PHOTOCHROMIC AND PHOTORESPONSIVE PROPERTIES OF METHACRYLIC POLYMERS BEARING IN THE SIDE CHAIN THE OPTICALLY ACTIVE MOIETY OF (R)- OR (S)-HYDROXYSUCCINIMIDE

The photochromic and photoresponsive properties of a series of optically active azoaromatic polymers, containing in the side-chain the rigid (S)- and/or (R)-hydroxysuccinimide residue, have been investigated in solution and in the solid state as thin films by observing the trans-cis photoisomerization of the azobenzene chromophore, and the results compared to the corresponding monomeric (S)- and (R)- model compounds. The presence of exciton splitting due to dipole-dipole interactions between the trans-azoaromatic rings in the Circular Dichroism (CD) spectra confirms the intrinsic chirality of the macromolecules. Upon photoisomerization, the CD couplet progressively disappears giving finally rise to a single band at the photostationary state. The thin films of the polymers display the same chiroptical properties as the solution, thus suggesting that the macromolecules maintain chiral conformations also in the solid amorphous state. The conformational changes of the side-chain azobenzene moieties occurring upon trans-cis and cis-trans photoisomerization are discussed in comparison with the chiroptical properties shown by the chiral polymer poly[(S)-(+)-2-methacryloyloxy-N-phenylsuccinimide], purposely synthesized as a polymeric model lacking of the azochromophoric group, and are associated to an order-disorder conformational transition of the macromolecular structure.