Fig. 2. (a) Photographs and schematic representation of the molecular arrangements of 1 showing different photoluminescence upon applying external stimuli. A molecule of 1 is denoted as a rectangle. (b) Photographs of the powder forms of 2 showing different photoluminescence under UV light at 365 nm. (c) Schematic representation of the solid state molecular arrangements of 2, in which a molecule of 2 is denoted as a rectangle, with the colors of the corresponding emission. Solvent molecules are denoted as red circles. (d) Specific procedures for the interconversion of the four emitting states of 2.