Circularly polarized electroluminescence from an achiral fluorophore induced by co-assembly with chiral polymers

Abstract

Recently, much attention has been paid to circularly polarized luminescence (CPL) organic light-emitting diodes (CP-OLEDs) from achiral fluorophores through an intermolecular chirality induction mechanism. In this paper, we developed a new strategy for CP-OLEDs of achiral fluorophores induced by helical co-assembly between chiral polymers and an achiral fluorophore. In this paper, we synthesized three chiral 1,1′-binaphthyl-based polymers (R/S-P1, R/S-P2 and R/S-P3) with different side chain alkyl groups (n-C₄H₉; n-C₆H₁₃; n-C₈H₁₇), which can act as chirality inducers and form chiral co-assemblies with an achiral pyrenyl fluorophore (Bpy). At a 50% doping weight ratio of R/S-P2 inducer with Bpy, this kind of chiral co-assembly (R/S-P2-Bpy) can exhibit helical nano fibers and emit a strong deep blue CPL signal (λ_em = 420 nm, dissymmetry factor |g_em| = 0.042) in spin-coated films after annealing (120 °C). Moreover, the stable CP-OLEDs using R/S-P2-Bpy as the device emitting layer (EML) can emit strong CP-EL with an electroluminescence dissymmetry factor |g_EL| of up to 0.021.