Protonation effect on the electronic structure of small PAHs: Acenaphthylene and Acenaphthene

The low lying singlet and triplet electronic excited states of neutral and protonated Acenaphthylene (C12H8, ACYN) and Acenaphthene (C12H10, ACN) have been investigated extensively by RI–MP2 and RI–CC2 methods. The first and second electronic excited tates (S1, S2) of protonated ACYN and ACN have ππ∗ nature and lie in the visible or UV region. Similar to naphthalene, anthracene, and other linear PAHs, the protonation of ACYN and ACN leads to a strong red shift of the electronic transition as compared to the neutral molecule. The calculations indicate a charged transfer character of S1–S0 transition in protonated ACYN and ACN as well as protonated naphthalene.