O=C(Nc1ccc2nn(-c3ccccc3)nc2c1)c1ccc(-c2cccc(Cl)c2)o1
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?