Porphyrinic dyads and triads assembled around iridium(III) bis-terpyridine: Photoinduced electron transfer processes

Article abstract of DOI:10.1021/ic010416t

Multicomponent arrays based on a central iridium(III) bis-terpyridine complex (Ir) used as assembling metal and free-base, zinc(II) or gold(III) tetraaryl-porphyrins (PH₂, PZn, PAu) have been designed to generate intramolecular photoinduced cha

Full text of DOI:10.1021/ic010416t

Inorg. Chem. 2001, 40, 5507-5517
5507
Porphyrinic Dyads and Triads Assembled around Iridium(III) Bis-terpyridine:
Photoinduced Electron Transfer Processes
Isabelle M. Dixon,§ Jean-Paul Collin,*,§ Jean-Pierre Sauvage,*,§ and Lucia Flamigni*,‡
Laboratoire de Chimie Organo-Mine´rale, UMR 7513 CNRS, Universite´ Louis Pasteur, Institut Le Bel,
4, rue Blaise Pascal, 67070 Strasbourg, France, and Istituto FRAE-CNR, Via P. Gobetti 101,
40129 Bologna, Italy
ReceiVed April 17, 2001
Multicomponent arrays based on a central iridium(III) bis-terpyridine complex (Ir) used as assembling metal and
free-base, zinc(II) or gold(III) tetraaryl-porphyrins (PH2, PZn, PAu) have been designed to generate intramolecular
photoinduced charge separation. The rigid dyads PH2-Ir, PZn-Ir, PAu-Ir, and the rigid and linear triads
PH2-Ir-PAu, PZn-Ir-PAu, as well as the individual components Ir, PH2, PZn, PAu have been synthesized
and characterized by various techniques including electrochemistry. Their photophysical properties either in
acetonitrile or in dichloromethane and toluene have been determined by steady-state and time-resolved methods.
In acetonitrile, excitation of the triad PH2-Ir-PAu leads to a charge separation with an efficiency of 0.5 and a
resulting charge-separated (CS) state with a lifetime of 3.5 ns. A low-lying triplet localized on PH2 and the
presence of the heavy Ir(III) ion offer the CS state an alternative deactivation path through the triplet state. The
behavior of the triad PZn-Ir-PAu in dichloromethane is rather different from that of PH2-Ir-PAu in acetonitrile
since the primary electron transfer to yield PZn+-Ir--PAu is not followed by a secondary electron transfer. In
this solvent, both unfavorable thermodynamic and electronic parameters contribute to the inefficiency of the
second electron-transfer reaction. In contrast, in toluene solutions, the triad PZn-Ir-PAu attains a CS state
with a unitary yield and a lifetime of 450 ns. These differences can be understood in terms of ground-state charge-
transfer interactions as well as different stabilization of the intermediate and final CS states by solvent.
Introduction
chromophore and primary electron donor, while a gold(III)-
metalated porphyrin serves as electron acceptor.4 In a modular
Artificial photosynthesis has been a very active area of
research for more than 3 decades, with the elaboration and study
of models of natural systems or of synthetic devices aimed at
converting light energy into chemical or electrical energy. An
important source of inspiration has been the disclosure of the
structure of bacterial photosynthetic Reaction Centers (RC).1
In the past 20 years, many light-triggered charge separation
molecular systems have been designed to mimick the processes
taking place in the RC.2 Porphyrins have been used as
components of such devices since the very beginning, due to
their resemblance with natural components and due to the fact
that the redox and spectroscopic properties of these chro-
mophores can be widely varied by the use of electroactive or
bulky substituents and by their coordination to different transi-
tion metals.3
strategy,5 the electro-active components are assembled around
an octahedral transition metal complex of the bis-terpyridine
type, allowing the construction of linear triads with fixed
intercomponent distances. Ruthenium(II) bis-terpyridine is a
well-known complex6 which can act as electron relay between
two porphyrins.7 A detailed photophysical study on the systems
based on Ru(II) bis-terpyridine has evidenced that the presence
of a relatively low-lying excited-state allows parasitic energy
transfer to take place between the chromophore in its excited
state and the central metal complex.8 Therefore ruthenium has
to be replaced by another transition metal in order to prevent
the undesired energy transfer.
An iridium(III) bis-terpyridine unit was selected on the basis
of its photophysical9,10 and electrochemical properties,10 and on
In the models elaborated by the Strasbourg group in the course
of the past decade, a free-base or zinc(II) porphyrin is used as
(3) The porphyrin handbook; Kadish, K. M.; Smith, K. M., Guilard, R.
Eds, Academic Press, 2000.
* To whom correspondence should be sent. E-mail: sauvage@chimie.u-
strasbg.fr; flamigni@frae.bo.cnr.it.
(4) Heitz, V.; Chardon-Noblat, S.; Sauvage, J.-P. Tetrahedron Lett. 1991,
32, 197.
§ Universite´ Louis Pasteur.
(5) Harriman, A.; Sauvage, J.-P. Chem. Soc. ReV. 1996, 41.
(6) Maestri, M.; Armaroli, N.;. Balzani, V.; Constable, E. C.; Cargill
Thompson, A. M. W. Inorg. Chem. 1995, 34, 2759. Sauvage, J.-P.;
Collin, J.-P.; Chambron, J.-C.; Guillerez, S.; Coudret, C.; Balzani, V.;
Barigelletti, F.; De Cola, L.; Flamigni, L. Chem. ReV. 1994, 94, 993.
Collin, J.-P.; Gavin˜a, P.; Heitz, V.; Sauvage, J.-P. Eur. J. Inorg. Chem.
1998, 1.
‡ Istituto FRAE-CNR.
(1) Deisenhofer, J.; Epp, O.; Miki, K.; Huber, R.; Michel, H. Nature 1985,
318, 618. Deisenhofer, J.; Michel, H. EMBO J. 1989, 8, 2149. Huber,
R. Angew. Chem., Int. Ed. Engl. 1989, 101, 849; 28, 848.
(2) Gust, D.; Moore, T. A.; Moore, A. L. Acc. Chem. Res. 1993, 26, 198
and references therein. Wasielewski, M. R. Chem. ReV. 1992, 92, 435
and references therein. Kurreck, H.; Huber, M. Angew. Chem., Int.
Ed. Engl. 1995, 107, 929; 34, 849. Osuka, A.; Nakajima, S.; Okada,
T.; Taniguchi, S.; Nozaki, K.; Ohno, T.; Yamazaki, I.; Nishimura,
Y.; Mataga, N. Angew. Chem., Int. Ed. Engl. 1996, 108, 98; 35, 92.
Imahori, H.; Yamada, K.; Hasegawa, M.; Taniguchi, S.; Okada, T.;
Sakata, Y. Angew. Chem., Int. Ed. Engl. 1997, 109, 2740; 36, 2626.
Wiederrecht, G. P.; Niemczyk, M. P.; Svec, W. A.; Wasielewski, M.
R. J. Am. Chem. Soc. 1996, 118, 81 and references therein.
(7) Harriman, A.; Odobel, F.; Sauvage, J.-P. J. Am. Chem. Soc. 1995,
117, 9461.
(8) (a) Flamigni, L.; Barigelletti, F.; Armaroli, N.; Collin, J.-P.; Sauvage,
J.-P.; Williams, J. A. G. Chem. Eur. J. 1998, 4, 1744. (b) Flamigni,
L.; Barigelletti, F.; Armaroli, N.; Ventura, B.; Collin, J.-P.; Sauvage,
J.-P.; Williams, J. A. G. Inorg. Chem. 1999, 38, 661.
(9) Ayala, N. P.; Flynn, C. M., Jr.; Sacksteder, L. A.; Demas, J. N.;
DeGraff, B. A. J. Am. Chem. Soc. 1990, 112, 3837.
10.1021/ic010416t CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/06/2001

5508 Inorganic Chemistry, Vol. 40, No. 22, 2001
Chart 1. Structures of the Arrays and of the Modelsa
Dixon et al.
Chart 2a
a The lozenges are porphyrins and the arcs of circle represent
terpyridine coordinating sites.
The unsymmetrical porphyrin 1 bearing one terpy substituent
was prepared following a Suzuki coupling procedure between
a porphyrin bearing a boronic ester (9) and 4′-bromo-2,2′:6′,2′′-
terpyridine (Br-terpy).13 Selective and quantitative protection
of the boronic acid site of 4-formylphenylboronic acid with 2,2-
dimethylpropane-1,3-diol gave the corresponding boronic ester
8 in quantitative yield. This boronic ester bearing an aldehydic
function was used in the synthesis of porphyrin 9 under
Lindsey’s conditions.14 It was reacted with pyrrole and 3,5-
ditertiobutylbenzaldehyde15 in chloroform for 1 h, under Lewis-
acid catalysis by boron trifluoride etherate (Chart 3). The
hereafter formed porphyrinogen was irreversibly oxidized by
chloranil. The isolated yield of the mono-boronic porphyrin
(A3B) was limited to 4% by the difficulty to separate it by
column chromatography from the trans bis (boronic) porphyrin
(A2B2), identified by 1H NMR. This is due to their very similar
polarities and molecular weights. However is it possible to make
the Suzuki coupling with Br-terpy on this mixture of A3B and
A2B2-types porphyrins, respectively forming the mono- and bis-
terpy substituted porphyrins, which are easier to separate. Doing
this, we evaluated the yield of formation of A3B porphyrin to
about 10%, which is usual for a statistical synthesis of
unsymmetrical porphyrins.
a Some of the compounds have a double nomenclature, the numbers
being used in the synthetic part.
the basis of what one can expect from a third-row transition
metal, in terms of the kinetic inertness of the coordination sphere
which allows the construction of unsymmetrical arrays. Iridium-
(III) polyimine complexes have highly energetic excited states11
which avoid the risk of energy transfer from a porphyrinic
component, and a relatively good ability to accept electrons.
Following relatively mild reaction conditions developed re-
cently,10 porphyrinic triads PH2-Ir-PAu and PZn-Ir-PAu12
were synthesized. The schematic structures of the triads and
relevant dyads and reference compounds are represented in Chart
1. Their synthesis and the photophysical studies either in
acetonitrile or in dichloromethane and toluene will be reported
in this paper.
Results and Discussion
Design and Synthetic Strategy. Chart 2 summarizes (a) the
principle of photoinduced electron tranfer processes in the triads
and (b) the strategy used in their synthesis.
The unsymmetrical porphyrin 1 (Chart 3) illustrates the strong
point of the modular approach employed here: once the ligand
1 is available in sufficient quantity, the dyads and triads are
obtained by playing in the right order with the coordination
chemistry of zinc(II), iridium(III) and gold(III).
A Suzuki coupling16 reaction of porphyrin 9 with Br-terpy
in the presence of sodium carbonate and palladium tetrakis-
triphenylphosphine allowed the formation of terpy-substituted
porphyrin 1. It was isolated by chromatography on alumina in
79% yield.
(10) Collin, J.-P.; Dixon, I. M.; Sauvage, J.-P.; Williams, J. A. G.;
Barigelletti, F.; Flamigni, L. J. Am. Chem. Soc. 1999, 121, 5009.
(11) Dixon, I. M.; Collin, J.-P.; Sauvage, J.-P.; Flamigni, L.; Encinas, S.;
Barigelletti, F. Chem. Soc. ReV. 2000, 29, 385.
(12) Dixon, I. M.; Collin, J.-P.; Sauvage, J.-P.; Barigelletti, F.; Flamigni,
L. Angew. Chem., Int. Ed. 2000, 39, 1292; Flamigni, L, Dixon, I. M.,
Collin, J.-P. Sauvage J.-P. J. Chem. Soc. Chem. Commun. 2000, 2479.
(13) Whittle, B.; Batten, S. R.; Jeffery, J. C.; Rees, L. H.; Ward, M. D. J
Chem. Soc., Dalton Trans. 1996, 4249.
(14) Lee, C.-H.; Lindsey, J. S. Tetrahedron 1994, 50, 11427.
(15) Newman, M. S.; Lee, L. F. J. Org. Chem. 1972, 37, 4448.
(16) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Comm. 1981, 11, 513.

Porphyrinic Dyads and Triads
Inorganic Chemistry, Vol. 40, No. 22, 2001 5509
Chart 3
Chart 4
Table 1. Cyclic Voltammetry Data of the Dyads and Reference
Compounds in CH3CN and CH2Cl2
Metalation of 1 with gold(III) was achieved by reaction of
the free-base porphyrin and potassium tetrachloroaurate to give
the corresponding AuIII porphyrin 2+ in 89% yield.17 (Chart 3).
The gold(III) dyad 34+ was prepared by reaction of porphyrin
2+ with previously prepared Ir(Ar-terpy)Cl3,10 by heating them
in ethylene glycol under argon for 3 h at 140 °C. 34+ was
isolated in 96% yield after chromatography on silica gel (Chart
4).
Eox1/2 (V vs SCE)
Ered1/2 (V vs SCE)
P
2+/P+ P+/P terpy/terpy- terpy-/terpy2- P/P- P-/P2-
CH3CN
-0.78 -0.94
Ir
PAu
PH2-Ir
-0.63 -1.02
0.96
-0.78 -0.94 -1.17
PZn-Ir 0.95 0.62 (irr) -0.79 -0.95
In the case of the free-base or zinc porphyrin, the first
coordination of iridium was achieved on the porphyrin-
substituted terpy itself. The trichloride precursor 10 was obtained
in 58% isolated yield following the conditions developed for
highly soluble terpys,10 i.e., by reaction of porphyrin 1 with
IrCl3‚4H2O in refluxing ethanol for 2h30. It is remarkable that
metalation is highly selective: Au(III) reacts with the porphyrin
site only whereas Ir(III) leads exclusively to the terpy complex.
The free-base dyad 43+ was prepared by reacting precursor 10
with Ar-tpy in refluxing ethylene glycol under argon for 25 min,
and was isolated in 66% yield on a 40-mg scale. The free-base
triad 64+ (Chart 4) was obtained by reaction of the same
precursor 10 with gold(III) porphyrin 2+ in refluxing ethylene
glycol under argon for 25 min.
PAu-Ir
-0.75 -0.91 -0.59 -1.11
CH2Cl2
PH2
PZn
PAu
PH2-Ir
PZn-Ir
PAu-Ir
0.86
0.68
-1.28
1.09
1.08
-0.70
-1.24
-1.23
0.88
0.68
-0.72
-0.71
-0.72
-0.88
-0.87
-0.87
-0.66
Electrochemistry
The redox characteristics of the dyads PH2-Ir, PAu-Ir,
PZn-Ir, and the reference compounds Ir, PAu, PH2, and PZn
(see Chart 1) examined by cyclic voltammetry in CH3CN and
CH2Cl2 are reported in Table 1. Due to the insolubility of the
reference compounds PH2 and PZn in CH3CN their redox
potentials are given only in CH2Cl2. Monoelectronic waves
observed for all redox processes were easily assigned to their
individual components. As in the case of similar dyads involving
tetraarylporphyrin and Rh(III) terpyridine complexes18 the redox
6
4+ was isolated on the same scale as the dyad in 33% yield,
as well as the bis-gold PAu-Ir-PAu array. The zinc series
was obtained by metalation of the free-base dyad and triad to
give the zinc dyad PZn-Ir and the zinc triad PZn-Ir-PAu
in 80-100% yield.
(17) Jamin, M. E.; Iwamoto, R. T. Inorg. Chim. Acta 1978, 27, 135.
(18) Odobel, F. Thesis, Strasbourg, 1994.

5510 Inorganic Chemistry, Vol. 40, No. 22, 2001
Dixon et al.
Table 3. Transient Absorption Data for PH2-Ir-PAu and Models
at 298 K in Nitriles:a Excitation at 532 nm except Otherwise
Specified
state
τ (ns)
Φb
PH2
PAu
PH2-Ir
3PH2
3PAu
3PH2
200000
1.4
8000
0.075
1.4
2000
1.4
0.04
3.5
0.6c
1c
0.1
1
1
0.6
1
1
PH2+-Ir-
3PAu
PAu-Ir
PH2-Ir-PAu
3PH2
3PAu
PH2+-Ir--PAud
PH2+-Ir-PAu-d
0.5
Figure 1. Molar absorption coefficients of the models PH2 (___), Ir
(‚‚‚), PAu (-‚-‚-), and of the triad PH2-Ir-PAu (___) in acetonitrile
solutions. In the inset the region of the porphyrin Q-bands is expanded.
a Acetonitrile except for PH2, dissolved in a mixture of acetonitrile/
butyronitrile (2:1). b Yields calculated on the basis of the photons
absorbed by the PZn (or PAu) unit only. At 532 nm the partition of
photons in the triad is: 25% on PH2, 75% on PAu. In the dyads, the
porphyrins absorb 100% light upon excitation in the visible. c From
ref 31. d Selective excitation of PH2 at 598 nm.
Table 2. Luminescence Properties and Energy Levels of the
Excited States of PH2-Ir-PAu and Models in Nitrilesa
298 K
77 K
state λmax (nm) τ (ns) Φfluo
λ
max (nm) τ (µs) E (eV)b
Irc
PH2
3Ir
506
652
2400d 0.029d 494
39
2.51
1.92
1.47f
e
1PH2
3PH2
3PAu
1PH2
3PAu
8.3 0.15f
647
840f
710
648
705
650
0.011
6000f
PAug
10; 100 1.75
0.012 1.91
16; 100 1.76
0.011 1.91
PH2-Ire
PAu-Irg
652
652
0.03 0.002
0.03 0.001
PH2-Ir-PAue 1PH2
3PAu
706g 20; 150g 1.75g
a
Acetonitrile at 298 K except for PH2, dissolved in a mixture of
b
acetonitrile/butyronitrile (2:1), butyronitrile at 77 K. Energy levels
c
from the emission maxima at 77 K. Excitation at 355 nm, from ref
10. d Air equilibrated. Excitation at 592 nm for steady state and at
e
f
g
532 nm for time resolved. From ref 31. Excitation at 405 nm for
steady state and 532 nm for time-resolved experiments.
potentials observed are almost identical in the dyads and in the
reference compounds. As a consequence, only weak interactions
are expected between the components in the dyads and in the
triads. Therefore localized description of the individual subunits
could be used to predict exergonicity of energy and electron-
transfer reactions. Due to the generally small shift observed
between the redox potentials of arrays and the reference
compounds it is difficult to conclude about ground-state donor-
acceptor interactions. A more sensitive method such as electronic
spectroscopy could permit a better detection (vide infra).
Figure 2. Transient absorbance changes upon selective excitation of
the PH2 unit by a 35 ps laser pulse. (a) Excitation at 532 nm (3 mJ) of
acetonitrile solutions of PH2-Ir, the inset shows the decay at 620 nm
and the instrumental response (- - -). (b) Excitation at 598 nm (0.5 mJ)
of acetonitrile solutions of PH2-Ir-PAu, the inset shows the biex-
ponential decay at 620 nm.
biexponential decay of the gold porphyrin triplet of 10-20 µs
and 100-150 µs. Table 2 summarizes the luminescence
properties at 298 and 77 K for the arrays and the pertinent
models together with the energy levels of the emitting states,
derived from the emission maxima at 77 K.
Photophysics
PH2-Ir-PAu Triad and Related Models in Acetonitrile.
Ground-State Absorption and Luminescence. The absorption
spectrum of acetonitrile solutions of PH2-Ir-PAu is reported
in Figure 1 with those of the model components PH2, PAu,
and Ir. At 298 K, the luminescence intensity of the free base
porphyrin is quenched in acetonitrile solutions of PH2-Ir and
of PH2-Ir-PAu to about 99% and time-resolved emission
experiments indicate that the lifetime of the singlet excited state
of the free base is reduced from 8.3 ns to 30 ps in PH2-Ir and
PH2-Ir-PAu (Table 2). The quenching does not occur in a
butyronitrile glass at 77 K, where the lifetime of the model
porphyrin, 11 ns, is maintained in both arrays (Table 2). The
gold porphyrin does not emit at room temperature because of a
very short singlet lifetime; at 77 K the phosphorescence of the
triplet can be detected as a steady-state spectrum both in the
model and in the arrays PAu-Ir and PH2-Ir-PAu. Deter-
mination by time-resolved techniques (λexc) 532 nm) indicate
that the phosphorescence of the gold porphyrin is present
unquenched in both arrays at 77 K, displaying the typical
Time-Resolved Absorption. Transient absorbance determi-
nations at ambient temperature (λexc ) 532 nm) in acetonitrile
solutions of PH2-Ir-PAu and PAu-Ir allowed to detect the
triplet state of the gold porphyrin which decays with a lifetime
of 1.4 ns, typical of the model PAu in acetonitrile. An evaluation
of the yield of formation of the gold porphyrin triplet, by taking
into consideration only the photons absorbed by the gold
porphyrin unit (calculated according to the ratio of the molar
absorption coefficient of the components at 532 nm), gives a
value identical to that of the model PAu, i.e., 1 (Table 3).
Excitation at 532 nm of the dyad PH2-Ir produces a selective
excitation of the free-base porphyrin moiety. The resulting
spectrum, Figure 2a, displays a maximum at 470 nm and a broad
band in the region 600-700 nm with superimposed bleaching
features of the Q-bands of the porphyrin at 645 nm. Its formation
occurs during the laser pulse and is complete at the end of the

Porphyrinic Dyads and Triads
Inorganic Chemistry, Vol. 40, No. 22, 2001 5511
The cases of the dyads will be discussed first. Upon excitation
of PH2-Ir in the visible, selective excitation to the singlet
1
excited-state localized on the free-base porphyrin, PH2-Ir,
occurs. This state decays with a rate of 3.3 × 1010 s-1, as
determined in a time-resolved luminescence experiment, by a
process which we assign to an electron-transfer reaction to form
the CS state PH2+-Ir-, where the transferred electron is
localized on the terpy ligand of the complex. The absorption
spectrum detected at the end of a 35 ps pulse and displayed in
Figure 2a, consistent with the spectrum of a free-base porphyrin
cation,2,7 is assigned to this CS state. Its decay occurs with an
overall rate of 1.33 × 1010 s-1, in part to the underlying triplet
state localized on the free base porphyrin, 3PH2-Ir, and in part
to the ground state. The yield of 3PH2-Ir, 0.1, allows to derive
the rate of the individual deactivation processes which are
calculated to be 1.3 × 109 s-1 and 1.2 × 1010 s-1 for the
deactivation to the triplet and to the ground state respectively
(Figure 3a). In the case of the other dyad PAu-Ir (Figure 3b)
the interpretation is straightforward: upon excitation in the
visible only the gold porphyrin unit is excited and it behaves
exactly as the model, irrespective of the appended iridium
complex unit. This is expected since no energy transfer nor
electron transfer (see Table 1 and Table 2), are feasible.
Inspection of Figure 3c, where the levels of the triad PH2-
Ir-PAu are reported, shows that in addition to the states already
considered for the dyads, a further charge-separated state is
present, corresponding to the oxidation of the PH2 unit and the
reduction of the PAu unit, PH2+-Ir-PAu-. This state is lower
in energy than the CS state already seen in the case of the dyad,
with the hole localized on the free base and the electron localized
on the terpy of the iridium complex, PH2+-Ir--PAu, and can
be formed by the latter by a further electron-transfer step. Upon
excitation at 532 nm both free-base porphyrin and gold
porphyrin units are excited. The gold porphyrin triplet, PH2-
Ir-3PAu which is detected by transient absorbance, behaves
as the model and decays back to the ground-state irrespective
of the presence of the other units. The free-base singlet, 1PH2-
Ir-PAu, can be detected by luminescence and displays a strong
quenching (lifetime 30 ps) similar to the one detected in the
case of the dyad PH2-Ir. Therefore the quenching was assigned
to the same electron-transfer process as in the model dyad,
leading in this case to the CS state PH2+-Ir--PAu. Detection
of this state by transient absorbance requires selective excitation
at 598 nm of the free-base unit to prevent masking of the weak
CS state absorbance by the gold porphyrin-localized triplet
which displays a strong band around 620 nm. At the end of the
35 ps pulse at 598 nm, the spectrum is essentially identical to
the one detected in the dyad (Figure 2a-b), therefore confirming
our assignment to PH2+-Ir--PAu. The decay is nevertheless
faster, the lifetime being 40 ps compared to 75 ps of the dyad,
indicating that a further reaction competes to deplete this state
with respect to the case of the dyad. The reaction is a further
electron transfer step, leading to the fully CS state PH2+-Ir-
PAu- which is responsible for the residual absorbance after
140 ps (Figure 2b) and which decays with a lifetime of 3.5 ns.
The reaction rate of this electron-transfer step can be calculated
by comparison with the overall rate of decay of the dyad, 1.33
× 1010 s-1, and turns out to be 1.2 × 1010 s-1, from which a
yield of formation of the fully CS state of 0.5 is derived. The
recombination of the fully CS state can occur to the ground
state but also to the triplet state localized on the free-base
Figure 3. Schematic energy level diagram: (a) PH2-Ir; (b) PAu-
Ir; (c) PH2-Ir-PAu in acetonitrile.
pulse; the decay is exponential with a lifetime of 75 ps and
displays a complete recovery to the pre-pulse absorbance.
Selective excitation of the PH2 moiety was performed on the
triad PH2-Ir-PAu at 598 nm, by shifting with a Raman cell
the 532 nm pulse (See Experimental Section for details). At
the end of the pulse a spectrum very similar to the one detected
for the dyad was recorded, which decayed faster than in the
case of the dyad (40 ps lifetime) and evolved to a residual
absorbance decaying with a lifetime of 3.5 ns (Figure 2b).
Determinations performed by nanosecond laser flash photolysis
over a wider time window give information on the triplet state
localized on free-base porphyrin. The lifetime of this triplet in
air-free acetonitrile is 8 µs for PH2-Ir and 2 µs for PH2-Ir-
PAu, greatly reduced with respect to the model PH2 (200 µs).
The absolute yield of these triplets in the dyad and triad were
determined with respect to the photons absorbed by the free-
base moiety only, and turned out to be 0.1 and 0.6 for PH2-Ir
and PH2-Ir-PAu respectively. The results of transient absor-
bance experiments, both in the picosecond and in the nano- and
microsecond range, are summarized in Table 3.
Photoinduced Processes. The above results can be inter-
preted on the basis of the current theories on photoinduced
electron transfer.19 As clearly shown by the spectroscopic and
electrochemical data these arrays show a very modest electronic
coupling between the components, and therefore can be
discussed in terms of the properties of the individual compo-
nents. A schematic energy level layout for the lowest states of
the systems is reported in Figure 3. This has been drawn from
the spectroscopic energy levels of the excited state (Table 2)
and from a simplified evaluation of the energy of the charge-
separated (CS) state which only takes into consideration the
half wave potentials for the oxidation of the electron donor and
the reduction of the electron acceptor in acetonitrile (Table 1).
(19) Marcus, R. A.; Sutin, N. Biochim. Biophys. Acta 1985, 811, 265 and
references therein; Closs, G. L.; Miller, J. R. Science 1988, 240, 440
and references therein; Electron Transfer-From Isolated molecules to
biomolecules, Part 1; Jortner J., Bixon, M., Eds.; John Wiley & Sons:
New York, 1999.
3
porphyrin PH2-Ir-PAu, whose energy is ca. 0.1 eV lower.
A determination of the yield of this triplet formation, 0.6, clearly
indicates that the CS state quantitatively recombines to the triplet

5512 Inorganic Chemistry, Vol. 40, No. 22, 2001
Dixon et al.
localized on the free-base porphyrin. Formation of the excited
triplet state of a component has often been reported in
multicomponent synthetic arrays upon recombination of the
charge separated state.20,21 This is reminiscent of what is
occurring in photosynthetic organisms in nature, where recom-
bination of the primary charge-separated state to the triplet state
of chlorophyll or bacteriochlophyll can take place in particular
when the full charge separation event is precluded.22 This
process in the bacterial reaction center leads to sensitization of
singlet oxygen and can kill the cell, in the absence of a suitable
protection by carotenoids.23
crossing from the triplet localized on the free-base porphyrin
to the ground-state singlet in the arrays, leading to a remarkable
decrease of the triplet lifetime from 200 µs in the model PZn
to 8 µs and 2 µs for PH2-Ir and PH2-Ir-PAu, respectively
(Table 3). The absence of any porphyrin quenching at 77 K in
a rigid glass is rationalized by the expected destabilization by
several hundreds of meV of the CS state energy levels, caused
by the rigidity of the solvent which does not allow reorientation
about the CS state,25 and would make endergonic the primary
electron-transfer step.
After a thorough determination of the photophysical properties
of the model units and model dyads it has been demonstrated
that, upon excitation in the visible, the triad system PH2-Ir-
PAu can effectively yield charge separation with an efficiency
of 0.5 and a resulting CS state with 3.5 ns lifetime. The presence
of a low-lying triplet localized on the free-base porphyrin and
the effect of the heavy Ir(III) ion in promoting a singlet-to-
triplet spin rephasing offers the CS state an alternative deactiva-
tion through the triplet state.
PZn-Ir-PAu Triad and Related Models in Dichlo-
romethane and Toluene. Stability and Solubility. As evi-
denced by the preparative procedures of the reference com-
pounds and the various dyads and triads (heating at 140-196
°C), all the compounds studied are thermally very stable. The
iridium(III)-containing component is photochemically extremely
stable but the porphyrins can lead to photodecomposition,
especially in nitrile solvent. Other solvents, namely dichlo-
romethane and toluene, were used to overcome possible
photochemical degradations. In toluene, the triad PZn-Ir-PAu
and the reference compounds PZn and PAu are soluble whereas
PZn-Ir and PAu-Ir are only very slightly soluble. All models
and arrays, including the dyads PZn-Ir and PAu-Ir are
soluble in dichloromethane. Surprisingly, in dichloromethane
the model PZn displayed photochemical instability upon high
energy laser irradiation but the arrays were perfectly stable and
were studied in this solvent only. The reference iridium(III)
complex Ir was insoluble both in toluene and dichloromethane
but it could readily be dissolved in CH3CN. For this compound,
reference is made to properties displayed in acetonitrile solution.
Ground-State Absorption and Luminescence. The absorp-
tion spectra of PZn, PAu and PZn-Ir-PAu in dichoromethane
is reported in Figure 4a with the spectrum of Ir in acetonitrile.
Figure 4b shows the absorption of the same array and the model
porphyrins in toluene, with the spectrum of Ir in acetonitrile.
The luminescence of the PZn moiety in the arrays is nearly
completely quenched in both solvents and time-resolved experi-
ments indicate that the lifetime of the zinc porphyrin singlet is
shorter than our resolution time, 20 ps (Table 4). The fluores-
cence of the zinc porphyrin moiety can be detected in the arrays
in both solvents in glass at 77 K together with the phospho-
rescence bands localized on the triplet gold porphyrin and triplet
zinc porphyrin. The luminescence data of the excited states at
ambient temperature in the two solvents and the energy levels
of the states, as derived from the emission maxima at 77 K, are
summarized in Table 4.
In the dyad the CS state PH2+-Ir- decays rather fast and
mainly to the singlet ground state while the fully CS state in
the triad, PH2+-Ir-PAu-, recombines slower and essentially
to the triplet state. The different behavior of the dyad and triad
both in terms of lifetimes and in terms of spin multiplicity of
the product of the recombination reaction are correlated and
can be rationalized, having in mind that the primary CS state
formed upon electron transfer from a singlet excited state has
initially a singlet character and that recombination to a triplet
state requires the change of the CS state to a triplet character.
Recombination to the ground state has a rather high driving
force, 1.55 eV for the triad and 1.75 eV for the dyad, which
very likely places the reactions in the “Marcus inverted region”
where the rate is expected to drop with increasing driving force.
On the contrary, recombination to the triplet (∆G ) -0.08 eV
and ∆G ) -0.28 eV) are in the “normal” region.19 In the case
of PH2+-Ir- (and PH2+-Ir--PAu), the close coupling of the
electron and hole, localized on the terpyridine ligand and on
the π system of the tetrapyrrole macrocycle respectively, leads
to a rapid charge recombination. By contrast, in PH2+-Ir-
PAu- the large distance between the hole and electron (ca. 2
nm) and the nature of the connecting bridge which is a poor
conductor from the electronic viewpoint,24 would make the
recombination to the ground state slow. Therefore, while in the
dyad there is little time for the original singlet to rephase, the
longer lifetime of the fully CS state PH2+-Ir-PAu- could
allow for a spin rephasing of the original singlet CS state. Once
the CS state has evolved to triplet, the recombination to the
3
lower triplet state localized on the porphyrin PH2-Ir-PAu
can occur. A systematic study of the effect of the bridge length
in an homogeneous series of donor-acceptor systems on the
spin multiplicity of the charge recombination product has clearly
shown that the ratio of triplet to singlet increases with the length
of the bridge and also parallels the increase in lifetime of the
CS state.21 In the present case the presence of the heavy Ir(III)
ion is expected to greatly favor the singlet-to-triplet conversion
in the CS state by enhancing spin-orbit coupling. The same
effect should be responsible for the increase of the intersystem
(20) Hasharoni, K.; Levanon, H.; Greenfield, S. R.; Gosztola, D. J.; Svec,
W. A.; Wasielewski, M. R. J. Am. Chem. Soc. 1995, 117, 8055.
Maggini, M.; Guldi, D. M.; Mondini, S.; Scorrano, G.; Paolucci, F.;
Ceroni, P.; Roffia, S. Chem. Eur. J. 1998, 4, 1992. Kuciauskas, D.;
Liddell, P. A.; Moore, A. L.; Moore, T. A.; Gust, D. J. Am. Chem.
Soc. 1998, 120, 10880. Martin, N.; Sa´nchez, L.; Herranz, M. A.; Guldi,
D. M.. J. Phys. Chem. A 2000, 104, 4648.
(21) Roest, M. R.; Oliver, A. M.; Paddon-Row, M. N.; Verhoeven, J. W.
J. Phys. Chem. A 1997, 101, 4867.
(22) See for example: Regev, A.; Nechustai, R.; Levanon, H.; Thornber,
J. P. J. Phys. Chem. 1989, 93, 2421.
(23) Griffith, M.; Sistrom, W. R.; Cohen-Bazire G.; Stanter, R. Y. Nature
1955, 176, 1211. Cogdell, R. J.; Frank, H. A. Biochim. Biophys. Acta
1987, 895, 63.
(24) A similar Ru(II) bis-terpy bridge was shown to be a modest electron
conductor in a triplet-triplet energy transfer process occurring in a
similar porphyrinic array by a Dexter mechanism and involving
electron and hole migration through the bridging complex.8b
Time-Resolved Absorption. Dichloromethane Solutions.
Upon excitation of the PAu-Ir dyad at 532 nm with a 35 ps
laser pulse, the triplet localized on the gold porphyrin is formed,
with the typical band around 620 nm and a lifetime of 1.4 ns,
as displayed by the model PAu in the same solvent (Table 5).
Selective excitation of the PZn unit in PZn-Ir yields a transient
spectrum with an intense band maximized at 670 nm, decaying
(25) Gaines, G. L., III; O’Neil, M. P.; Swec, W. A.; Niemczyk, M. P.;
Wasielewski, M. R.J. Am. Chem. Soc. 1991, 113, 719.

Porphyrinic Dyads and Triads
Inorganic Chemistry, Vol. 40, No. 22, 2001 5513
Table 5. Transient Absorption Data for PZn-Ir-PAu and Models
b
in Dichloromethanea and Toluene, Excitation at 532 nm; Ir Is
Insoluble in Both Solvents, Dyads PZn-Ir and PAu-Ir Are
Insoluble in Toluene
state
τ (ns)
Φc
PZna
3PZn
3PZn
3PAu
3PAu
3PZn
250000
300000
1.4
1
1
1
1
PZnb
PAua
PAub
2.5
PZn-Ira
< 0.05
PZn+-Ir-
3PAu
0.120
1.4
PAu-Ira
1
< 0.05
1
PZn-Ir-PAua
3PZn
3PAu
1.4
0.110
PZn+-Ir--PAu
PZn+-Ir-PAu-
3PZn
PZn-Ir-PAub
7000
2.5
e 0.020
450
e 0.1
3PAu
PZn+-Ir--PAu
PZn+-Ir-PAu-
d
a Dichloromethane. b Toluene. c Relative yields calculated on the
basis of the photons absorbed by the PZn (or PAu) unit only. At 532
nm the partition of photons in the triad is in dichloromethane: 25%
on PZn, 75% on PAu, in toluene: 28% on PZn, 72% on PAu. In the
Figure 4. Molar absorption coefficients of the models PZn (___), PAu
(-‚-‚-) and of the triad PZn-Ir-PAu (___) in dichloromethane solutions.
Ir (‚‚‚) is in acetonitrile solution.
d
dyads only the porphyrins absorb light upon visible excitation. The
Table 4. Luminescence Properties and Energy Levels of the
Excited States of PZn-Ir-PAu and Models in Dichloromethanea
and Toluene;b Ir Is Insoluble in Both Solvents, Dyads PZn-Ir and
PAu-Ir Are Insoluble in Toluene
absolute yield is measured to be 1.2 ( 0.3 (See text)
298 K
77 K
state λmax (nm) τ (ns)
Φfluo
0.064
λmax (nm) E (eV)b
PZna
PZnb
1PZnc
3PZnc
1PZnc
3PZnc
3PAud
3PAud
1PZnc
3PZnc
3PAud
596
1.8
606
770
596
776
712
712
620
790
712
614
790
716
606
786
716
2.05
1.61
2.08
1.60
1.74
1.74
2.00
1.57
1.74
2.02
1.60
1.73
2.05
1.58
1.73
596
2.2
0.08
PAua
PAub
PZn-Ira
e 0.020 1 × 10-4
e 0.020 8 × 10-5
e 0.020 6 × 10-4
PAu-Ira
PZn-Ir-PAua 1PZnc
3PZnc
3PAud
PZn-Ir-PAub 1PZnc
3PZnc
3PAud
a Dichloromethane. b Toluene. c Excitation at 560 nm for steady state;
correction for the absorbance of other units in the array was applied
when necessary. Excitation at 532 nm for time resolved. d Excitation
at 405 nm.
Figure 5. Transient absorbance changes upon excitation at 532 nm
(35 ps pulse, 3.5 mJ) in dichloromethane solutions. (a) PZn-Ir,
spectrum at the end of the laser pulse; the inset shows the decay at
660 nm. (b) PZn-Ir-PAu, spectrum at the end of the pulse (b) and
at 170 ps after the end of pulse (O); the inset shows the decay at 660
nm.
with a lifetime of 120 ps (Figure 5a). The spectrum is consistent
with that of a Zn porphyrin cation2,7 and assigned to the PZn+-
Ir- charge-separated state. Upon excitation of the triad PZn-
Ir-PAu at 532 nm, both the PZn unit and the PAu units absorb
photons, 25% and 75% respectively, as derived by the molar
absorption coefficients of the components. The results of
picosecond transient absorption experiments are reported in
Figure 5b. The spectrum at the end of the pulse, displaying a
maximum around 640 nm, decays with a lifetime of 110 ps in
a spectral region maximized around 670 nm, where the species
detected in the dyad shows a strong band. Therefore this band
is assigned to the same transient as in the dyad, the CS state
PZn+-Ir--PAu. The absorption recorded 170 ps after the end
of the pulse is typical of the triplet localized on the gold
porphyrin, with a band at 620 nm and a lifetime of 1.4 ns.
Experiments on a longer time scale by a nanosecond laser
photolysis apparatus showed that in air-free dichloromethane
solutions no residual absorbance was left after the decay of the
above species, and no triplet localized on the zinc porphyrin
could be detected. This indicates an upper limit of 0.05 for the
3
yield of the PZn-Ir-PAu state (Table 5).
Toluene Solutions. The properties of the models are reported
in Table 5; to note that the lifetime of the gold porphyrin triplet
is increased to 2.5 nanoseconds in this solvent with respect to
the 1.4 ns of acetonitrile and dichloromethane solutions. Upon
excitation of PZn-Ir-PAu at 532 nm both PZn and PAu units
absorb photons, 28% and 72% respectively. The spectrum
detected at the end of a 35 ps pulse at 532 nm (Figure 6) shows
a red-shifted absorption with a stronger band below 500 nm
3
with respect to the spectrum of PAu (reported in the same
figure). Therefore in PZn-Ir-PAu there is, in addition to the
3
absorbance of the PAu, a contribution from a species with a
band maximized around 670 nm which is formed faster than

5514 Inorganic Chemistry, Vol. 40, No. 22, 2001
Dixon et al.
Figure 6. Transient absorbance changes upon excitation at 532 nm
(35 ps pulse, 3.5 mJ) detected at the end of the pulse in a toluene
solution of PZn-Ir-PAu (b) and PAu (s). The inset shows the rise
at 680 nm of the transient absorbance in PZn-Ir-PAu (b) compared
to the rise of a standard (∇) whose formation is immediate with the
laser excitation (See Experimental Section for details).
Figure 8. Schematic energy level diagram: (a) PZn-Ir-PAu in
dichloromethane (b) PZn-Ir-PAu in toluene. The CS state levels
are based on electrochemical data in dichloromethane, with some
adjustment for solvent polarity considerations (see text).
Figure 7. Transient absorbance changes upon excitation at 532 nm
(18 ns pulse, 1 mJ) detected at the end of the pulse in a toluene solution
of PZn-Ir-PAu. In the inset the decay of the spectrum in air-free
toluene solution is reported.
in dichloromethane confirm the above expectations (Figure 8a).
The absence of alternative possibility of deactivation for PZn+-
Ir-PAu- is expected to greatly enhance the lifetime of the CS
state which now can only deactivate directly to the ground state,
a process characterized by a large driving force (∆G ca. -1.35
eV) very likely falling in the “Marcus inverted region”.19
Unfortunately, the fully CS state in CH2Cl2 could never be
detected as explained below.
The absorption spectra in dichloromethane solutions (Figure
4a) indicate that in this solvent the spectrum of the array is not
the simple superimposition of the components but there is a
broad tail extending from 600 to 700 nm. This could be ascribed
to the presence of a charge-transfer band due to the interaction
in the ground state between the reductant PZn (E1/2 ) 0.68 V
vs SCE) and the oxidant Ir (E1/2 ) -0.71 V vs SCE). The tail
is not present, or present to a much lower extent in the apolar
toluene solvent (Figure 4b) which supports our assignment. The
existence of charge-transfer interactions in the ground state
between the components in multicomponent porphyrinic systems
containing a good electron acceptor has been reported before.26
our resolution, since its rise time cannot be resolved from the
instrumental response (inset of Figure 6). After the decay of
the gold porphyrin triplet, which occurs with a lifetime of ca.
2.5 ns as in the model, the former absorbance maximized around
670 nm is left as a residual. It can be detected unaltered in a
nanosecond laser flash photolysis experiment, where the spec-
trum reported in Figure 7 is registered at the end of a 18 ns
laser pulse at 532 nm. The lifetime of this species in air-free
solution is 450 ns (inset of Figure 7) and is unaffected by the
concentration of the array in the solution and by the energy of
the laser; air equilibration reduces the lifetime to 310 ns. On
the basis of spectral and kinetic evidences such species is
identified as the CS state PZn+-Ir-PAu-. In air-free solution
a rather weak transient absorbance is left after the decay of the
450 ns species; this has a lifetime of 7 µs and a spectrum
consistent with that of the triplet zinc porphyrin. The yield of
3
formation of the zinc porphyrin triplet PZn-Ir-PAu calcu-
3
lated against PZn and taking into consideration the photons
Excitation of PZn-Ir in the visible range produces the singlet
absorbed by the PZn unit only is e 0.1. The data derived by
transient absorbance determinations are summarized in Table
5.
1
excited-state localized on the zinc porphyrin unit, PZn-Ir,
which decays with a rate g 5 × 1010 s-1, faster than our
resolution in the luminescence experiments (20 ps). The
absorption spectrum of the product (Figure 5a) displays a
maximum at 660-670 nm typical of the zinc porphyrin cation,
arising from the CS state PZn+-Ir-, which decays by charge
recombination with a rate of 8.3 × 109 s-1. The dyad PAu-Ir
does not show any difference in reactivity with respect to that
of the chromophore PAu. The behavior of the triad PZn-Ir-
PAu in dichloromethane (Figure 8a) is rather different from
that of the related PH2-Ir-PAu in acetonitrile (Figure 3c).
Photoinduced Processes. The results obtained with the
system PH2-Ir-PAu, previously discussed, show that a
deactivation path to a low-lying triplet is rate determining for
the lifetime of the CS state PH2+-Ir-PAu-. The study on the
zinc porphyrin derivative was undertaken because, given the
higher energy of the excited states (Tables 2 and 4) and the
stronger reductant ability of the PZn unit with respect to the
PH2 unit (Table 1), an inversion in the energy ordering of the
CS state and the triplet state was expected.
Dichloromethane Solutions. The schematic energy levels
for the dyads PZn-Ir, PAu-Ir and the triad PZn-Ir-PAu
(26) Armaroli, N.; Marconi, G.; Echegoyen, L.; Bourgeois, J.-P.; Diederich,
F. Chem. Eur.J. 2000, 6, 1629

Porphyrinic Dyads and Triads
Inorganic Chemistry, Vol. 40, No. 22, 2001 5515
Once the primary electron transfer has occurred to yield PZn+-
Ir--PAu, with a rate g 5 × 1010 s-1 as in the case of the
model dyad, the electron-transfer reaction does not proceed
further to form PZn+-Ir -PAu-, but PZn+-Ir--PAu decays
back to the ground state with approximately the same rate
polar toluene both CS states and the ground state are destabilized
with respect to the more polar dichloromethane but PZn+-
Ir--PAu is expected to be more destabilized than PZn+-Ir-
PAu- with respect to the ground state PZn-Ir-PAu. This can
be explained, in a rather qualitative approach, with the distribu-
tion of charges on the units of the array in the ground and CS
states. In PZn+-Ir-PAu- the charge distribution is: +1, +3,
0, i.e., identical, but reverse with respect to the ground state
PZn-Ir-PAu: 0, +3, +1. Therefore we expect that the energy
gap between the final CS state PZn+-Ir-PAu- and the ground
state is little affected by the polarity of the solvent. In PZn+-
Ir--PAu, on the contrary, the charge distribution is +1, +2,
+1 and a less polar solvent (toluene) could stabilize less this
state with respect to the ground state than a more polar solvent
(dichloromethane) can. In conclusion we expect that the energy
level of PZn+-Ir--PAu is raised in energy when in toluene
solutions while the PZn+-Ir-PAu- state remains nearly
unaltered with respect to the energy level in dichloromethane
solutions. This would affect slightly the driving force for the
primary electron transfer (0.66 eV in dichloromethane) which
still remains very fast, but would increase the driving force for
the secondary electron transfer (0.05 eV in dichloromethane),
allowing for the secondary electron transfer to compete ef-
ficiently with the back recombination in the case of toluene.
The increase in the level of PZn+-Ir--PAu in toluene with
respect to dichloromethane could also explain the formation of
a sizable amount of triplet 3PZn-Ir-PAu, whose energy level
is now nearly iso-energetic with the primary CS state PZn+-
Ir--PAu (Figure 8b and Table 5).
displayed by the dyad, 9 × 109 s-1
.
The reason for the inefficiency of the secondary forward
electron transfer in the PZn-Ir-PAu triad, can be explained
by the simultaneous occurrence of unfavorable thermodynamic
and electronic parameters. The driving force for the secondary
electron-transfer step is in fact very small (∆G ) -0.05 eV)
and this would be sufficient to make the reaction inefficient. In
addition, the presence of a charge transfer interaction in the
ground state between the PZn and Ir units, as suggested by the
ground state absorption spectrum, could result in the presence
of a corresponding low energy excited state with a charge
transfer character (exciplex). This state, localized on the PZn
and the Ir units, could be strongly mixed with the true CS state
PZn+-Ir--PAu. As a consequence of the mixing the distribu-
tion of the extra electron on the ligands of the Ir unit in the CS
state PZn+-Ir--PAu could be rather unsymmetrical, with a
higher probability for the electron to be localized on the terpy
close to the PZn. This circumstance would make more difficult
the subsequent electron-transfer step to the gold porphyrin unit,
linked on the opposite terpy. Direct detection of an exciplex
state and its role in the formation of charge-separated states in
a similar donor-acceptor array has been recently reported.27
Toluene Solutions. The energy level diagram in toluene is
reported in Figure 8b. The energy levels are essentially similar
to those in dichloromethane, except for the CS state levels which
we expect to be affected by the different polarity of the two
solvents.
Conclusion
Two triads incorporating iridium (III) as assembling metal
and playing the role of electron relay and two different
porphyrins respectively electron donor (PH2 or PZn) and
secondary electron acceptor (PAu) have been synthesized and
characterized. Their electrochemical and photophysical proper-
ties have been studied in the light of the properties of
corresponding dyads (PH2-Ir, PZn-Ir, PAu-Ir) and indi-
vidual components (PH2, PZn, PAu).
No electrochemical data are available in this solvent and we
can only make qualitative considerations on the basis of the
different polarities of the two media. PZn-Ir is insoluble in
this solvent and a good piece of information is missing. In any
case our experimental observations on PZn-Ir-PAu tell us
that, upon quenching of the luminescence of zinc porphyrin with
a rate g 5 × 1010 s-1, a spectrum appears within our resolution
(20 ps) and contains a contribution, in addition to that of PZn-
Ir-3PAu, of a long-lived species with a strong band around
660-670 nm. The lifetime of the species is 450 ns in air-free
solution, rather different from that of the triplet 3PZn which is
7 µs in this experiment. The spectral features are in full
agreement with those of the zinc porphyrin cation and we
identify this species as the fully CS state PZn+-Ir-PAu-,
formed by a very fast (k g 5 × 1010 s-1) secondary electron
transfer from PZn+-Ir--PAu. An estimation of the yield of
the fully CS state measured against the photons absorbed by
the PZn moiety can come from the literature spectroscopic data
of the zinc tetraphenylporphyrin cation28 and this results in 1.2
( 0.3 (See Experimental Section for details).
The photoinduced processes observed in the dyads and triads
are very dependent on thermodynamic parameters as well as
on the nature of the solvent. It has been demonstrated that in
acetonitrile the triad PH2-Ir-PAu leads to a fully CS state
with a lifetime of 3.5 ns. The energy ordering of the triplet state
of PH2 and of the final CS state PH2+-Ir-PAu- is responsible
of this short lifetime. For the triad PZn-Ir-PAu in di-
choromethane the primary electron-transfer to yield PZn+-
Ir--PAu is not followed by a secondary electron transfer due
to both thermodynamic and electronic unfavorable parameters.
By contrast, in toluene, PZn-Ir-PAu has been shown to yield,
upon excitation in the visible region, a fully charge-separated
state with a unitary yield and a lifetime of 450 ns. It is interesting
to note that the two electron-transfer processes leading to the
CS state are very fast and could not be time-resolved. Contrary
to the most common expectations, full charge separation occurs
in an apolar solvent and not in a more polar solvent, where
charge-transfer interactions in the ground state and a too small
driving force preclude the efficient completion of the sequential
electron-transfer steps. In an apolar solvent, ground state-charge-
transfer interactions are suppressed and a different stabilization
of the intermediate and final CS states determines the favorable
conditions for an efficient and complete sequential electron
transfer.
Comparison of PZn-Ir-PAu Behavior in Dichloromethane
and in Toluene Solutions. The reason for the different behavior
of the triad in toluene with respect to dichloromethane has
mainly to be assigned to the absence in the former of a charge
transfer interaction between the PZn and Ir units, as shown from
the ground state absorption spectra, but also very likely to a
higher driving force for the PZn+-Ir--PAu f PZn+-Ir-
PAu- electron-transfer reaction in toluene. In fact, in the less
(27) Tkachenko, N. V.; Rantala, L.; Tauber, A. Y.; Helaja, J.; Hynninen,
P. H.; Lemmetyinen, H. J. Am. Chem. Soc. 1999, 121, 9378.
(28) Fajer, J.; Borg, D. C.; Forman, A.; Dolphin, D.; Felton, R. H. J. Am.
Chem. Soc. 1970, 92, 3451.

5516 Inorganic Chemistry, Vol. 40, No. 22, 2001
Dixon et al.
8. 4-Formylphenylboronic acid (1 g, 6.67 mmol) and 2,2-dimeth-
ylpropane-1,3-diol (695 mg, 6.67 mmol) were refluxed in distilled
benzene (20 mL) for 2h30. The crude mixture was evaporated to
Experimental Section
Photophysics. The solvents used for photophysical determinations
are Spectroscopic Grade (C. Erba). Absorption spectra were recorded
with a Perkin-Elmer Lambda 9 spectrophotometer. Uncorrected emis-
sion spectra were detected by a Spex Fluorolog II spectrofluorimeter,
which was equipped with a phosphorimeter accessory (1934D) for the
determination of phosphorescence spectra. Time-resolved luminescence
apparatus was based on a Nd:YAG laser (35 ps pulse duration, 532
nm, 1 mJ) and a Streak Camera.29 Lifetimes longer than 2 ns were
detected with a Time Correlated Single Photon Counting apparatus with
1 ns resolution Phosphorescence lifetimes were determined by a Nd:
YAG laser (18 ns pulse, 532 nm, 2 mJ) and a photomultiplier
Hamamatsu R936.30
Transient absorbance in the picosecond range made use of a pump
and probe system based on a Nd:YAG laser (35 ps pulse, 532 nm,
2-4 mJ) and an OMA detector.31 The instrumental response profile
was obtained by measuring the buildup of the absorption of a solution
of DODCI (3-3′-diethyloxadicarbocyanine) in methanol at 450 nm.32
Zero time was assumed to be at the complete evolution of the absorption
of the sample. For excitation at 598 nm the second harmonic (532 nm)
was Raman shifted by a C6D12 cell: 30 mJ at 532 were collimated on
a 10 cm cell, the resulting Raman line at 598 nm was selected by colored
filters and the residual 532 nm wave was diverted by a dichroic 45
degree mirror. The energy at 598 nm was ca. 0.5 mJ.
1
dryness, and H NMR showed the reaction to be quantitative (1.45 g
of colorless solid). 1H NMR (200 MHz, CDCl3), (ppm): 10.05 (s, 1H,
CHO); 7.97 (d, 2H, HAr, 3J ) 8.1 Hz); 7.85 (d, 2H, HAr, 3J ) 8.1 Hz);
3.80 (s, 4H, CH2); 1.05 (s, 6H, CH3).
9. All the glassware was dried in an oven and allowed to cool in a
desiccator. Compound 8 (400 mg, 1.84 mmol) and 3,5-ditertiobutyl-
benzaldehyde (1.2 g, 5.52 mmol, 3 eq) were placed in a 1-L three-
necked flask. Chloroform (750 mL) was transferred into the reaction
flask via cannula. This mixture was degassed and stirred for 10 min
under argon. Pyrrole (0.51 mL, 7.5 mmol, 4 eq) was injected with a
syringe. This mixture was stirred for 10 min. Boron trifluoride etherate
(0.28 mL, 2.2 mmol, 1.2 eq) was added with a syringe, the solution
immediately turning yellow. This mixture was stirred in the dark for
1h30, during which the solution darkened. Chloranil (1.97 g, 8 mmol,
excess) was added, the argon inlet was replaced by a silicagel tube
and the mixture was refluxed for 30 min. After cooling to room
temperature (RT), the crude reaction mixture was washed with water
(2 × 250 mL) and evaporated to dryness. It was purified by repeated
chromatography on silica, eluted with CH2Cl2 (up to 3% MeOH) and
gave 80 mg of the desired unsymmetrical porphyrin 9 (4%), and 10
mg of symmetrical (trans) bis-boronic porphyrin (0.5%). Other fractions
(150 mg overall) contained a mixture of pure 9 and bis-boronic
Yields and lifetime of absorbing species in the 10 ns-1000 µs range
were determined by a laser flash photolysis apparatus with a Nd:YAG
laser (18 ns pulse, 532 nm, 2-4 mJ).33 The yields of triplets in the
arrays were determined against the model porphyrin in the same solvent
as a standard, by comparing absorbances of the triplets at wavelength
longer than ground-state absorbance (620 nm for PAu, 650 nm for
PZn, 680 nm for PH2). The yield of the state PZn+-Ir-PAu- was
determined by using a molar absorption coefficient of 1 × 104 M-1cm-1
at 680 nm28 and as actinometer was used zinc tetraphenylporphyrin in
toluene with a triplet yield of 0.81 and a ∆ꢀ at 470 nm of 7.3 × 104
1
porphyrin. H NMR (A3B, 9) (200 MHz, CDCl3), δ (ppm): 8.92-
8.85 (m, 8H, pyrroles); 8.26 (d, 2H, H1, 3J ) 7.7 Hz); 8.19 (d, 2H, H2,
3J ) 7.7 Hz); 8.10 (s, 6H, Ho); 7.81 (s, 3H, Hp); 3.96 (s, 4H, CH2);
t
1
1.54 (s, 54H, Bu); 1.19 (s, 6H, CH3); -2.65 (broad s, 2H, NH). H
NMR (trans-A2B2, bis-boronic porphyrin) (200 MHz, CDCl3), δ
3
3
(ppm): 8.88 (d, 4H, pyrroles, J ) 4.7 Hz); 8.84 (d, 4H, pyrroles, J
) 4.7 Hz); 8.24 (d, 2H, H1, J ) 8 Hz); 8.18 (d, 2H, H2, J ) 8 Hz);
3
3
4
4
8.09 (d, 4H, Ho, J ) 1.7 Hz); 7.80 (t, 2H, Hp, J ) 1.7 Hz); 3.95 (s,
8H, CH2); 1.55 (s, 36H, tBu); 1.18 (s, 12H, CH3); -2.72 (s, 2H, NH).
1. All solutions were carefully degassed before their introduction in
the reaction flask. 4′-Bromoterpy (31 mg, 0.098 mmol) was placed in
a 50-mL two-necked flask. Toluene (1 mL) was added, followed by
solid Pd(PPh3)4 (23 mg, 0.2 eq) and a 2M aqueous solution of sodium
carbonate (0.5 mL). A solution of 9 (104 mg, 0.098 mmol) was
transferred via cannula, first by partially dissolving the porphyrin in
absolute EtOH (2.5 mL) and subsequently dissolving the rest with
toluene (3 × 2 mL). After degassing once more, the reaction mixture
was heated at 100 °C and under argon for 24 h. The crude mixture
was chromatographed on Al2O3 (from pure hexane to pure CH2Cl2) to
yield 92 mg of 1 (0.077 mmol, 79%). 1H NMR (200 MHz, CDCl3), δ
(ppm): 9.09 (s, 2H, H3′+H5′), 8.94 (m, 8H, pyrroles), 8.83 (m, 2H,
H3), 8.80 (m, 2H, H6), 8.42 (d, 2H, H2, 3J ) 8.4 Hz), 8.32 (d, 2H, H1,
M-1 cm-1 34
.
Air-free solutions were bubbled with argon for 5 min and stored in
a vacuum tight homemade cells. For luminescence experiments at 77
K, quartz capillary tubes were immersed in liquid nitrogen contained
in a homemade quartz dewar.
Electrochemistry. Cyclic voltammetry was carried out in MeCN
or CH2Cl2 solution, using Bu4NPF6 as supporting electrolyte, a Pt
working electrode, a Pt counter-electrode, and SCE as reference. The
typical sweep rate was 100 mV/s, and the window used was from
-1.4V to +1.3V. Some waves were poorly reversible, probably due
to the adsorption of the species on the electrode.
Synthesis. The commercial starting materials were obtained from
Acros, Aldrich, Fluka, Lancaster, or Merck. IrCl3‚4H2O was obtained
from Pressure Chemical Co., and IrCl3 was given by Johnson Matthey.
Some starting materials were prepared following literature proce-
dures: 4′-formylphenyl-2,2′:6′,2′′-terpyridine,35 4′-bromo-2,2′:6′,2′′-
terpyridine,13 4′(3,5-ditertiobutylphenyl)-2,2′:6′,2′′-terpyridine (Ar-
terpy),10 and Ir(Ar-terpy)Cl3.10 The solvents were distilled over the
appropriate drying agents, and pyrrole was filtered over alumina before
use. All charged species were isolated as PF6 salts. In the NMR
assignments, the protons of the terpyridines are referred to as Ar-tpy,
PH2-tpy, or PAu-tpy, the protons of the para-phenylene spacers are
labeled 1 and 2. The protons on the 3,5-ditBuPh groups are labeled
o,o′ and p,p′ on a porphyrin and o′′ and p′′ on Ar-tpy.
4
4
3J ) 8.4 Hz), 8.13 (d, 4H, Ho, J ) 2 Hz), 8.11 (d, 2H, Ho′, J ) 2
Hz), 7.96 (ddd, 2H, H4, 3J ) 7.7 Hz, 4J ) 2 Hz), 7.82 (m, 3H, Hp+Hp′),
7.42 (ddd, 2H, H5, 3J ) 7.7 Hz, 4J ) 1.4 Hz), 1.55 (s, 54H, tBu), -2.64
(s, 2H, NH). MS (FAB+), m/z: 1182.9 ([M]+).
2+ (PAu). Compound 1 (55 mg, 0.047 mmol), KAuCl4 (44 mg, 0.117
mmol), and NaOAc (15.2 mg, 0.185 mmol) were heated to reflux in
degassed AcOH (5 mL), under argon and in the dark, for 8 h. UV-
Visible absorption spectroscopy confirmed the disappearance of about
90% of the free-base porphyrin. AcOH was evaporated and the crude
mixture was dissolved in CH2Cl2 and washed with a 0.2M aqueous
KPF6 solution. The organic layer was washed with 5% aqueous Na2-
CO3 (4 × 100 mL) and with water (3 × 100 mL). The aqueous layer
was extracted with CH2Cl2 (3 × 50 mL), dried over MgSO4 and filtered.
MgSO4 was stirred with CH2Cl2 overnight. The organic layers were
combined, evaporated and chromatographed on alumina (CH2Cl2/EtOH,
0-15%) to give 2+ as a deep red-orange solid in 89% yield (63 mg).
34+ (PAu-Ir). 2+ (15 mg, 0.098 mmol) and Ir(Ar-tpy)Cl3 (7 mg,
0.097 mmol) were heated to 140 °C in degassed ethylene glycol (5
mL), under argon and in the dark, for 3 h. The solvent was evaporated
under reduced pressure. The crude mixture was dissolved in acetone,
precipitated by the addition of a 0.2M aqueous KPF6 solution and
filtered. After chromatography on silica (acetone/water/saturated aque-
ous KNO3 solution: 100/0/0 to 95/10/0.2), anion exchange with KPF6,
chromatography on fine silica (same eluent: 100/0/0 to 100/10/0.5)
(29) Flamigni, L. J. Phys. Chem. 1993, 97, 9566.
(30) Flamigni, L.; Armaroli, N.; Barigelletti, F.; Chambron, J.-C.; Sauvage,
J.-P., Solladie´, N.New J. Chem. 1999, 23, 1151.
(31) Flamigni, L.; Armaroli, N.; Barigelletti, F.; Balzani, V.; Collin, J.-P.;
Dalbavie, J.-O.; Heitz, V.; Sauvage, J.-P. J. Phys. Chem. 1997, 101,
5936.
(32) Flamigni, L. J. Phys. Chem. 1992, 96, 3331.
(33) Hubig, S. M.; Rodgers, M. A. J. In Handbook of Organic Photo-
chemistry; Scaiano, J. C., Ed.; C.R.C. Press: Boca Raton, FL, 1989;
Vol. I, Chapter 13.
(34) Tanelian, C.; Wolff, C. J. Phys. Chem. 1995, 99, 9825.
(35) Collin, J.-P.; Heitz, V.; Sauvage, J.-P. Tetrahedron Lett. 1991, 32,
5977.

Porphyrinic Dyads and Triads
Inorganic Chemistry, Vol. 40, No. 22, 2001 5517
and anion exchange again, 34+ was obtained in a 96% yield (24 mg,
0.093 mmol) as a red solid. H NMR (400 MHz, CDCl3), δ (ppm):
(s, 4H, PH2-pyrroles); 8.83-8.73 (m, 8H, H1+H2); 8.39 (dd, 4H,
1
3
4
H4+H4′′, J ) 7.8 Hz); 8.21 (d, 4H, PAu-Ho, J ) 1.8 Hz); 8.20 (d,
3
3
4H, PH2-Ho, 4J ) 1.8 Hz); 8.19 (d, 2H, PAu-Ho′, 4J ) 1.8 Hz); 8.16
9.50 (d, 2H, pyrroles, J ) 5.2 Hz); 9.42 (d, 2H, pyrroles, J ) 5.2
3
3
4
Hz); 9.41 (d, 2H, pyrroles, J ) 5.4 Hz); 9.37 (d, 2H, pyrroles, J )
(d, 2H, PH2-Ho′, J ) 1.7 Hz); 8.12-8.10 (m, 3H, PAu-Hp+Hp′);
5.4 Hz); 9.13 (s, 2H, H3′+H5′ PAu-tpy); 8.68 (d, 2H, H2, 3J ) 8.2 Hz);
8.00-7.98 (m, 3H, PH2-Hp+Hp′); 7.96-7.92 (m, 4H, H3+H3′′); 7.70-
7.65 (m, 4H, H5+H5′′); 1.60 (s, 36H, PAu-tBu); 1.59 (s, 18H, PAu-t-
Bu′); 1.58 (s, 36H, PH2-tBu); 1.57 (s, 18H, PH2-tBu′); -2.67 (broad s,
2H, NH). MS (FAB+), m/z: 3187.4 ([M-PF6+H]+), 3042.4 ([M-
2PF6+H]+), 2896.4 ([M-3PF6]+), 2751.4 ([M-4PF6]+). 1H NMR (PAu-
Ir-PAu) (400 MHz, CD3CN, 60 °C), δ (ppm): 9.41 (s, 4H, H3′+H5′);
3
8.66 (s, 2H, H3′+H5′ Ar-tpy); 8.63 (d, 2H, H3 PAu-tpy, J ) 8.3 Hz);
3
3
8.49 (d, 2H, H1, J ) 8.1 Hz); 8.43 (d, 2H, H3 Ar-tpy, J ) 7.9 Hz);
8.08 (d, 4H, Ho, 4J ) 1.7 Hz); 8.06 (d, 2H, Ho′, 4J ) 1.6 Hz); 8.01 (d,
3
3
2H, H4 PAu-tpy, J ) 7.3 Hz); 7.98 (d, 2H, H4 Ar-tpy, J ) 7.7 Hz);
7.95 (t, 3H, Hp+Hp′, 4J ) 1.6 Hz); 7.88 (d, 2H, Ho′′, 4J ) 1.6 Hz); 7.82
3
3
3
3
(d, 2H, H6 PAu-tpy, J ) 5.4 Hz); 7.76 (d, 2H, H6 Ar-tpy, J ) 5.4
9.38 (d, 4H, pyrroles, J ) 4.8 Hz); 9.35 (d, 4H, pyrroles, J ) 4.8
3
3
Hz); 7.59 (s, 1H, Hp′′); 7.54 (dd, 2H, H5 PAu-tpy, J ) 6.7 Hz); 7.46
Hz); 9.28 (s, 8H, pyrroles); 8.89 (d, 4H, H6+H6′′, J ) 7.7 Hz); 8.73
(dd, 2H, H5 Ar-tpy, 3J ) 6.7 Hz); 1.55 (s, 72H, tBu). A nonambiguous
attribution could be established on the basis of a 400 MHz ROESY
spectrum. MS (FAB+), m/z: 2425.9 ([M-PF6]+), 2280.9 ([M-2PF6]+),
2135.9 ([M-3PF6]+), 1988.9 ([M-4PF6]+), 1377.2 ([M-Ir(Artpy)-4PF6]+,
100%), 1068.6 ([M-3PF6]2+), 994.9 ([M-4PF6]2+).
(d, 4H, H1, 3J ) 7.5 Hz); 8.63 (d, 4H, H2, 3J ) 7.5 Hz); 8.30 (dd, 4H,
H4+H4′′, 3J ) 7.7 Hz); 8.11 (d, 8H, Ho, 4J ) 2.0 Hz); 8.08 (d, 4H, Ho′,
4J ) 2.0 Hz); 8.00 (m, 6H, Hp+Hp′); 7.87 (d, 4H, H3+H3′′, J ) 6.7
3
t
Hz); 7.61 (m, 4H, H5+H5′′); 1.51 (s, 108H, Bu).
53+ (PZn-Ir). Compound 43+ (24 mg, 0.011 mmol) was refluxed
with Zn(OAc)2‚2H2O (4 equiv, 10 mg, 0.044 mmol) in absolute MeOH
(10 mL)/MeCN (15 mL) under argon and in the dark for 3 h (the
metalation process was monitored by UV-Vis absorption spectros-
copy). The crude mixture was purified by chromatography on silica
(acetone/water/saturated aqueous KNO3 solution from 100/0/0 to 100/
10/0.3) to give pure 53+ as a red-brown solid in 80% yield (20 mg,
10. 1 (40 mg, 0.034 mmol) was dissolved in hot absolute ethanol
(25 mL). IrCl3‚4H2O (18 mg, 0.048 mmol) in absolute ethanol (15 mL)
was then added dropwise, and this mixture was refluxed in the dark
for 2h30. The green crude mixture was washed with 5% aqueous Na2-
CO3, which caused a red product to precipitate. It was filtered, dissolved
in CH2Cl2 and chromatographed twice on alumina (CH2Cl2/EtOH:
100/0 to 98/2 and 100/0 to 99/1, respectively) to give 10 in a 58%
yield (29.5 mg, 0.020 mmol) as a red-brown solid. 1H NMR (400 MHz,
CDCl3), δ (ppm): 9.67 (d, 2H, H6, 3J ) 5.6 Hz); 8.96 (d, 2H, pyrroles,
1
0.009 mmol). H NMR (400 MHz, CD3CN), δ (ppm): 9.45 (s, 2H,
H3′+H5′); 9.08 (s, 2H, H3′+H5′ tButerpy); 8.97 (AB quartet, 4H, pyrroles,
3J ) 4.7 Hz); 8.89 (m, 6H, pyrroles+H3); 8.83 (d, 2H, H3 tButerpy, 3J
) 7.5 Hz); 8.68 (m, 4H, H1+H2); 8.30 (m, 4H, H4+H4 tButerpy); 8.13
3
3J ) 4.8 Hz); 8.93 (s, 4H, pyrroles); 8.88 (d, 2H, pyrroles, J ) 4.8
3
Hz); 8.58 (s, 2H, H3′+H5′); 8.51 (d, 2H, H3, J ) 8 Hz); 8.31 (d, 2H,
4
4
(d, 4H, Ho, J ) 1.6 Hz); 8.10 (2H, d, 2H, Ho′, J ) 1.9 Hz); 8.01 (d,
2H, Ho tButerpy, 4J ) 1.8 Hz); 7.93 (m, 3H, Hp+Hp′); 7.88 (t, 1H, Hp
tButerpy, 4J ) 1.6 Hz); 7.85 (d, 2H, H6, 3J ) 4.8 Hz); 7.77 (d, 2H, H6
H2, 3J ) 8 Hz); 8.16 (d, 2H, H1, 3J ) 8 Hz); 8.10 (d, 4H, Ho, 4J ) 1.6
4
3
Hz); 8.08 (d, 2H, Ho′, J ) 1.6 Hz); 8.01 (ddd, 2H, H4, J ) 7.9 Hz,
4J ) 1.8 Hz); 7.81 (m, 3H, Hp+Hp′); 7.76 (ddd, 2H, H5, J ) 6.5 Hz,
3
tButerpy, J ) 5.0 Hz); 7.58 (m, 4H, H5+H5 tButerpy); 1.56 (s, 36H,
3
4J ) 1.7 Hz); 1.58 (s, 54H, tBu); -2.65 (broad s, 2H, NH). MS (FAB+),
m/z: 1481.8 ([M]+), 1444.8 ([M-Cl]+), 1410.1 ([M-2Cl]+), 1375.2 ([M-
3Cl]+), 1182.9 ([M-3Cl-Ir]+).
tBu); 1.55 (s, 36H, tBu). MS (FAB+), m/z: 2294.3 ([M]+), 2150.4 ([M-
PF6]+), 2004.3 ([M-2PF6]+), 1858.1 ([M-3PF6]+), 1074.4 ([M-PF6]2+),
1002.4 ([M-2PF6]2+), 929.4 ([M-3PF6]2+).
43+ (PH2-Ir). 10 (40 mg, 0.027 mmol) and Ar-tpy (12 mg, 0.028
mmol) were heated to reflux in degassed ethylene glycol (10 mL), under
Ar and in the dark, for 25 min. After cooling to RT, 0.2M aqueous
KPF6 was added (10 mL) to precipitate a dark brown solid, which was
subsequently filtered off. After chromatography on alumina (CH2Cl2/
EtOH: 100/0 to 97/3), 27 mg of pure dyad were obtained (after anion
exchange with KPF6). The impure red-brown fraction was subjected
to chromatography on silica (acetone/water/saturated aqueous KNO3
solution: 100/0/0 to 100/10/0.4) and anion exchange yielded an
additional 13 mg of pure 43+ (66% overall yield, 0.018 mmol) as a
red-brown solid. 1H NMR (400 MHz, CD3CN), δ (ppm): 9.45 (s, 2H,
H3′+H5′); 9.08 (s, 2H, H3′+H5′ Ar-tpy); 8.99-8.97 (m, 4H, pyrroles);
74+ (PZn-Ir-PAu). Compound 63+ (15 mg, 0.0045 mmol) was
refluxed with Zn(OAc)2‚2H2O (4 equiv, 4 mg, 0.018 mmol) in absolute
MeOH (3 mL)/MeCN (3 mL) under argon and in the dark for 2 h (the
metalation process was monitored by UV-Vis absorption spectro-
scopy). The crude mixture was purified by chromatography on silica
(acetone/water/saturated aqueous KNO3 solution from 100/0/0 to 100/
10/0.3) to give pure 74+ as a red-brown solid in nearly quantitative
yield (15 mg, 0.0044 mmol).
1H NMR (400 MHz, CD3CN) δ (ppm): 9.49-9.42 (m, 8H, pyrroles-
PAu); 9.37 (s, 4H, H3′+H5′); 8.99 (m, 4H, pyrroles-PZn); 8.93 (d, 4H,
H6, 3J ) 8.2 Hz); 8.90 (s, 4H, pyrroles-PZn); 8.80-8.70 (m, 8H,
3
4
3
H1+H2); 8.36 (dd, 4H, H4, J ) 7.8 Hz); 8.18 (d, 4H, Ho-PAu, J )
8.90 (s, 4H, pyrroles); 8.89 (d, 2H, H3, J ) 7.7 Hz); 8.84 (d, 2H, H3
4
4
Ar-tpy), 3J ) 7.8 Hz); 8.72-8.68 (m, 4H, H1+H2); 8.34-8.27 (m, 4H,
1.7 Hz); 8.16 (d, 2H, Ho′-PAu, J ) 1.7 Hz); 8.15 (d, 4H, Ho-PZn, J
) 2.0 Hz); 8.11 (d, 2H, Ho′-PZn, J ) 1.9 Hz); 8.09-8.06 (m, 3H,
4
H4); 8.16 (d, 4H, Ho, 4J ) 1.9 Hz); 8.13 (d, 2H, Ho′, 4J ) 1.7 Hz); 8.02
4
Hp+Hp′-PAu); 7.95-7.90 (m, 7H, Hp+Hp′-PZn+H3); 7.68-7.62 (m,
4H, H5); 1.58 (s, 36H, tBu-PAu); 1.57 (s, 36H, tBu-PZn); 1.56 (s, 18H,
tBu′-PAu); 1.55 (s, 18H, tBu′-PZn). MS (FAB+), m/z: 3249.3 ([M+H-
PF6]+), 3105.2 ([M-2PF6]+), 2960.2 ([M-3PF6]+), 2813.1 ([M-4PF6]+),
1552.1 ([M-2PF6]2+), 1479.1 ([M-3PF6]2+), 1408.1 ([M-4PF6]2+), 1376.1
([M-4PF6-Zn+3H-terpyPAu]+, ie [PH3-Ph-terpy-Ir]+, 100%).
(d, 2H, Ho′′, J ) 1.9 Hz); 7.97-7.94 (m, 3H, Hp+Hp′); 7.89 (t, 1H,
4
3
4
Hp′′, J ) 1.7 Hz); 7.84 (dd, 2H, H6, J ) 5.5 Hz, J ) 0.8 Hz); 7.77
3
4
(dd, 2H, H6 Ar-tpy), J ) 5.8 Hz, J ) 0.8 Hz); 7.61-7.54 (m, 4H,
H5); 1.56 (s, 36H, tBu); 1.55 (s, 18H, tBu′); 1.54 (s, 18H, tBu′′); -2.71
(broad s, 2H, NH). MS (FAB+), m/z: 2231.8 ([M]+), 2085.8 ([M-PF6]+),
1940.8 ([M-2PF6]+), 1795.9 ([M-3PF6]+), 1374.7 ([M-3PF6-Ar-tpy]+),
1182.7 ([M-3PF6-Ir-Ar-tpy]+), 1043.5 ([M-PF6]2+), 970.9 ([M-2PF6]2+),
898.5 ([M-3PF6]2+), 598.2 ([M-3PF6]3+), 422.3 ([Ar-tpy]+).
Acknowledgment. We thank the French CNRS and the
Italian CNR for financial support. We thank European Com-
mission COST program D11/0004/98 and the French Ministry
of Education, Research and Technology for a fellowship to
I.M.D. We are also grateful to Johnson Matthey for a generous
loan of IrCl3.
64+ (PH2-Ir-PAu). Compound 10 (59 mg, 0.040 mmol) and 2+
(55 mg, 0.036 mmol) were heated to reflux in degassed ethylene glycol
(30 mL), under Ar and in the dark, for 25 min. After cooling,
precipitation by addition of 0.2M aqueous KPF6 (30 mL), and filtration
of the precipitate, the crude mixture was purified by chromatography
on alumina (CH2Cl2/EtOH from 100/0 to 50/50) and on silica (acetone/
water/saturated aqueous KNO3 solution from 100/0/0 to 100/10/0.3)
to give pure 64+ in a 33% yield (39 mg, 0.012 mmol) as a red-brown
solid. The bis-gold analogue PAu-Ir-PAu was isolated in 8% yield
(10 mg, 0.003 mmol). About 1% PH2-tpy was also formed by
decoordination of the iridium(III), and 10% of both starting materials
were recovered after chromatography. 1H NMR (64+) (400 MHz, CD3-
CN), δ (ppm): 9.51-9.45 (m, 8H, PAu-pyrroles); 9.39 (s, 4H, H3′+H5′);
Supporting Information Available: Fluorescence spectra and time-
resolved luminescence of PH2 and PH2-Ir-PAu in acetonitrile and
butyronitrile; fluorescence spectra of PZn and of PZn-Ir-PAu in
dichloromethane and toluene; schematic energy level diagram of PZn-
Ir and PAu-Ir in dichloromethane. This material is available free of
charge via the Internet at http://pubs.acs.org.
3
9.02 (m, 4H, PH2-pyrroles); 8.96 (d, 4H, H6+H6′′, J ) 8.2 Hz); 8.93
IC010416T