COc1ccc(-c2c/c(=N\c3nc(-c4ccccc4)c(C)s3)c3ccccc3o2)cc1O
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?