Photoluminescence and crystal structures of chiro-optical 1,1′-Bi-2-naphthol crystals and their inclusion compounds with dimethyl sulfoxide

Crystal structures of (R)-(+)-1,1′-bi-2-naphthol (BINOL), (R,S)-(±)-BINOL, (S)-(-)-BINOL, (R,S)-(±)-BINOL·DMSO, (R)-(+)-BINOL·2DMSO, (R,S)-(±)-BINOL·2DMSO, and (S)-(-)-BINOL·2DMSO (DMSO = dimethyl sulfoxide) were determined and related to their photoluminescence measurements systematically. The intensities of both excitation and emission bands of BINOL tended to rise as the average distance between BINOL molecules increased. The polarity of DMSO in the inclusion compounds with DMSO probably induced a different magnitude of the Davydov splitting and the degree of shifting of the levels of BINOL molecules. The stabilization of the excited state and the lowering of its energy led to a red-shifted emission. It was proven that photoluminescence of lumophore molecules in the solid state was able to be fine-tuned through supramolecular organization and the host-guest interaction by crystallization of a racemic compound (i.e., co-crystallization of R and S enantiomers), by formation of an enantiomorph, and by solvation with different stoichiometric ratios of a guest solvent. Therefore, this kind of supramolecular organization has significant design and characterization implications for organic solid-state lasers and devices.