Photochromism and proton transfer reaction cycle of new internally H-bonded Schiff bases

A family of new Schiff bases, derivatives of hydroquinone, has been synthesized. Their synthesis, spectroscopy and photophysics are reported. Two molecules, having one or two internal H-bonds, reveal photochromic properties. Two transients absorbing in the visible have been detected and kinetically separated: one, with lifetime approximate to 300 ps, lambda(max) = 570 nm, was assigned as the S-1 --> S-n absorption of the primary product of single proton transfer, the second, with lifetime 1.2 ms, lambda(max) = 540 nm, was interpreted as the photochromic modification of the molecule.