π‐Extended Bodipy Self‐Assembly as Supramolecular Photonic Security Ink and Optical Waveguide

Abstract

AbstractIridescent photonic materials have wide‐ranging applications in security printing, and optical devices. While the commonly used photonic materials are based on polymers or inorganic colloidal particles, self‐assembled small molecules are rarely exploited. Herein, a Bodipy (Bodipy‐PE‐2) self‐assembly is reported that forms a layered photonic structure upon thermal annealing, exhibiting angle‐dependent iridescence of green and pink with a luminescence shift from yellow to red. The micro‐ and nano‐periodicity associated with the layered structure and the phase transformation due to the annealing are responsible for the observed properties. The single‐crystal analysis reveals the critical role of weak dispersive interactions (C–H···π, C–H···O, and N–H···F) in the crystal packing and a possible phase change in the formation of the layered structure. A stimuli‐responsive ink prepared with the annealed powder using polyethylene glycol as a vehicle medium exhibits reversible emission change between red and yellow upon heating and solvent exposure, respectively. A composite gel of the annealed Bodipy‐PE‐2 and polystyrene displays angle‐dependent color change and optical waveguiding properties. The self‐assembled Bodipy‐PE‐2 obtained from toluene exhibits active and passive waveguiding properties when excited with 532 and 633 nm laser sources.