OC1(c2cccs2)C[N+](c2ccc(Br)cc2)=C2SCCCN21.[Br-]
An acid's negative base-10 logarithmic dissociation constant (pKa) follows directly from its underlying thermodynamics; the negative pKa is directly proportional to its standard Gibbs free energy change. What is the negative pKa value of this molecule?