Fig. 2. Photophysical properties and crystal structures of X1R and X2R compounds. (A) Photoluminescence spectra of 9,9-dimethylxanthane, X1B and X2B in THF solution (10 μM) at room temperature. (B) PL spectra of 9,9-dimethylxanthane, X1N, and X2N in THF solution (10 μM) at room temperature. (C) PL spectra of 9,9-dimethylxanthane, anthracene, X1A and X2A in THF solution (10 μM) at room temperature. (D) Molecular geometry of X1B, X1N and X1A in single crystals with dihedral angles (θ) between R moieties and 9,9-dimethylxanthane scaffold. (E) Molecular packing modes in X1B, X1N and X1A crystals. (F) Molecular geometry of X2B, X2N and X2A in single crystals with centroid distances between two R moieties. (G) Molecular packing modes in X2B, X2N and X2A crystals.