This paper presents the synthesis, MO calculations, and photochemical and photophysical properties of
cis-[Ru(
bpy)
2(3Amdpy
2oxaNBE)](PF
6)
2 (
2), where
bpy is 2,2'-
bipyridine and 3Amdpy
2oxaNBE is the novel 5,6-
bis(3-amidopyridine)-7-oxanor
bornene chelate-ligand (
1). Complex
2 is considered in relation to the
cis-[Ru(
bpy)
2(3Amnpy)
2](PF
6)
2 (
3) analogous complex, where 3Amnpy is 3-aminopyridine. Complexes
2 and
3 exhi
bit a
bsorptionsnear 350 nm and in the 420-500 nm region attri
buta
ble to a contri
bution from MLCT transitions (d
bpy andd
L; L = 3Amdpy
2oxaNBE or 3Amnpy). Whereas complex
3 is photochemically reactive, complex
2 showsluminescence either at 77 K or at room temperature in fluid solution. The emission of
2 assigna
ble as an MLCT(Ru
bpy) emission is characterized
by a long lifetime at room temperature (650 ns in CH
3CN and 509 ns inH
2O). It is independent of
bda.gif" BORDER=0 >
irr,
but it is temperature dependent; i.e., it increases as the temperature is lowered.Considering the chelate ring of
1 contri
butes to the sta
bility of the complex
2 under continuous light irradiation, thedifference in the primary photoprocesses of
3 (loss of 3Amnpy) and
2 (luminescence) may
be caused
by a loweringof the lowest excited state from
3 to
2. The surface crossing to the lowest MC state value of 987 cm
-1 (similar tothat of [Ru(
bpy)
3]
2+) will
be prevented in the case of complex
2, and as a result, efficient 3Amdpy moiety losscannot occur. The electronic depopulation of the {Ru(
bpy)
2} unit and population of a
bpy* or
bital upon excitationare evident
by comparing the photophysical properties with those of a [Ru(
bpy)
3]
2+ related complex. Moreover, areduction of a
bpy ligand in the MLCT excited state is indicated
by time-resolved spectra that show features typicalof
bpy
bull.gif">-. The photocatalytic property of
2 is spectroscopically demonstrated
by oxidative quenching using eithermethylviologen
2+ or [RuCl(NH
3)
5]
+2 electron-acceptor ions.