O=C1/C(=C/c2cccc([N+](=O)[O-])c2)N=C(c2ccccc2)N1c1nc2ccc(Sc3ccccc3)cc2[nH]1
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?