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The [M0O(bdt)~]-/[MoO(bdt)~]2-(H2bdt = benzene-I ,2-dithiol) redox couple, in dimethylformamide solution, is a fully reversible process at €+ = -350 mV vs. standard calomel electrode and each of these anions has been characterised by X-ray crystallo raphy; the metal-ligand bond lengths of the former are slightly shorter than those of the latter, MoV-0 = 1.668(3) 1, MolV-0 = 1.699(6) A, mean MoV-S = 2.377(1) A, MolV-S = 2.388(2) A.

1991 photochemistry, radiation chemistry, chemoluminescence photochemistry, radiation chemistry, chemoluminescence O 0160 -094Effect on MLCT Excited States of Electronic Delocalization in the Acceptor Ligand.-Metal to ligand charge transfer (MLCT) excited states of (Ru(bpy))2+ ( bpy: 2,2'-bipyridyl) and related complexes are utilized as sensitizers of photochemical electron transfer. To circumvent limitations of these complexes (decrease of lifetimes of the excited states with increase of the wavelength of the light absorbed), the ligand-bridged complex ( III) is prepared which does not undergo trans/cis isomerization even after an extended photolysis period. It has an absorption feature at 500 nm in addition to a dπ → π* transition at 460 nm; ( III)* emits at 750 nm. From the experimental results (including cyclic voltammetry) it is concluded that the lowest lying excited state in ( III)* is a MLCT state in which the excited electron is on the (II) ligand. The lifetime of (III)* (1.31 ± 0.05 µs; MeCN, 298 K) is surprisingly long as is that of some analogous complexes having (II) as a ligand. So a new strategy is opened for the design of MLCT based photosensitizers operating much further in the red while maintaining acceptable lifetimes.

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