Sign inversion in magnetic circularly polarised luminescence of fused aromatics with 1.6 T N-up/S-up Faraday geometry

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 (g MCPL 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.

Magnetic Circularly Polarized Luminescence in the Photoexcited States of Racemic [n]Helicenes (n=3-5,7) in Tetrahydrofuran and Dimethyl Sulfoxide Solutions

This paper reports the first magnetic circularly polarized luminescence (MCPL) characteristics of racemic helicenes, including four unsubstituted [n]helicenes (n=3,4,5,7) and two [4]helicene derivatives bearing methoxy substituents, in tetrahydrofuran (THF) and dimethyl sulfoxide (DMSO) solutions. The value of |g_MCPL | was calculated to be of the order of 10^-3  T^-1 within 350-430 nm under the north-up (N-up) and south-up (S-up) Faraday geometries in an external magnetic field of 1.6 T. The [n]-dependent MCPL signs were altered by the N-up and S-up geometries.

Sign dependence of MCPL spectra on type and position of substituent groups of pyrene and phenanthrene derivatives

Diamagnetic achiral pyrene and phenanthrene derivatives substituted with electron-donating hydroxyl/methoxy groups and electron-withdrawing carboxylic acid groups exhibited clear magnetic circularly polarised luminescence (MCPL) spectra at 360-460 nm in dilute solvents upon the application of N-up and S-up Faraday geometries under an external magnetic field of 1.6 T. Their MCPL signs were also susceptible upon application of the same Faraday geometry.