Photo-alignment kinetics of azobenzene in the nanopores of the metal-organic framework HKUST-1

Azobenzene molecules in the pores of metal-organic frameworks can be aligned by polarized light. To use this effect for an opto-optical switch in data processing, it needs to be enhanced and its kinetics must be understood. Here, we study the switching kinetics in detail which is enabled by a six-fold increase in switching contrast reached by 2-step azobenzene loading process. We observe bi-exponential behavior over time and correlate it with a rate-equation model. The bi-exponential behavior of the switching with non-polarized light proofs that the azobenzene molecules align parallel to the propagation direction of the light, in addition to the known alignment perpendicular to the polarization plane. • Well visible alignment of adsorbed molecules in metal-organic frameworks by polarized light. • Bi-exponential alignment kinetics. • Rate-equation model with bi-exponential time behavior. • Proof of longitudinal alignment in addition to the alignment perpendicular to the polarization plane.