Synthesis and chiroptical properties of optically active methacrylic polymers bearing the (S)- and/or (R)-2-hydroxysuccinimide moiety linked to thetrans-azobenzene group in the side chain

The synthesis of chiral liquid-crystalline polymers of well-controlled structure (linear and three-armed star-shaped) with distinct average chain lengths and low polydispersity was achieved by atom transfer radical polymerisation (ATRP) of a new optically active monomer (S)-4-[6-(2-methacryloyloxypropanoyloxy)hexyloxy)]-4'-ethoxyazobenzene [(S)-ML6A], containing the L-lactic residue of one absolute configuration in the side-chain. All the obtained polymeric samples, characterised by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarised optical microscopy (POM), exhibit a smectic A(1/2) (fully interdigitated) liquid-crystalline phase and high cleaning points, with transition temperatures dependent on the average polymerisation degree and the macromolecular structure. The chirality originated at the molecular level by the asymmetric functionality of the L-lactic acid residue provides the polymers, in the smectic phase, of highly homogeneous conformations with a prevailing chirality related to the presence of H-aggregates having conformational dissymmetry of one prevailing screw-sense. By irradiating with circularly polarised light (CPL), it is possible to photomodulate the chiroptical properties of these intrinsically chiral polymeric thin films. Upon irradiation with left-handed CPL (l-CPL), the circular dichroism (CD) spectra of the films show enhancement of ellipticity and a net inversion of sign. The effect is reversible and the mirror image of the CD spectrum can be restored by pumping with right-handed CPL radiation (r-CPL). The results show the ability of l-CPL to invert the supramolecular chirality of the materials and demonstrate the essential role of azoaromatic aggregates.

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Supramolecular Chirality and Reversible Chiroptical Switching in New Chiral Liquid‐Crystal Azopolymers

Barberá

Giorgini

Paris

et al. 2008

Chemistry A European J

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Synthesis of Optically Active Photoresponsive Multifunctional Polymer Containing the Side‐Chain Azocarbazole Chromophore

Angiolini

Benelli

Giorgini

et al. 2006

Macro Chemistry & Physics

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Summary: A new optically active photochromic polymethacrylate containing the carbazole moiety, deriving from the chiral monomer (S)‐(4‐cyanophenyl)‐(3‐{9‐[2‐(2‐methacryloyloxypropanoyloxy)ethyl]carbazolyl})diazene [(S)‐MLECA] has been prepared and fully characterized with the aim to obtain a multifunctional derivative possessing at the same time chemical moieties suitable to NLO and optical storage, to chiroptical switches, and to photorefractive and photoconductive applications. Spectroscopic, thermal and chiroptical characterizations clearly indicate the occurrence of dipolar interactions between chromophores and the presence of an ordered chiral conformation of one prevailing helical handedness, at least for chain segments of the macromolecules.Structure of poly[(S)‐MLECA].magnified imageStructure of poly[(S)‐MLECA].

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Photochromic and Photoresponsive Properties of Methacrylic Polymers Bearing Optically Active Hydroxysuccinimide in the Side Chain

Angiolini

Benelli

Giorgini

2007

Macro Chemistry & Physics

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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 photoisomerisation of the azobenzene chromophore, and the results are 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 CD spectra confirms the intrinsic chirality of the macromolecules. 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.magnified image

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Synthesis and chiroptical properties of optically active methacrylic polymers bearing the (S)- and/or (R)-2-hydroxysuccinimide moiety linked to thetrans-azobenzene group in the side chain

Cited by 29 publications

References 18 publications

Supramolecular Chirality and Reversible Chiroptical Switching in New Chiral Liquid‐Crystal Azopolymers

Supramolecular Chirality and Reversible Chiroptical Switching in New Chiral Liquid‐Crystal Azopolymers

Synthesis of Optically Active Photoresponsive Multifunctional Polymer Containing the Side‐Chain Azocarbazole Chromophore

Photochromic and Photoresponsive Properties of Methacrylic Polymers Bearing Optically Active Hydroxysuccinimide in the Side Chain

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