Simultaneously measuring the dichroism and the dielectric response of an azobenzene-doped organic glass former

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We have designed an experimental setup allowing to simultaneously measure both the dielectric response of a supercooled liquid and the dynamics of azobenzene chromophores dispersed in it. Both the azobenzene chromophores and the organic glass former have been synthesized with similar reaction paths: they are chemically similar, apart from the azobenzene group responsible for the strong optical absorption in the [350; 450 nm] range for the chromophores, while the embedding supercooled liquid is optically transparent. This material is deposited on transparent electrodes with an inter-electrode gap as small as 4 µm—obtained thanks to optical lithographic techniques. We show that our setup is sensitive enough to measure the coupling between the dielectric macroscopic response and the isomerization dynamics of 1% of chromophores excited by a 0.5–5 mW/cm2 light beam. We demonstrate that this coupling neither comes from the heating of the sample due to the light absorption nor from changes of the sample shape with light. Finally, we discuss the few physical effects, which may give rise to this coupling, and show that our experiment could test some recent predictions done in the framework of random first order transition theory of the glassy state.