Effect of pressure on photochromic furylfulgide
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The effect of pressure on photochromic furylfulgide is investigated using monodispersed molecules in solution and molecules in a single crystal by measuring the optical absorption at room temperature under pressure provided using a diamond anvil cell. Monodispersed open-ring (E-form) and closed-ring (C-form) isomers in solution are stable under high pressure; however, pressure-induced E → C isomerisation is observed in a single crystal composed of E-form molecules above 3.0 GPa without UV irradiation. Photochromism of furylfulgide can be observed under high pressures up to 5.0 GPa in both monodispersed molecules and single crystals. In a single crystal, photoinduced conversion from the E-form to the C-form accelerates above a critical value when the fraction of C-form molecules becomes relatively large; this critical value depends on the applied pressure. The acceleration is due to the effect of the surrounding molecules, i.e., destabilisation of E-form molecules surrounded by a sufficient number of photoconverted C-form molecules results in conversion of the E-form molecule without the absorption of a photon.