Intrinsically Switchable Electroactive Fluorophores Based on λ 5 ‐Biphosphinines**

Abstract The synthesis and full characterization of a family of stable λ 5 ‐biphosphinines connected in 4,4‐position through a variety of π‐conjugated bridges is reported. The impact of the π‐bridge on the optical (absorption/emission) and redox properties was investigated using a joint experimental/theoretical approach. In contrast to the π‐extended ones, the λ 5 ‐biphosphinines directly connected through a C−C bond in 4,4‐position display two easily accessible and reversible oxidations highlighting their multi‐stage redox character. The in situ formed radical cations are studied by spectro‐electrochemistry and electron paramagnetic resonance. Finally, electrochemical modulation of fluorescence (electrofluorochromism) was performed and revealed the potential of these intrinsically switchable electroactive fluorophores for further applications as switchable materials.