Switching hydrogen bonds to readily interconvert two room-temperature long-term stable crystalline polymorphs in chiral molecular perovskites.

It is challenging to endow polymorphs with both long-term stability and easy interconvertibility. We demonstrate an interesting example that two room-temperature polymorphs could be long-term stable yet easily interconvertible, at a pressure of ∼4.8 MPa and a temperature of 120 °C, by switching hydrogen bonds via collective reorientation of organic cations in chiral molecular perovskites.