This, together with a complete lack of photosensitized 1O2
generation typical for porphyrins,6 C60 and many of its
derivatives,7 suggests an efficient photoinduced energy transfer
from the porphyrin to the fullerene.
Detailed comparative investigations on electron and energy
transfer processes of 3 and related systems including those with
different central metals and additional addends like electron
acceptors and dendrimers are currently under way.
We thank the ‘Volkswagen Stiftung’ for financial support.
Notes and references
† Detailed procedures for the synthesis and spectroscopic data of 1 and 2
will be reported elsewhere.
‡ Spectroscopic data for 3: 1H NMR (400 MHz, CDCl3, 25 °C) d 8.82–8.75
(8 H, m), 8.27 (2 H, d), 8.19 (2 H, d), 7.93 (2 H, d), 7.80–7.64 (10 H, m),
7.37 (2 H, d), 5.15 (2 H, dt), 4.77 (2 H, dt), 4.49 (4 H, t), 3.93 (6 H, s); 13
C
Fig. 2 Electronic absorption spectra of 2 (dashed line) and 3 in CH2Cl2 at c
= 3.5 3 1026 mol dm23
NMR (100.5 MHz, CDCl3, 25 °C) d 163.53, 163.49, 156.57, 150.19,
150.08, 150.04, 147.91, 145.07, 144.98, 144.67, 144.60, 144.03, 143.47,
143.43, 142.81, 142.74, 142.63, 142.33, 142.08, 142.00, 141.82, 141.62,
141.51, 141.44, 141.38, 141.33, 141.16, 140.85, 140.74, 139.96, 139.59,
138.44, 138.41, 138.00, 137.95, 137.91, 134.40, 134.15, 132.08, 132.03,
131.79, 131.74, 127.72, 127.41, 126.77, 126.55, 126.42, 125.27, 121.40,
120.43, 115.17, 70.72, 70.06, 67.30, 65.11, 53.87, 49.16; UV/VIS
lmax(CH2Cl2)/nm (e/dm3 mol21 cm21) 240 (109000), 260 (110200), 315
(50900), 407 (sh, 38400), 429 (273900), 552 (26200); FT-IR (KBr) n/cm21
3053, 3021, 2950, 2922, 2867, 1750, 1596, 1576, 1480, 1433, 1237, 1108,
1069, 1003, 796, 702, 527; FAB-MS m/z 1714 (M+).
.
In the MM+ minimized structure of 3 (Fig. 1) the average
distance between the four pyrrole N atoms and the Zn atom of
the macrocycle and their nearest neighbours on the fullerene
moiety is 3.4 Å. The shortest distance between the Zn atom and
a fullerene C atom is only 3.0 Å and therefore even shorter than
the interplanar distance in graphite.
Electroanalytical investigations on 3 using cyclic voltam-
metry and differential pulse voltammetry reveal two oxidative
and six reductive electron transfer processes which are also
present in either the parent porphyrin 2 or the trans-2-bis(di-
ethylmalonate) 4.5 Only slight shifts, for example of 16 mV, to
a more negative potential for the first porphyrin oxidation are
detected.§ Compared with 2 the Soret- and Q-bands of 3 show
a bathochromic shift and decrease of the molar absorption
coefficients indicating a considerable photoinduced interaction
between the two chromophores (Fig. 2). Also photophysical
analyses of 3 reflect the close proximity and stacking interaction
between the corresponding p-systems. Time-dependent lumi-
nescence measurements reveal a complete quenching of the
typical porphyrin fluorescence with a maximum at about 500
nm which is present in the monoadduct dyad 5.1 However, a
1
2
1
§ Formal potentials (E°/V): 2 Eox = 0.273, Eox = 0.712, Ered = 21.898,
2
1
2
1
2
Ered = 22.234; 3 Eox = 0.257, Eox = 0.712, Ered = 21.156, Ered
6
=
=
=
3
4
5
21.487, Ered = 21.741, Ered = 21.898, Ered = 22.085, Ered
4
1
2
3
22.300; 4 Ered = 21.102, Ered = 21.467, Ered = 21.910, Ered
5
21.987, Ered = 22.325. The redox potentials E° were determined from
r
cyclic voltammograms (mean value of corresponding Ep and Ep°) and
differential pulse voltammograms in 0.22 mmolar solutions of 3 in CH2Cl2–
NBu4PF6 (0.1
M) at Pt/Ir using a Ag–AgClO4 (0.01 M)/NBu4PF6 (0.01
M
)/acetonitrile reference electrode and were recalculated against internal
Fc/Fc+ (DV = 0.21 V).
Note added in proof.
A
macrocyclic trans-1 fullerene–porphyrin
conjugate was recently obtained by F. Diederich (personal communica-
tion).
1 E. Dietel, A. Hirsch, J. Zhou and A. Rieker, J. Chem. Soc., Perkin Trans.
2, 1998, 1357.
2 J.-F. Nierengarten, V. Gramlich, F. Cardullo and F. Diederich, Angew.
Chem., 1996, 108, 2242.
3 F. Li, K. Yang, J. S. Tyhonas, K. A. MacCrum and J. S. Lindsey,
Tetrahedron, 1997, 53, 12339.
4 (a) C. Bingel, Chem. Ber., 1993, 126, 1957; (b) C. Bingel, presentation at
the meeting ‘New Perspectives in Fullerene Chemistry and Physics’,
October 10–12, 1994, Rome.
O
O
Ph
O
N
O
OMe
N
Zn
N
N
Ph
Ph
5 F. Djojo, A. Herzog, I. Lamparth, F. Hampel and A. Hirsch, Chem. Eur.
J., 1996, 2, 1537.
6 (a) B. Röder, Biophys. Chem., 1990, 35, 303; (b) S. Oelkers, SPIE Proc.,
1994, 2325, 116; (c) B. Röder, C. Zimmermann and R. Herter, SPIE
Proc., 1994, 2325, 80; (d) W. Spiller and S. Hackbarth, J. Porphyrins
Phthalocyanines, 1998, 2, 145.
7 J. W. Arbogast, A. P. Darmanyan, C. S. Foote, Y. Rubin, F. Diederich,
M. M. Alvarez, S. J. Anz and R. L. Whetten, J. Phys. Chem., 1991, 95,
11.
5
new luminescence band at 850 nm was found. The lumines-
cence intensity increases with decreasing temperature. The
luminescence decay can be fitted double exponentially with the
decay times t1 = 2.84 ns and t2 = 0.42 ns. The relative
amplitudes of the decay times were calculated to be 2.12:1.
Received in Cambridge, UK, 29th May 1998; 8/04047H
1982
Chem. Commun., 1998