188B - 189B excitations (Table S1 and Fig. S3w). This
assignment is also supported by data shown below. The
Ru - Nꢀ transition is only slightly solvent dependent both
These features will make them excellent candidates for NIR
electrochromic devices.16 Work is under way to construct
other [M-bridge-N]nÆ hybrid systems where a metal compo-
nent and an organic amine unit are covalently connected by a
conjugated bridge.
+
in terms of shape and energy (Fig. 4, 1084, 1050, 1066, and
1084 nm for CH2Cl2, CH3CN, THF, and DMF, respectively).
This suggests that the Ru–N coupling is very strong. The
electronic coupling parameter Hab in acetonitrile is roughly
estimated to be 2760 cmÀ1, according to the Hush formula14
Notes and references
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Hab = 2.06 Â 10À2 (emax
nmaxDn1/2)
1/2/(rab), where rab is taken
to be the DFT-calculated Ru–N distance (6.16 A). However,
this value is underestimated because the effective electron transfer
distance is much smaller than the geometrical separation15 due to
a charge delocalization and it can be taken only as a low limit of
the actual value.
Fig. 5a and b show the vis/NIR spectral changes of 12+
upon one-electron reduction or oxidation in acetonitrile or
dichloromethane. When 12+ was reduced to 1+ by slowly
+
adding 1 equiv. hydrazine hydrate, the Ru - Nꢀ NIR
transition decreased continuously until it disappeared. At the
same time, a peak at 540 nm increased, which could be
interpreted as the recovery of the ligand-to-ligand-charge-
transfer (triarylamine - pyridines, associated with the S3
+
and S6 excitations of 1+, Table S1w) transitions after Nꢀ
was reduced back to a neutral amine. When 12+ was oxidized
to 13+ by slowly adding one equivalent of SbCl5, the
+
Ru - Nꢀ NIR transition decreased as well. Interestingly,
a very intense peak appeared at 714 nm, which arises from the
+
electronic transition of the triarylamine radical cation (Nꢀ
)
itself. TDDFT results of 13+ predict that this peak is mainly
associated with its 187B - 189B excitation with an admixture
of the 182B - 188B excitation (Table S1 and Fig. S4w). A
similar peak at 810 nm was previously found for one-electron
6 W. Kaim, Coord. Chem. Rev., 2011, 255, 2503.
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A. Persoons, C. Rovira and J. Veciana, Angew. Chem., Int. Ed.,
2004, 43, 5266.
oxidized species of 32+ 12
It is clear from these results that the
.
NIR band at 1050 nm is only observed in the form of 12+
,
but not 1+ and 13+, which agrees with the nature of the
+
Ru - Nꢀ transition.
As for complex 2+, it does not show any NIR absorption
itself. However, upon transformation into 22+ by adding
1 equiv. SbCl5, MLCT transitions of 2+ at 520 nm decreased
and a broad and shallow band between 600 and 1300 nm
appeared (Fig. 5c, emax = 2600 MÀ1cmÀ1). This band is
ascribed to the ligand-to-metal-charge-transfer (LMCT) tran-
sition. More precisely, it is of the character of the N - RuIII
excitation, as suggested by the TDDFT computations of 22+
(188B - 189B excitation, Table S1 and Fig. S7w). Upon
further addition of SbCl5, the generated 22+ was oxidized to
9 (a) C. Coudret, S. Fraysse and J.-P. Launay, Chem. Commun.,
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D. M. Tooke, A. L. Spek, F. Hartl, R. W. A. Havenith, G. P. M.
van Klink and G. van Koten, Inorg. Chem., 2009, 48, 1887;
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Chem., 2009, 48, 9644; (e) Y.-W. Zhong, S.-H. Wu, S. E.
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¨
(b) V. Coropceanu, M. Malagoli, J. M. Andre and J. L. Bredas,
´ ´
J. Am. Chem. Soc., 2002, 124, 10519; (c) A. Szeghalmi,
M. Erdmann, V. Engel, M. Schmitt, S. Amthor, V. Kriegisch,
G. Noll, R. Stahl, C. Lambert, D. Leusser, D. Stalke, M. Zabel and
¨
J. Popp, J. Am. Chem. Soc., 2004, 126, 7834.
+
23+ and an intense peak at 904 nm arising from the Nꢀ
species showed up (Fig. 5d). TDDFT results indicate that this
band is mainly associated with its 187B - 188B excitation
(Table S1 and Fig. S8w). These interpretations are consistent
with the assignment of the electrochemical behaviors of 2+
(Fig. 3b), where the RuII/III process proceeded before oxida-
tion of the amine moiety.
11 (a) C.-J. Yao, Y.-W. Zhong and J. Yao, J. Am. Chem. Soc., 2011,
133, 15697; (b) L.-Z. Sui, W.-W. Yang, C.-J. Yao, H.-Y. Xie and
Y.-W. Zhong, Inorg. Chem., 2012, 51, 1590.
12 C.-J. Yao, J. Yao and Y.-W. Zhong, Inorg. Chem., 2011, 50, 6847.
13 (a) Y. Sun and S. Wang, Inorg. Chem., 2009, 48, 3755; (b) K. C. D.
Robson, B. D. Koivisto, T. J. Gordon, T. Baumgartner and
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In conclusion, we present in this contribution a new type of
mixed-valent system consisting of mixed organic and inorganic
asymmetric redox species. The covalent hybrid 1n+ of triaryl-
amine and cyclometalated ruthenium displays two consecutive
and widely separated redox couples at considerably low
potentials and strong redox-switchable NIR absorptions.
14 (a) N. S. Hush, Prog. Inorg. Chem., 1967, 8, 391; (b) N. S. Hush,
Electrochim. Acta, 1968, 13, 1005.
15 A. Heckmann, S. Amothor and C. Lambert, Chem. Commun.,
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16 (a) C.-J. Yao, Y.-W. Zhong, H.-J. Nie, H. D. Abruna and J. Yao,
J. Am. Chem. Soc., 2011, 133, 20720; (b) M. D. Ward, J. Solid
State Electrochem., 2005, 9, 778.
c
5682 Chem. Commun., 2012, 48, 5680–5682
This journal is The Royal Society of Chemistry 2012