Monitoring the Spin States of Ferrous Ions by Fluorescence Spectroscopy in Spin‐Crossover–Fluorescent Hybrid Materials.

Abstract: The grafts of fluorophores 9‐anthraldehyde (AD) and 9‐phenanthrenecarboxaldehyde (PD), respectively, on the one‐dimensional spin‐crossover compound [Fe(L)3](ClO4)2 (FeL, L=4‐amino‐1,2,4‐triazole) by post‐synthetic aldimine condensation reactions produced two spin‐crossover (SCO)–fluorescent hybrid materials, that is, FeL‐AD and FeL‐PD. The spin‐crossover critical temperatures of the two materials both centered at <italic>T</italic>c↓=254 and <italic>T</italic>c↑=256 K, whereas the fluorescence intensities of the two materials featured functions of the temperature that strictly synchronized with the spin‐crossover processes, which showed that the ligand‐centered fluorescence was dominated by the spin states of the ferrous ions. The bifunctional entities (spin‐crossover centers and fluorophores) in FeL‐AD or FeL‐PD showed spectral band overlap that purported the Förster resonance energy transfer mechanism of such spin‐crossover–fluorescence correlation. The post‐synthetic modification of SCO materials and the relationship between the fluorescence and the SCO may be helpful in the development of multifunctional materials that can be sensitive to multiple stimuli. [ABSTRACT FROM AUTHOR]