Photoinduced Polymorphism of Fluorescent Organic Molecules in Solid State

Abstract A new organic molecule is found to be able to form different fluorescent aggregation states in both single crystals and powders. When irradiated with ultraviolet light, single crystals and powders exhibit an in situ change in the fluorescence color from blue to green and then to chartreuse without changing the chemical groups. This stems from photoinduced changes in the molecular conformation and packing in the solid state. Two or three fluorescence colors can be displayed simultaneously in a single organic crystal by controlling the irradiation time. Under irradiation with intense ultraviolet light, deformations, movements and in situ welding of crystals can be achieved by utilizing the photothermal effect. This work demonstrates a new strategy for inducing different behaviors of organic solid state with stimulation by single‐wavelength light.