Solvent Effects on.Acridine Polymorphism

H-1 NMR dilution experiments were used to monitor self-association of acridine in solution in four different solvents. The pattern of complexation-induced changes in chemical shift is similar in chloroform, methanol, and carbon tetrachloride, which implies that the aggregate has a similar structure in these three solvents. However, the chemical shift pattern is different in acetone, implying a different aggregate structure. Crystallization by evaporation and by crash cooling from these solvents gave the stable polymorph III in all cases, except for the crash cooling experiment in acetone, which gave the metastable polymorph VII. This result suggests that the supramolecular aggregate structure, which is formed in solution, influences the solid state structure obtained on crystallization.