Light-Induced Excited Spin-State Trapping (LIESST) is a well-known phenomenon in spin-crossover (SCO) materials, studied since 1982 in solution and 1984 in the solid state, as it offers some interesting prospects in data storage. In this paper we discuss the influence of metal dilution on the lifetime of the photo-induced state in two 1D chain solid solution series: [FexZn1−x(btzp)3](BF4)2 and [FexZn1−x(endi)3](BF4)2 {btzp = 1,2-bis(tetrazol-1-yl)propane and endi = 1,2-bis(tetrazol-1-yl)ethane}. For each composition, we have determined the thermal spin transition temperature, T1/2, and the relaxation temperature of the photoinduced high-spin state, T(LIESST). A detailed analysis of the relaxation kinetics allowed a discussion of the evolution of this lifetime as a function of metal dilution