Photochemical isomerization around the C=N double bonds of N-methoxy-1-(1-pyrenyl)methanimine in the excited state

N-Methoxy-1-(1-pyrenyl) methanimine (VII) undergoes mutual isomerization between the Z and E isomers around the C=N double bond on triplet sensitization. The quantum yields of Z --> E isomerization increase linearly with the initial Z isomer concentration exceeding unity. Furthermore, a considerably long-lived triplet state assigned to the E triplet is observed on laser photolysis. On the basis of these experimental findings, the mechanism of isomerization of VII, proceeding by a dual two-way and one-way mode, is discussed.