Dispersion-controlled excited-state dynamics of azobenzenes

Weak interactions, like London dispersion forces, can be essential to the structure and stability of molecular systems. However, in the past they have often been considered secondary, which has led to reduced attention to their role in ultrafast excited state processes and photo reactions. In this work, we investigate the impact of London dispersion on the excited state behavior of the iconic photoswitch azobenzene using time-resolved spectroscopy and excited-state molecular dynamics. We show that these interactions prolong the excited state lifetimes and prevent the direct passage through the conical intersection. We thus coin the term of “dispersion-controlled excited-state dynamics” and shine new light on the nature of the famous photo isomerization of the investigated azobenzenes.