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Methylene blue intercalates more effectively into poly[dGdC] (K = (1.6 [+-] 0.4) [times] 10[sup 6] M[sup [minus]1]) than poly[dAdT] (K = (1.6 [+-] 0.5) [times] 10[sup 4] M[sup [minus]1]); in the latter case, intercalation competes with surface binding (K = (2.3 [+-] 0.6) [times] 10[sup 4] M[sup [minus]1]). Intercalation is accompanied by a dramatic reduction in the lifetime of the first excited singlet state, causing decreases in quantum yields for both fluorescence and formation of the triplet state. In the case of methylene blue intercalated into poly[dGdC], transient absorption spectroscopic measurements have shown that the excited singlet state of the dye abstracts a hydrogen atom (or an electron) from an adjacent nucleic acid base, presumed to be guanine on thermodynamic grounds. The rate constants for forward and reverse transfers, respectively, are (2.5 [+-] 0.3) [times] 10[sup 11] and (3.3 [+-] 0.4) [times] 10[sup 10] s[sup [minus]1]. The rate constant for the forward transfer in poly[dAdT] is (1.4 [+-] 0.5) [times] 10[sup 10] s[sup [minus]1] and is presumed to be slower than that of the reverse transfer. Using thermodynamic arguments, it is concluded that the quenching processes involve hydrogen atom transfer from guanine or adenine to the excited singlet state ofmore » methylene blue. 48 refs., 4 figs.« less

The rates of photoinduced electron transfer (ET) in a series of donor-acceptor molecules (4,4'-R 2 -2,2'-bipyridine) 2 Ru(1-(4-CH 3 -2,2'-bipyridine-4'-yl-(CH 2 ) n )-4,4'-bipyridinediium-1'-R') 4+ (R=H, CH 3 ; R'=CH 3 , CH 2 CN; n=1, 2) were studied by picosecond flash photolysis/transient absorbance techniques. The rate of intramolecular forward ET (MLCT quenching) in acetonitrile varied with -ΔG o according to classical Marcus theory for n=2, but not for n=1

Bisgold(III) bisporphyrins, in which a 1,10-phenanthroline spacer imposes a constrained geometry, have been synthesized. Mash photolysis studies indicate that, at high laser intensity, triplet exciton annihilation occurs with a diffusion coefficient of 4×10 -5 cm 2 s -1 . Two such molecules coordinate to a copper(I) ion, via the 1,10-phenanthroline spacers, to form a porphyrin ensemble in which triplet exciton annihilation competes with electron transfer from the copper(I) complex to a gold porphyrin triplet

Obtention de derives monoradical trication et diradical de cation par reduction de 3 dimethyl-1'1''' polymethylene-1,1'' bis-bipyridylium-4,4'. Etude des caracteristiques spectrales et electrochimiques d'equilibre de ces composes et cinetique de leurs reactions de reduction, oxydation et dismutation

Two (d/sup 8/.d/sup 8/)psigma binuclear complexes, Pt/sub 2/(pop)/sub 4//sup 5 -/ (pop = P/sub 2/O/sub 5/H/sub 2//sup 2 -/) and Rh/sub 2/(TMB)/sub 4//sup +/ (TMB = 2,5-dimethyl-2,5-diisocyanohexane), have been generated by pulse radiolysis of aqueous and acetonitrile solutions, respectively, of the corresponding d/sup 8/.d/sup 8/ species. An intense absorption system attributable to the allowed dsigma* ..-->.. psigma transition is observed in the spectrum of each of the transients (420 nm, Pt/sub 2/(pop)/sub 4//sup 5 -/; 570 nm, Rh/sub 2/(TMB)/sub 4//sup +/).