Energy Transfer by a Hopping Mechanism in Dinuclear Ir^III/Ru^II Complexes: A Molecular Wire?

Abstract

The synthesis and electrochemical and photophysical properties of a series of heterodinuclear ruthenium-iridium complexes linked by a modular para-phenylene bridge [Ir-ph(n)-Ru]3+ (Ir=Ir(ppyFF)2bpy, Ru=Ru(bpy)3, ppyFF=2-(2,4-difluorophenyl)pyridine), bpy=2,2'-bipyridine, ph=phenylene, n=2, 3, 4, 5) are reported. The use of a high-energy iridium complex, which can act as an energy donor when coupled to the lower energy ruthenium-based component, allows the investigation of photoinduced energy transfer from the excited iridium-centre to the ruthenium fragment (energy acceptor). The rate constants of the energy-transfer processes are determined by time-resolved emission and sub-picosecond transient absorption spectroscopy. Interestingly, there is almost no decrease in transfer efficiency or rates as the length between the two chromophores (number of spacers) is increased. This "molecular wire" behavior indicates the dominance of the incoherent hopping mechanism, allowing a very fast energy transfer over long distances (with n = 5 the metal-to-metal distance is estimated to be 32.5 Angstrom). This is the first case in which such behavior is observed for metal complexes, and could lead to new development in molecular electronics.

On the Conjugation Length for Oligo(ethynylnaphthalene)‐Based Molecular Rods

“…[16] Closely related research has been directed towards the construction of molecular photonic devices based on highly conjugated organic substrates bridging photoactive terminals. [17,18] The most popular organic modules for building into conductive wires are simple aromatic units such a thiophene, [19] phenylene, [20] biphenylene, [21] fluorene [22] and anthracene. [23] In many cases, the aryl groups are connected through vinyl or acetylene spacer groups that themselves help to modify and control the electronic properties.…”

Energy Transfer in a Hybrid IrIII Carbene–PtII Acetylide Assembly for Efficient Hydrogen Production

“…This is also confirmed by the fact that ar ise emission lifetime and an increase in quantum efficiency of 1 relative to that of 3 can be observed. [22] The time-resolved luminescence decays for 1 were recorded as af unction of the emission wavelengths.T he lifetime decays are wavelength dependent when the monitoring wavelength is changed from 580 nm to 680 nm ( Figure S6 in the Supporting Information), indicating of the occurrence of energy migration.…”

Synthesis and Photophysical Properties of Rhenium(I)-Alkynyl Molecular Rectangles

“…Meyer and co-workers 37 reported an intense transient absorption at 450600 nm, which is characteristic of a 4,4'-bpylocalized MLCT excited state in Re(I) complexes. Castellano and co-workers 38 postulated that one could potentially observe significantly extended to the longer lived ligand localized states of alkynyl ligands [40][41][42][43] . Hence the prolonged lifetimes observed for 2 and 3 might be due to the triplet state localized on the Re(I) chromophores being in equilibrium with the triplet states associated with the Since the distance from Re(I) component to naphthalene/anthracene unit is less than 1 nm the most probable mechanism for energy transfer is Dexter mechanism 44 .…”