A rapid screening of Ru(II) photosensitizers

Linear Multinuclear RuII Photosensitizers

“…All of the new complexes are better sensitizers than [Ru(ttpy) 2 ] 2ϩ , [4] with higher k f and χ values. This may reflect generally longer τ values owing to a greater π-delocalization and π* stabilization in the bridging ligands which, as discussed earlier, are the preferred sites for the excited electrons.…”

“…Both, then, also depend on the photophysical properties that govern the production of Ru II *, including ε and τ. However, the ratio k q /k f (ϭ [MV 2ϩ ] 0 /χ Ϫ 1) was previously shown to equal k r [MV 2ϩ ] 0 /k t [TEOA] 0 , [4] where k r and k t are the second-order rate constants for the reactions of the Ru III photoproduct with the MV ·ϩ co-product (reverse electron transfer) and with TEOA (trapping), respectively. This ratio is therefore a measure of the competition between the non-productive and productive fates of the Ru III form of the sensitizer.…”

“…In real-life photoredox applications, there would be no sacrificial donor present, but the excited state could be reductively quenched at an electrode surface or by a reversibly reduced electron relay molecule such as MV 2ϩ at an illuminated organic-aqueous interface. Comparisons between sensitizers in terms of the kinetic parameters governing this process have previously enabled us to probe steric, electrostatic and solvent effects on activity, [16,20,21] and we wished, in the present work, to probe the effect of increasing the Ru chain length N. Using our standard protocol, [4] we measured the time courses of MV ·ϩ development at room temperature in CH 3 CN at 600 nm with a sensitizer concentration of 4 ϫ 10 Ϫ5 . The key results presented in Table 1 are the first-order rate constants k f and k q for MV ·ϩ formation and anaerobic quenching, respectively, and the anaerobic yields χ, RET , the Marcus activation energies for the forward and reverse electron transfers, respectively, for end-on approaches by MV 2ϩ/·ϩ to the terminal metals.…”

“…[(ttpy)Ru(A)Ru(ttpy)](PF 6 ) 4 showed only two sets of terpy signals reflecting the higher symmetry, including a phenylene singlet and 3Ј/5Ј-H singlets at δ ϭ 9.19 and 9.05 ppm for metal-bound terpy units of A and ttpy, respectively.…”

“…[4] Comparisons were also made with [Ru(ttpy) 2 ] 2ϩ (ttpy ϭ 4Ј-p-tolyl-2,2Ј:6Ј,2ЈЈ-terpyridine), a related complex of known τ (0.95 ns in CH 3 CN). [5] This paper provides full details of that work and extends it by exploring the photoactivity of several new complexes of related bridging ligands, namely the meta isomer of A (ligand B) and the dipyrazinylpyridine (dpp) analogues of A and B (ligands C and D).…”