Unique 2D Face Topologies in Naphthyl‐Appended Naphtho[k]fluoranthene‐Based 3D Crystals for Optical Waveguide

Abstract Molecular crystals exhibiting optical waveguiding are strongly dependent on total internal reflection, molecular stacking arrangements, spatial distributions of transition dipole moments, and topologies. Fluoranthene derivatives are popular fluorescent dyes that have not yet been engineered into crystalline optical materials. Here, a naphthyl‐appended naphtho[k]fluoranthene that exhibits efficient fluorescence in solution and in the solid state is newly synthesized through a one‐pot Pd‐catalyzed reaction of 1,8‐dibromonapthalene. It selectively gives two crystal topologies derived from direction‐specific crystal growth. Using spatially resolved photoluminescence analyses, the direction‐oriented light that propagates along these topologies (each face of the crystal) is investigated. There are different optical‐loss coefficients along the various directions on each face. Therefore, face‐specific waveguiding depends on molecular arrangements. Anisotropic waveguiding in each face is observed. Overall, these results suggest potential applications of fluoranthene crystals and their topological 2D planes as optical waveguides and integrated optical circuits.