Direct spectroscopy of contact charge transfer states: possible consequences for tryptophan excited-state deactivation pathways by O2 and formation of reactive oxygen species.

This paper demonstrates that photodetachment photoelectron spectroscopy (PD-PES) of non-covalently bound heteromolecular anion clusters allows direct access to neutral contact charge transfer (CCT) states. The 2,2'-bithiophene.indole cluster is investigated as a model system in such a way that both chromophores have similar optical excitation cross-sections and hence the PD-PES shows the signature of both molecules.