inorganic chemistry

In the UV/Vis absorption spectrum, a broad band at
labs¼370 nm and a more intense one at 292 nm are attributed
to transitions to the^1 MLCT and the^1 pp*(^1 LC) excited states,
respectively. Such characteristics are common for many rhe-
nium(I) diimine carbonyl complexes (Table I). The emission spec-
trum comprises a single broad band, which arises from a
transition from the lowest^3 MLCT excited state to the ground
state. The lifetime of the^3 MLCT excited state is relatively short
(Table I).
In the case of the rhenium(I) bipyridine tricarbonyl complexes
with a phosphorous ligand such as3ain Table I, both the^1 MLCT
absorption and the emission bands are blue shifted because of
the stronger LF induced by the phosphorous ligand. This causes
the lifetime of the^3 MLCT excited state to be longer. The
photophysical parameters of some typical Re(I) complexes are
summarized in Table I (5,26).
Concerning the relaxation processes of Ru(II) tris(diimine)
complexes whose lowest excited state is the^3 MLCT state, a good
linear relationship between the logarithm of the nonradiative
decay rate (kd) and the energy gap (E 00 (^3 MLCT)), the energy dif-
ference from the ground state to the^3 MLCT state, is observed.
This is termed as the Energy Gap Law(5,27). In a series of rhe-
nium(I) bipyridine tricarbonyl complexes, such a linear correla-
tion was also observed (Fig. 4) (26,27), where the net

300

0

5

e(10

3 M

–1

cm

–1

)

400

MLCT

in MeCN

p–p∗

500

Wavelength / nm

600 700

Intensit

y^

(a.u.

)

FIG. 3. UV/Vis absorption and emission spectra of fac-Re(bpy)
(CO) 3 Cl (1a) complex measured in an CH 3 CN solution.

142 HIROYUKI TAKEDAet al.