Excited-state relaxation dynamics of Ru(dcbpy)2(NCS)2, studied by fluorescence upconversion spectroscopy

Excited-state relaxation dynamics of a ruthenium-based dye (Ru(dcbpy)(2)(NCS)(2)) has been investigated by femtosecond fluorescence upconversion spectroscopy. Understanding the dynamics of excited-state relaxation in this sensitizer molecule is of key importance in designing efficient photochemical storage devices. This letter presents the first direct observation of the singlet emissive state in this dye in solution, upon excitation at 410 nm. The Franck-Condon excited state is observed to decay fast (43+/-10 fs) in ethanol and is attributed to a highly competitive intersystem crossing (ISC) and relaxation to the lowest singlet state (internal conversion, IC). From the kinetics recorded at different wavelengths, it proposed that the excited molecule undergoes a cascade relaxation along the multitude of electronic singlet levels, with a high chance for the ISC. The lifetime of some of the singlet states has been evaluated as 43 +/- 10, 87 +/- 13, and 162 +/- 40 fs at 600, 650, and 700 nm, respectively. The results have been discussed in comparison with the report on [Ru(bpy)(3)](2+) and gives first-hand information about the intriguing excited-state relaxation process in the RuN3 complex.