Dissertation

|3.1 Brominated Phenanthrolines - A Gate to new Bridging Ligands|
45 000
1.0
37 500
/ l mol -1 cm -1
30 000
22 500
15 000
0.5
Relative Emission / a.u.
7 500
0
300 400 500 600 700 800
Wavelength / nm
0
Figure 52: Absorption spectra of the [Ru(tbbpy) 3-n (phenBr 2 ) n ] 2+ -series (n = 0, 1, 2, 3) in
dichloromethane and corresponding concentration independent relative emission upon excitation
at 467 nm. [Ru(tbbpy) 3 ] 2+ : Abs. (—), Em. (- -), Ru(phenBr 2 ): Abs. (—), Em. (- -), Ru(phenBr 2 ) 2 :
Abs. (—), Em. (- -), Ru(phenBr 2 ) 3 : Abs. (—), Em. (- -).
the bathochromic and hyprochromic shoulders are slightly sensitive to the solvent and thus
suggests an instantaneous sensing of the formation of the dipolarity of the excited structure
[Ru 3+ (̂LL) 2 (̂LL − )] 2+ . The “camel hump” shape of the band can be expained by a combination of
effects which result of the distorted octahedral geometry which might influence the energy levels
of the MLCT-involved ruthenium centered t 2g -orbitals (as seen in the homoleptic complexes) and
the different ligand centered LUMO ( ̂LL) energies (in the heteroleptic complexes).
The emission behavior of the [Ru(tbbpy) 3-n (phenBr 2 ) n
] 2+ -series in acetonitrile exhibits a similar
tendency. A blue shift of the emission band and an increase in the relative emission intensity can be
(n = 1)
observed with increasing number of the phenanthroline ligands (λ max = 631 nm > λ
> λ
(n = 3)
max.
(n = 2)
max
= 621 nm
= 600 nm). This can be explained by the phenanthroline-centered emission (Kasha’s
rule). Interestingly, the homoleptic complex [Ru(tbbpy) 3 ] 2+
(λ
(n = 0)
max
exhibits an emission maximum
= 615 nm) and an emission intensity which is between the phenBr 2 -substituted complexes.
Obviously, no lower lying phenanthroline centered 3 MLCT emission is available in this complex,
so that emission is only possible from the higher lying tbbpy-centered 3 MLCT state (compare
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