OCc1ccc[n+](/C(C([S-])=Nc2cccc3ccccc23)=C(/O)c2ccc(Cl)s2)c1
An acid's negative base-10 logarithmic dissociation constant (pKa) follows directly from its underlying thermodynamics; the negative pKa is directly proportional to its standard Gibbs free energy change. What is the negative pKa value of this molecule?