The Structure of Diphenyl Ether-Methanol in the Electronically Excited and Ionic Ground States: A Combined IR/UV Spectroscopic and Theoretical Study

Diphenyl ether offers competing docking sites for methanol: the ether oxygen acts as a common hydrogen-bond acceptor and the system of each phenyl ring allows for OH- interactions driven by electrostatic, induction, and dispersion forces. Based on investigations in the electronic ground state (S-0), we present a detailed study of the electronically excited state (S-1) and the ionic ground state (D-0), in which an impact on the structural preference is expected compared with the S-0 state. Dispersion forces in the electronically excited state were analyzed by comparing the computed binding energies at the coupled-cluster-singles (CCS) and approximate coupled-cluster-singles-doubles levels of theory (CC2 approximation). By applying UV/IR/UV spectroscopy, we found a more strongly bound OH- structure in the S-1 state compared with the S-0 state, in agreement with spin-component-scaled CC2 calculations. A structural rearrangement into a non-hydrogen-bonded structure takes places upon ionization in the D-0 state, which was revealed by using IR photodissociation spectroscopy and confirmed by theory.