Drastic solvent effect on thermal back reaction of spiroperimidine photochromic compounds

The photochromic behavior of two spiroperimidine compounds, 2,3-dihydro-2-spiro-7′-(8’-imino-7′,8′-dihydronaphthalen-1’-amine)perimidine, PNI and 2,3-dihydro-2-spiro-4′-[8′-aminonaphthalen-1′(4H)-one]perimidine, PNO-p has been studied by absorption and transient absorption spectroscopies. Both PNI and PNO-p exhibit extremely large solvent effect on the thermal back reaction from the colored (open) to the initial (close) state. The lifetime of the colored state ranges from 600 μs (methanol) to 22 days (acetonitrile) at room temperature. The relative energies of isomers have been estimated by the DFT calculations.