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

Abstract

Novel optically active polymethacrylates, namely poly[(S)‐3‐methacryloyloxy‐1‐(4‐azobenzene)pyrrolidine] and poly[(S)‐3‐methacryloyloxy‐1‐(4′‐nitro‐4‐azobenzene)pyrrolidine], have been synthesized by radical polymerization of the corresponding monomers, prepared in turn through a synthetic route preserving the asymmetric center by any racemization reaction. These homopolymers are characterized by the presence in the side chain of an optically active pyrrolidinyl ring linked to the trans‐azoaromatic system through the nitrogen atom. The optical activity of the polymers in solution appears much higher than that observed with the low molecular weight models, purposely synthesized for comparison. Circular dichroism spectra of the synthesized products demonstrated that, in solution, the macromolecules assume highly homogeneous conformations with a prevailing chirality to a larger extent with respect to analogous systems previously investigated. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3257–3268, 1999

Photomodulation of the Chiroptical Properties of New Chiral Methacrylic Polymers with Side Chain Azobenzene Moieties

“…In particular, we have considered two homopolymers, poly[(S)-MAP-N] [7] and poly[(S)-MAP-C] [8] (Scheme 1), obtained by radical polymerisation of the corresponding enantiomerically pure optically active monomers (S)-3-methacryloxy-1-(4'-nitro-4-azobenzene)pyrrolidine [(S)-MAP-N] and (S)-3-methacryloxy-1-(4'-cyano-4-azobenzene)pyrrolidine [(S)-MAP-C], respectively. These derivatives do not display LC behaviour and are characterised by enhanced thermal properties with respect to the previously reported analogous methacrylic polymer pDR1 M, in which the azoaromatic dye 4'-[(2-hydroxyethyl)ethylamino]-4-nitroazobenzene (Disperse Red 1) is linked to the side chain through an ester bond, and which shows interesting optical storage properties.…”

“…[7] While the positions of the UV bands do not change on going from the model compounds to the polymers in solution and in the solid state, the absorption in the visible region is quite sensitive to chromophore aggregation. Indeed, remarkable blue shifts are observed on comparing the solution spectra of the polymers with those of the model compounds (11 and 19 nm for poly[(S)-MAP-C] and poly[(S)-MAP-N], respectively).…”

“…In dilute solution, such behaviour is typical of exciton splitting determined by cooperative interactions between side chain azobenzene chromophores arranged in a mutual chiral geometry of one prevailing handedness. [7,8,11] The presence of a rigid chiral moiety of one prevailing absolute configuration, interposed between the main chain of the polymer and the azoaromatic chromophore, favours the adoption of a chiral conformation of one prevailing helical handedness, at least within chain segments of the macromolecules in solution.…”

“…[7,8] In correspondence with the first strong absorption band in the visible region, they show two intense dichroic signals of opposite sign, with the crossover point [12] close to the position of the maximum absorption. Positions and intensities of the two components of the visible CD couplet, expressed both as ellipticity normalised for the thickness and in molar units, are reported in Table 2, along with those of the polymers and As shown in Figure 2, the couplets are asymmetric and the crossover points (Table 2) do not strictly coincide with the maxima of the visible absorption bands (Table 1).…”

Chiral Polyolefins

“…The polymerization of (S)-3-methacryloyloxy-1-(4-azobenzene) pyrrolidine ((S)-MAP) (6g) and (S)-3-methacryloyloxy-1-(4¢-nitro-4-azobenzene) pyrrolidine ((S)-MAP-N) (6h) yielded polymers that form a one-handed helix, showing extended conjugation of the aromatic chromophores compared to model compounds. [93] The polymers had unusually high glass transition temperatures of 169 C and 208 C for poly((S)-MAP) (6g) and poly((S)-MAP-N) (6h), respectivelyÐtemperatures much higher than comparable methacrylic polymers, and above the 160 C temperature desired for NLO applications. [95,101,102] Further, the functional group on the azobenzene was changed by polymerizing (S)-3- …”