Integrated experimental and computational spectroscopy study on π-stacking interaction: the anisole dimer.

Integrated experimental and computational results help to clarify the nature of the intermolecular interactions in a simple, isolated π-stacked dimer prepared in a molecular beam. The properties of bimolecular anisole complexes are examined and discussed in terms of the local/supramolecular nature of the electronic wavefunctions. Experimental resonance-enhanced multi-photon ionization spectra of clusters with different isotopic compositions confirmed the fundamentally localized nature of the S(1)←S(0) electronic transition. A detail analysis of the experimental results however shows the existence of non-negligible excitonic coupling for the excited-state wavefunctions leading to the doubling of the single-molecule vibronic levels in the S(1) state, with a splitting of about 30 cm(-1). Theoretical simulation of the vibrationally resolved electronic spectra and computations of the excitonic coupling convincingly support the experimental findings. The overall combined experimental/theoretical study allows a detailed description of the stacking interaction in the anisole dimer.