The cyano-bridged trinuclear complex Ru(CN)4[Cr(cyclam)(CN)2]2 has been synthesized and characterized. The absorption spectrum is dominated by an intense Ru(II) → Cr(III) charge transfer (intervalence transfer) band. Excitation into this band leads to efficient (η ≈ 1) population of the Cr(III)-centered doublet state, which gives rise to a characteristic phosphorescent emission (Φ = 1.3 × 10-2, τ = 300 μs). The process which connects absorption and emission ([-Ru(III)-Cr(II)] → [-Ru(II)-*Cr(III)]) is an excited-state charge recombination, i.e., a back electron transfer process producing a locally excited state rather than the ground state of the complex. The efficiency of this unusual process depends on the peculiar energetics of the system (activationless crossing between [-Ru(III)-Cr(II)] and [-Ru(II)-*Cr(III)], strongly "inverted" situation between [-Ru(III)-Cr(II)] and [-Ru(II)-Cr(III)]). The sequence in which the electronic states of this dyad system are interconverted (ground state → charge-transfer state → locally excited state → ground state) is the reverse of that usually observed in photoinduced electron transfer. © 1993 American Chemical Society.
Excited-State Charge Recombination in a Ru(II)-Cr(III) Polynuclear Complex
INDELLI, Maria Teresa;SCANDOLA, Franco
1993
Abstract
The cyano-bridged trinuclear complex Ru(CN)4[Cr(cyclam)(CN)2]2 has been synthesized and characterized. The absorption spectrum is dominated by an intense Ru(II) → Cr(III) charge transfer (intervalence transfer) band. Excitation into this band leads to efficient (η ≈ 1) population of the Cr(III)-centered doublet state, which gives rise to a characteristic phosphorescent emission (Φ = 1.3 × 10-2, τ = 300 μs). The process which connects absorption and emission ([-Ru(III)-Cr(II)] → [-Ru(II)-*Cr(III)]) is an excited-state charge recombination, i.e., a back electron transfer process producing a locally excited state rather than the ground state of the complex. The efficiency of this unusual process depends on the peculiar energetics of the system (activationless crossing between [-Ru(III)-Cr(II)] and [-Ru(II)-*Cr(III)], strongly "inverted" situation between [-Ru(III)-Cr(II)] and [-Ru(II)-Cr(III)]). The sequence in which the electronic states of this dyad system are interconverted (ground state → charge-transfer state → locally excited state → ground state) is the reverse of that usually observed in photoinduced electron transfer. © 1993 American Chemical Society.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
