Exciton coupling in molecular salts of 2-(1,8-naphthalimido)ethanoic acid and cyclic amines: modulation of the solid-state luminescence

In this study we have purposely altered the solid state luminescence properties of 2-(1,8-naphthalimido)ethanoic acid (NEaH) (0) via molecular salts formation with cyclic amines such as 1,4-diazabicyclo[2.2.2]octane (DABCO), quinuclidine (ABCO), 3-quinuclidinol (OH-ABCO), and piperazine (PIP). All crystalline materials have been characterized in the solid state via single-crystal and variable temperature powder X-ray diffraction and thermal methods; luminescence spectra in the solid state have been recorded. Exciton interactions have been determined with quantum-chemical calculations for all molecular organic salts, and tuning of their magnitude in response to changes in the crystal packing has been demonstrated. It is suggested that the variations in photoluminescence can be interpreted on the basis of the different excitonic interactions amongst the naphthalimide moieties.