Optically active polymers bearing side‐chain photochromic moieties: synthesis and chiroptical properties of methacrylic and acrylic homopolymers with pendant L‐lactic acid or L‐alanine residues connected to trans‐4‐aminoazobenzene

Abstract

SUMMARYNovel optically active monomers such as trans-(S)-4-(2-methacryloylaminopropanoylamino)azobenzene, trans-(S)-4-(2-methacryloyloxypropanoylamino)azobenzen~ and trans-(S)-4-(2-acryloylaminopropanoylamino)azobenzene have been prepared and homopolymerized by free radical initiation. Circular dichroism spectra of the resulting polymeric systems, as compared with those obtained for the corresponding low molecular weight analogues, purposely synthesized, allow one to suggest that the macromolecules assume in solution conformations with different homogeneity and prevailing chirality, depending on their structural requirements and solvent interactions.

Synthesis and chiroptical properties of optically active photochromic methacrylic polymers bearing in the side chain the (S)-3-hydroxypyrrolidinyl group conjugated with thetrans-azoaromatic chromophore

“…The optical purities of monomers and models were assessed by 1 3 ] as chiral shift reagent. 13 When a racemic sample of (R,S)-MAP or (R,S)-PAP in CDCl 3 solution was treated with Pr(hfc) 3 , a remarkable shift of all the resonances of the pyrrolidine ring protons, accompanied by doubling into signals of equal intensities, was produced (Fig.…”

“…The presence of conformational dissymmetry, with a predominant handedness in the macromolecular system, induces a chiral perturbation on the electronic transitions of the achiral photochromic chromophore; hence, it is observed that circular dichroism (CD) bands, related to the UV absorptions of the aromatic chromophore, yield information on the conformational properties of the macromolecules in solution when either the azo group is in the more stable trans configuration or the extent of cis configuration is gradually increased by photoisomerization with light of suitable wavelength. Indeed, when the sidechain azobenzene chromophore was connected to the backbone through the L-lactic acid residue, such as in the homopolymers of trans-(S)-4-(2-methacryloyloxypropanoylamino)azobenzene and trans-(S)-(2-acryloyloxypropanoylamino)azobenzene [poly-(MLA) and poly(ALA), respectively], 1,3 strong CD exciton couplets indicative of a rather highly ordered conformational homogeneity of the above macromolecules with a significant prevalence of one single chirality were observed. Upon trans-cis photoisomerization, the exciton splitting progressively disappeared, finally giving rise to a single band that was attributed to incapability by cis-azobenzene chromophores to give exciton coupling through dipole-dipole interactions between the aromatic rings.…”

Effects of Side-Chain Structure and Solvent on Intramolecular Hydrogen Bonding in Isotactic Poly(methacrylamide)s

“…Dependence of CD spectra on the solvent is also reported on a radically polymerized polymethacrylate having pendant L-lactic acid derivatized with trans-4-aminoazobenzene. 8 Apparently, partial destruction of the "fully hydrogen-bonded structure" by dioxane, which will result in an increase in the relative content of the "partially hydrogen-bonded structure" having free and partially hydrogen-bonded amide groups, strongly affects the overall CD spectrum. The latter structure is suggested to give, in the 1 Bb band of the naphthyl chromophore, an exciton coupling of negative chirality with the first and second Cotton effects being negative and positive, respectively.…”

Azobenzene Polymers for Photonic Applications

“…When allowed to assemble as a transmembrane structure, the aggregate could be reversibly formed and destroyed using light, which allowed for reversible photoswitching of ion transport (Higuchi et al, 1995a). Related experiments on methacrylates (Chen et al, 1997a;Angiolini et al, 1995) and polypeptides (Sisido et al, 1991b) showed that a polymer's chiral helix could be reversibly suppressed on irradiation. In a series of polyisocyanate polymers, it could be selected whether irradiation would suppress or increase chirality (Mu¨ller and Zentel, 1996;Maxein and Zentel, 1995).…”