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 (S-1, S-2) of protonated ACYN and ACN have pi pi* 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 S-1-S-0 transition in protonated ACYN and ACN as well as protonated naphthalene. (C) 2011 Elsevier B.V. All rights reserved.