COc1ccc(C2=NN(c3ccccc3)C[N+](c3ccc(OC)cc3)=N2)cc1.[Br-]
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?