Photoacoustic Monitoring of the Macroscopic Orientational Order in Disperse Red 1 Azo-Dye-Based Dissolutions

The polarized pulsed-laser photoacoustic (PLPA) methodology was implemented to characterize the macroscopic molecular orientational order as a function of the applied electric field in an azo-dye-based dissolution. It is shown in this work that photoacoustic signals are highly sensitive to the material anisotropy when PLPA analyses are performed. In particular, the macroscopic molecular symmetries and structural organization of rod-like azo-dyes (Disperse Red 1: DR1) prepared in heavily loaded toluene dissolutions, have been studied. Experiments evidence unambiguous information concerning the molecular organization detected via simultaneous optical transmission and PLPA measurements. Indeed, in the electrically poled stage, it is shown that the Fourier, correlation, and root-mean-square analyses performed on the PLPA signals, as functions of the incident linear polarization of the laser source (orthogonal states P_in and S_in , respectively), reveal the main optical axis, symmetry, and structure of the aligned compounds in the liquid phase. An important advantage of the PLPA method is that it can be implemented with poor or null optical transmission anisotropic materials.