O=C(N/C(=C\c1c(O)ccc2ccccc12)c1nc2ccccc2[nH]1)c1ccccc1
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?