Control of photochemical, photophysical, electrochemical, and photocatalytic properties of rhenium(I) complexes using intramolecular weak interactions between ligands

Intramolecular interactions between ligands have been successfully applied as a novel tool for controlling various properties of a series of cis, trans- [Re(dmb) (CO)(2) (PR3) (PR'(3))](+)-type complexes (dmb = 4,4'-dimethyl-2,2'-bipyridine), in the ground state and in the excited state and in the one-electron reduced form. For rhenium complexes with two triarylphosphine ligands, P(p-XPh)3, the dmb ligand was sandwiched by four aryl rings having CH(aryl)-pi(pyridine)-pi(aryl) interactions. On the other hand, complexes with one triarylphosphine ligand and one trialkylphosphite ligand, P(OR)(3), had pi-pi and CH-pi interactions between each pyridine ring in the dmb ligand and the aryl group in the P(p-XPh)(3), Various properties of these two series of rhenium complexes were compared with those of complexes having two trialkylphosphite ligands, which do not interact through space with the dmb ligand. Properties of the complexes associated mainly with the dmb ligand are strongly affected by the intramolecular interactions: (1) UV/vis absorptions to the pi-pi* and (MLCT)-M-1 excited states were both red-shifted, but (2) emission from the (MLCT)-M-3 excited state was blue-shifted; (3) the lifetime of the 3MLCT excited state was prolonged up to 3-fold; (4) the reduction potential in the ground state was positively shifted by 110 mV with pi-pi and CH -pi interactions and by 180-200 mV with the CH-pi-pi interactions. (5) In the excited states, the oxidation power of the complex was also enhanced by the intramolecular interactions. (6) In the corresponding one-electron-reduced species cis, trans-[Re(dmb(-.))(CO)(2)(PR3)(PR'(3))], the intramolecular interactions are maintained and strongly affected their UV/vis spectra. (7) Photocatalysis for CO2 reduction was significantly enhanced only by the CH-pi-pi interaction.