Magnetic circularly polarized luminescence from spin flip transitions in a molecular ruby

Magnetic circularly polarized luminescence (MCPL), i.e. the possibility of generating circularly polarized
luminescence in the presence of a magnetic field in achiral or racemic compounds, is a technique of
rising interest. Here we show that the far-red spin–flip (SF) transitions of a molecular Cr(III) complex give
intense MCD (magnetic circular dichroism) and in particular MCPL (gMCPL up to 6.3 × 10−3 T−1) even at
magnetic fields as low as 0.4 T. Cr(III) doublet states and SF emission are nowadays the object of many
investigations, as they may open the way to several applications. Due to their nature, such transitions can
be conveniently addressed by MCPL, which strongly depends on the zero field splitting and Zeeman
splitting of the involved states. Despite the complexity of the nature of such states and the related
photophysics, the obtained MCPL data can be rationalized consistently with the information recovered
with more established techniques, such as HFEPR (high-frequency and -field electron paramagnetic
resonance). We anticipate that emissive molecular Cr(III) species may be useful in magneto-optical
devices, such as magnetic CP-OLEDs.