The dye-sensitized solar cell dye Z-907, [RuLL'(NCS)(2)] may loose a thiocyanate ligand at elevated temperatures(80-100 degrees C) by ligand exchange with the solar cell additive 4-tert-butylpyridine(4-TBP) or the electrolyte solvent 3-methoxypropionitrile(3-MPN). The mechanism in homogeneous solution proceeds via three equilibrium reactions Eqs.(1)-(3) with the solvent complex[RuLL'(NCS)(3-MPN)] as an intermediate: [RuLL'(NCS)(2)]+3-MPN = [RuLL'(NCS)(3-MPN)](+)+NCS(-) (1) [RuLL'(NCS)(3-MPN)](+)+4-TBP = [RuLL'(NCS)(4-TBP)](+)+3-MPN (2) [RuLL'(NCS)(2)]+4-TBP = [RuLL'(NCS)(4-TBP)](+)+NCS (3) A similar mechanism describes the heterogeneous substitution reactions of Z-907 attached to the surface of TiO(2) particles with 3-MPN and 4-TBP. All the six homogeneous and heterogeneous rate constants were obtained at 100 degrees C by monitoring the decay of Z-907 and product formation in test-tube experiments by HPLC coupled to UV/vis and electrospray mass spectrometry. A half-life time t(1/2) 150 h was obtained for the Z-907 dye bound to TiO(2) nanocrystalline particle sat 85 degrees C in the presence of 4-TBP and 3-MPN. Dye-sensitized solarcells (DSC) with Z-907 as a sensitizer and application of the so-called "non-robust'' electrolytes containing 4-TBP and 3-MPN is therefore not expected to be able to pass a 1000 h thermal stress test at 85 degrees C. Addition of thiocyanate to the cell electrolyte may however, eliminate or reduce the problems caused by dye thiocyanate ligand substitution in DSC cells. (C) 2009 Elsevier B. V. All rights reserved.