<p>The chiral Boranil dye (LB(O)-Br) exhibits polymorphism forming two distinctly different structures in the solid state. Polymorph I crystallises in the space group <i>I</i>4₁/<i>a</i> and exhibits C-H‧‧‧O and C-H‧‧‧Br interactions to produce a columnar structure with 3D connectivity. Polymorph II crystallises in <i>P</i>2₁/<i>c</i> and, in addition to C-H‧‧‧O contacts, forms Br‧‧‧O halogen bonds and edge-to-face π-interactions to give a 2D layered structure. Given the propensity of these compounds to fluoresce in the crystalline state, polymorphism of these structures is an important factor to consider when designing dyes of this kind for solid-state applications.</p> Graphical abstract <p></p> <p>An overlay highlights the areas of the title molecule and its analogue that vary most in terms of conformation.</p>