Push–Pull Dyes for Yellow to NIR Emitting Electrochemical Cells
Maxime Rémond, Jongun Hwang, Jinbo Kim, Saeon Kim, Dong‐Hwan Kim, Christophe Bucher, Yann Bretonnière, Chantal Andraud, Eunkyoung Kim
Abstract
Abstract Push–pull (D‐π‐A) dyes are explored for organic light‐emitting electrochemical cells (LECs) taking advantages of their tunability in the intramolecular charge transfer (CT) through a π‐bridge between donor and acceptor. These dyes present high thermal stability beyond 290 °C and fluorescence quantum yields ( Φ f ), and simple thin film processability. The fluorene‐based dyes with diphenylamine donor (DPF) show high tunability in electroluminescence wavelength up to 825 nm that corresponds to the most red‐shifted metal‐free LECs reported to date. The DPFs show high irradiance under a low working voltage in the presence of poly(9‐vinylcarbazole) (PVK) and 2,5‐bis(5‐ tert ‐butyl‐benzoxazol‐2‐yl)thiophene (BBOT) hosts. As the CT distance of dyes is increased, V on of the LECs is decreased, since Φ f and lifetime of dyes are higher. Furthermore, the smaller angle between the π‐bridge and acceptor (A πA ) of dye is critical to increase irradiance, for a closer dye–host proximity. Thus a DPF dye with the lowest A πA (dye I) affords the highest irradiance of 425 µW cm −2 (>220 Cd m −2 ) among the dyes in this study. Therefore push–pull dyes could provide a rational material design principle toward near‐infrared emitting LECs.