c1cc(-c2ccc(-c3ccc(-c4ccc(-c5cccc6nsnc56)[nH]4)c4nsnc34)[nH]2)c2nsnc2c1
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?