t, J ) 6
Hz, 2 H), 4.22 (t, J ) 6 Hz, 2 H), 7.03 (d, J ) 8 Hz, 1 H), 7.64
(dd, J ) 8 and 4 Hz, 1 H), 7.79 (AB, J ) 8 Hz, 2 H), 7.84 (dd, J
) 8 and 2 Hz, 1 H), 7.91 (d, J ) 2 Hz, 1 H), 8.06 (d, J ) 8 Hz,
1 H), 8.25 (d, J ) 8 Hz, 1 H), 8.29 (d, J ) 8 Hz, 1 H), 9.23 (dd,
J ) 4 and 2 Hz, 1 H). 13C NMR (50 MHz, CDCl3): 14.1, 22.7,
26.0, 26.1, 29.3, 29.4, 26.4, 29.7, 31.9, 69.2, 69.6, 113.5, 113.6,
120.3, 121.1, 122.8, 125.8, 126.4, 127.2, 129.0, 132.6, 136.0, 136.6,
146.0, 146.4, 149,4, 150.2, 150.7, 157.4. Anal. Calcd for C42H60O2N2‚
1/2H2O: C 79.56, H 9.70, N 4.42. Found: C 79.66, H 9.61, N
4.29.
Compound 8. DCC (100 mg, 4.8 mmol) was added to a stirred
solution of 6 (150 mg, 0.2 mmol), 7 (250 mg, 0.4 mmol), and
DMAP (10 mg) in CH2Cl2 (35 mL) at 0 °C. After 1 h, the mixture
was allowed to slowly warm to room temperature (within 1 h),
then stirred for 72 h, filtered, and evaporated. Column chromatog-
raphy on SiO2 (hexane/CH2Cl2 1:1) yielded 8 (270 mg, 73%) as a
colorless glassy product. IR (CH2Cl2): 1727, 1746 (CdO). 1H NMR
(200 MHz, CDCl3): 0.81 (m, 18 H), 1.10-1.60 (m, 108 H), 1.73
(m, 8 H), 1.88 (m, 4 H), 3.53 (s, 4 H), 3.88 (t, J ) 6 Hz, 8 H), 4.11
(t, J ) 6 Hz, 2 H), 4.20 (t, J ) 6 Hz, 2 H), 5.10 (s, 4 H), 5.35 (s,
4 H), 6.37 (t, J ) 2 Hz, 2 H), 6.44 (d, J ) 2 Hz, 4 H), 7.09 (d, J
) 8 Hz, 1 H), 7.48 (t, J ) 2 Hz, 1 H), 7.80 (s, 2 H), 8.00-8.15
(m, 4 H), 8.28 (d, J ) 7 Hz, 1 H), 8.31 (d, J ) 7 Hz, 1 H), 8.42
(d, J ) 2 Hz, 2 H). 13C NMR (50 MHz, CDCl3): 14.1, 22.7, 26.0,
26.1, 26.2, 29.2, 29.3, 29.4, 29.5, 29.6, 29.6, 29.6, 29.7, 31.9, 41.5,
66.9, 67.2, 69.0, 69.1, 69.6, 101.1, 106.3, 106.6, 113.5, 113.6, 119.8,
119.9, 121.1, 125.5, 126.4, 127.4, 127.5, 128.17, 128.7, 132.3,
136.3, 136.7, 137.0, 137.2, 140.4, 145.9, 149.2, 151.0, 155.5, 156.9,
160.4, 166.2. Anal. Calcd for C118H180N2O14: C 76.58, H 9.80, N
1.51. Found: C 76.78, H 9.90, N 1.49.
Compound 4. A mixture of TIPSCl (1.0 mL, 4.7 mmol),
imidazole (0.59 g, 8.6 mmol), and 3 (0.47 g, 31.71 mmol) in DMF
(15 mL) was stirred at room temperature for 48 h and evaporated.
The residue was taken up with Et2O, washed with brine, dried
(MgSO4), filtered, and evaporated. Column chromatography on SiO2
(CH2Cl2/hexane 1:1) yielded 4 (1.06 g, 93%) as a colorless oil. 1H
NMR (200 MHz, CDCl3): 0.90-1.20 (m, 42 H), 4.80 (s, 4 H),
7.40 (s, 3 H). 13C NMR (50 MHz, CDCl3): 12.0, 18.0, 64.4, 121.6,
122.2, 127.2, 143.8. Anal. Calcd for C26H49Si2O2Br: C 59.06, H
9.35. Found: C 58.81, H 9.41.
Compound 5. A 1.7 M t-BuLi solution in pentane (2.3 mL, 3.9
mmol) was added by syringe to an argon-flushed, stirred solution
of 4 (1.0 g, 1.9 mmol) in dry THF (15 mL) at -78 °C. After 2 h,
the resulting yellow solution was allowed to warm to 0 °C (over 1
h), and then added under argon to a degassed solution of 2 (0.98 g,
1.5 mmol) in dry THF (15 mL) cooled to 0 °C (ice-water bath).
The resulting dark red mixture was stirred for 5 h, and then
hydrolyzed with water. CH2Cl2 was added and the bright yellow
organic layer decanted. The aqueous layer was extracted with
CH2Cl2 (3×), and the combined organic layers were thereafter
rearomatized by addition of MnO2 (30 g), dried (MgSO4), and
filtered; the filtrate was then evaporated to dryness. Column
chromatography on SiO2 (CH2Cl2/0.5% MeOH) yielded 5 (1.23 g,
Compound 9. DBU (0.1 mL, 0.6 mmol) was added to a stirred
solution of C60 (98 mg, 0.1 mmol), I2 (80 mg, 0.3 mmol), and 8
(250 mg, 0.1 mmol) in toluene (200 mL) at room temperature. The
solution was stirred for 12 h at room temperature, filtered through
a short plug of SiO2 (toluene then CH2Cl2/MeOH 95:5), and
evaporated. Column chromatography on SiO2 (CH2Cl2) yielded 12
(130 mg, 38%) as a dark orange glassy product. IR (CH2Cl2): 1740
(CdO). 1H NMR (400 MHz, CDCl3): 0.85 (m, 18 H), 1.15-1.65
(m, 108 H), 1.75 (m, 8 H), 1.88 (m, 4 H), 3.84 (t, J ) 6 Hz, 8 H),
4.12 (t, J ) 6 Hz, 2 H), 4.27 (t, J ) 6 Hz, 2 H), 5.28 (d, J ) 12
Hz, 2 H), 5.29 (AB, J ) 12 Hz, 4 H), 6.01 (d, J ) 12 Hz, 2 H),
6.36 (t, J ) 2 Hz, 2 H), 6.49 (d, J ) 2 Hz, 4 H), 7.08 (d, J ) 8 Hz,
1 H), 7.63 (broad s, 1 H), 7.81 (AB, J ) 8 Hz, 2 H), 7.97 (dd, J
) 8 and 2 Hz,1 H), 8.11 (d, J ) 8 Hz, 1 H), 8.13 (d, J ) 2 Hz, 1
H), 8.20 (d, J ) 8 Hz, 1 H), 8.29 (d, J ) 8 Hz, 1 H), 8.36 (d, J )
8 Hz, 1 H), 8.39 (broad s, 2 H). 13C NMR (50 MHz, CDCl3): 9.9,
14.0, 14.1, 22.7, 25.3, 26.1, 26.3, 29.3, 29.4, 29.5, 29.6, 29.7, 30.1,
31.9, 36.9, 49.1, 66.9, 67.5, 68.1, 68.7, 69.1, 69.6, 70.6, 73.3, 101.6,
107.1, 113.3, 113.6, 119.9, 120.9, 124.2, 125.5, 125.6, 126.5, 127.6,
128.2, 132.4, 134.4, 135.8, 136.1, 136.6, 136.8, 137.0, 137.2, 137.9,
140.0, 141.0, 141.1, 142.3, 142.7, 143.2, 143.6, 143.7, 143.9, 144.2,
144.3, 144.6, 144.9, 145.2, 145.3, 145.6, 145.7, 146.1, 147.4, 148.7,
149.3, 150.9, 155.2, 156.9, 160.4, 162.6, 162.7. FAB-MS: 2568.1
(MH+, calcd for C178H177O14N2: 2568.3). Anal. Calcd for
1
75%) as a colorless glassy product. H NMR (200 MHz, CDCl3):
0.89 (t, J ) 6 Hz, 6 H), 1.10-1.60 (m, 78 H), 1.89 (m, 4 H), 4.10
(t, J ) 6 Hz, 2 H), 4.23 (t, J ) 6 Hz, 2 H), 5.02 (s, 4 H), 7.04 (d,
J ) 7 Hz, 1 H), 7.68 (d, J ) 2 Hz, 1 H), 7.78 (s, 2 H), 8.01 (d, J
) 2 Hz, 1 H), 8.08 (dd, J ) 7 and 2 Hz, 1 H), 8.13 (t, J ) 2 Hz,
1 H), 8.14 (d, J ) 7 Hz, 1 H), 8.23 (d, J ) 2 Hz, 2 H), 8.27 (d, J
) 7 Hz, 1 H), 8.31 (d, J ) 7 Hz, 1 H). 13C NMR (50 MHz,
CDCl3): 12.1, 14.1, 18.1, 22.7, 26.1, 26.2, 29.3, 29.4, 29.5, 29.5,
29.7, 31.9, 65.3, 69.2, 69.5, 113.4, 119.6, 120.2, 121.0, 123.6, 124.5,
125.6, 125.9, 127.5, 127.9, 132.4, 136.7, 136.8, 139.1, 142.2, 145.9,
149.1, 150.8, 156.6, 157.1. Anal. Calcd for C68H108O4N2‚H2O: C
78.85, H 10.71, N 2.71. Found: C 78.76, H 10.81, N 2.69.
Compound 6. A 1 M TBAF solution in THF (3.7 mL, 3.7 mmol)
was added to a stirred solution of 5 (1.18 g, 1.1 mmol) in THF (30
mL) at 0 °C. After 30 min, the reaction mixture was evaporated.
The residue was taken up with CH2Cl2, washed with water, dried
(MgSO4), filtered, and evaporated. Column chromatography on SiO2
(CH2Cl2/5% MeOH) yielded 6 (0.87 g, quantitative) as a colorless
glassy product. 1H NMR (200 MHz, CDCl3): 0.88 (t, J ) 7 Hz, 6
C
178H176O14N2: C 83.27, H 6.91, N 1.09. Found: C 83.10, H 6.90,
N 1.08.
Compound Cu. A solution of Cu(CH3CN)4.BF4 (16 mg, 0.05
mmol) in CH3CN (5 mL) was added under an argon atmosphere at
room temperature to a stirred, degassed solution of 5 (90 mg, 0.08
mmol) in CH2Cl2 (10 mL). The solution turned dark red instanta-
neously, indicating the formation of the complex. After 1 h, the
solvents were evaporated. Column chromatography on SiO2 (CH2Cl2/
8792 Inorganic Chemistry, Vol. 42, No. 26, 2003

Fullerene-Phenanthroline Cu(I) Complexes
5% MeOH) yielded Cu (92 mg, 96%) as a dark red glassy
compound. H NMR (200 MHz, CDCl3): 0.85-1.60 (m, 168 H),
The samples were placed in fluorimetric 1 cm path cuvettes and,
when necessary, purged from oxygen by four freeze-pump-thaw
cycles at 2 × 10-6 Torr. Absorption spectra were recorded with a
Perkin-Elmer λ40 spectrophotometer. Uncorrected emission spectra
were obtained with a Spex Fluorolog II spectrofluorimeter (continu-
ous 150 W Xe lamp), equipped with a Hamamatsu R-928
photomultiplier tube. The corrected spectra were obtained via a
calibration curve determined with a procedure described earlier.33
Fluorescence quantum yields obtained from spectra on an energy
scale (cm-1) were measured with the method described by Demas
and Crosby54 using as standards an air-equilibrated solution of
[Os(phen)3]2+ in acetonitrile (Φem ) 0.005).55
1
1.76 (m, 8 H), 3.20 (t, J ) 6 Hz, 4 H), 3.64 (t, J ) 6 Hz, 4 H),
3.95 (s, 8 H), 6.04 (d, J ) 8 Hz, 2 H), 6.95 (m, 6 H), 7.38 (m, 4
H), 7.82 (d, J ) 8 Hz, 2 H), 7.86 (d, J ) 8 Hz, 2 H), 7.96 (AB, J
) 8 Hz, 4 H), 8.44 (d, J ) 8 Hz, 4 H), 8.46 (d, J ) 8 Hz, 4 H).
13C NMR (50 MHz, CDCl3): 11.8, 14.1, 22.7, 25.7, 26.1, 29.1,
29.4, 29.5, 29.6, 29.7, 31.9, 64.2, 68.8, 69.1, 111.6, 113.5, 121.3,
123.9, 124.4, 124.5, 124.9, 126.0, 126.6, 127.7, 128.0, 131.1, 137.0,
138.1, 141.2, 143.3, 143.5, 147.8, 150.1, 156.4, 156.8. Anal. Calcd
for C136H216O8Si4N4CuBF4: C 71.09, H 9.47, N 2.44. Found: C
70.96, H 9.51, N 2.31.
Compound F-Cu-F. A solution of Cu(CH3CN)4‚BF4 (6 mg,
0.02 mmol) in CH3CN (2 mL) was added under an argon
atmosphere at room temperature to a stirred, degassed solution of
12 (80 mg, 0.03 mmol) in CH2Cl2 (10 mL). After 1 h, the solvents
were evaporated. Column chromatography on SiO2 (CH2Cl2)
yielded F-Cu-F (76 mg, 92%) as a dark red glassy compound.
1H NMR (400 MHz, CDCl3): 0.71-1.70 (m, 276 H), 3.19 (m, 2
H), 3.40 (m, 2 H), 3.64-3.90 (m, 20 H), 4.43 (d, J ) 12 Hz, 2 H),
4.57 (d, J ) 12 Hz, 2 H), 4.99 (d, J ) 12 Hz, 2 H), 5.21 (d, J )
12 Hz, 2 H), 5.30 (d, J ) 12 Hz, 2 H), 5.46 (d, J ) 12 Hz, 2 H),
5.58 (d, J ) 12 Hz, 4 H), 6.28 (t, J ) 2 Hz, 4 H), 6.37 (d, J ) 8
Hz, 2 H), 6.44 (d, J ) 2 Hz, 4 H), 6.47 (d, J ) 2 Hz, 4 H), 6.50
(m, 2 H), 7.20 (broad s, 2 H), 7.30 (broad s, 2 H), 7.34 (dd, J ) 8
and 2 Hz, 2 H), 7.38 (d, J ) 2 Hz, 2 H), 7.85 (d, J ) 8 Hz, 2 H),
8.17 (d, J ) 8 Hz, 2 H), 8.19 (AB, J ) 8 Hz, 4 H), 8.55 (d, J )
8 Hz, 2 H), 8.56 (d, J ) 8 Hz, 2 H). 13C NMR (50 MHz, CDCl3):
14.1, 22.7, 26.1, 29.3, 29.4, 26.4, 29.7, 31.9, 50.1, 65.6, 67.0, 68.1,
68.7, 68.9, 69.3, 70.7, 101.9, 107.0, 107.2, 112.6, 127.8, 128.2,
131.4, 135.5, 135.8, 136.2, 136.4, 136.5, 137.8, 139.6, 141.1, 141.2,
142.2, 142.7, 142.8, 143.3, 143.6, 143.8, 143.9, 144.2, 144.3, 144.7,
144.9, 145.3, 145.5, 145.7, 145.8, 146.0, 146.2, 147.5, 148.5, 148.9,
149.3, 150.4, 156.1, 156.5, 160.3, 160.4, 162.5, 162.6, 162.7.
MALDI-TOF-MS: 5198.6 ([M - BF4-]+, calcd for C356H352O28-
N4Cu: 5198.3). Anal. Calcd for C356H352O28N4CuBF4: C 80.91,
H 6.71, N 1.06. Found: C 80.81, H 6.93, N 1.02.
The steady-state IR luminescence spectra were obtained with
an Edinburgh FLS920 spectrometer equipped with Hamamatsu
R5509-72 supercooled photomultiplier tube (193 K) and a TM300
emission monochromator with NIR grating blazed at 1000 nm. An
Edinburgh Xe900 450 W xenon arc amp was used as light source.
The determination of the relative yields of singlet oxygen sensitiza-
tion for F and Cu-F was obtained by monitoring the intensity of
the steady-state singlet oxygen luminescence at 1270 nm.56 Solu-
tions with the same optical density and solvent (CH2Cl2) were used,
making corrections due to these factors unnecessary.56
Emission lifetimes in the nanosecond and picosecond time scale
were determined with an Edinburgh FLS920 time correlated single
photon counting spectrometer. The light source is a Hamamatsu
PLP-02 SLDH-041 laser diode working at 1 MHz repetition rate
(λexc ) 405 nm, 40 ps pulse width); the detector was a red-sensitive
Peltier cooled Hamamatsu R-928 photomultiplier tube. The time
resolution of the system is 30 ps after deconvolution.
The fullerene triplet lifetimes were obtained by using the second
harmonic (532 nm) of a Nd:YAG laser (JK Lasers) with 20 ns
pulse and 1-2 mJ of energy per pulse. The details on the flash-
photolysis system are reported elsewhere.57
Experimental uncertainties are estimated to be (8% for lifetime
determinations, (20% for emission quantum yields, (5% for
relative emission intensities in the NIR, and (1 nm and (5 nm
for absorption and emission peaks, respectively.
Molecular Modeling. The Molecular Dynamics studies have
been performed on SGI Origin 200 and Octane2 workstations using
the Discover 3 software from Accelrys (www.accelrys.com) with
the pcff force field. The previously minimized structures were
allowed to equilibrate for 500 ps at a 300 K isotherm by the MD
simulation (in the NVT ensemble with a time step of 1 fs).
Electrochemistry. The electrochemical studies were carried out
in CH2Cl2 (Fluka, spectroscopic grade used without further purifica-
tion) containing 0.1 M Bu4NPF6 (Merck, electrochemical grade)
as supporting electrolyte. A classical three electrode cell was
connected to a computerized electrochemical device Autolab (Eco
Chemie B. V. Utrecht, Holland) driven by GPSE software running
on a personal computer. The working electrode was a glassy carbon
disk (3 mm in diameter), the auxiliary electrode a platinum wire
and the reference electrode an aqueous Ag/AgCl reference electrode.
All potentials are given versus Fc/Fc+ used as internal standard.
Photophysical Measurements. The spectroscopic investigations
were carried out in CH2Cl2 (Carlo Erba, spectrofluorimetric grade).
Acknowledgment. This research was supported by the
CNR, the CNRS, the French Ministry of Research (ACI
Jeunes Chercheurs), and the EU for the RTN Contract
HPRN-CT-2002-00171. Y.R. thanks the Direction de la
Recherche of the French Ministry of Research and G.A. the
Spinner Agency (Regione Emilia-Romagna, Italy) for their
fellowships. We further thank L. Oswald for technical help,
M. Schmitt for high field NMR spectra, and J.-M. Strub for
MS measurements.
IC035146O
(54) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991.
(55) Kober, E. M.; Caspar, J. V.; Lumpkin, R. S.; Meyer, T. J. J. Phys.
Chem. 1986, 90, 3722.
(56) Wirp, C.; Gusten, H.; Brauer, H. D. Ber. Bunsen-Ges. Phys. Chem.
1996, 100, 1217.
(57) Flamigni, L. J. Phys. Chem. 1992, 96, 3331.
Inorganic Chemistry, Vol. 42, No. 26, 2003 8793