Helical shape memory of screw-sense switchable polysilanes in cast films

The optically active poly [{(R)-3,7-dimethyloctyl-(S)-3-methylpentylsilane}-co-Idecylisobutylsilanell(PS-1) underwent a thermodriven helix-helix transition at 13 degreesC in isooctane. The casting of polymer solution from the pre- and post-transition temperatures led to P (righthanded) or M (left-handed) helical films, which gave positive and negative Cotton circular dichroism (CD) signals, respectively. This result suggests that the helical sense of PS-1 below and above transition temperature in the homogeneous solution was memorized in the cast films. Furthermore, the CD spectra of P- and M-helical films were mirror images to each other at 319 nm, indicating the 7(3) helical pitch of the polymers with opposite helical sense.