A Bifunctional Amorphous Polymer Exhibiting Equal Linear and Circular Photoinduced Birefringences

Abstract

The large and reversible photoinduced linear and circular birefringences in azo-compounds are at the basis of the interest in these materials, which are potentially useful for several applications. Since the onset of the linear and circular anisotropies relies on orientational processes, which typically occur on the molecular and supramolecular length scale, respectively, a circular birefringence at least one order of magnitude lower than the linear one is usually observed. Here, the synthesis and characterization of an amorphous polymer with a dimeric repeating unit containing a cyanoazobenzene and a cyanobiphenyl moiety are reported, in which identical optical linear and circular birefringences are induced for proper light dose and ellipticity. A pump-probe technique and an analytical method based on the Stokes-Mueller formalism are used to investigate the photoinduced effects and to evaluate the anisotropies. The peculiar photoresponse of the polymer makes it a good candidate for applications in smart functional devices.

Tuning the Thermal Properties of Azopolymers Synthesized by Post‐Functionalization of Poly(propargyl Methacrylate) with Azobenzene Azides: Influence on the Generation of Linear and Circular Birefringences

“…A pump‐probe technique and the Stokes–Mueller matrix formalism was adopted to photoinduce and evaluate the linear (Δ n lin ) and circular (Δ n circ ) birefringences of µm‐thick polymer films . The samples were prepared by melting the polymers at T = 120 °C, well above the T g , and confining them between two glass plates.…”

“…Samples were exposed to a single pump beam at λ = 457 nm (Ar + laser Innova 90C, Coherent Inc.), while a probe beam (He–Ne laser 05‐LHP‐201, Melles Griot) at λ = 633 nm, far from the absorption band of the polymers, was used to investigate the photoinduced linear and circular anisotropies. Both the pump and probe beams passed through the proper quarter‐wavelength plate in order to span the ellipticity range, from linear () to left circular (), keeping the major axis of the ellipse along the vertical axis . The pump beam was expanded to a spot size of 4 mm and the radiation dose was fixed at 5 J cm −2 .…”

“…The photoinduced birefringences (Δ n lin and Δ n circ ) were evaluated from the corresponding optical retardances LB = (πΔ n lin d )/λ (Equation (1)) and CB = (πΔ n circ d )/λ (Equation (2)) by means of a two gratings polarimeter (TGP), where d is the thickness of the film and λ the probe wavelength. The values of LB and CB were calculated from the Stokes vector of the transmitted probe beam for two different polarization states of the incident probe: left circular and linear (along horizontal‐axis) polarizations, respectively .…”

“…The polymer was a random polymethacrylate containing pendant 4‐cyanoazobenzene and 4‐cyanobiphenyl moieties in a 60:40 molar ratio, which are well‐known promesogenic units. More recently, an amorphous polymer was reported in which comparable optical linear and circular birefringences were induced using proper light dose and ellipticity . This amorphous polymer was the polymethacrylate P‐cCNB/eAZO with a repeating unit containing both 4‐cyanoazobenzene and 4‐cyanobiphenyl moieties whose structure is collected in Figure .…”

Photo-Orientation Phenomena in Photochromic Liquid Crystalline Azobenzene-Containing Polymethacrylates with Different Spacer Length

“…[5][6][7][8][9][10][11][12] From the other hand, an action of polarized light induces photo-orientation processes and alignment of chromophores in direction perpendicular to the polarization plane of the incident light. [13][14][15][16][17][18][19][20] Another interesting direction of the research is connected with investigation of the surface topography of LC polymer systems and, especially, manipulation of surface relief by light irradiation. In a number of previous works, the ability of light control of surface topography has been demonstrated.…”