protonation/deprotonation at the excited state: computational evidence

Dear All,
 I would like to suggest in my paper that nitrogen atom in my molecule
 (urocanic acid) becomes more basic upon excitation. Is it enough to
 demonstrate that a particular atom, in my case nitrogen, has significantly
 increased electron density at the excited state when comparing HOMO and LUMO
 molecular orbital
 I did literature search - not much outcome.
 Any references would be of great help - thanks in advance.