Cocrystal Engineering of Benzothiazole Emitters Enables Emission Bandwidth Modulation via Supramolecular Rigidity Control

A direct correlation between lattice topology and full width at half-maximum (fwhm) shows how specific noncovalent interactions (halogen bonding and hydrogen bonding) enable supramolecular control of photophysical responses. However, controlling emission bandwidth in purely organic materials remains a key challenge for achieving high-color-purity optoelectronic performance, because conventional fluorophores often suffer from spectral broadening caused by intermolecular disorder in the solid state. Here, we present a cocrystallization-based strategy to narrow the fwhm of benzothiazole emitters without any complex chromophore redesign. Two benzothiazole derivatives ( 1 and 2 ) were cocrystallized with 1,4-diiodotetrafluorobenzene ( DITFB ), a halogen-bond donor, to systematically modulate supramolecular packing. Single-crystal X-ray diffraction revealed that 1·DITFB forms a rigid lattice through cooperative halogen and hydrogen bonding, suppressing excited-state structural relaxation and reducing the fwhm from 83 to 45 nm. In contrast, 2·DITFB, affected by steric repulsion from fluorine atoms, adopts a less compact structure, resulting in bandwidth broadening. This clear structure–property correlation demonstrates that lattice rigidity directly governs emission bandwidth, establishing cocrystal engineering as an effective design principle for narrowband organic emitters without relying on complex chromophore redesign or device-level optimization.