Photoisomerization and realignment of nitroazobenzene lying planar in a multilayer assembly

Here, we describe the optical and thermal isomerization kinetics, and photoinduced realignment properties of 2-nitro-4-methoxy-azobenzene tethered to an azacrown-type multi-cation (HNA) or a linear cationic poly(methacrylamide) (PNA) in solution and in a multilayered film. The thermal back-isomerization of HNA in solution followed ‘zeroth-order’ kinetics, whereas that of PNA confirmed to a first-order exponential function. UV/vis spectrometry tilt angle analysis of the azobenzenes in a multilayer film (composed of HNA/ι-carrageenan (CAG) bilayers) is lying relatively flat (θ = 23.2 ± 1.3°, with respect to the substrate surface). It was found that the orientation of the azobenzenes in the multilayer films significantly influenced the realignment of the transition moment of the photochromic moieties (with regard to the polarization of the irradiation light). The order parameter S (which gives an indication of the dichroic level), induced on the (HNA/CAG) multilayer film was found to be 20 times larger than that observed for the (PNA/CAG) film, in which the chromophores were isotropically distributed.

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► Photo-induced isomerization of azobenzene (lying relatively flat) in a film was described.
► Thermal back-isomerization of an azacrown-type multi-cation in solution followed ‘zeroth-order’ kinetics.
► The dichroic level depends on the inclination angle between the polarization of incident light and the chromophore.