Helical Ladder Oligomers Exhibit Amplified Circularly Polarized Emission
Christoffer Bræstrup, Xiao Xiao, Francisco García‐González, Theis Brock‐Nannestad, Daniel Aranda, Si Tong Bao, Daniel Čavlović, Haoyu Jiang, Fay Ng, Colin Nuckolls, Fabrizio Santoro, Michael Pittelkow
Abstract
Abstract Establishing design principles to engineer molecules that exhibit strong circularly polarized luminescence (CPL)‐brightness across the UV, visible and NIR spectral range remains an unsolved challenge. To achieve a large CPL‐brightness, the main difficulty is to optimize the luminescence dissymmetry factor g lum . Herein is described the discovery that a multi‐helicene system based on a series of annulated [6]helicenes and perylenediimides, exhibits larger‐than‐linear amplification of g lum with helicene length. Large enhanced fluorescent quantum yields and large extinction coefficients are also observed for this length series. Consequently, this series of oligomers exhibit exceptional CPL brightness (B CPL ) above 1 × 10 3 mol −1 cm −1 . Using computational methods based on density functional theory (DFT), the experimental trend shows that the increase of glum is due to the progressive alignment of magnetic (|m|) and electric transition (|µ|) dipole moment vectors, as the helical backbone grows longer.