Light-induced excited spin state trapping in a transition-metal complex: The hexa-1-propyltetrazole-iron (II) tetrafluoroborate spin-crossover system

Abstract

We report the first example of a light-induced conversion of the low-spin (LS) state ( 1A 1g) to the high-spin (HS) state ( 5T 2g) in the spin-crossover iron (II) complex [Fe(ptz) 6] (BF 4) 2, where ptz = 1-propyltetrazole. The spin state conversion is quantitative, and the trapped HS state does not decay within many hours at temperatures < 50 K. At α 50 K the excited HS state relaxes back to the normal LS state. Around 135 K, one sees the well-known thermally induced spin transition LS ( 1A 1) α HS ( 5T 2). Mössbauer studies demonstrate unambiguously this hitherto unknown photophysical phenomenon which we call “light-induced excited spin state trapping” (LIESST).