Communication
ChemComm
kinetics, resulting in a decrease of the mid-IR signal, have been
4 M. K. Nazeeruddin, E. Baranoff and M. Gr ¨a tzel, Sol. Energy, 2011, 85,
1
172–1178.
generally observed for dye–TiO
range from hundreds of ps to ms.
ponents t and t are assigned to charge recombination. The
2
systems with decays that typically
5
6
J. Li and N. Wu, Catal. Sci. Technol., 2015, 5, 1360–1384.
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3
5–37
Thus, the longer com-
2
3
t1 = 9 ps component is faster than is typically observed and may
be due to geminate charge recombination to the ground or the
triple state of the dye. In addition, it has been previously
reported that ‘‘hot’’ electrons injected from energies above
the CB edge can relax down to the CB edge, also resulting in
a decrease in the IR absorption cross-section and reduced
signal arising from the reduced density of states, as previously
7
P. Xu, C. L. Gray, L. Xiao and T. E. Mallouk, J. Am. Chem. Soc., 2018,
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9
D. Wang, S. L. Marquard, L. Troian-Gautier, M. V. Sheridan,
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1
0 M. K. Brennaman, R. J. Dillon, L. Alibabaei, M. K. Gish, C. J. Dares,
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3
7
observed for Ru(II) and Re(I) complexes, as well as a Mo2
3
6
paddlewheel complex. Herein, the 600 nm excitation of 1 11 I. Purnama, Salmahaminati, M. Abe, M. Hada, Y. Kubo and
1
J. Y. Mulyana, Dalton Trans., 2019, 48, 688–695.
2 J. Sun, Y. Yu, A. E. Curtze, X. Liang and Y. Wu, Chem. Sci., 2019, 10,
results in ultrafast electron injection from the hot ML-LCT
state, placing the electron B0.8 V above the TiO CB. Therefore,
1
2
5519–5527.
the short component may be ascribed to back electron transfer 13 S. Mozaffari, M. R. Nateghi and M. B. Zarandi, Renewable Sustainable
Energy Rev., 2017, 71, 675–686.
2
or to ‘‘hot’’ electron cooling within TiO . Similar results are
observed for 2@TiO upon 520 nm excitation (Fig. S9, ESI†).
2
The electron injection efficiencies for 1 and 2 are calculated to
be 97% and 95%, respectively (ESI†).
1
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1
In conclusion, this work represents the first example of charge
1
2 2
injection into a semiconductor, TiO nanoparticles, by a Rh
1
17 K. Hara, Z.-S. Wang, T. Sato, A. Furube, R. Katoh, H. Sugihara,
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3
ponding ML-LCT excited state. The geometry of the complexes 18 S. Ito, H. Miura, S. Uchida, M. Takata, K. Sumioka, P. Liska, P. Comte,
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1
9 Z. Li, N. A. Leed, N. M. Dickson-Karn, K. R. Dunbar and C. Turro,
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localized on Rh (d*)/DTolF(p*) HOMO and electrons are on the
2
menp(p*) or dmeb(p*) LUMOs. From the excited state reduction 20 T. J. Whittemore, H. J. Sayre, C. Xue, T. A. White, J. C. Gallucci and
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2
1 T. J. Whittemore, A. Millet, H. J. Sayre, C. Xue, B. S. Dolinar,
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1
2
ML-LCT states of 1 and 2 into TiO is thermodynamically
3
favorable, but not from their ML-LCT states, consistent with
absence of a slower component. The panchromatic dirhodium
complexes represent a new family of photosensitizers able to
harvest more lower energy photons than traditional dyes to make
better use of the solar spectrum. The synthetic modification of
the bridging or chelating ligands can be used to tune the
energetics of the excited states to further develop this class of
near-IR light absorbing dyes.
2
2
2
2
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2
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Conflicts of interest
3
3
3
There are no conflicts to declare.
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