O=C(c1ccccc1)c1cc[n+](C2=C([N-]S(=O)(=O)c3ccccc3)C(=O)c3ccccc3C2=O)cc1
An acid's negative base-10 logarithmic dissociation constant (pka) follows directly from its underlying thermodynamics; pKa is directly proportional to its standard Gibbs free energy change. What is the pka value of this molecule?