RESUMO
Multi-metallic complexes based on {Ru-Cr}, {Ru-Ru} and {Ru-Ru-Cr} fragments are investigated for their light-harvesting and long-range energy transfer properties. We report the synthesis and characterization of [Ru(tpy)(bpy)(µ-CN)Ru(py)4Cl]2+ and [Ru(tpy)(bpy)(µ-CN)Ru(py)4(µ-NC)Cr(CN)5]. The intercalation of {RuII(py)4} linked by cyanide bridges between {Ru(tpy)(bpy)} and {Cr(CN)5} results in efficient, distant energy transfer followed by emission from the Cr moiety. Characterization of the energy transfer process based on photophysical and ultrafast time-resolved absorption suggests the delocalization of holes in the excited state, providing a pathway for energy transfer between the end moieties. The proposed mechanism opens the door to utilize this family of complexes as an appealing platform for the design of antenna compounds as the properties of the fragments could be tuned independently.
RESUMO
A series of cyanide-bridged bimetallic compounds of the general formula [Ru(L)(bpy)(µ-NC)(M)](2-/-/2+) (L = tpy, 2,2'-6',2''-terpyridine, or tpm, tris(1-pyrazolyl)methane, bpy = 2,2'-bipyridine, M = Ru(II)(CN)5, Os(III)(CN)5, Os(II)(CN)5, Ru(II)(py)4(CN), py = pyridine) have been synthesized and fully characterized. Most of them present MLCT emission (λ = 690-730 nm, Φ = 10(-3)-10(-4)) and their photophysical properties resemble the ones of the respective mononuclear Ru(L)(bpy) species. The exception is when M is Os(III)(CN)5, where an intramolecular electron transfer quenching mechanism is proposed. The conditions that should be met for avoiding the reductive or oxidative quenching of the excited state are also discussed.
RESUMO
Non-adiabatic excited-state molecular dynamics is used to study the ultrafast intramolecular energy transfer between two-, three-, and four-ring linear polyphenylene ethynylene chromophore units linked through meta-substitutions. Twenty excited-state electronic energies, with their corresponding gradients and nonadiabatic coupling vectors were included in the simulations. The initial laser excitation creates an exciton delocalized between the different absorbing two-ring linear PPE units. Thereafter, we observe an ultrafast directional change in the spatial localization of the transient electronic transition density. The analysis of the intramolecular flux of the transition density shows a sequential through-bond two-ringâthree-ringâfour-ring transfer as well as an effective through-space direct two-to-four ring transfer. The vibrational excitations of C≡C stretching motions change according to that. Finally, a mechanism of unidirectional energy transfer is presented based on the variation of the energy gaps between consecutive electronic excited states in response to the intramolecular flux of the transition density. The mechanism resembles a Shishiodoshi Japanese bamboo water fountain where, once the electronic population has been transferred to the state directly below in energy, the two states decouple thereby preventing energy transfer in the opposite direction.
RESUMO
We report the synthesis, structure and properties of the cyanide-bridged dinuclear complex ions [Ru(L)(bpy)(µ-NC)M(CN)(5)](2-/-) (L = tpy, 2,2';6',2''-terpyridine, or tpm, tris(1-pyrazolyl)methane, bpy = 2,2'-bipyridine, M = Fe(II), Fe(III), Cr(III)) and the related monomers [Ru(L)(bpy)X](2+) (X = CN(-) and NCS(-)). All the monomeric compounds are weak MLCT emitters (λ = 650-715 nm, Ï ≈ 10(-4)). In the Fe(II) and Cr(III) dinuclear systems, the cyanide bridge promotes efficient energy transfer between the Ru-centered MLCT state and a Fe(II)- or Cr(III)-centered d-d state, which results either in a complete quenching of luminescence or in a narrow red emission (λ ≈ 820 nm, Ï ≈ 10(-3)) respectively. In the case of Fe(III) dinuclear systems, an electron transfer quenching process is also likely to occur.
RESUMO
The ultrafast dynamics of electronic and vibrational energy transfer between two- and three-ring linear poly(phenylene ethynylene) units linked by meta-substitution is studied by nonadiabatic molecular dynamics simulations. The molecular dynamics with quantum transitions (1, 2) method is used including an "on the fly" calculation of the potential energy surfaces and electronic couplings. The results show that during the first 40 fs after a vertical photoexcitation to the S(2) state, the nonadiabatic coupling between S(2) and S(1) states causes a fast transfer of the electronic populations. A rapid decrease of the S(1)-S(2) energy gap is observed, reaching a first conical intersection at approximately 5 fs. Therefore, the first hopping events take place, and the S(2) state starts to depopulate. The analysis of the structural and energetic properties of the molecule during the jumps reveals the main role that the ethynylene triple bond plays in the unidirectional energy transfer process.