COc1ccccc1N1C(=N)S/C(=C\c2ccc(-c3ccccc3C(=O)O)o2)C1=O
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?