Quenching of Fluorescence in Bodipy‐Derived Trifluoromethyl Enaminone Ligands upon Coordination to Copper(II)

Abstract

AbstractThe synthesis of two trifluoromethyl‐derived enaminone ligands, L1H (bidentate) and L2H2, (tridentate), which bear a fluorescent 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (Bodipy) moiety, leads to the preparation and characterization of two CuII complexes {[Cu(L1)2]·2(CH2Cl2) (A) and [Cu4(L2)4]·4(C4H8O2) (B)} that exhibit different architectures. The magnetic properties of the cubane‐like complex B evidence a dominant ferromagnetic behavior characterized by exchange coupling constants J1 = +20.56(3) cm–1 and J2 = –10.29(2) cm–1. Indeed, whereas the luminescence properties of the Bodipy‐derived trifluoromethyl enaminones L1H and L2H2 are typical of the Bodipy skeleton, the emission is totally quenched in both mononuclear (A) and cubane (B) CuII complexes. To elucidate this quenching phenomenon, the Rehm–Weller equation has been used based on experimental cyclic voltammetry redox potential measurements. The result remains ambiguous for complexes A and B, and the origin of the quenching phenomenon, photoinduced electron transfer (PET) versus energy transfer (Förster or Dexter), cannot be deduced.