Photoinduced single-crystal-to-single-crystal phase transition and photosalient effect of a gold(i) isocyanide complex with shortening of intermolecular aurophilic bonds.

We report the first photoinduced single-crystal-to-single-crystal (SCSC) phase transition of a gold complex that involves the shortening of intermolecular aurophilic bonds. This is also the first solid state photochromism of a gold complex. Upon UV irradiation, the blue-emitting crystals of the gold(i) isocyanide complex () transform into the weakly yellow-emitting polymorph . X-ray diffraction analyses reveal that this phase transition proceeds in an SCSC manner. After phase transition from to , the intermolecular Au···Au separation decreases from 3.5041(14) to 3.2955(6) Å, resulting in a red-shifted emission. The photoinduced shortening of the aurophilic bond in the excited state initiates the change in the crystal structure from to . Moreover, the crystal showed a photosalient effect: the crystals jump upon irradiation with strong UV light owing to the phase transition into . The aurophilic bond formation in the crystal generates the mechanical movement of the crystal.