Induction of circularly polarized electroluminescence from an achiral light-emitting polymer via a chiral small-molecule dopant

Abstract

By simply doping the conventional light-emitting polymer F8BT with a helically chiral aromatic molecule, it is shown that substantial levels of CP-electroluminescence can be generated directly. Both photoluminescent and electroluminescent emission from the polymer are observed to become circularly polarized, with the sign of the CP emission directly determined by the handedness of the dopant.

Figure 1

a) Molecular structures of 1-aza[6]helicene right- (P or (+)) and left- (M or (−)) handed enantiomers. b) Molecular structure of the light-emitting polymer F8BT. c) Single-layer PLED device structure consisting of a 1-aza[6]helicene-doped F8BT thin film sandwiched between a PEDOT:PSS-coated ITO anode and a Ca/Al cathode; right- and left-handed σ⁺ and σ⁻ circularly polarized electroluminescent polymer emission was respectively generated from (+)- and (−)-1-aza[6]helicene-doped devices.

Figure 2

F8BT doped with varying ratios (% by weight) of 1-aza[6]helicene: a) absorption (solid curves) and photoluminescence (PL) (dashed curves) spectra of F8BT doped with (+)-1-aza[6]helicene; b) CD spectra of F8BT doped with (+)-1-aza[6]helicene (solid curves) and (−)-1-aza[6]helicene (dashed curves); c) CP-PL spectra of F8BT doped with (+)-1-aza[6]helicene; d) CP-PL spectra of F8BT doped with 7% (by weight) (+)-1-aza[6]helicene (filled symbols) and 6% (by weight) (−)-1-aza[6]helicene (open symbols).

Figure 3

a) Molecular structure of P (or +) [7]helicene. b) CP-PL spectra of F8BT films doped with 52% (by weight) (+)- and (−)-[7]helicene.

Figure 4

a) Variation of current J (circles) and luminosity L (squares) with applied voltage V. b,c) EL spectra (b) and CP-EL spectra (c) of the PLED device (see Figure 1c) containing a light-emitting layer of F8BT doped with 7% (by weight) of (+)-1-aza[6]helicene (solid symbols) and 6% (by weight) (−)-1-aza[6]helicene (open symbols). d) J–V–L curves of an undoped F8BT PLED with EL spectrum as the inset.