Hole tunneling and hopping in a Ru(bpy)3(2+)-phenothiazine dyad with a bridge derived from oligo-p-phenylene.

A molecular dyad was synthesized in which a Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) photosensitizer and a phenothiazine redox partner are bridged by a sequence of tetramethoxybenzene, p-dimethoxybenzene, and p-xylene units. Hole transfer from the oxidized metal complex to the phenothiazine was triggered using a flash-quench technique and investigated by transient absorption spectroscopy. Optical spectroscopic and electrochemical experiments performed on a suitable reference molecule in addition to the above-mentioned dyad lead to the conclusion that hole transfer from Ru(bpy)(3)(3+) to phenothiazine proceeds through a sequence of hopping and tunneling steps: Initial hole hopping from Ru(bpy)(3)(3+) to the easily oxidizable tetramethoxybenzene unit is followed by tunneling through the barrier imposed by the p-dimethoxybenzene and p-xylene spacers.

Accelerated hole transfer across a molecular double barrier.

We report on a dyad in which photoinduced hole transfer through a non-uniform molecular double barrier is more than one order of magnitude more rapid than hole transfer across a comparable uniform (rectangular) tunneling barrier.

Tuning the rates of long-range charge transfer across phenylene wires.

Walking a tight wire: Phototriggered charge transfer across a tetra-p-dimethoxybenzene bridge is three orders of magnitude faster than that across a structurally similar tetra-p-xylene spacer, despite equal reaction driving forces in both cases [picture: see text]. This result is interpreted in terms of markedly different donor-bridge energy gaps.

Energy transfer from rhenium(I) complexes to covalently attached anthracenes and phenanthrenes.

The synthesis and photophysical properties of a series of chromophore-quencher complexes are reported. They are all comprised of a luminescent rhenium(I) tricarbonyl diimine complex that is covalently attached to anthracene or phenanthrene moieties via rigid rod-like p-xylene bridges of variable lengths. Rhenium-to-anthracene energy transfer is strongly exergonic (-DeltaG0 approximately 0.

A supramolecular cup-and-ball C60-porphyrin conjugate system.

In addition to the ammonium-crown ether recognition, pi-stacking interactions between the C60 sphere and the porphyrin moiety have been evidenced in a supramolecular complex obtained from a porphyrin-crown ether conjugate and a fullerene derivative bearing an ammonium unit.