Control over Excited State Intramolecular Proton Transfer and Photoinduced Tautomerization: Influence of the Hydrogen-Bond Geometry

The influence of H‐bond geometry on the dynamics of excited state intramolecular proton transfer (ESIPT) and photoinduced tautomerization in a series of phenol‐quinoline compounds is investigated. Control over the proton donor–acceptor distance (dDA) and dihedral angle between the proton donor–acceptor subunits is achieved by introducing methylene backbone straps of increasing lengths to link the phenol and quinoline. We demonstrate that a long dDA correlates with a higher barrier for ESIPT, while a large dihedral angle opens highly efficient deactivation channels after ESIPT, preventing the formation of the fully relaxed tautomer photoproduct. H‐bond geometry rules! Correlations between H‐bond structural parameters and the dynamics of ESIPT and photoinduced tautomerization have been investigated in a series of H‐bonded phenols (see figure).