[sergei_DSc]

For a given compound whose pKa* (excited state) is lower, meaning that its enthalpy of deprotonation is lower vs. ground state (S0), what is the physical explanation for this phenomenon? Anyone?
P Chem is not my background so I dont know if this answer involves quantum mechanics or if there is no concrete answer (just a qualitative explanation that the change in electronic structure=change in physical properties)
Thanks!

[FeLiXe]

The idea is that electron density is moved around. if you have an OH group and the excited state takes away electron density from there, it will be more acidic.