Solvent-sensitive signs and magnitudes of circularly polarised luminescence and circular dichroism spectra: probing two phenanthrenes as emitters endowed with BINOL derivatives.

A C2-symmeric binaphthyl framework bearing phenanthrene as the emitter exhibited circularly polarised luminescence (CPL) in dilute solutions. The CPL and circular dichroism signs of the luminophores were altered by solvents (chloroform, methanol, acetonitrile, and dimethylformamide). DFT and TD-DFT calculations indicated that the dihedral angle between the phenanthrene and naphthyl rings was responsible for the apparent sign inversion. The role of solvent molecules in the ground and photoexcited states was discussed based on Hansen solubility parameters (δ, δd, δp and δh).

Concentration-dependent circularly polarized luminescence (CPL) of chiral N,N'-dipyrenyldiamines: sign-inverted CPL switching between monomer and excimer regions under retention of the monomer emission for photoluminescence.

Herein, an unprecedented switching of circularly polarized luminescence (CPL) is described for chiral 4,6-bis(1-(pyren-1-ylamino)propyl)dibenzo[b,d]furan (1). The CPL band of chiral diamine 1, which contains two pyrene rings, can be switched between the monomer and excimer emission regions under concomitant inversion of the handedness, simply by changing the concentration of the fluorophore. In contrast, the maximum photoluminescence (PL) intensity is always observed in the monomer region, regardless of the concentration. The reversal of the intensity ratio of monomer and excimer emission between PL and CPL was attributed to a stronger CPL (|gem| = ∼3-4 × 10-3) contribution from the minor excimer component, which should exhibit an efficient chiral environment around the dimeric pyrenes.