A Fast,Visible‐Light‐Sensitive Azobenzene for Bioorthogonal Ligation

Azobenzenes have been used as photoresponsive units for the control of numerous biological processes. Primary prerequisites for such applications are site‐selective incorporation of photoswitchable units into biomolecules and the possibility of using non‐destructive and deep‐tissue‐penetrating visible light for the photoisomerization. Here we report a push–pull azobenzene that readily undergoes a Staudinger–Bertozzi ligation with azide groups, that can be addressed with visible light (>440 nm) and exhibits the solvato‐ and acidochromism typical for push–pull systems. The thermal relaxation in aqueous environment proceeds on the low‐millisecond timescale, thus enabling control over biological processes on similar timescales. The approach is demonstrated in the modification of a quartz surface and in the incorporation of an azobenzene unit into a functional peptide, the third zinc finger in the mammalian factor Sp1.