Single-photon ionization induced C-C or C-N bond formation in pyrrole clusters

The formation of photodimers of nitrogen heterocyclic compounds (NHCs) can partially explain the DNA damage due to radiation. Pyrrole and its derivatives, as major components of DNA, are used to understand the phenomena at the molecular level. With the aid of vacuum ultraviolet (VUV)-infrared (IR) spectroscopy and theoretical calculations, herein, we explore the possibility of the formation of a new C-C or C-N bond in pyrrole (py) clusters in a supersonic jet after single-photon ionization. Both neutral (py)₂ and (py)₃ clusters are stabilized by multiple interactions, such as N-H⋯π hydrogen bonds and π⋯π interactions. With 118 nm light ionization of the (py)₂, we elucidate that the two py are more inclined to be stabilized by a newly formed C-C or C-N covalent bond, besides the π-stacked parallel structure of (py)₂⁺. The (py)₃⁺ with a C-C or C-N covalent bonded (py)₂⁺ core mainly contributes to the IR spectrum of (py)₃⁺. The present results are helpful to elucidate the mechanism of DNA damage at a molecular level.