Spiropyran dimer toward photo-switchable molecular machine

The change in polarity and structure between spiro (Sp) and merocyanine (MC) of spiropyran was analyzed by preparing photo-switchable polymer (BIPSD). The nitro-group used was reduced to an amine under acidic conditions followed by neutralization. The photochroism study of the spriropyran dimer, BIPSD, was carried out using a medium-pressure mercury lamp equipped with a Pyrex water-cooling jacket without filters. The BIPSD toluene solution was a pale orange color, changing to blue-green after 3 min of UV irradiation. The color change correlated with the increase in absorption indicated the transformation of Sp to the MC form. The NMR spectra of BIPSD revealed that there was no difference in their spectra from the original solution, despite the obvious color change