Mechano-responsive circularly polarized luminescence of organic solid-state chiral emitters

Abstract

Two difluoro-boron β-diketonate complexes bearing chiral amido groups have been synthesized. Their mechano-responsive luminescence and chiroptical properties have been investigated in the solid state. Both compounds display a bright blue-green emission and a significant circularly polarized luminescence (CPL) signal in the crystalline state, with |g_lum| values as high as 2.2–2.4 × 10⁻². A bathochromic shift in emission, together with a decrease of |g_lum| values to c.a. 3 × 10⁻³, is induced upon application of a shearing stress. For the DFB-Hex-amide compound, interestingly, sign inversion of the anisotropy factor g_lum is observed under mechanical stimulation (“mechano-CPL effect”), which can be rationalized by a switching between monomer and excimer emission.