Molecular photoswitches based on spiro-acridansElectronic supplementary information (ESI) available: Full synthetic details pertaining to the preparation of new compounds, crystallographic information file (CIF) for compound 4a; and analysis of thermal back reactions (transient decay curves and absorption spectra). CCDC 919797. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3cc41135d

Thermally reversible photochromic spiro-acridans have been synthesized for the first time. They exhibit high ring opening efficiencies. As the formed zwitterions do not possess a merocyanine structure their lifetime is in the range of milliseconds to seconds. An observed side reaction can be avoided by suitable substitution of hydrogen atoms. Photochromic spiro-acridans, synthesized for the first time, exhibit high ring opening efficiencies.