Spontaneous Formation of Complex Periodic Superstructures under High Interferential Illumination of Small-Molecule-Based Photochromic Materials

A series of push-pull azo compounds containing bulky substituents are synthesized, yielding fully amorphous materials with glass-transition temperatures above 200 degrees C. Thin films are subjected to holographic illumination and show superior bulk photomigration in terms of speed and efficiency compared to materials exhibiting similar electronic and photochromic properties in the solid state. The reported results give evidence that a microscopic consideration of the free volume rather than macroscopic parameters like the glass-transition temperature should to be adopted to interpret the matrix stiffness and its deformation ability. Irradiation performed at higher laser intensity produces periodic superstructures whose height is five to six times as high as the initial film thickness. The surface tension and instability effects are put forward to interpret the growth of such superstructures.