O=C(c1ccc2c(c1)nc(S)n1c3ccccc3nc21)N1CCN(c2cccc(Cl)c2)CC1
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?