Azobenzene-containing Alternating and Random Metathesis Copolymers toward Gaining More Insight into Photoisomerization Properties

Using alternating diene metathesis (ALTMET) polycondensation and acyclic diene metathesis (ADMET) polymerization, two kinds of alternating and random copolymers from electron-deficient azobenzene (azo)-functionalized alpha,omega-diene monomers that are photoresponsive molecules and comonomers such as electron-rich carbazole or fluorene-functionalized diene or diacrylate monomers were synthesized. All of these copolymers were tailored to explore the effects of alternating and random monomer sequences and electron transfer capability on the self-assembly morphology and photoresponsive properties. As expected, the distinct absorption features from azo units in these copolymers are observed in their optical spectra, which cannot be achieved by traditional azo-containing homo- and copolymers. Because of the presence of stiff and electron-rich carbazole or fluorene motifs, the ability and efficiency of photoisomerization was depressed to some extent according to the sequential differences of two monomers and the electron effect in the copolymer chain. Moreover, the sizes and morphologies of alternating copolymers can be modulated through the methylene spacer and sequence of rigid conjugated motifs generating diverse nanostructures leading to a different chain mobility, which ultimately exhibited the unique photoisomerization behaviors. These interesting findings not only demonstrate a facile and efficient method for constructing azo-carbazole and azo-fluorene metathesis copolymers but also expand the optical properties of azo-containing polymers.