Ultrafast singlet energy transfer competes with intersystem crossing in a multi-center transition metal polypyridine complex

Transition metal polypyridine complexes are finding widespread applications within many areas of chemistry. For their light-induced processes, the generally accepted picture is that all function emanates from triplet states because the singlet states initially prepared by light absorption are depopulated via intersystem crossing on the 100-fs time scale, before they are significantly involved in chemical reactions. Here we show that this is not always true. With ultrafast spectroscopy applied to a (ruthenium)(3)-osmium complex we show that transition metal polypyridine complexes can be designed where energy transfer between excited singlet states located on different metal centers efficiently competes with intersystem crossing, thus decreasing population of the lower-lying triplet states and concomitant energy loss. (C) 2004 Elsevier B.V. All rights reserved.