Solvent Switching of Intramolecular Energy Transfer in Bichromophoric Systems:  Photophysics of (2,2‘-Bipyridine)tetracyanoruthenate(II)/Pyrenyl Complexes

Abstract

The supramolecular systems [Ru(Pyr(n)bpy)(CN)(4)](2-) (n = 1, 2), where one and two pyrenyl units are linked via two-methylene bridges to the [Ru(bpy)(CN)(4)](2-) chromophore, have been synthesized. The photophysical properties of these systems, which contain a highly solvatochromic metal complex moiety, have been investigated in water, methanol, and acetonitrile. In all solvents, prompt and efficient singlet-singlet energy transfer takes places from the pyrene to the inorganic moiety. Energy transfer at the triplet level, on the other hand, is dramatically solvent dependent. In water, the metal-to-ligand charge transfer (MLCT) emission of the Ru-based chromophore is completely quenched, and rapid (200 ps for n = 1) irreversible triplet energy transfer to the pyrene units is detected in ultrafast spectroscopy. In acetonitrile, the MLCT emission is practically unaffected by the presence of the pyrenyl chromophore, implying the absence of any intercomponent triplet energy transfer. In methanol, triplet energy transfer leads to an equilibrium between the excited chromophores, with considerable elongation of the MLCT lifetime. The investigation of the [Ru(Pyr(n)bpy)(CN)(4)](2-) systems in methanol provided a very detailed and self-consistent picture: (i) The initially formed MLCT state relaxes toward equilibrium in 0.5-1.3 ns (n = 1, 2), as monitored both by ultrafast transient absorption and by time-correlated single photon counting. (ii) The two excited chromophores decay with a common lifetime of 260-450 ns (n = 1, 2), as determined from the decay of MLCT emission (slow component) and of the pyrene triplet absorption. (iii) These equilibrium lifetimes are fully consistent with the excited-state partition of 12-6% MLCT (n = 1-2), independently measured from preexponential factors of the emission decay. Altogether, the results demonstrate how site-specific solvent effects can be used to control the direction of intercomponent energy flow in bichromophoric systems.

Improving photosensitization for photochemical CO2-to-CO conversion

“…By contrast, Ru-4 showed a small hypochromic shift at 670 nm (148.7 cm −1 ), suggesting an 3 IL emissive state. For Ru-2 , an emission band between 600 and 800 nm was observed at 77 K, which matched well with the phosphorescence of pyrene [ 51 ]. Thus, this indicated a pyrenyl localized emissive state.…”

Supramolecular tuning of energy transfer efficiency and direction in a bis(styryl) dye–crown ether conjugate

“…The control of the FRET direction can be also accomplished by protonation/deprotonation of the donor or acceptor unit as has been shown for oligophenylene vinylene (OPV) phenanthroline [10] and OPV fullerene [11] dyads and for multichromophoric BODIPY systems [12,13]. In addition, sev eral intriguing examples of switchable FRET directions have been re ported that use site specific solvent effects [14], temperature changes [15] or the electronic difference between cation binding sites [16,17]. Nevertheless, molecules or molecule assemblies that enable the fine regulation of the energy transfer processes based on supramolecular interactions are still rare and their discovery and development remains a topical challenge.…”

Pyrene-based metal–organic framework NU-1000 photocatalysed atom-transfer radical addition for iodoperfluoroalkylation and (Z)-selective perfluoroalkylation of olefins by visible-light irradiation

“…3b), both phenomena evidenced the photoinduced singlet-singlet EnT process from excited-state NU-1000 to the peruoroalkyl iodide molecules. [62][63][64][65] As previously mentioned, the ATRA reaction hugely diminished in the presence of O 2 (DE T1/S 1 ¼ ca. 95 kJ mol À1 ) as an effective triplet energy quencher of excited state (Table 1, entry 10).…”