COST D19 International Workshop on Nanochemistry, Sept 26-28 2002, Vienna, Austria

1. Towards Practical Molecular Devices:
the Incorporation of a Solid Substrate as an
Active Component in Molecular Assemblies
Noel M. O’Boyle,a Wesley R. Browne,a Steve Welter,b Ron T.F. Jukes,b Luisa De Cola,b Colin G. Coates,c
John J. McGarvey,c Johannes G. Vosa
a National Centre for Sensor Research, School of Chemical Sciences, Dublin City University, Dublin 9, Ireland
b Molecular Photonics Group, IMC, University of Amsterdam, Nieuwe Achtergracht 166, NL-1018 WV Amsterdam, the Netherlands
c Queens University Belfast, School of Chemistry, Belfast BT9 5AG, Northern Ireland
N
Ru(bpy)2(H2dcb) N N
Introduction Ru
Figure 2
N N
Ruthenium polypyridyl complexes have been widely used as covalently
bound dyes in solar energy devices based on nanocrystalline TiO2. In HOOC N
COOH
addition it has been shown that nanocrystalline TiO2 surfaces modified
with dinuclear RuOs polypyridyl complexes respond in a uniform
manner to irradiation as shown below in Figure 1.
Results
The emission spectrum and absorption spectra (both steady-state and
transient) of [Ru(bpy)2(dcb)2-] are shown in Figure 3 while the emission
Ru Os Ru Os lifetimes obtained for the partially deuteriated complexes are shown in the
Table A. Deuteriation reduces the rate of non-radiative deactivation of the
Figure 1 e- excited state. This leads to increased emission lifetimes provided the
excited state is based on the deuteriated ligand.
e-
2+
Ru(bpy)3
180000
Ru(bpy)2(dcb)
e-
160000
0.4
140000
In most cases the molecular components have been covalently attached 120000
via 4,4’-dicarboxy-2,2’-bipyridine (H2dcb) type ligands. It is generally
Counts per second
Absorbance
100000
assumed that in these assemblies injection into the TiO2 surface is
enhanced by the fact that the excited state is based on the dcb2- ligand. 0.2
80000 Figure 3
60000
This assumption is tested here for the model compound
[Ru(bpy)2(dcb)2-] (see Figure 2) by the use of deuteriation in 40000
combination with emission lifetime measurements and resonance 20000
Raman spectroscopy. 0.0 0
400 500 600 700 800
Deuteriation Wavelength (nm)
D 3C D D CD 3 HOOC D D COOH
D 2O [O]
D D D D Excited-state resonance Raman measurements (Figure 4) clearly show
N N NaOD N N N N
D D D D that the excited state is localised on the dcb2-. Resonances due to the
d6-H2dcb dcb3–• anion radical are observed at 1312 and 1212 cm-1.
Scheme 1
1491 cm
1450 cm
bpy bpy 3- 3-
1604 cm
dcb* dcb* 3- [Ru([H8]-bpy)2([H6]-dcb )]
2-
dcb*
1312 cm
2-
1212 cm
[Ru([H8]-bpy)2([D6]-dcb )]
 (ns)
-1
2-
-1
[Ru([D8]-bpy)2([H6]-dcb )]
-1
2-
[Ru([D8]-bpy)2([D6]-dcb )]
-1
-1
Ru(bpy)2 (dcb2-) 562
Table A Figure 4
Ru(bpy)2(d6 -dcb2-) 633
Ru(d8-bpy)2(dcb2-) 573
Ru(d8-bpy)2(d6-dcb2-) 679
1600 1500 1400 1300 1200
-1
Wavenumber in cm
Conclusions
Both the variation in emission lifetime as well as the rR spectra observed confirm that the excited state in bpy/dcb2- complexes is dcb2- based. The
results clearly indicate that deuteriation is a powerful method for the study of the nature of the excited state in complexes of ruthenium.
Acknowledgements
This work was supported by Enterprise Ireland and COST D19.
The National Centre for Sensor Research