Synthesis and Structure–Property Relations of a Series of Photochromic Molecular Glasses for Controlled and Efficient Formation of Surface Relief Nanostructures

R. Walker, H. Audorff, L. Kador, H.-W. Schmidt

2009, in: Advanced Functional Materials Adv. Funct. Mater. (2009) Bd.: 19 Hnr.: 16 S.: 2630 - 2638

Abstract:
This paper reports on the synthesis and properties of a new series of photochromic molecular glasses and their structure–property relations with respect to a controlled and efficient formation of surface relief nanostructures. The aim of the paper is to establish a correlation between molecular structure, optical susceptibility, and the achievable surface relief heights. The molecular glasses consist of a triphenylamine core and three azobenzene side groups attached via an ester linkage. Structural variations are performed with respect to the substitution at the azobenzene moiety in order to promote a formation of a stable amorphous phase and to tune absorption properties and molecular dynamics. Surface relief gratings (SRGs) and complex surface patterns can easily be inscribed via holographic techniques. The modulation heights are determined with an equation adapted from the theory for thin gratings, and the values are confirmed with AFM measurements. Temperature-dependent holographic measurements allow for monitoring of SRG build-up and decay and the stability at elevated temperatures, as well as determination of the glass transition temperature. SRG modulation heights of above 600 nm are achieved. These are the highest values reported for molecular glasses to date. The surface patterns of the molecular glasses are stable enough to be copied in a replica molding process. It is demonstrated that the replica can be used to transfer the surface pattern onto a common thermoplastic polymer.